Power supply help!

gary f · 14th April 2006, 07:26 PM

Simple question I guess

I'm building this circuit to supply plates for my amp at 315 and 305 volt. Main transfo is 275-0-275 volt.

Right now, in theory, I should get less than 300 volt at point A and B, but I get 420 volt approximately. WHY?

I should have maybe 250 volt. Am I correct?

Thank you
F

wa2ise · 14th April 2006, 07:43 PM

If there isn't enough of a load, the voltage will be higher. With no load, the filter caps will eventually charge up to 275 times 1.414 volts, about 385V for a powerline at 120V, but if your powerline is a little higher, and the 275-0-275V secondary is its voltage under load, these two factors would put the unloaded output voltage even higher to the 420V you're seeing.

gary f · 14th April 2006, 07:46 PM

There is no load right now...

Did not thought that this could cause a problem....
Thanks

Should I put my tubes in and try?
F

gary f · 14th April 2006, 07:49 PM

And my power line is 125 volt AC. Very interresting
F

Uchi Deshi · 14th April 2006, 07:54 PM

Did you measured it without load?

gary f · 14th April 2006, 07:56 PM

Yes I did. No load.

Is that bad??

F

Uchi Deshi · 14th April 2006, 07:58 PM

Yes. Absence of load causes higher voltage.If you convinced that your amp is good you can, but better solution is putting high power resistor.

Sheldon · 16th April 2006, 05:06 AM

http://www.duncanamps.com/psud2/

PSUD is your friend. It's free, it's easy, it works.

Sheldon

lndm · 16th April 2006, 09:52 AM

Is your transformer an old one that would have given 275/0/275 back when mains voltage was lower? Your result does not seem surprising. The resistor will develop a voltage drop only after there is current running through it. Connect your amp and the rails should come right down.

Sherman · 17th April 2006, 12:27 PM

Quote:

Originally posted by gary f
And my power line is 125 volt AC. Very interresting
F

You should also try measuring the AC voltage with a true RMS meter. I believe you'll then find your AC mains at 120V or less.

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14th April 2006, 07:43 PM	#2
wa2ise diyAudio Member Join Date: Apr 2005 Location: NJ	If there isn't enough of a load, the voltage will be higher. With no load, the filter caps will eventually charge up to 275 times 1.414 volts, about 385V for a powerline at 120V, but if your powerline is a little higher, and the 275-0-275V secondary is its voltage under load, these two factors would put the unloaded output voltage even higher to the 420V you're seeing.

14th April 2006, 07:46 PM	#3
gary f diyAudio Member Join Date: Aug 2003 Location: Quebec city	There is no load right now... Did not thought that this could cause a problem.... Thanks Should I put my tubes in and try? F

14th April 2006, 07:49 PM	#4
gary f diyAudio Member Join Date: Aug 2003 Location: Quebec city	And my power line is 125 volt AC. Very interresting F

14th April 2006, 07:54 PM	#5
Uchi Deshi diyAudio Member Join Date: Apr 2006 Location: Poland	Did you measured it without load?

14th April 2006, 07:56 PM	#6
gary f diyAudio Member Join Date: Aug 2003 Location: Quebec city	Yes I did. No load. Is that bad?? F

14th April 2006, 07:58 PM	#7
Uchi Deshi diyAudio Member Join Date: Apr 2006 Location: Poland	Yes. Absence of load causes higher voltage.If you convinced that your amp is good you can, but better solution is putting high power resistor.

16th April 2006, 05:06 AM	#8
Sheldon diyAudio Member Join Date: Dec 2003 Location: San Diego	http://www.duncanamps.com/psud2/ PSUD is your friend. It's free, it's easy, it works. Sheldon

16th April 2006, 09:52 AM	#9
lndm diyAudio Member Join Date: Mar 2006 Location: nsw	Is your transformer an old one that would have given 275/0/275 back when mains voltage was lower? Your result does not seem surprising. The resistor will develop a voltage drop only after there is current running through it. Connect your amp and the rails should come right down.