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Old 19th February 2006, 11:56 PM   #1
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Default 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...
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Old 20th February 2006, 12:34 AM   #2
paulb is offline paulb  Canada
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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?
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Old 20th February 2006, 12:44 AM   #3
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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!
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Old 20th February 2006, 01:17 AM   #4
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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?
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Old 20th February 2006, 11:06 AM   #5
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bump
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Old 20th February 2006, 01:14 PM   #6
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Are the transformers identical? Have you measured with a load on the PSU?
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Old 20th February 2006, 09:09 PM   #7
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No, I haven't applied a load. The measurements are unloaded. 1K 2 watt OK? To each side and GND and then test + to -?
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Old 21st February 2006, 03:48 PM   #8
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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?
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Old 21st February 2006, 06:21 PM   #9
paulb is offline paulb  Canada
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We don't know.
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Old 21st February 2006, 06:31 PM   #10
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"We" as in "scientists, physicists and hobbyists"?

Cool.
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