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Bob Engelhardt
Guest

Mon Jul 29, 2019 1:45 am   



I was looking for a 120-120 isolation transformer on eBay and I kept
finding 120-240/480 transformers. There are 2 secondaries on these
(connect in parallel or series). It occurred to me that I could use one
of these as a 120-120 by using one secondary as input and the other
secondary as output. I know that this is theoretically possible, but
are there practical reasons why it wouldn't work?

Also: if one of these 120-240/480 transformers is rated 500VA, that
means 1 amp on the secondary, right? I.e., 1A at 480v.

Thanks,
Bob

John Larkin
Guest

Mon Jul 29, 2019 4:45 am   



On Sun, 28 Jul 2019 19:56:47 -0400, Bob Engelhardt
<BobEngelhardt_at_comcast.net> wrote:

Quote:
I was looking for a 120-120 isolation transformer on eBay and I kept
finding 120-240/480 transformers. There are 2 secondaries on these
(connect in parallel or series). It occurred to me that I could use one
of these as a 120-120 by using one secondary as input and the other
secondary as output. I know that this is theoretically possible, but
are there practical reasons why it wouldn't work?

Also: if one of these 120-240/480 transformers is rated 500VA, that
means 1 amp on the secondary, right? I.e., 1A at 480v.

Thanks,
Bob


You can use a 120/240-to-anything transformer as a 120-120 isolation
tranny. Connect one half of the official primary to the line and use
the other half as the isolated output. Ignore the "secondary". The
power rating will be a bit less than specified because you're not
using all the copper.


--

John Larkin Highland Technology, Inc

lunatic fringe electronics

Jasen Betts
Guest

Mon Jul 29, 2019 6:38 am   



On 2019-07-28, Bob Engelhardt <BobEngelhardt_at_comcast.net> wrote:
Quote:
I was looking for a 120-120 isolation transformer on eBay and I kept
finding 120-240/480 transformers. There are 2 secondaries on these
(connect in parallel or series). It occurred to me that I could use one
of these as a 120-120 by using one secondary as input and the other
secondary as output. I know that this is theoretically possible, but
are there practical reasons why it wouldn't work?

Also: if one of these 120-240/480 transformers is rated 500VA, that
means 1 amp on the secondary, right? I.e., 1A at 480v.

Thanks,
Bob


it depends how much isolation you need, using two secondaries, or
two primaries as halves of an isolation transformer only gets you
functional insulation, not any kind of safety isolation.

if the output is grounded and the input is fused, that may be enough.

--
When I tried casting out nines I made a hash of it.

default
Guest

Mon Jul 29, 2019 11:45 am   



On Sun, 28 Jul 2019 19:56:47 -0400, Bob Engelhardt
<BobEngelhardt_at_comcast.net> wrote:

Quote:
I was looking for a 120-120 isolation transformer on eBay and I kept
finding 120-240/480 transformers. There are 2 secondaries on these
(connect in parallel or series). It occurred to me that I could use one
of these as a 120-120 by using one secondary as input and the other
secondary as output. I know that this is theoretically possible, but
are there practical reasons why it wouldn't work?

Also: if one of these 120-240/480 transformers is rated 500VA, that
means 1 amp on the secondary, right? I.e., 1A at 480v.

Thanks,
Bob


You can, that is the intent on providing the duel windings.

Phil Allison
Guest

Mon Jul 29, 2019 1:45 pm   



Bob Engelhardt wrote:
Quote:

I was looking for a 120-120 isolation transformer on eBay and I kept
finding 120-240/480 transformers. There are 2 secondaries on these
(connect in parallel or series). It occurred to me that I could use one
of these as a 120-120 by using one secondary as input and the other
secondary as output. I know that this is theoretically possible, but
are there practical reasons why it wouldn't work?


** A 120-120 transformer does not have equal windings, the secondary has additional turns to allow for the regulation factor of the unit. Might be anywhere from 4 to 20% extra turns on the output side.

Also, a properly made 120-120 would also have good insulation between the two windings rather than them being overlaid or wound bifilar.

Another factor is magnetising current - transformer primaries are sized to allow for the extra current but secondaries are not since there is none.



Quote:
Also: if one of these 120-240/480 transformers is rated 500VA, that
means 1 amp on the secondary, right? I.e., 1A at 480v.



** Yep - the VA rating describes what rms current x voltage available from the secondary.


..... Phil

Phil Allison
Guest

Mon Jul 29, 2019 1:45 pm   



default wrote:
Quote:


You can, that is the intent on providing the duel windings.



** I guess those "duel" winding get to really fight it out ?



.... Phil

Phil Allison
Guest

Mon Jul 29, 2019 1:45 pm   



John Larkin wrote:

Quote:


You can use a 120/240-to-anything transformer as a 120-120 isolation
tranny. Connect one half of the official primary to the line and use
the other half as the isolated output.


** The secondary voltage available under load will be lower than the input - depending on the regulation of the particular unit.


Quote:
Ignore the "secondary". The
power rating will be a bit less than specified because you're not
using all the copper.


** Actually it will be higher for the same reason.

With rated current in both halves of the primary, having no secondary current means the unit will run cooler - allowing up to 41% increase in primary current.

AC supply transformers are tricky things.


.... Phil

default
Guest

Mon Jul 29, 2019 8:45 pm   



On Mon, 29 Jul 2019 05:11:41 -0700 (PDT), Phil Allison
<pallison49_at_gmail.com> wrote:

Quote:
default wrote:


You can, that is the intent on providing the duel windings.



** I guess those "duel" winding get to really fight it out ?

You are right, I screwed up, and it wasn't so you could show how petty
and insecure you really are.

Phil Allison
Guest

Tue Jul 30, 2019 1:45 am   



default = another idiot troll wrote:

Quote:

default wrote:


You can, that is the intent on providing the duel windings.



** I guess those "duel" winding get to really fight it out ?

You are right, I screwed up, and it wasn't so you could show how petty
and insecure you really are.



** No sense of humour = typical ASD fucked troll.


..... Phil

Bob Engelhardt
Guest

Tue Jul 30, 2019 2:45 am   



Thanks for the replies; I've decided not to use a transformer.

Bob Engelhardt
Guest

Tue Jul 30, 2019 2:45 am   



On 7/29/2019 8:09 AM, Phil Allison wrote:
Quote:
** A 120-120 transformer does not have equal windings, the secondary has additional turns to allow for the regulation factor of the unit. Might be anywhere from 4 to 20% extra turns on the output side.

Also, a properly made 120-120 would also have good insulation between the two windings rather than them being overlaid or wound bifilar.

Another factor is magnetising current - transformer primaries are sized to allow for the extra current but secondaries are not since there is none.

....


Thanks - I had overlooked that. It might not have mattered (lower
output might have been OK), but I'm not going to use one now.

Bob Engelhardt
Guest

Tue Jul 30, 2019 2:45 am   



On 7/29/2019 9:03 PM, AK wrote:
Quote:
I have one you can have for free. You just have to pay postage.

It weighs in at 9 lbs.

Bando Shielded Power Transformer Yamaha BD21A35E-0004


Thanks, but my need for one has gone away.

AK
Guest

Tue Jul 30, 2019 2:45 am   



On Monday, July 29, 2019 at 8:03:42 PM UTC-5, AK wrote:
Quote:
On Sunday, July 28, 2019 at 6:57:45 PM UTC-5, Bob Engelhardt wrote:
I was looking for a 120-120 isolation transformer on eBay and I kept
finding 120-240/480 transformers. There are 2 secondaries on these
(connect in parallel or series). It occurred to me that I could use one
of these as a 120-120 by using one secondary as input and the other
secondary as output. I know that this is theoretically possible, but
are there practical reasons why it wouldn't work?

Also: if one of these 120-240/480 transformers is rated 500VA, that
means 1 amp on the secondary, right? I.e., 1A at 480v.

Thanks,
Bob

I have one you can have for free. You just have to pay postage.

It weighs in at 9 lbs.

Bando Shielded Power Transformer Yamaha BD21A35E-0004


I forgot this.

This came from a Yamaha 240 watt receiver.

AK
Guest

Tue Jul 30, 2019 2:45 am   



On Sunday, July 28, 2019 at 6:57:45 PM UTC-5, Bob Engelhardt wrote:
Quote:
I was looking for a 120-120 isolation transformer on eBay and I kept
finding 120-240/480 transformers. There are 2 secondaries on these
(connect in parallel or series). It occurred to me that I could use one
of these as a 120-120 by using one secondary as input and the other
secondary as output. I know that this is theoretically possible, but
are there practical reasons why it wouldn't work?

Also: if one of these 120-240/480 transformers is rated 500VA, that
means 1 amp on the secondary, right? I.e., 1A at 480v.

Thanks,
Bob


I have one you can have for free. You just have to pay postage.

It weighs in at 9 lbs.

Bando Shielded Power Transformer Yamaha BD21A35E-0004

Phil Allison
Guest

Tue Jul 30, 2019 4:45 am   



Bob Engelhardt wrote:
Quote:

Phil Allison wrote:
** A 120-120 transformer does not have equal windings, the secondary has additional turns to allow for the regulation factor of the unit. Might be anywhere from 4 to 20% extra turns on the output side.

Also, a properly made 120-120 would also have good insulation between the two windings rather than them being overlaid or wound bifilar.

Another factor is magnetising current - transformer primaries are sized to allow for the extra current but secondaries are not since there is none..

...

Thanks - I had overlooked that. It might not have mattered (lower
output might have been OK), but I'm not going to use one now.


** Funny how we get the same question here regularly - and the same answers..

Larkin posts his usual naïve bullshit and I correct him with the real facts.

He has commented, more than once, that he treats usenet posting as a big joke.

What he doe not realise is how that makes him look like a big joke.



..... Phil

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