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

# transformer thermals

Started by ●August 4, 2020

Reply by ●August 5, 20202020-08-05

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

Reply by ●August 5, 20202020-08-05

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

Reply by ●August 5, 20202020-08-05

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

Reply by ●August 5, 20202020-08-05

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.

Reply by ●August 5, 20202020-08-05

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 itWhat 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=1You 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?

Reply by ●August 5, 20202020-08-05

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

Reply by ●August 5, 20202020-08-05

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. > > >.... PhilUnloaded, 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

Reply by ●August 5, 20202020-08-05

Reply by ●August 5, 20202020-08-05

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=1Why 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.