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elektroda.net NewsGroups Forum Index - Electronics - **Variac current question**

Guest

Sat Nov 24, 2012 3:28 pm

I have a variable transformer, http://www.faqs.org/docs/electric/AC/02149.png

If the current in the load (set in the middle at say 120 volts) is 3 amps, I assume the current from the source (240 volts) will be 1.5 amps. Does this mean that the current in half the windings is 4.5 amps (3 plus 1.5), or 1.5 amps (3 minus 1.5), or will the load current be out of phase with the source?

--

http://petersparrots.com

http://petersphotos.com

A man goes into a library and asks for a book on suicide.

The librarian says, "Fuck off, you won't bring it back!"

Guest

Sun Nov 25, 2012 1:57 pm

Lieutenant Scott wrote:

I have a variable transformer,

http://www.faqs.org/docs/electric/AC/02149.png

If the current in the load (set in the middle at say 120 volts) is 3

amps, I assume the current from the source (240 volts) will be 1.5

amps. Does this mean that the current in half the windings is 4.5 amps

(3 plus 1.5), or 1.5 amps (3 minus 1.5), or will the load current be out

of phase with the source?

http://www.faqs.org/docs/electric/AC/02149.png

If the current in the load (set in the middle at say 120 volts) is 3

amps, I assume the current from the source (240 volts) will be 1.5

amps. Does this mean that the current in half the windings is 4.5 amps

(3 plus 1.5), or 1.5 amps (3 minus 1.5), or will the load current be out

of phase with the source?

Looong time since I used a variable transformer (and then it was a

stepped transformer), but you can look at it better by considering

Power, i.e. if your load is using 360 Watts (120v x 3amps), so your

primary winding must be delivering at least that much power, so

360W/240V gives 1.5Amps (In reality it will be a bit more (1.6A maybe),

due to losses with-in the transformer).

So the transformer would have two totally separate windings, one (the

Primary) creating a magnetic field which induces the voltage into the

secondary winding to supply the loads current.

How the phases relate to each other ....... I think they end up in

phase, depending on the actual load!

HTH

Daniel

Guest

Sun Nov 25, 2012 5:57 pm

On Sun, 25 Nov 2012 12:57:49 -0000, Daniel47_at_teranews.com <dxmm_at_albury.nospam.net.au> wrote:

Lieutenant Scott wrote:

I have a variable transformer,

http://www.faqs.org/docs/electric/AC/02149.png

If the current in the load (set in the middle at say 120 volts) is 3

amps, I assume the current from the source (240 volts) will be 1.5

amps. Does this mean that the current in half the windings is 4.5 amps

(3 plus 1.5), or 1.5 amps (3 minus 1.5), or will the load current be out

of phase with the source?

Looong time since I used a variable transformer (and then it was a

stepped transformer), but you can look at it better by considering

Power, i.e. if your load is using 360 Watts (120v x 3amps), so your

primary winding must be delivering at least that much power, so

360W/240V gives 1.5Amps (In reality it will be a bit more (1.6A maybe),

due to losses with-in the transformer).

So the transformer would have two totally separate windings, one (the

Primary) creating a magnetic field which induces the voltage into the

secondary winding to supply the loads current.

How the phases relate to each other ....... I think they end up in

phase, depending on the actual load!

I have a variable transformer,

http://www.faqs.org/docs/electric/AC/02149.png

If the current in the load (set in the middle at say 120 volts) is 3

amps, I assume the current from the source (240 volts) will be 1.5

amps. Does this mean that the current in half the windings is 4.5 amps

(3 plus 1.5), or 1.5 amps (3 minus 1.5), or will the load current be out

of phase with the source?

Looong time since I used a variable transformer (and then it was a

stepped transformer), but you can look at it better by considering

Power, i.e. if your load is using 360 Watts (120v x 3amps), so your

primary winding must be delivering at least that much power, so

360W/240V gives 1.5Amps (In reality it will be a bit more (1.6A maybe),

due to losses with-in the transformer).

So the transformer would have two totally separate windings, one (the

Primary) creating a magnetic field which induces the voltage into the

secondary winding to supply the loads current.

How the phases relate to each other ....... I think they end up in

phase, depending on the actual load!

What confused me about the Variac was it only has one winding.

If it was a normal transformer stepping from 240 to 120 volts, the currents are easy to work out.

But with the Variac, the current going through the load is in the same coil as the primary current from the supply. I would think it goes the *opposite* way if they're in phase, as source and load share a common neutral at the bottom, so this would mean LESS current in total flows in the bottom half of the coil? (Subtracting one current from the other).

--

http://petersparrots.com

http://petersphotos.com

Why isn;t the apostrophe next to the L? Who ever uses the semicolon???

Guest

Mon Nov 26, 2012 1:40 pm

Lieutenant Scott wrote:

On Sun, 25 Nov 2012 12:57:49 -0000, Daniel47_at_teranews.com

dxmm_at_albury.nospam.net.au> wrote:

Lieutenant Scott wrote:

I have a variable transformer,

http://www.faqs.org/docs/electric/AC/02149.png

If the current in the load (set in the middle at say 120 volts) is 3

amps, I assume the current from the source (240 volts) will be 1.5

amps. Does this mean that the current in half the windings is 4.5 amps

(3 plus 1.5), or 1.5 amps (3 minus 1.5), or will the load current be out

of phase with the source?

Looong time since I used a variable transformer (and then it was a

stepped transformer), but you can look at it better by considering

Power, i.e. if your load is using 360 Watts (120v x 3amps), so your

primary winding must be delivering at least that much power, so

360W/240V gives 1.5Amps (In reality it will be a bit more (1.6A maybe),

due to losses with-in the transformer).

So the transformer would have two totally separate windings, one (the

Primary) creating a magnetic field which induces the voltage into the

secondary winding to supply the loads current.

How the phases relate to each other ....... I think they end up in

phase, depending on the actual load!

What confused me about the Variac was it only has one winding.

If it was a normal transformer stepping from 240 to 120 volts, the

currents are easy to work out.

But with the Variac, the current going through the load is in the same

coil as the primary current from the supply. I would think it goes the

*opposite* way if they're in phase, as source and load share a common

neutral at the bottom, so this would mean LESS current in total flows in

the bottom half of the coil? (Subtracting one current from the other).

dxmm_at_albury.nospam.net.au> wrote:

Lieutenant Scott wrote:

I have a variable transformer,

http://www.faqs.org/docs/electric/AC/02149.png

If the current in the load (set in the middle at say 120 volts) is 3

amps, I assume the current from the source (240 volts) will be 1.5

amps. Does this mean that the current in half the windings is 4.5 amps

(3 plus 1.5), or 1.5 amps (3 minus 1.5), or will the load current be out

of phase with the source?

Looong time since I used a variable transformer (and then it was a

stepped transformer), but you can look at it better by considering

Power, i.e. if your load is using 360 Watts (120v x 3amps), so your

primary winding must be delivering at least that much power, so

360W/240V gives 1.5Amps (In reality it will be a bit more (1.6A maybe),

due to losses with-in the transformer).

So the transformer would have two totally separate windings, one (the

Primary) creating a magnetic field which induces the voltage into the

secondary winding to supply the loads current.

How the phases relate to each other ....... I think they end up in

phase, depending on the actual load!

What confused me about the Variac was it only has one winding.

If it was a normal transformer stepping from 240 to 120 volts, the

currents are easy to work out.

But with the Variac, the current going through the load is in the same

coil as the primary current from the supply. I would think it goes the

*opposite* way if they're in phase, as source and load share a common

neutral at the bottom, so this would mean LESS current in total flows in

the bottom half of the coil? (Subtracting one current from the other).

Gee, didn't even notice you were talking about a Variac!!

O.K., what I explained above was for a normal Transformer which would

have two connections for the primary winding and two for the secondary

winding.

Now if you connect the two "Earth" or "Neutral" connections together,

you do end up with an (effective) three connection device, with both the

primary winding and the secondary sharing the third connection.

I think my mathematics still applies!!

Daniel

Guest

Mon Nov 26, 2012 2:12 pm

On Mon, 26 Nov 2012 12:40:18 -0000, Daniel47_at_teranews.com <dxmm_at_albury.nospam.net.au> wrote:

Lieutenant Scott wrote:

On Sun, 25 Nov 2012 12:57:49 -0000, Daniel47_at_teranews.com

dxmm_at_albury.nospam.net.au> wrote:

Lieutenant Scott wrote:

I have a variable transformer,

http://www.faqs.org/docs/electric/AC/02149.png

If the current in the load (set in the middle at say 120 volts) is 3

amps, I assume the current from the source (240 volts) will be 1.5

amps. Does this mean that the current in half the windings is 4.5 amps

(3 plus 1.5), or 1.5 amps (3 minus 1.5), or will the load current be out

of phase with the source?

Looong time since I used a variable transformer (and then it was a

stepped transformer), but you can look at it better by considering

Power, i.e. if your load is using 360 Watts (120v x 3amps), so your

primary winding must be delivering at least that much power, so

360W/240V gives 1.5Amps (In reality it will be a bit more (1.6A maybe),

due to losses with-in the transformer).

So the transformer would have two totally separate windings, one (the

Primary) creating a magnetic field which induces the voltage into the

secondary winding to supply the loads current.

How the phases relate to each other ....... I think they end up in

phase, depending on the actual load!

What confused me about the Variac was it only has one winding.

If it was a normal transformer stepping from 240 to 120 volts, the

currents are easy to work out.

But with the Variac, the current going through the load is in the same

coil as the primary current from the supply. I would think it goes the

*opposite* way if they're in phase, as source and load share a common

neutral at the bottom, so this would mean LESS current in total flows in

the bottom half of the coil? (Subtracting one current from the other).

Gee, didn't even notice you were talking about a Variac!!

O.K., what I explained above was for a normal Transformer which would

have two connections for the primary winding and two for the secondary

winding.

Now if you connect the two "Earth" or "Neutral" connections together,

you do end up with an (effective) three connection device, with both the

primary winding and the secondary sharing the third connection.

I think my mathematics still applies!!

Daniel

On Sun, 25 Nov 2012 12:57:49 -0000, Daniel47_at_teranews.com

dxmm_at_albury.nospam.net.au> wrote:

Lieutenant Scott wrote:

I have a variable transformer,

http://www.faqs.org/docs/electric/AC/02149.png

If the current in the load (set in the middle at say 120 volts) is 3

amps, I assume the current from the source (240 volts) will be 1.5

amps. Does this mean that the current in half the windings is 4.5 amps

(3 plus 1.5), or 1.5 amps (3 minus 1.5), or will the load current be out

of phase with the source?

Looong time since I used a variable transformer (and then it was a

stepped transformer), but you can look at it better by considering

Power, i.e. if your load is using 360 Watts (120v x 3amps), so your

primary winding must be delivering at least that much power, so

360W/240V gives 1.5Amps (In reality it will be a bit more (1.6A maybe),

due to losses with-in the transformer).

So the transformer would have two totally separate windings, one (the

Primary) creating a magnetic field which induces the voltage into the

secondary winding to supply the loads current.

How the phases relate to each other ....... I think they end up in

phase, depending on the actual load!

What confused me about the Variac was it only has one winding.

If it was a normal transformer stepping from 240 to 120 volts, the

currents are easy to work out.

But with the Variac, the current going through the load is in the same

coil as the primary current from the supply. I would think it goes the

*opposite* way if they're in phase, as source and load share a common

neutral at the bottom, so this would mean LESS current in total flows in

the bottom half of the coil? (Subtracting one current from the other).

Gee, didn't even notice you were talking about a Variac!!

O.K., what I explained above was for a normal Transformer which would

have two connections for the primary winding and two for the secondary

winding.

Now if you connect the two "Earth" or "Neutral" connections together,

you do end up with an (effective) three connection device, with both the

primary winding and the secondary sharing the third connection.

I think my mathematics still applies!!

Daniel

The thing is my 3 amps and my 1.5 amps are in the same wire. If they're opposing that's fine, if they're not it adds to 4.5 amps and gets hotter. My thinking is when the current is flowing from top to bottom from the source, that it will flow bottom to top in your secondary (or in mine back through the same wire, subtracting from the current. (The source getting the "negative" on the "earth" side at the same time as the source does the same).

--

http://petersparrots.com

http://petersphotos.com

"I was walking down fifth avenue today and I found a wallet, and I was gonna keep it, rather than return it, but I thought: well, if I lost a hundred and fifty dollars, how would I feel? And I realized I would want to be taught a lesson."

-- Emo Philips

Guest

Tue Nov 27, 2012 10:55 am

Lieutenant Scott wrote:

On Mon, 26 Nov 2012 12:40:18 -0000, Daniel47_at_teranews.com

dxmm_at_albury.nospam.net.au> wrote:

Lieutenant Scott wrote:

On Sun, 25 Nov 2012 12:57:49 -0000, Daniel47_at_teranews.com

dxmm_at_albury.nospam.net.au> wrote:

Lieutenant Scott wrote:

I have a variable transformer,

http://www.faqs.org/docs/electric/AC/02149.png

If the current in the load (set in the middle at say 120 volts) is 3

amps, I assume the current from the source (240 volts) will be 1.5

amps. Does this mean that the current in half the windings is 4.5

amps

(3 plus 1.5), or 1.5 amps (3 minus 1.5), or will the load current

be out

of phase with the source?

Looong time since I used a variable transformer (and then it was a

stepped transformer), but you can look at it better by considering

Power, i.e. if your load is using 360 Watts (120v x 3amps), so your

primary winding must be delivering at least that much power, so

360W/240V gives 1.5Amps (In reality it will be a bit more (1.6A maybe),

due to losses with-in the transformer).

So the transformer would have two totally separate windings, one (the

Primary) creating a magnetic field which induces the voltage into the

secondary winding to supply the loads current.

How the phases relate to each other ....... I think they end up in

phase, depending on the actual load!

What confused me about the Variac was it only has one winding.

If it was a normal transformer stepping from 240 to 120 volts, the

currents are easy to work out.

But with the Variac, the current going through the load is in the same

coil as the primary current from the supply. I would think it goes the

*opposite* way if they're in phase, as source and load share a common

neutral at the bottom, so this would mean LESS current in total flows in

the bottom half of the coil? (Subtracting one current from the other).

Gee, didn't even notice you were talking about a Variac!!

O.K., what I explained above was for a normal Transformer which would

have two connections for the primary winding and two for the secondary

winding.

Now if you connect the two "Earth" or "Neutral" connections together,

you do end up with an (effective) three connection device, with both the

primary winding and the secondary sharing the third connection.

I think my mathematics still applies!!

Daniel

The thing is my 3 amps and my 1.5 amps are in the same wire. If they're

opposing that's fine, if they're not it adds to 4.5 amps and gets

hotter. My thinking is when the current is flowing from top to bottom

from the source, that it will flow bottom to top in your secondary (or

in mine back through the same wire, subtracting from the current. (The

source getting the "negative" on the "earth" side at the same time as

the source does the same).

dxmm_at_albury.nospam.net.au> wrote:

Lieutenant Scott wrote:

On Sun, 25 Nov 2012 12:57:49 -0000, Daniel47_at_teranews.com

dxmm_at_albury.nospam.net.au> wrote:

Lieutenant Scott wrote:

I have a variable transformer,

http://www.faqs.org/docs/electric/AC/02149.png

If the current in the load (set in the middle at say 120 volts) is 3

amps, I assume the current from the source (240 volts) will be 1.5

amps. Does this mean that the current in half the windings is 4.5

amps

(3 plus 1.5), or 1.5 amps (3 minus 1.5), or will the load current

be out

of phase with the source?

Looong time since I used a variable transformer (and then it was a

stepped transformer), but you can look at it better by considering

Power, i.e. if your load is using 360 Watts (120v x 3amps), so your

primary winding must be delivering at least that much power, so

360W/240V gives 1.5Amps (In reality it will be a bit more (1.6A maybe),

due to losses with-in the transformer).

So the transformer would have two totally separate windings, one (the

Primary) creating a magnetic field which induces the voltage into the

secondary winding to supply the loads current.

How the phases relate to each other ....... I think they end up in

phase, depending on the actual load!

What confused me about the Variac was it only has one winding.

If it was a normal transformer stepping from 240 to 120 volts, the

currents are easy to work out.

But with the Variac, the current going through the load is in the same

coil as the primary current from the supply. I would think it goes the

*opposite* way if they're in phase, as source and load share a common

neutral at the bottom, so this would mean LESS current in total flows in

the bottom half of the coil? (Subtracting one current from the other).

Gee, didn't even notice you were talking about a Variac!!

O.K., what I explained above was for a normal Transformer which would

have two connections for the primary winding and two for the secondary

winding.

Now if you connect the two "Earth" or "Neutral" connections together,

you do end up with an (effective) three connection device, with both the

primary winding and the secondary sharing the third connection.

I think my mathematics still applies!!

Daniel

The thing is my 3 amps and my 1.5 amps are in the same wire. If they're

opposing that's fine, if they're not it adds to 4.5 amps and gets

hotter. My thinking is when the current is flowing from top to bottom

from the source, that it will flow bottom to top in your secondary (or

in mine back through the same wire, subtracting from the current. (The

source getting the "negative" on the "earth" side at the same time as

the source does the same).

No, think of a see-saw.....The current flows in at the pivot point and

each flows towards one of the ends...the 3 amps (being heavier) goes to

the bottom end, and flows out to load and back to the pivot point (the

"centre tap").

The 1.5'ish amps flows out the top, off to the mains supply and back to

the pivot point (the "centre tap").

The only place that both currents are flowing together is at the centre

tap, and then they go their own ways!

And, at the centre tap (and only at the tap), you may have both the 1.5

amps (main winding current) and the 3 amps (secondary current) flowing,

and, depending on the phase angle between them, the amount of current

flowing at any particular time, at the centre tap could be anywhere

between 1.5 amps and 4.5 amps! But, in the windings the most current

would be 3 Amps.

Daniel

Guest

Tue Nov 27, 2012 2:02 pm

On Tue, 27 Nov 2012 09:55:33 -0000, Daniel47_at_teranews.com <dxmm_at_albury.nospam.net.au> wrote:

Lieutenant Scott wrote:

On Mon, 26 Nov 2012 12:40:18 -0000, Daniel47_at_teranews.com

dxmm_at_albury.nospam.net.au> wrote:

Lieutenant Scott wrote:

On Sun, 25 Nov 2012 12:57:49 -0000, Daniel47_at_teranews.com

dxmm_at_albury.nospam.net.au> wrote:

Lieutenant Scott wrote:

Looong time since I used a variable transformer (and then it was a

stepped transformer), but you can look at it better by considering

Power, i.e. if your load is using 360 Watts (120v x 3amps), so your

primary winding must be delivering at least that much power, so

360W/240V gives 1.5Amps (In reality it will be a bit more (1.6A maybe),

due to losses with-in the transformer).

So the transformer would have two totally separate windings, one (the

Primary) creating a magnetic field which induces the voltage into the

secondary winding to supply the loads current.

How the phases relate to each other ....... I think they end up in

phase, depending on the actual load!

What confused me about the Variac was it only has one winding.

If it was a normal transformer stepping from 240 to 120 volts, the

currents are easy to work out.

But with the Variac, the current going through the load is in the same

coil as the primary current from the supply. I would think it goes the

*opposite* way if they're in phase, as source and load share a common

neutral at the bottom, so this would mean LESS current in total flows in

the bottom half of the coil? (Subtracting one current from the other).

Gee, didn't even notice you were talking about a Variac!!

O.K., what I explained above was for a normal Transformer which would

have two connections for the primary winding and two for the secondary

winding.

Now if you connect the two "Earth" or "Neutral" connections together,

you do end up with an (effective) three connection device, with both the

primary winding and the secondary sharing the third connection.

I think my mathematics still applies!!

Daniel

The thing is my 3 amps and my 1.5 amps are in the same wire. If they're

opposing that's fine, if they're not it adds to 4.5 amps and gets

hotter. My thinking is when the current is flowing from top to bottom

from the source, that it will flow bottom to top in your secondary (or

in mine back through the same wire, subtracting from the current. (The

source getting the "negative" on the "earth" side at the same time as

the source does the same).

No, think of a see-saw.....The current flows in at the pivot point and

each flows towards one of the ends...the 3 amps (being heavier) goes to

the bottom end, and flows out to load and back to the pivot point (the

"centre tap").

The 1.5'ish amps flows out the top, off to the mains supply and back to

the pivot point (the "centre tap").

The only place that both currents are flowing together is at the centre

tap, and then they go their own ways!

And, at the centre tap (and only at the tap), you may have both the 1.5

amps (main winding current) and the 3 amps (secondary current) flowing,

and, depending on the phase angle between them, the amount of current

flowing at any particular time, at the centre tap could be anywhere

between 1.5 amps and 4.5 amps! But, in the windings the most current

would be 3 Amps.

Daniel

On Mon, 26 Nov 2012 12:40:18 -0000, Daniel47_at_teranews.com

dxmm_at_albury.nospam.net.au> wrote:

Lieutenant Scott wrote:

On Sun, 25 Nov 2012 12:57:49 -0000, Daniel47_at_teranews.com

dxmm_at_albury.nospam.net.au> wrote:

Lieutenant Scott wrote:

Looong time since I used a variable transformer (and then it was a

stepped transformer), but you can look at it better by considering

Power, i.e. if your load is using 360 Watts (120v x 3amps), so your

primary winding must be delivering at least that much power, so

360W/240V gives 1.5Amps (In reality it will be a bit more (1.6A maybe),

due to losses with-in the transformer).

So the transformer would have two totally separate windings, one (the

Primary) creating a magnetic field which induces the voltage into the

secondary winding to supply the loads current.

How the phases relate to each other ....... I think they end up in

phase, depending on the actual load!

What confused me about the Variac was it only has one winding.

If it was a normal transformer stepping from 240 to 120 volts, the

currents are easy to work out.

But with the Variac, the current going through the load is in the same

coil as the primary current from the supply. I would think it goes the

*opposite* way if they're in phase, as source and load share a common

neutral at the bottom, so this would mean LESS current in total flows in

the bottom half of the coil? (Subtracting one current from the other).

Gee, didn't even notice you were talking about a Variac!!

O.K., what I explained above was for a normal Transformer which would

have two connections for the primary winding and two for the secondary

winding.

Now if you connect the two "Earth" or "Neutral" connections together,

you do end up with an (effective) three connection device, with both the

primary winding and the secondary sharing the third connection.

I think my mathematics still applies!!

Daniel

The thing is my 3 amps and my 1.5 amps are in the same wire. If they're

opposing that's fine, if they're not it adds to 4.5 amps and gets

hotter. My thinking is when the current is flowing from top to bottom

from the source, that it will flow bottom to top in your secondary (or

in mine back through the same wire, subtracting from the current. (The

source getting the "negative" on the "earth" side at the same time as

the source does the same).

No, think of a see-saw.....The current flows in at the pivot point and

each flows towards one of the ends...the 3 amps (being heavier) goes to

the bottom end, and flows out to load and back to the pivot point (the

"centre tap").

The 1.5'ish amps flows out the top, off to the mains supply and back to

the pivot point (the "centre tap").

The only place that both currents are flowing together is at the centre

tap, and then they go their own ways!

And, at the centre tap (and only at the tap), you may have both the 1.5

amps (main winding current) and the 3 amps (secondary current) flowing,

and, depending on the phase angle between them, the amount of current

flowing at any particular time, at the centre tap could be anywhere

between 1.5 amps and 4.5 amps! But, in the windings the most current

would be 3 Amps.

Daniel

I think that's the same as what I'm saying.

So 1.5 amps comes from the source to the bottom common point (common connection to source and load), and goes through the load to the centre tap.

The other 1.5 amps the load is getting is circulating through the bottom half of the coil: centre tap to bottom, then through the load, back to the centre tap.

I make that 1.5 amps in all the coil though.

Another clue might be that the Variac states that 3A LOAD is the maximum, no matter what voltage you've selected by moving the centre tap.

There must be a physics book on this somewhere online.....

--

http://petersparrots.com

http://petersphotos.com

Why isn;t the apostrophe next to the L? Who ever uses the semicolon???

Guest

Tue Nov 27, 2012 3:49 pm

Lieutenant Scott wrote:

On Tue, 27 Nov 2012 09:55:33 -0000, Daniel47_at_teranews.com

dxmm_at_albury.nospam.net.au> wrote:

Lieutenant Scott wrote:

On Mon, 26 Nov 2012 12:40:18 -0000, Daniel47_at_teranews.com

dxmm_at_albury.nospam.net.au> wrote:

Lieutenant Scott wrote:

On Sun, 25 Nov 2012 12:57:49 -0000, Daniel47_at_teranews.com

dxmm_at_albury.nospam.net.au> wrote:

Lieutenant Scott wrote:

Looong time since I used a variable transformer (and then it was a

stepped transformer), but you can look at it better by considering

Power, i.e. if your load is using 360 Watts (120v x 3amps), so your

primary winding must be delivering at least that much power, so

360W/240V gives 1.5Amps (In reality it will be a bit more (1.6A

maybe),

due to losses with-in the transformer).

So the transformer would have two totally separate windings, one (the

Primary) creating a magnetic field which induces the voltage into the

secondary winding to supply the loads current.

How the phases relate to each other ....... I think they end up in

phase, depending on the actual load!

What confused me about the Variac was it only has one winding.

If it was a normal transformer stepping from 240 to 120 volts, the

currents are easy to work out.

But with the Variac, the current going through the load is in the same

coil as the primary current from the supply. I would think it goes

the

*opposite* way if they're in phase, as source and load share a common

neutral at the bottom, so this would mean LESS current in total

flows in

the bottom half of the coil? (Subtracting one current from the

other).

Gee, didn't even notice you were talking about a Variac!!

O.K., what I explained above was for a normal Transformer which would

have two connections for the primary winding and two for the secondary

winding.

Now if you connect the two "Earth" or "Neutral" connections together,

you do end up with an (effective) three connection device, with both

the

primary winding and the secondary sharing the third connection.

I think my mathematics still applies!!

Daniel

The thing is my 3 amps and my 1.5 amps are in the same wire. If they're

opposing that's fine, if they're not it adds to 4.5 amps and gets

hotter. My thinking is when the current is flowing from top to bottom

from the source, that it will flow bottom to top in your secondary (or

in mine back through the same wire, subtracting from the current. (The

source getting the "negative" on the "earth" side at the same time as

the source does the same).

No, think of a see-saw.....The current flows in at the pivot point and

each flows towards one of the ends...the 3 amps (being heavier) goes to

the bottom end, and flows out to load and back to the pivot point (the

"centre tap").

The 1.5'ish amps flows out the top, off to the mains supply and back to

the pivot point (the "centre tap").

The only place that both currents are flowing together is at the centre

tap, and then they go their own ways!

And, at the centre tap (and only at the tap), you may have both the 1.5

amps (main winding current) and the 3 amps (secondary current) flowing,

and, depending on the phase angle between them, the amount of current

flowing at any particular time, at the centre tap could be anywhere

between 1.5 amps and 4.5 amps! But, in the windings the most current

would be 3 Amps.

Daniel

I think that's the same as what I'm saying.

So 1.5 amps comes from the source to the bottom common point (common

connection to source and load), and goes through the load to the centre

tap.

dxmm_at_albury.nospam.net.au> wrote:

Lieutenant Scott wrote:

On Mon, 26 Nov 2012 12:40:18 -0000, Daniel47_at_teranews.com

dxmm_at_albury.nospam.net.au> wrote:

Lieutenant Scott wrote:

On Sun, 25 Nov 2012 12:57:49 -0000, Daniel47_at_teranews.com

dxmm_at_albury.nospam.net.au> wrote:

Lieutenant Scott wrote:

Looong time since I used a variable transformer (and then it was a

stepped transformer), but you can look at it better by considering

Power, i.e. if your load is using 360 Watts (120v x 3amps), so your

primary winding must be delivering at least that much power, so

360W/240V gives 1.5Amps (In reality it will be a bit more (1.6A

maybe),

due to losses with-in the transformer).

So the transformer would have two totally separate windings, one (the

Primary) creating a magnetic field which induces the voltage into the

secondary winding to supply the loads current.

How the phases relate to each other ....... I think they end up in

phase, depending on the actual load!

What confused me about the Variac was it only has one winding.

If it was a normal transformer stepping from 240 to 120 volts, the

currents are easy to work out.

But with the Variac, the current going through the load is in the same

coil as the primary current from the supply. I would think it goes

the

*opposite* way if they're in phase, as source and load share a common

neutral at the bottom, so this would mean LESS current in total

flows in

the bottom half of the coil? (Subtracting one current from the

other).

Gee, didn't even notice you were talking about a Variac!!

O.K., what I explained above was for a normal Transformer which would

have two connections for the primary winding and two for the secondary

winding.

Now if you connect the two "Earth" or "Neutral" connections together,

you do end up with an (effective) three connection device, with both

the

primary winding and the secondary sharing the third connection.

I think my mathematics still applies!!

Daniel

The thing is my 3 amps and my 1.5 amps are in the same wire. If they're

opposing that's fine, if they're not it adds to 4.5 amps and gets

hotter. My thinking is when the current is flowing from top to bottom

from the source, that it will flow bottom to top in your secondary (or

in mine back through the same wire, subtracting from the current. (The

source getting the "negative" on the "earth" side at the same time as

the source does the same).

No, think of a see-saw.....The current flows in at the pivot point and

each flows towards one of the ends...the 3 amps (being heavier) goes to

the bottom end, and flows out to load and back to the pivot point (the

"centre tap").

The 1.5'ish amps flows out the top, off to the mains supply and back to

the pivot point (the "centre tap").

The only place that both currents are flowing together is at the centre

tap, and then they go their own ways!

And, at the centre tap (and only at the tap), you may have both the 1.5

amps (main winding current) and the 3 amps (secondary current) flowing,

and, depending on the phase angle between them, the amount of current

flowing at any particular time, at the centre tap could be anywhere

between 1.5 amps and 4.5 amps! But, in the windings the most current

would be 3 Amps.

Daniel

I think that's the same as what I'm saying.

So 1.5 amps comes from the source to the bottom common point (common

connection to source and load), and goes through the load to the centre

tap.

No, the load current goes to the centre point, not the bottom point

The other 1.5 amps the load is getting is circulating through the bottom

half of the coil: centre tap to bottom, then through the load, back to

the centre tap.

I make that 1.5 amps in all the coil though.

Another clue might be that the Variac states that 3A LOAD is the

maximum, no matter what voltage you've selected by moving the centre tap.

There must be a physics book on this somewhere online.....

Back to the beginning, forget that you have a Variac, just think of a

transformer with four connection points. The Primary winding is

connected to the mains and the secondary winding is connected to the load.

Current flows from the wall socket, into one terminal of the Primary

winding, flows through the Primary, and current then flows back to the

wall socket. No if's, no maybe's.

The alternating current flowing in the Primary produces a fluctuating

magnetic field around the Primary winding. This fluctuating magnetic

field also cuts the windings of the Secondary winding. This induces a

voltage into the Secondary winding. If there is no load connected, there

is no load current flowing, just voltage at the Secondary winding

terminals. Because the is no load, load current will be zero!

Now when you connect a load to the Secondary winding, the voltage

induced into the Secondary winding causes a current to flow from one end

of the Secondary winding, out through the load and back in the other end

of the secondary winding. Totally separate from the Primary.

The Primary current has not gone anywhere near the secondary winding,

but the Primary current has caused the magnetic field which then caused

the Secondary current.

Daniel

Guest

Tue Nov 27, 2012 5:48 pm

On Tue, 27 Nov 2012 14:49:56 -0000, Daniel47_at_teranews.com <dxmm_at_albury.nospam.net.au> wrote:

Lieutenant Scott wrote:

On Tue, 27 Nov 2012 09:55:33 -0000, Daniel47_at_teranews.com

dxmm_at_albury.nospam.net.au> wrote:

Lieutenant Scott wrote:

On Mon, 26 Nov 2012 12:40:18 -0000, Daniel47_at_teranews.com

dxmm_at_albury.nospam.net.au> wrote:

Lieutenant Scott wrote:

Gee, didn't even notice you were talking about a Variac!!

O.K., what I explained above was for a normal Transformer which would

have two connections for the primary winding and two for the secondary

winding.

Now if you connect the two "Earth" or "Neutral" connections together,

you do end up with an (effective) three connection device, with both

the

primary winding and the secondary sharing the third connection.

I think my mathematics still applies!!

Daniel

The thing is my 3 amps and my 1.5 amps are in the same wire. If they're

opposing that's fine, if they're not it adds to 4.5 amps and gets

hotter. My thinking is when the current is flowing from top to bottom

from the source, that it will flow bottom to top in your secondary (or

in mine back through the same wire, subtracting from the current. (The

source getting the "negative" on the "earth" side at the same time as

the source does the same).

No, think of a see-saw.....The current flows in at the pivot point and

each flows towards one of the ends...the 3 amps (being heavier) goes to

the bottom end, and flows out to load and back to the pivot point (the

"centre tap").

The 1.5'ish amps flows out the top, off to the mains supply and back to

the pivot point (the "centre tap").

The only place that both currents are flowing together is at the centre

tap, and then they go their own ways!

And, at the centre tap (and only at the tap), you may have both the 1.5

amps (main winding current) and the 3 amps (secondary current) flowing,

and, depending on the phase angle between them, the amount of current

flowing at any particular time, at the centre tap could be anywhere

between 1.5 amps and 4.5 amps! But, in the windings the most current

would be 3 Amps.

Daniel

I think that's the same as what I'm saying.

So 1.5 amps comes from the source to the bottom common point (common

connection to source and load), and goes through the load to the centre

tap.

No, the load current goes to the centre point, not the bottom point

The other 1.5 amps the load is getting is circulating through the bottom

half of the coil: centre tap to bottom, then through the load, back to

the centre tap.

I make that 1.5 amps in all the coil though.

Another clue might be that the Variac states that 3A LOAD is the

maximum, no matter what voltage you've selected by moving the centre tap.

There must be a physics book on this somewhere online.....

Back to the beginning, forget that you have a Variac, just think of a

transformer with four connection points. The Primary winding is

connected to the mains and the secondary winding is connected to the load.

Current flows from the wall socket, into one terminal of the Primary

winding, flows through the Primary, and current then flows back to the

wall socket. No if's, no maybe's.

The alternating current flowing in the Primary produces a fluctuating

magnetic field around the Primary winding. This fluctuating magnetic

field also cuts the windings of the Secondary winding. This induces a

voltage into the Secondary winding. If there is no load connected, there

is no load current flowing, just voltage at the Secondary winding

terminals. Because the is no load, load current will be zero!

Now when you connect a load to the Secondary winding, the voltage

induced into the Secondary winding causes a current to flow from one end

of the Secondary winding, out through the load and back in the other end

of the secondary winding. Totally separate from the Primary.

The Primary current has not gone anywhere near the secondary winding,

but the Primary current has caused the magnetic field which then caused

the Secondary current.

Daniel

On Tue, 27 Nov 2012 09:55:33 -0000, Daniel47_at_teranews.com

dxmm_at_albury.nospam.net.au> wrote:

Lieutenant Scott wrote:

On Mon, 26 Nov 2012 12:40:18 -0000, Daniel47_at_teranews.com

dxmm_at_albury.nospam.net.au> wrote:

Lieutenant Scott wrote:

Gee, didn't even notice you were talking about a Variac!!

O.K., what I explained above was for a normal Transformer which would

have two connections for the primary winding and two for the secondary

winding.

Now if you connect the two "Earth" or "Neutral" connections together,

you do end up with an (effective) three connection device, with both

the

primary winding and the secondary sharing the third connection.

I think my mathematics still applies!!

Daniel

The thing is my 3 amps and my 1.5 amps are in the same wire. If they're

opposing that's fine, if they're not it adds to 4.5 amps and gets

hotter. My thinking is when the current is flowing from top to bottom

from the source, that it will flow bottom to top in your secondary (or

in mine back through the same wire, subtracting from the current. (The

source getting the "negative" on the "earth" side at the same time as

the source does the same).

No, think of a see-saw.....The current flows in at the pivot point and

each flows towards one of the ends...the 3 amps (being heavier) goes to

the bottom end, and flows out to load and back to the pivot point (the

"centre tap").

The 1.5'ish amps flows out the top, off to the mains supply and back to

the pivot point (the "centre tap").

The only place that both currents are flowing together is at the centre

tap, and then they go their own ways!

And, at the centre tap (and only at the tap), you may have both the 1.5

amps (main winding current) and the 3 amps (secondary current) flowing,

and, depending on the phase angle between them, the amount of current

flowing at any particular time, at the centre tap could be anywhere

between 1.5 amps and 4.5 amps! But, in the windings the most current

would be 3 Amps.

Daniel

I think that's the same as what I'm saying.

So 1.5 amps comes from the source to the bottom common point (common

connection to source and load), and goes through the load to the centre

tap.

No, the load current goes to the centre point, not the bottom point

The other 1.5 amps the load is getting is circulating through the bottom

half of the coil: centre tap to bottom, then through the load, back to

the centre tap.

I make that 1.5 amps in all the coil though.

Another clue might be that the Variac states that 3A LOAD is the

maximum, no matter what voltage you've selected by moving the centre tap.

There must be a physics book on this somewhere online.....

Back to the beginning, forget that you have a Variac, just think of a

transformer with four connection points. The Primary winding is

connected to the mains and the secondary winding is connected to the load.

Current flows from the wall socket, into one terminal of the Primary

winding, flows through the Primary, and current then flows back to the

wall socket. No if's, no maybe's.

The alternating current flowing in the Primary produces a fluctuating

magnetic field around the Primary winding. This fluctuating magnetic

field also cuts the windings of the Secondary winding. This induces a

voltage into the Secondary winding. If there is no load connected, there

is no load current flowing, just voltage at the Secondary winding

terminals. Because the is no load, load current will be zero!

Now when you connect a load to the Secondary winding, the voltage

induced into the Secondary winding causes a current to flow from one end

of the Secondary winding, out through the load and back in the other end

of the secondary winding. Totally separate from the Primary.

The Primary current has not gone anywhere near the secondary winding,

but the Primary current has caused the magnetic field which then caused

the Secondary current.

Daniel

Yes I understand a normal transformer. But... in your example above, is the current flowing in the same direction in the primary and secondary? I know it's AC, but think of the first half of the sine wave.

Now think of the Variac. The "secondary" is actually half of the primary. One half of the coil is just a bit of primary. The other half of the coil is BOTH half the primary and all the secondary. So this part of the winding carries TWO currents. It matters if the currents are in the same direction, as they might either add or subtract from each other.

--

http://petersparrots.com

http://petersphotos.com

The easiest way to find something lost around the house is to buy a replacement.

Guest

Mon Dec 10, 2012 3:18 pm

Lieutenant Scott wrote:

On Tue, 27 Nov 2012 14:49:56 -0000, Daniel47_at_teranews.com

dxmm_at_albury.nospam.net.au> wrote:

Lieutenant Scott wrote:

dxmm_at_albury.nospam.net.au> wrote:

Lieutenant Scott wrote:

<Snip>

Back to the beginning, forget that you have a Variac, just think of a

transformer with four connection points. The Primary winding is

connected to the mains and the secondary winding is connected to the

load.

Current flows from the wall socket, into one terminal of the Primary

winding, flows through the Primary, and current then flows back to the

wall socket. No if's, no maybe's.

The alternating current flowing in the Primary produces a fluctuating

magnetic field around the Primary winding. This fluctuating magnetic

field also cuts the windings of the Secondary winding. This induces a

voltage into the Secondary winding. If there is no load connected, there

is no load current flowing, just voltage at the Secondary winding

terminals. Because the is no load, load current will be zero!

Now when you connect a load to the Secondary winding, the voltage

induced into the Secondary winding causes a current to flow from one end

of the Secondary winding, out through the load and back in the other end

of the secondary winding. Totally separate from the Primary.

The Primary current has not gone anywhere near the secondary winding,

but the Primary current has caused the magnetic field which then caused

the Secondary current.

Daniel

Yes I understand a normal transformer. But... in your example above, is

the current flowing in the same direction in the primary and secondary?

I know it's AC, but think of the first half of the sine wave.

Now think of the Variac. The "secondary" is actually half of the

primary. One half of the coil is just a bit of primary. The other half

of the coil is BOTH half the primary and all the secondary. So this

part of the winding carries TWO currents. It matters if the currents

are in the same direction, as they might either add or subtract from

each other.

Not possible, Scotty, you cannot have both Primary and Secondary

currents flowing in one part of the (primary & Secondary) winding and

just Primary current flowing in the remainder of the (primary) winding.

Cannot happen!!

As for the phase relationships between totally separated Primary and

Secondary windings, this can depend on the load connected to the

Secondary (i.e. is the load purely resistive or capacitively reactive or

inductively reactive. And the phase relationship would also depend if

the "top" or the "bottom" of the Secondary is connected to the bottom of

the Primary winding!!

Forget a transformer.....think of two series resistors with a centre

take-off point, say a nine ohm resistor and a one ohm resistor with ten

volts applied across the combination. One amp of current would be

flowing through the two resistors, with nine volts developed across the

nine ohm resister and one volt across the one ohm resistor.

Now, if you connect another resistor across the one ohm resistor, you

don't get an increase of current flowing through the one ohm resistor to

provide the current that would flow through the additional resistor.

Daniel

Guest

Mon Dec 10, 2012 5:54 pm

On Mon, 10 Dec 2012 14:18:53 -0000, Daniel47_at_teranews.com <dxmm_at_albury.nospam.net.au> wrote:

Lieutenant Scott wrote:

On Tue, 27 Nov 2012 14:49:56 -0000, Daniel47_at_teranews.com

dxmm_at_albury.nospam.net.au> wrote:

Lieutenant Scott wrote:

Snip

Back to the beginning, forget that you have a Variac, just think of a

transformer with four connection points. The Primary winding is

connected to the mains and the secondary winding is connected to the

load.

Current flows from the wall socket, into one terminal of the Primary

winding, flows through the Primary, and current then flows back to the

wall socket. No if's, no maybe's.

The alternating current flowing in the Primary produces a fluctuating

magnetic field around the Primary winding. This fluctuating magnetic

field also cuts the windings of the Secondary winding. This induces a

voltage into the Secondary winding. If there is no load connected, there

is no load current flowing, just voltage at the Secondary winding

terminals. Because the is no load, load current will be zero!

Now when you connect a load to the Secondary winding, the voltage

induced into the Secondary winding causes a current to flow from one end

of the Secondary winding, out through the load and back in the other end

of the secondary winding. Totally separate from the Primary.

The Primary current has not gone anywhere near the secondary winding,

but the Primary current has caused the magnetic field which then caused

the Secondary current.

Daniel

Yes I understand a normal transformer. But... in your example above, is

the current flowing in the same direction in the primary and secondary?

I know it's AC, but think of the first half of the sine wave.

Now think of the Variac. The "secondary" is actually half of the

primary. One half of the coil is just a bit of primary. The other half

of the coil is BOTH half the primary and all the secondary. So this

part of the winding carries TWO currents. It matters if the currents

are in the same direction, as they might either add or subtract from

each other.

Not possible, Scotty, you cannot have both Primary and Secondary

currents flowing in one part of the (primary & Secondary) winding and

just Primary current flowing in the remainder of the (primary) winding.

Cannot happen!!

As for the phase relationships between totally separated Primary and

Secondary windings, this can depend on the load connected to the

Secondary (i.e. is the load purely resistive or capacitively reactive or

inductively reactive. And the phase relationship would also depend if

the "top" or the "bottom" of the Secondary is connected to the bottom of

the Primary winding!!

On Tue, 27 Nov 2012 14:49:56 -0000, Daniel47_at_teranews.com

dxmm_at_albury.nospam.net.au> wrote:

Lieutenant Scott wrote:

Snip

Back to the beginning, forget that you have a Variac, just think of a

transformer with four connection points. The Primary winding is

connected to the mains and the secondary winding is connected to the

load.

Current flows from the wall socket, into one terminal of the Primary

winding, flows through the Primary, and current then flows back to the

wall socket. No if's, no maybe's.

The alternating current flowing in the Primary produces a fluctuating

magnetic field around the Primary winding. This fluctuating magnetic

field also cuts the windings of the Secondary winding. This induces a

voltage into the Secondary winding. If there is no load connected, there

is no load current flowing, just voltage at the Secondary winding

terminals. Because the is no load, load current will be zero!

Now when you connect a load to the Secondary winding, the voltage

induced into the Secondary winding causes a current to flow from one end

of the Secondary winding, out through the load and back in the other end

of the secondary winding. Totally separate from the Primary.

The Primary current has not gone anywhere near the secondary winding,

but the Primary current has caused the magnetic field which then caused

the Secondary current.

Daniel

Yes I understand a normal transformer. But... in your example above, is

the current flowing in the same direction in the primary and secondary?

I know it's AC, but think of the first half of the sine wave.

Now think of the Variac. The "secondary" is actually half of the

primary. One half of the coil is just a bit of primary. The other half

of the coil is BOTH half the primary and all the secondary. So this

part of the winding carries TWO currents. It matters if the currents

are in the same direction, as they might either add or subtract from

each other.

Not possible, Scotty, you cannot have both Primary and Secondary

currents flowing in one part of the (primary & Secondary) winding and

just Primary current flowing in the remainder of the (primary) winding.

Cannot happen!!

As for the phase relationships between totally separated Primary and

Secondary windings, this can depend on the load connected to the

Secondary (i.e. is the load purely resistive or capacitively reactive or

inductively reactive. And the phase relationship would also depend if

the "top" or the "bottom" of the Secondary is connected to the bottom of

the Primary winding!!

I know, because one cancels the other out, it's more like the magnetic force pushing against the existing current and reducing it. But you can think of it as adding and subtracting currents.

Forget a transformer.....think of two series resistors with a centre

take-off point, say a nine ohm resistor and a one ohm resistor with ten

volts applied across the combination. One amp of current would be

flowing through the two resistors, with nine volts developed across the

nine ohm resister and one volt across the one ohm resistor.

Now, if you connect another resistor across the one ohm resistor, you

don't get an increase of current flowing through the one ohm resistor to

provide the current that would flow through the additional resistor.

take-off point, say a nine ohm resistor and a one ohm resistor with ten

volts applied across the combination. One amp of current would be

flowing through the two resistors, with nine volts developed across the

nine ohm resister and one volt across the one ohm resistor.

Now, if you connect another resistor across the one ohm resistor, you

don't get an increase of current flowing through the one ohm resistor to

provide the current that would flow through the additional resistor.

I find that more confusing - as a transformer is actually creating the voltage on the output.

--

http://petersparrots.com

http://petersphotos.com

You've heard of "Virgin Wool from New Zealand?"

It's a myth.

Guest

Tue Dec 11, 2012 2:18 pm

Lieutenant Scott wrote:

On Mon, 10 Dec 2012 14:18:53 -0000, Daniel47_at_teranews.com

dxmm_at_albury.nospam.net.au> wrote:

Lieutenant Scott wrote:

On Tue, 27 Nov 2012 14:49:56 -0000, Daniel47_at_teranews.com

dxmm_at_albury.nospam.net.au> wrote:

Lieutenant Scott wrote:

Snip

Back to the beginning, forget that you have a Variac, just think of a

transformer with four connection points. The Primary winding is

connected to the mains and the secondary winding is connected to the

load.

Current flows from the wall socket, into one terminal of the Primary

winding, flows through the Primary, and current then flows back to the

wall socket. No if's, no maybe's.

The alternating current flowing in the Primary produces a fluctuating

magnetic field around the Primary winding. This fluctuating magnetic

field also cuts the windings of the Secondary winding. This induces a

voltage into the Secondary winding. If there is no load connected,

there

is no load current flowing, just voltage at the Secondary winding

terminals. Because the is no load, load current will be zero!

Now when you connect a load to the Secondary winding, the voltage

induced into the Secondary winding causes a current to flow from one

end

of the Secondary winding, out through the load and back in the other

end

of the secondary winding. Totally separate from the Primary.

The Primary current has not gone anywhere near the secondary winding,

but the Primary current has caused the magnetic field which then caused

the Secondary current.

Daniel

Yes I understand a normal transformer. But... in your example above, is

the current flowing in the same direction in the primary and secondary?

I know it's AC, but think of the first half of the sine wave.

Now think of the Variac. The "secondary" is actually half of the

primary. One half of the coil is just a bit of primary. The other half

of the coil is BOTH half the primary and all the secondary. So this

part of the winding carries TWO currents. It matters if the currents

are in the same direction, as they might either add or subtract from

each other.

Not possible, Scotty, you cannot have both Primary and Secondary

currents flowing in one part of the (primary & Secondary) winding and

just Primary current flowing in the remainder of the (primary) winding.

Cannot happen!!

As for the phase relationships between totally separated Primary and

Secondary windings, this can depend on the load connected to the

Secondary (i.e. is the load purely resistive or capacitively reactive or

inductively reactive. And the phase relationship would also depend if

the "top" or the "bottom" of the Secondary is connected to the bottom of

the Primary winding!!

I know, because one cancels the other out, it's more like the magnetic

force pushing against the existing current and reducing it. But you can

think of it as adding and subtracting currents.

Forget a transformer.....think of two series resistors with a centre

take-off point, say a nine ohm resistor and a one ohm resistor with ten

volts applied across the combination. One amp of current would be

flowing through the two resistors, with nine volts developed across the

nine ohm resister and one volt across the one ohm resistor.

Now, if you connect another resistor across the one ohm resistor, you

don't get an increase of current flowing through the one ohm resistor to

provide the current that would flow through the additional resistor.

I find that more confusing - as a transformer is actually creating the

voltage on the output.

dxmm_at_albury.nospam.net.au> wrote:

Lieutenant Scott wrote:

On Tue, 27 Nov 2012 14:49:56 -0000, Daniel47_at_teranews.com

dxmm_at_albury.nospam.net.au> wrote:

Lieutenant Scott wrote:

Snip

Back to the beginning, forget that you have a Variac, just think of a

transformer with four connection points. The Primary winding is

connected to the mains and the secondary winding is connected to the

load.

Current flows from the wall socket, into one terminal of the Primary

winding, flows through the Primary, and current then flows back to the

wall socket. No if's, no maybe's.

The alternating current flowing in the Primary produces a fluctuating

magnetic field around the Primary winding. This fluctuating magnetic

field also cuts the windings of the Secondary winding. This induces a

voltage into the Secondary winding. If there is no load connected,

there

is no load current flowing, just voltage at the Secondary winding

terminals. Because the is no load, load current will be zero!

Now when you connect a load to the Secondary winding, the voltage

induced into the Secondary winding causes a current to flow from one

end

of the Secondary winding, out through the load and back in the other

end

of the secondary winding. Totally separate from the Primary.

The Primary current has not gone anywhere near the secondary winding,

but the Primary current has caused the magnetic field which then caused

the Secondary current.

Daniel

Yes I understand a normal transformer. But... in your example above, is

the current flowing in the same direction in the primary and secondary?

I know it's AC, but think of the first half of the sine wave.

Now think of the Variac. The "secondary" is actually half of the

primary. One half of the coil is just a bit of primary. The other half

of the coil is BOTH half the primary and all the secondary. So this

part of the winding carries TWO currents. It matters if the currents

are in the same direction, as they might either add or subtract from

each other.

Not possible, Scotty, you cannot have both Primary and Secondary

currents flowing in one part of the (primary & Secondary) winding and

just Primary current flowing in the remainder of the (primary) winding.

Cannot happen!!

As for the phase relationships between totally separated Primary and

Secondary windings, this can depend on the load connected to the

Secondary (i.e. is the load purely resistive or capacitively reactive or

inductively reactive. And the phase relationship would also depend if

the "top" or the "bottom" of the Secondary is connected to the bottom of

the Primary winding!!

I know, because one cancels the other out, it's more like the magnetic

force pushing against the existing current and reducing it. But you can

think of it as adding and subtracting currents.

Forget a transformer.....think of two series resistors with a centre

take-off point, say a nine ohm resistor and a one ohm resistor with ten

volts applied across the combination. One amp of current would be

flowing through the two resistors, with nine volts developed across the

nine ohm resister and one volt across the one ohm resistor.

Now, if you connect another resistor across the one ohm resistor, you

don't get an increase of current flowing through the one ohm resistor to

provide the current that would flow through the additional resistor.

I find that more confusing - as a transformer is actually creating the

voltage on the output.

"a transformer is actually creating the voltage on the output" in

exactly the same way as, in your impractical transformer, the primary

current flowing through the "secondary" winding creates the secondary

current .......... *ain't going to happen!!*

Daniel

Guest

Tue Dec 11, 2012 3:26 pm

On Tue, 11 Dec 2012 13:18:22 -0000, Daniel47_at_teranews.com <dxmm_at_albury.nospam.net.au> wrote:

Lieutenant Scott wrote:

On Mon, 10 Dec 2012 14:18:53 -0000, Daniel47_at_teranews.com

dxmm_at_albury.nospam.net.au> wrote:

Lieutenant Scott wrote:

On Tue, 27 Nov 2012 14:49:56 -0000, Daniel47_at_teranews.com

dxmm_at_albury.nospam.net.au> wrote:

Lieutenant Scott wrote:

Snip

Back to the beginning, forget that you have a Variac, just think of a

transformer with four connection points. The Primary winding is

connected to the mains and the secondary winding is connected to the

load.

Current flows from the wall socket, into one terminal of the Primary

winding, flows through the Primary, and current then flows back to the

wall socket. No if's, no maybe's.

The alternating current flowing in the Primary produces a fluctuating

magnetic field around the Primary winding. This fluctuating magnetic

field also cuts the windings of the Secondary winding. This induces a

voltage into the Secondary winding. If there is no load connected,

there

is no load current flowing, just voltage at the Secondary winding

terminals. Because the is no load, load current will be zero!

Now when you connect a load to the Secondary winding, the voltage

induced into the Secondary winding causes a current to flow from one

end

of the Secondary winding, out through the load and back in the other

end

of the secondary winding. Totally separate from the Primary.

The Primary current has not gone anywhere near the secondary winding,

but the Primary current has caused the magnetic field which then caused

the Secondary current.

Daniel

Yes I understand a normal transformer. But... in your example above, is

the current flowing in the same direction in the primary and secondary?

I know it's AC, but think of the first half of the sine wave.

Now think of the Variac. The "secondary" is actually half of the

primary. One half of the coil is just a bit of primary. The other half

of the coil is BOTH half the primary and all the secondary. So this

part of the winding carries TWO currents. It matters if the currents

are in the same direction, as they might either add or subtract from

each other.

Not possible, Scotty, you cannot have both Primary and Secondary

currents flowing in one part of the (primary & Secondary) winding and

just Primary current flowing in the remainder of the (primary) winding.

Cannot happen!!

As for the phase relationships between totally separated Primary and

Secondary windings, this can depend on the load connected to the

Secondary (i.e. is the load purely resistive or capacitively reactive or

inductively reactive. And the phase relationship would also depend if

the "top" or the "bottom" of the Secondary is connected to the bottom of

the Primary winding!!

I know, because one cancels the other out, it's more like the magnetic

force pushing against the existing current and reducing it. But you can

think of it as adding and subtracting currents.

Forget a transformer.....think of two series resistors with a centre

take-off point, say a nine ohm resistor and a one ohm resistor with ten

volts applied across the combination. One amp of current would be

flowing through the two resistors, with nine volts developed across the

nine ohm resister and one volt across the one ohm resistor.

Now, if you connect another resistor across the one ohm resistor, you

don't get an increase of current flowing through the one ohm resistor to

provide the current that would flow through the additional resistor.

I find that more confusing - as a transformer is actually creating the

voltage on the output.

"a transformer is actually creating the voltage on the output" in

exactly the same way as, in your impractical transformer, the primary

current flowing through the "secondary" winding creates the secondary

current .......... *ain't going to happen!!*

Daniel

On Mon, 10 Dec 2012 14:18:53 -0000, Daniel47_at_teranews.com

dxmm_at_albury.nospam.net.au> wrote:

Lieutenant Scott wrote:

On Tue, 27 Nov 2012 14:49:56 -0000, Daniel47_at_teranews.com

dxmm_at_albury.nospam.net.au> wrote:

Lieutenant Scott wrote:

Snip

Back to the beginning, forget that you have a Variac, just think of a

transformer with four connection points. The Primary winding is

connected to the mains and the secondary winding is connected to the

load.

Current flows from the wall socket, into one terminal of the Primary

winding, flows through the Primary, and current then flows back to the

wall socket. No if's, no maybe's.

The alternating current flowing in the Primary produces a fluctuating

magnetic field around the Primary winding. This fluctuating magnetic

field also cuts the windings of the Secondary winding. This induces a

voltage into the Secondary winding. If there is no load connected,

there

is no load current flowing, just voltage at the Secondary winding

terminals. Because the is no load, load current will be zero!

Now when you connect a load to the Secondary winding, the voltage

induced into the Secondary winding causes a current to flow from one

end

of the Secondary winding, out through the load and back in the other

end

of the secondary winding. Totally separate from the Primary.

The Primary current has not gone anywhere near the secondary winding,

but the Primary current has caused the magnetic field which then caused

the Secondary current.

Daniel

Yes I understand a normal transformer. But... in your example above, is

the current flowing in the same direction in the primary and secondary?

I know it's AC, but think of the first half of the sine wave.

Now think of the Variac. The "secondary" is actually half of the

primary. One half of the coil is just a bit of primary. The other half

of the coil is BOTH half the primary and all the secondary. So this

part of the winding carries TWO currents. It matters if the currents

are in the same direction, as they might either add or subtract from

each other.

Not possible, Scotty, you cannot have both Primary and Secondary

currents flowing in one part of the (primary & Secondary) winding and

just Primary current flowing in the remainder of the (primary) winding.

Cannot happen!!

As for the phase relationships between totally separated Primary and

Secondary windings, this can depend on the load connected to the

Secondary (i.e. is the load purely resistive or capacitively reactive or

inductively reactive. And the phase relationship would also depend if

the "top" or the "bottom" of the Secondary is connected to the bottom of

the Primary winding!!

I know, because one cancels the other out, it's more like the magnetic

force pushing against the existing current and reducing it. But you can

think of it as adding and subtracting currents.

Forget a transformer.....think of two series resistors with a centre

take-off point, say a nine ohm resistor and a one ohm resistor with ten

volts applied across the combination. One amp of current would be

flowing through the two resistors, with nine volts developed across the

nine ohm resister and one volt across the one ohm resistor.

Now, if you connect another resistor across the one ohm resistor, you

don't get an increase of current flowing through the one ohm resistor to

provide the current that would flow through the additional resistor.

I find that more confusing - as a transformer is actually creating the

voltage on the output.

"a transformer is actually creating the voltage on the output" in

exactly the same way as, in your impractical transformer, the primary

current flowing through the "secondary" winding creates the secondary

current .......... *ain't going to happen!!*

Daniel

http://petersphotos.com/temp/transformer.jpg

Correct so far?

Where I've written "?A", it has to add up to 1.5A upwards, otherwise you'd be getting current from nowhere - 3 amps has to come out of the centre tap.

I see this as the 1.5A flowing down (round the source circuit), plus the 3A flowing up round the load circuit. 1.5 down plus 3 up = 1.5 up.

--

http://petersparrots.com

http://petersphotos.com

Why are they called buildings, when they're already finished? Shouldn't they be called builts?

Guest

Fri Jan 04, 2013 2:14 pm

Lieutenant Scott wrote:

On Tue, 11 Dec 2012 13:18:22 -0000, Daniel47_at_teranews.com

dxmm_at_albury.nospam.net.au> wrote:

Lieutenant Scott wrote:

On Mon, 10 Dec 2012 14:18:53 -0000, Daniel47_at_teranews.com

dxmm_at_albury.nospam.net.au> wrote:

Lieutenant Scott wrote:

On Tue, 27 Nov 2012 14:49:56 -0000, Daniel47_at_teranews.com

dxmm_at_albury.nospam.net.au> wrote:

Lieutenant Scott wrote:

Snip

Back to the beginning, forget that you have a Variac, just think of a

transformer with four connection points. The Primary winding is

connected to the mains and the secondary winding is connected to the

load.

Current flows from the wall socket, into one terminal of the Primary

winding, flows through the Primary, and current then flows back to

the

wall socket. No if's, no maybe's.

The alternating current flowing in the Primary produces a fluctuating

magnetic field around the Primary winding. This fluctuating magnetic

field also cuts the windings of the Secondary winding. This induces a

voltage into the Secondary winding. If there is no load connected,

there

is no load current flowing, just voltage at the Secondary winding

terminals. Because the is no load, load current will be zero!

Now when you connect a load to the Secondary winding, the voltage

induced into the Secondary winding causes a current to flow from one

end

of the Secondary winding, out through the load and back in the other

end

of the secondary winding. Totally separate from the Primary.

The Primary current has not gone anywhere near the secondary winding,

but the Primary current has caused the magnetic field which then

caused

the Secondary current.

Daniel

Yes I understand a normal transformer. But... in your example

above, is

the current flowing in the same direction in the primary and

secondary?

I know it's AC, but think of the first half of the sine wave.

Now think of the Variac. The "secondary" is actually half of the

primary. One half of the coil is just a bit of primary. The other

half

of the coil is BOTH half the primary and all the secondary. So this

part of the winding carries TWO currents. It matters if the currents

are in the same direction, as they might either add or subtract from

each other.

Not possible, Scotty, you cannot have both Primary and Secondary

currents flowing in one part of the (primary & Secondary) winding and

just Primary current flowing in the remainder of the (primary) winding.

Cannot happen!!

As for the phase relationships between totally separated Primary and

Secondary windings, this can depend on the load connected to the

Secondary (i.e. is the load purely resistive or capacitively

reactive or

inductively reactive. And the phase relationship would also depend if

the "top" or the "bottom" of the Secondary is connected to the

bottom of

the Primary winding!!

I know, because one cancels the other out, it's more like the magnetic

force pushing against the existing current and reducing it. But you can

think of it as adding and subtracting currents.

Forget a transformer.....think of two series resistors with a centre

take-off point, say a nine ohm resistor and a one ohm resistor with ten

volts applied across the combination. One amp of current would be

flowing through the two resistors, with nine volts developed across the

nine ohm resister and one volt across the one ohm resistor.

Now, if you connect another resistor across the one ohm resistor, you

don't get an increase of current flowing through the one ohm

resistor to

provide the current that would flow through the additional resistor.

I find that more confusing - as a transformer is actually creating the

voltage on the output.

"a transformer is actually creating the voltage on the output" in

exactly the same way as, in your impractical transformer, the primary

current flowing through the "secondary" winding creates the secondary

current .......... *ain't going to happen!!*

Daniel

http://petersphotos.com/temp/transformer.jpg

Correct so far?

Where I've written "?A", it has to add up to 1.5A upwards, otherwise

you'd be getting current from nowhere - 3 amps has to come out of the

centre tap.

I see this as the 1.5A flowing down (round the source circuit), plus the

3A flowing up round the load circuit. 1.5 down plus 3 up = 1.5 up.

dxmm_at_albury.nospam.net.au> wrote:

Lieutenant Scott wrote:

On Mon, 10 Dec 2012 14:18:53 -0000, Daniel47_at_teranews.com

dxmm_at_albury.nospam.net.au> wrote:

Lieutenant Scott wrote:

On Tue, 27 Nov 2012 14:49:56 -0000, Daniel47_at_teranews.com

dxmm_at_albury.nospam.net.au> wrote:

Lieutenant Scott wrote:

Snip

Back to the beginning, forget that you have a Variac, just think of a

transformer with four connection points. The Primary winding is

connected to the mains and the secondary winding is connected to the

load.

Current flows from the wall socket, into one terminal of the Primary

winding, flows through the Primary, and current then flows back to

the

wall socket. No if's, no maybe's.

The alternating current flowing in the Primary produces a fluctuating

magnetic field around the Primary winding. This fluctuating magnetic

field also cuts the windings of the Secondary winding. This induces a

voltage into the Secondary winding. If there is no load connected,

there

is no load current flowing, just voltage at the Secondary winding

terminals. Because the is no load, load current will be zero!

Now when you connect a load to the Secondary winding, the voltage

induced into the Secondary winding causes a current to flow from one

end

of the Secondary winding, out through the load and back in the other

end

of the secondary winding. Totally separate from the Primary.

The Primary current has not gone anywhere near the secondary winding,

but the Primary current has caused the magnetic field which then

caused

the Secondary current.

Daniel

Yes I understand a normal transformer. But... in your example

above, is

the current flowing in the same direction in the primary and

secondary?

I know it's AC, but think of the first half of the sine wave.

Now think of the Variac. The "secondary" is actually half of the

primary. One half of the coil is just a bit of primary. The other

half

of the coil is BOTH half the primary and all the secondary. So this

part of the winding carries TWO currents. It matters if the currents

are in the same direction, as they might either add or subtract from

each other.

Not possible, Scotty, you cannot have both Primary and Secondary

currents flowing in one part of the (primary & Secondary) winding and

just Primary current flowing in the remainder of the (primary) winding.

Cannot happen!!

As for the phase relationships between totally separated Primary and

Secondary windings, this can depend on the load connected to the

Secondary (i.e. is the load purely resistive or capacitively

reactive or

inductively reactive. And the phase relationship would also depend if

the "top" or the "bottom" of the Secondary is connected to the

bottom of

the Primary winding!!

I know, because one cancels the other out, it's more like the magnetic

force pushing against the existing current and reducing it. But you can

think of it as adding and subtracting currents.

Forget a transformer.....think of two series resistors with a centre

take-off point, say a nine ohm resistor and a one ohm resistor with ten

volts applied across the combination. One amp of current would be

flowing through the two resistors, with nine volts developed across the

nine ohm resister and one volt across the one ohm resistor.

Now, if you connect another resistor across the one ohm resistor, you

don't get an increase of current flowing through the one ohm

resistor to

provide the current that would flow through the additional resistor.

I find that more confusing - as a transformer is actually creating the

voltage on the output.

"a transformer is actually creating the voltage on the output" in

exactly the same way as, in your impractical transformer, the primary

current flowing through the "secondary" winding creates the secondary

current .......... *ain't going to happen!!*

Daniel

http://petersphotos.com/temp/transformer.jpg

Correct so far?

Where I've written "?A", it has to add up to 1.5A upwards, otherwise

you'd be getting current from nowhere - 3 amps has to come out of the

centre tap.

I see this as the 1.5A flowing down (round the source circuit), plus the

3A flowing up round the load circuit. 1.5 down plus 3 up = 1.5 up.

Sorry I've been away so long!!

Your diagram is not going to happen.....ever!!

Primary power = 240 Vp times 1.5 Ip equals 360 Watts

Secondary power = 120 Vs times 3.0 Is equals 360 watts

Secondary power equals Primary power, so no (i.e. zero, zilch) power can

be dissipated in the top half of the transformer, so zero voltage

developed across the top half of the transformer, so Vs must equal Vp,

i.e. 240 V not the 120 V your diagram shows.

Not going to happen....ever!! Sorry!!

Daniel

Guest

Fri Jan 04, 2013 8:23 pm

On Fri, 04 Jan 2013 13:14:54 -0000, Daniel47_at_teranews.com <dxmm_at_albury.nospam.net.au> wrote:

Lieutenant Scott wrote:

On Tue, 11 Dec 2012 13:18:22 -0000, Daniel47_at_teranews.com

dxmm_at_albury.nospam.net.au> wrote:

Lieutenant Scott wrote:

On Mon, 10 Dec 2012 14:18:53 -0000, Daniel47_at_teranews.com

dxmm_at_albury.nospam.net.au> wrote:

Lieutenant Scott wrote:

Snip

Not possible, Scotty, you cannot have both Primary and Secondary

currents flowing in one part of the (primary & Secondary) winding and

just Primary current flowing in the remainder of the (primary) winding.

Cannot happen!!

As for the phase relationships between totally separated Primary and

Secondary windings, this can depend on the load connected to the

Secondary (i.e. is the load purely resistive or capacitively

reactive or

inductively reactive. And the phase relationship would also depend if

the "top" or the "bottom" of the Secondary is connected to the

bottom of

the Primary winding!!

I know, because one cancels the other out, it's more like the magnetic

force pushing against the existing current and reducing it. But you can

think of it as adding and subtracting currents.

Forget a transformer.....think of two series resistors with a centre

take-off point, say a nine ohm resistor and a one ohm resistor with ten

volts applied across the combination. One amp of current would be

flowing through the two resistors, with nine volts developed across the

nine ohm resister and one volt across the one ohm resistor.

Now, if you connect another resistor across the one ohm resistor, you

don't get an increase of current flowing through the one ohm

resistor to

provide the current that would flow through the additional resistor.

I find that more confusing - as a transformer is actually creating the

voltage on the output.

"a transformer is actually creating the voltage on the output" in

exactly the same way as, in your impractical transformer, the primary

current flowing through the "secondary" winding creates the secondary

current .......... *ain't going to happen!!*

Daniel

http://petersphotos.com/temp/transformer.jpg

Correct so far?

Where I've written "?A", it has to add up to 1.5A upwards, otherwise

you'd be getting current from nowhere - 3 amps has to come out of the

centre tap.

I see this as the 1.5A flowing down (round the source circuit), plus the

3A flowing up round the load circuit. 1.5 down plus 3 up = 1.5 up.

Sorry I've been away so long!!

Your diagram is not going to happen.....ever!!

Primary power = 240 Vp times 1.5 Ip equals 360 Watts

Secondary power = 120 Vs times 3.0 Is equals 360 watts

Secondary power equals Primary power, so no (i.e. zero, zilch) power can

be dissipated in the top half of the transformer, so zero voltage

developed across the top half of the transformer, so Vs must equal Vp,

i.e. 240 V not the 120 V your diagram shows.

Not going to happen....ever!! Sorry!!

Daniel

On Tue, 11 Dec 2012 13:18:22 -0000, Daniel47_at_teranews.com

dxmm_at_albury.nospam.net.au> wrote:

Lieutenant Scott wrote:

On Mon, 10 Dec 2012 14:18:53 -0000, Daniel47_at_teranews.com

dxmm_at_albury.nospam.net.au> wrote:

Lieutenant Scott wrote:

Snip

Not possible, Scotty, you cannot have both Primary and Secondary

currents flowing in one part of the (primary & Secondary) winding and

just Primary current flowing in the remainder of the (primary) winding.

Cannot happen!!

As for the phase relationships between totally separated Primary and

Secondary windings, this can depend on the load connected to the

Secondary (i.e. is the load purely resistive or capacitively

reactive or

inductively reactive. And the phase relationship would also depend if

the "top" or the "bottom" of the Secondary is connected to the

bottom of

the Primary winding!!

I know, because one cancels the other out, it's more like the magnetic

force pushing against the existing current and reducing it. But you can

think of it as adding and subtracting currents.

Forget a transformer.....think of two series resistors with a centre

take-off point, say a nine ohm resistor and a one ohm resistor with ten

volts applied across the combination. One amp of current would be

flowing through the two resistors, with nine volts developed across the

nine ohm resister and one volt across the one ohm resistor.

Now, if you connect another resistor across the one ohm resistor, you

don't get an increase of current flowing through the one ohm

resistor to

provide the current that would flow through the additional resistor.

I find that more confusing - as a transformer is actually creating the

voltage on the output.

"a transformer is actually creating the voltage on the output" in

exactly the same way as, in your impractical transformer, the primary

current flowing through the "secondary" winding creates the secondary

current .......... *ain't going to happen!!*

Daniel

http://petersphotos.com/temp/transformer.jpg

Correct so far?

Where I've written "?A", it has to add up to 1.5A upwards, otherwise

you'd be getting current from nowhere - 3 amps has to come out of the

centre tap.

I see this as the 1.5A flowing down (round the source circuit), plus the

3A flowing up round the load circuit. 1.5 down plus 3 up = 1.5 up.

Sorry I've been away so long!!

Your diagram is not going to happen.....ever!!

Primary power = 240 Vp times 1.5 Ip equals 360 Watts

Secondary power = 120 Vs times 3.0 Is equals 360 watts

Secondary power equals Primary power, so no (i.e. zero, zilch) power can

be dissipated in the top half of the transformer, so zero voltage

developed across the top half of the transformer, so Vs must equal Vp,

i.e. 240 V not the 120 V your diagram shows.

Not going to happen....ever!! Sorry!!

Daniel

It was simply a rough diagram to work out the approximate current flow, I was assuming no losses!

--

http://petersparrots.com

http://petersphotos.com

A conclusion is simply the place where someone got tired of thinking.

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