Wiring secondaries of two power trafo's in parallel?

Klimon · 20th October 2005, 10:13 PM

Hello,

Am I right to think that parallelling the secondary ht windings of two identical power transformers (primaries also parallelled with respect to phase) will result in: same voltage as one trafo; current rating doubles; internal resistance is half of one trafo?

Are there any electrical drawbacks to this approach?

I could also go dual mono but the parallelled approach (if my suppositions are true that is) fits better for the amp I'm planning + needs less filter components...

Thanks

Tweeker · 20th October 2005, 10:23 PM

If they arent perfectly matched, they wont share current perfectly. Low value output resistors might possibly be called for.

Klimon · 20th October 2005, 10:43 PM

Okay - thanks!

I have four identical trafo's so will pick two with matching primary & secondary winding resistance.

Simon

DSP_Geek · 20th October 2005, 11:09 PM

Still not guaranteed. If one transformer outputs 40V, the other 39.9 V, and the secondary resistance is 0.2 ohms, then you have 0.5 amps flowing from the higher voltage one to the lower. Also the output voltage can change under load because primary and core losses might be different for the two as well, so you're really looking at a suboptimal situation.

I'd recommend dual mono. You'll feel virtuous doing it, too.

Cheers,
Francois.

Klimon · 21st October 2005, 12:22 AM

Back to dual mono than! And this time right ... my previous amps were meant to be dual mono but I accidently parallelled power trafo's on both occasions... strangely enough one plays perfectly while the other one almost burned both it's trafo's - ...

... I did experience the virtuous-feeling thing however

Brian Donaldson · 21st October 2005, 01:22 AM

You could parallel the primarys, then series the secondarys 4 ohm taps, then you'll have pretty good sharing, but they won't fight each other.

20th October 2005, 10:13 PM	#1
Klimon diyAudio Member Join Date: Apr 2005 Location: Leuven	Wiring secondaries of two power trafo's in parallel? Hello, Am I right to think that parallelling the secondary ht windings of two identical power transformers (primaries also parallelled with respect to phase) will result in: same voltage as one trafo; current rating doubles; internal resistance is half of one trafo? Are there any electrical drawbacks to this approach? I could also go dual mono but the parallelled approach (if my suppositions are true that is) fits better for the amp I'm planning + needs less filter components... Thanks

21st October 2005, 12:22 AM	#5
Klimon diyAudio Member Join Date: Apr 2005 Location: Leuven	Back to dual mono than! And this time right ... my previous amps were meant to be dual mono but I accidently parallelled power trafo's on both occasions... strangely enough one plays perfectly while the other one almost burned both it's trafo's - ...... I did experience the virtuous-feeling thing however

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20th October 2005, 10:23 PM	#2
Tweeker diyAudio Member Join Date: Dec 2004 Location: Cincinnati, Ohio	If they arent perfectly matched, they wont share current perfectly. Low value output resistors might possibly be called for.

20th October 2005, 10:43 PM	#3
Klimon diyAudio Member Join Date: Apr 2005 Location: Leuven	Okay - thanks! I have four identical trafo's so will pick two with matching primary & secondary winding resistance. Simon

20th October 2005, 11:09 PM	#4
DSP_Geek diyAudio Member Join Date: Aug 2003 Location: Santa Cruz, California	Still not guaranteed. If one transformer outputs 40V, the other 39.9 V, and the secondary resistance is 0.2 ohms, then you have 0.5 amps flowing from the higher voltage one to the lower. Also the output voltage can change under load because primary and core losses might be different for the two as well, so you're really looking at a suboptimal situation. I'd recommend dual mono. You'll feel virtuous doing it, too. Cheers, Francois.

21st October 2005, 01:22 AM	#6
Brian Donaldson diyAudio Member Join Date: Jan 2003 Location: Texas, Love it or leave it	You could parallel the primarys, then series the secondarys 4 ohm taps, then you'll have pretty good sharing, but they won't fight each other.