Uneven voltage on PS

chipco3434 · 19th February 2006, 11:56 PM

What causes an uneven voltage output on a +/- supply...

This should be a no-brainer but I have tranny of 30VAC and voltage of 40VDC. No problem. But it is +5VDC to GND and -35VDC to GND.

Tranny to bridge then to a couple rows of caps. GND comes from AC GNC "down the middle of the caps...

paulb · 20th February 2006, 12:34 AM

GND has to come from a source of some kind, the capacitors do not work well as a voltage divider as you have found. It should go to the centre tap of your transformer. If you have none, you would have to do something like a voltage doubler arrangement or a supply splitter circuit afterwards.
How much current do you need this supply to provide?

chipco3434 · 20th February 2006, 12:44 AM

I have no center tap...

Ah ha!

But I have made this 30VAC from two transformers of 15VAC... I guess I ought to connect the GND to the point where I connected the two trannys. Right?

Anyway, it would be nice to know the alternative.

A couple or three amps I reckon...

That would be plenty.

Thanks for the physics lesson!

chipco3434 · 20th February 2006, 01:17 AM

From where the two transformers are connected, I ran a wire to ground. DC voltage is now +20 and -32 after the caps and snubbers.

What gives?

chipco3434 · 20th February 2006, 11:06 AM

bump

pinkmouse · 20th February 2006, 01:14 PM

Are the transformers identical? Have you measured with a load on the PSU?

chipco3434 · 20th February 2006, 09:09 PM

No, I haven't applied a load. The measurements are unloaded. 1K 2 watt OK? To each side and GND and then test + to -?

chipco3434 · 21st February 2006, 03:48 PM

It works with a load. Each side with a R390 2 w and the voltage is ~20 on each side... within a few mV,

How come?

paulb · 21st February 2006, 06:21 PM

We don't know.

chipco3434 · 21st February 2006, 06:31 PM

"We" as in "scientists, physicists and hobbyists"?

Cool.

19th February 2006, 11:56 PM	#1
chipco3434 diyAudio Member Join Date: Feb 2004 Location: Racine, Wisconsin	Uneven voltage on PS What causes an uneven voltage output on a +/- supply... This should be a no-brainer but I have tranny of 30VAC and voltage of 40VDC. No problem. But it is +5VDC to GND and -35VDC to GND. Tranny to bridge then to a couple rows of caps. GND comes from AC GNC "down the middle of the caps...

20th February 2006, 01:14 PM	#6
pinkmouse diyAudio Moderator Join Date: Apr 2002 Location: Chatham, England	Are the transformers identical? Have you measured with a load on the PSU? __________________ Al I conceive of nothing, in religion, science or philosophy, that is more than the proper thing to wear, for a while. Charles Fort

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20th February 2006, 12:34 AM	#2
paulb diyAudio Member Join Date: Jun 2001 Location: Calgary	GND has to come from a source of some kind, the capacitors do not work well as a voltage divider as you have found. It should go to the centre tap of your transformer. If you have none, you would have to do something like a voltage doubler arrangement or a supply splitter circuit afterwards. How much current do you need this supply to provide?

20th February 2006, 12:44 AM	#3
chipco3434 diyAudio Member Join Date: Feb 2004 Location: Racine, Wisconsin	I have no center tap... Ah ha! But I have made this 30VAC from two transformers of 15VAC... I guess I ought to connect the GND to the point where I connected the two trannys. Right? Anyway, it would be nice to know the alternative. A couple or three amps I reckon... That would be plenty. Thanks for the physics lesson!

20th February 2006, 01:17 AM	#4
chipco3434 diyAudio Member Join Date: Feb 2004 Location: Racine, Wisconsin	From where the two transformers are connected, I ran a wire to ground. DC voltage is now +20 and -32 after the caps and snubbers. What gives?

20th February 2006, 11:06 AM	#5
chipco3434 diyAudio Member Join Date: Feb 2004 Location: Racine, Wisconsin	bump

20th February 2006, 09:09 PM	#7
chipco3434 diyAudio Member Join Date: Feb 2004 Location: Racine, Wisconsin	No, I haven't applied a load. The measurements are unloaded. 1K 2 watt OK? To each side and GND and then test + to -?

21st February 2006, 03:48 PM	#8
chipco3434 diyAudio Member Join Date: Feb 2004 Location: Racine, Wisconsin	It works with a load. Each side with a R390 2 w and the voltage is ~20 on each side... within a few mV, How come?

21st February 2006, 06:21 PM	#9
paulb diyAudio Member Join Date: Jun 2001 Location: Calgary	We don't know.

21st February 2006, 06:31 PM	#10
chipco3434 diyAudio Member Join Date: Feb 2004 Location: Racine, Wisconsin	"We" as in "scientists, physicists and hobbyists"? Cool.

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