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transformer thermals...

S

server

Guest
We can sense the primary current of this transformer, with a shunt and
an isolated delta-sigma ADC. The FPGA squares the samples and filters,
so we can pick that up and square root to get RMS current. The tranny
is rated for 240 VA, which would be 9.6 amps RMS in the primary.

So I ran it for a few hours with 10 amps DC in the primary. Temp rise
was about 26C in free air. I think people design transformers for
equal copper loss in the primary and secondary, so temp rise would
double when loaded in the system. But wafting a little air over it
cuts the rise in half or so, so I\'m back to something like 25 c rise
in real life, where there will be lots of air. So we\'ll set the
software shutdown at 12 amps maybe.

https://www.dropbox.com/s/ylm8dc1e14dwv7y/P900_Xfmr_Thermal.jpg?raw=1

https://www.dropbox.com/s/5b55ybfoq2pkp9v/P900_Xfmr_Thermal_2.jpg?raw=1




--

John Larkin Highland Technology, Inc

Science teaches us to doubt.

Claude Bernard
 
L

legg

Guest
On Tue, 04 Aug 2020 19:35:39 -0700, jlarkin@highlandsniptechnology.com
wrote:

We can sense the primary current of this transformer, with a shunt and
an isolated delta-sigma ADC. The FPGA squares the samples and filters,
so we can pick that up and square root to get RMS current. The tranny
is rated for 240 VA, which would be 9.6 amps RMS in the primary.

So I ran it for a few hours with 10 amps DC in the primary. Temp rise
was about 26C in free air. I think people design transformers for
equal copper loss in the primary and secondary, so temp rise would
double when loaded in the system. But wafting a little air over it
cuts the rise in half or so, so I\'m back to something like 25 c rise
in real life, where there will be lots of air. So we\'ll set the
software shutdown at 12 amps maybe.

https://www.dropbox.com/s/ylm8dc1e14dwv7y/P900_Xfmr_Thermal.jpg?raw=1

https://www.dropbox.com/s/5b55ybfoq2pkp9v/P900_Xfmr_Thermal_2.jpg?raw=1
....and the metal plate is supposed to simulate a chassis mounting?

A vibration/stress mounting will involve rubber gaskets, which will
actually increase Rth, and reduce surface area.

If you\'re using fans, you\'re using fans.

RL
 
P

Phil Allison

Guest
jla...@highlandsniptechnology.com wrote:

---------------------------------------
https://www.dropbox.com/s/ylm8dc1e14dwv7y/P900_Xfmr_Thermal.jpg?raw=1

https://www.dropbox.com/s/5b55ybfoq2pkp9v/P900_Xfmr_Thermal_2.jpg?raw=1
** Better way to monitor temp rise is via the copper resistance - as recommended in EU and other standards.

Rise in C = 256 x ( Rhot/Rcold -1 )

A cool breeze can easily double the VA rating of a toroidal tranny.


..... Phil
 
S

server

Guest
On Wed, 05 Aug 2020 00:09:11 -0400, legg <legg@nospam.magma.ca> wrote:

On Tue, 04 Aug 2020 19:35:39 -0700, jlarkin@highlandsniptechnology.com
wrote:


We can sense the primary current of this transformer, with a shunt and
an isolated delta-sigma ADC. The FPGA squares the samples and filters,
so we can pick that up and square root to get RMS current. The tranny
is rated for 240 VA, which would be 9.6 amps RMS in the primary.

So I ran it for a few hours with 10 amps DC in the primary. Temp rise
was about 26C in free air. I think people design transformers for
equal copper loss in the primary and secondary, so temp rise would
double when loaded in the system. But wafting a little air over it
cuts the rise in half or so, so I\'m back to something like 25 c rise
in real life, where there will be lots of air. So we\'ll set the
software shutdown at 12 amps maybe.

https://www.dropbox.com/s/ylm8dc1e14dwv7y/P900_Xfmr_Thermal.jpg?raw=1

https://www.dropbox.com/s/5b55ybfoq2pkp9v/P900_Xfmr_Thermal_2.jpg?raw=1

...and the metal plate is supposed to simulate a chassis mounting?
It keeps from burning the bench if the transformer smokes.



A vibration/stress mounting will involve rubber gaskets, which will
actually increase Rth, and reduce surface area.
Think so? It should reduce theta. Most anything conducts heat better
than air.

If you\'re using fans, you\'re using fans.
That\'s profound. Let me think that over.



--

John Larkin Highland Technology, Inc

Science teaches us to doubt.

Claude Bernard
 
W

whit3rd

Guest
On Tuesday, August 4, 2020 at 9:53:40 PM UTC-7, jla...@highlandsniptechnology.com wrote:
On Wed, 05 Aug 2020 00:09:11 -0400, legg <legg@nospam.magma.ca> wrote:

A vibration/stress mounting will involve rubber gaskets, which will
actually increase Rth, and reduce surface area.

Think so? It should reduce theta. Most anything conducts heat better
than air.
Still air conducts; moving air convects. Almost anything solid convects poorly
compared to air.

Moving heat is NOT a story of conduction alone.
 
C

Cydrome Leader

Guest
jlarkin@highlandsniptechnology.com wrote:
We can sense the primary current of this transformer, with a shunt and
an isolated delta-sigma ADC. The FPGA squares the samples and filters,
so we can pick that up and square root to get RMS current. The tranny
is rated for 240 VA, which would be 9.6 amps RMS in the primary.

So I ran it for a few hours with 10 amps DC in the primary. Temp rise
was about 26C in free air. I think people design transformers for
equal copper loss in the primary and secondary, so temp rise would
double when loaded in the system. But wafting a little air over it
What about the heat generated by losses in the secondary?

cuts the rise in half or so, so I\'m back to something like 25 c rise
in real life, where there will be lots of air. So we\'ll set the
software shutdown at 12 amps maybe.

https://www.dropbox.com/s/ylm8dc1e14dwv7y/P900_Xfmr_Thermal.jpg?raw=1

https://www.dropbox.com/s/5b55ybfoq2pkp9v/P900_Xfmr_Thermal_2.jpg?raw=1
You can even see on the label (looks sort of like a Noratel) the input is
266VA and output is rated 240VA. So depending on power factor at full
load, it could be upto 26 watts of loss, although I doubt a toroid that
size would have such a poor efficiency. The iron losses will surely be
less than 50% on a toroid. Maybe the maker can tell you the ratio?
 
P

Phil Allison

Guest
Cydrome Leader is Funny:

=======================
So I ran it for a few hours with 10 amps DC in the primary. Temp rise
was about 26C in free air. I think people design transformers for
equal copper loss in the primary and secondary, so temp rise would
double when loaded in the system.

What about the heat generated by losses in the secondary?
** Doubles the temp rise - as JL just claimed.


https://www.dropbox.com/s/ylm8dc1e14dwv7y/P900_Xfmr_Thermal.jpg?raw=1

https://www.dropbox.com/s/5b55ybfoq2pkp9v/P900_Xfmr_Thermal_2.jpg?raw=1

You can even see on the label (looks sort of like a Noratel) the input is
266VA and output is rated 240VA. So depending on power factor at full
load, it could be upto 26 watts of loss, although I doubt a toroid that
size would have such a poor efficiency. The iron losses will surely be
less than 50% on a toroid. Maybe the maker can tell you the ratio?
** PF has no effect - VA is all that matters, effectively just the RMS current. Iron losses are a watt or so per kg or iron. I mag is tiny.

So 20 watts copper loss, 6 watts for iron.

Regulation about 8%.

Toriods are very simple.


..... Phil
 
S

server

Guest
On Wed, 5 Aug 2020 01:21:10 -0700 (PDT), Phil Allison
<pallison49@gmail.com> wrote:

Cydrome Leader is Funny:

=======================

So I ran it for a few hours with 10 amps DC in the primary. Temp rise
was about 26C in free air. I think people design transformers for
equal copper loss in the primary and secondary, so temp rise would
double when loaded in the system.

What about the heat generated by losses in the secondary?


** Doubles the temp rise - as JL just claimed.


https://www.dropbox.com/s/ylm8dc1e14dwv7y/P900_Xfmr_Thermal.jpg?raw=1

https://www.dropbox.com/s/5b55ybfoq2pkp9v/P900_Xfmr_Thermal_2.jpg?raw=1

You can even see on the label (looks sort of like a Noratel) the input is
266VA and output is rated 240VA. So depending on power factor at full
load, it could be upto 26 watts of loss, although I doubt a toroid that
size would have such a poor efficiency. The iron losses will surely be
less than 50% on a toroid. Maybe the maker can tell you the ratio?
This transformer was made for us by Amgis. I specified it so I know
the ratios: 1 : 1.4 : 1.4 : 1.4 : 1.4. We have a relay board that
switches the secondaries to get four output voltage ranges.

** PF has no effect - VA is all that matters, effectively just the RMS current. Iron losses are a watt or so per kg or iron. I mag is tiny.

So 20 watts copper loss, 6 watts for iron.

Regulation about 8%.

Toriods are very simple.


.... Phil
Unloaded, the AC operating primary current is essentially zero, so I
don\'t think core loss is significant.

As an alternator simulator, voltage increases with frequency, which
keeps Imag low on the low end.

It\'s a weird application. We specialize in weird.



--

John Larkin Highland Technology, Inc

Science teaches us to doubt.

Claude Bernard
 
B

boB

Guest
On Tue, 04 Aug 2020 19:35:39 -0700, jlarkin@highlandsniptechnology.com
wrote:

We can sense the primary current of this transformer, with a shunt and
an isolated delta-sigma ADC. The FPGA squares the samples and filters,
so we can pick that up and square root to get RMS current. The tranny
is rated for 240 VA, which would be 9.6 amps RMS in the primary.

So I ran it for a few hours with 10 amps DC in the primary. Temp rise
was about 26C in free air. I think people design transformers for
equal copper loss in the primary and secondary, so temp rise would
double when loaded in the system. But wafting a little air over it
cuts the rise in half or so, so I\'m back to something like 25 c rise
in real life, where there will be lots of air. So we\'ll set the
software shutdown at 12 amps maybe.

https://www.dropbox.com/s/ylm8dc1e14dwv7y/P900_Xfmr_Thermal.jpg?raw=1

https://www.dropbox.com/s/5b55ybfoq2pkp9v/P900_Xfmr_Thermal_2.jpg?raw=1

Why aren\'t you measuring this transformer using AC ?

It is going to be hotter with AC.

DC will certainly give you a best case reference though.
 
M

Mike Coon

Guest
In article <5h5kifpi9csk1ps3r90q0ht7srn3qf1ucj@4ax.com>,
jlarkin@highlandsniptechnology.com says...
We can sense the primary current of this transformer, with a shunt and
an isolated delta-sigma ADC. The FPGA squares the samples and filters,
so we can pick that up and square root to get RMS current. The tranny
is rated for 240 VA, which would be 9.6 amps RMS in the primary.

So I ran it for a few hours with 10 amps DC in the primary. Temp rise
was about 26C in free air. I think people design transformers for
equal copper loss in the primary and secondary, so temp rise would
double when loaded in the system. But wafting a little air over it
cuts the rise in half or so, so I\'m back to something like 25 c rise
in real life, where there will be lots of air. So we\'ll set the
software shutdown at 12 amps maybe.

https://www.dropbox.com/s/ylm8dc1e14dwv7y/P900_Xfmr_Thermal.jpg?raw=1

https://www.dropbox.com/s/5b55ybfoq2pkp9v/P900_Xfmr_Thermal_2.jpg?raw=1
That reminds me of when I was a schoolboy my Dad got me inolved in
rewinding a transformer to get 20V AC from 240V mains. I don\'t remember
what the original secondary rating was.

This was ostensibly to run some 20V decorative candle bulbs for pretend
safe candles for the upcoming Christmas. Only when presents were opened
I discovered that the real reason was to power a 20V Meccano electric
motor (which I still have ~65 years later.)

Anyway, the relevance was that we put back only ~ half of the
laminations before trying it so see whether our calculation of the
turns-per-volt was correct. When we got 20V AC I went rushing off to
tell my Mum of our success (I was only junior!). Only to be called back
by my Dad shouting that the transformer was smoking...

After a pow-wow, we decided that maybe all the laminations were needed
to keep the losses within bounds, and finished re-building the core.
That transfomer gave years of service subsequently, and was not the only
one I built or rebuilt. I even used my Meccano to build a coil-winding
machine!

Mike.
 
J

John Larkin

Guest
On Wed, 05 Aug 2020 13:21:31 -0700, boB <boB@K7IQ.com> wrote:

On Tue, 04 Aug 2020 19:35:39 -0700, jlarkin@highlandsniptechnology.com
wrote:


We can sense the primary current of this transformer, with a shunt and
an isolated delta-sigma ADC. The FPGA squares the samples and filters,
so we can pick that up and square root to get RMS current. The tranny
is rated for 240 VA, which would be 9.6 amps RMS in the primary.

So I ran it for a few hours with 10 amps DC in the primary. Temp rise
was about 26C in free air. I think people design transformers for
equal copper loss in the primary and secondary, so temp rise would
double when loaded in the system. But wafting a little air over it
cuts the rise in half or so, so I\'m back to something like 25 c rise
in real life, where there will be lots of air. So we\'ll set the
software shutdown at 12 amps maybe.

https://www.dropbox.com/s/ylm8dc1e14dwv7y/P900_Xfmr_Thermal.jpg?raw=1

https://www.dropbox.com/s/5b55ybfoq2pkp9v/P900_Xfmr_Thermal_2.jpg?raw=1



Why aren\'t you measuring this transformer using AC ?
Because there\'s a 10-amp DC supply on the bench.

It is going to be hotter with AC.
Hardly any.

DC will certainly give you a best case reference though.
 
P

Piotr Wyderski

Guest
jlarkin@highlandsniptechnology.com wrote:

I think people design transformers for
equal copper loss in the primary and secondary
BTW, what is the source of this and similar rules of thumb (e.g. equal
copper and core losses)? Logic says that one should always design for
minimal total losses, given the economic constraints.

Best regards, Piotr
 
P

Phil Allison

Guest
boB wrote:

----------
Why aren\'t you measuring this transformer using AC ?

It is going to be hotter with AC.

DC will certainly give you a best case reference though.
** The standard test involves shorting the secondary with an amp meter and applying enough AC volts to the primary to get the rated current.

This will, after a time, establish the temp rise and copper losses.

DC only heats one winding and needs an expensive supply.

JL likes to do things the hard way.


..... Phil
 
J

John Larkin

Guest
On Wed, 5 Aug 2020 23:32:02 +0200, Piotr Wyderski
<peter.pan@neverland.mil> wrote:

jlarkin@highlandsniptechnology.com wrote:

I think people design transformers for
equal copper loss in the primary and secondary

BTW, what is the source of this and similar rules of thumb (e.g. equal
copper and core losses)? Logic says that one should always design for
minimal total losses, given the economic constraints.

Best regards, Piotr
I don\'t think transformers are usually designed for equal core and
copper losses. This one runs cold at full AC voltage but no load.

They are designed for equal primary and secondary copper losses at
full load, I think.

Cooling depends on surface area. You get more surface area by adding
more copper, and that relationship is not linear (the volume-surface
thing, like mice and elephants) so core loss might require a lot of
expensive copper.
 
J

John Larkin

Guest
On Wed, 5 Aug 2020 16:33:48 -0700 (PDT), Phil Allison
<pallison49@gmail.com> wrote:

boB wrote:

----------

Why aren\'t you measuring this transformer using AC ?

It is going to be hotter with AC.

DC will certainly give you a best case reference though.


** The standard test involves shorting the secondary with an amp meter and applying enough AC volts to the primary to get the rated current.

This will, after a time, establish the temp rise and copper losses.

DC only heats one winding and needs an expensive supply.

JL likes to do things the hard way.


.... Phil
The 10-amp DC supply was right there on the bench, plugged in even. We
may have an old Variac somewhere in the basement, but I haven\'t seen
it in years.

The DC measurement told me what I wanted to know. It wasn\'t hard.

The fan has a USB cable for power, and I didn\'t have a USB power
supply, but the oscilloscope has a memory stick connector on the
front, so I used it to run the fan. The scope was also right there,
plugged in too.

https://www.amazon.com/gp/product/B00080G0BK/ref=ppx_yo_dt_b_search_asin_image?ie=UTF8&psc=1

Really cool gadget.
 
P

Phil Allison

Guest
Piotr Wyderski wrote:

===============================
I think people design transformers for
equal copper loss in the primary and secondary

BTW, what is the source of this and similar rules of thumb (e.g. equal
copper and core losses)? Logic says that one should always design for
minimal total losses, given the economic constraints.
** The source is simple calculus that finds the minimum or maximum in a curve. It\'s also kinda obvious that if the primary and secondary run at different temps then you have one heating the other. Same goes for core and windings.

The issue with tape wound toriodals is their very sharp saturation curves - forcing the designer to keep away from that condition. Hence their low contribution to heat from the core.

Commercial toroidals are made using a clever machine passing wire through the centre hole - this sets a limit on the amount of copper that can be used.

I know of one amplifier designer who at my suggestion had the winder use his machine for the primary and wind the secondary by hand in order to fill the hole almost completely. This almost doubled the amount of copper used.

Along with a bit of fan cooling, the result was a 3kW rated amplfier that used a 1kW size transformer core.


...... Phil
 
W

whit3rd

Guest
On Wednesday, August 5, 2020 at 1:45:36 PM UTC-7, John Larkin wrote:
On Wed, 05 Aug 2020 13:21:31 -0700, boB <boB@K7IQ.com> wrote:

On Tue, 04 Aug 2020 19:35:39 -0700, jlarkin@highlandsniptechnology.com
wrote:


We can sense the primary current of this transformer, with a shunt and
an isolated delta-sigma ADC....
So I ran it for a few hours with 10 amps DC in the primary. Temp rise
was about 26C in free air.

Why aren\'t you measuring this transformer using AC ?

Because there\'s a 10-amp DC supply on the bench.


It is going to be hotter with AC.

Hardly any.
Iron lossses due to eddy currents and hysteresis aren\'t insignificant. It this
for variable frequency use? Those iron losses are frequency-dependent.
it might take a bunch of testing to characterize.

Early switchmode power supplies occasionally heatsinked the transformer cores...
 
P

Phil Allison

Guest
whit3rd is Witless wrote:

-------------------------
It is going to be hotter with AC.

Hardly any.

Iron lossses due to eddy currents and hysteresis aren\'t insignificant.
** They are with GOSS tape wound into a toroid.


It this for variable frequency use?
Those iron losses are frequency-dependent.
it might take a bunch of testing to characterize.
** No it wont.

JL\'s tranny is rated for 50/60Hz and will work fine with lower losses at any higher frequency. Core magnetisation goes DOWN with rising frequency for a given primary voltage.

Never seen an audio output tranny in your entire life ?


> Early switchmode power supplies occasionally heatsinked the transformer cores...

** So what ?


..... Phil
 
S

server

Guest
On Wed, 5 Aug 2020 18:01:49 -0700 (PDT), whit3rd <whit3rd@gmail.com>
wrote:

On Wednesday, August 5, 2020 at 1:45:36 PM UTC-7, John Larkin wrote:
On Wed, 05 Aug 2020 13:21:31 -0700, boB <boB@K7IQ.com> wrote:

On Tue, 04 Aug 2020 19:35:39 -0700, jlarkin@highlandsniptechnology.com
wrote:


We can sense the primary current of this transformer, with a shunt and
an isolated delta-sigma ADC....
So I ran it for a few hours with 10 amps DC in the primary. Temp rise
was about 26C in free air.

Why aren\'t you measuring this transformer using AC ?

Because there\'s a 10-amp DC supply on the bench.


It is going to be hotter with AC.

Hardly any.

Iron lossses due to eddy currents and hysteresis aren\'t insignificant. It this
for variable frequency use? Those iron losses are frequency-dependent.
it might take a bunch of testing to characterize.
200 Hz to 4K. This simulates a 6-pole PM alternator on a jet engine.
Primary current is very low when the transformer is unloaded.

It\'s a good transformer.



--

John Larkin Highland Technology, Inc

Science teaches us to doubt.

Claude Bernard
 
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