Uneven voltage on PS

[chipco3434]

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]

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]

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]

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]

bump

 

[pinkmouse]

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

 

[chipco3434]

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]

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]

We don't know.

 

[chipco3434]

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

Cool.

 

[SY]

"We" as in people who don't have the stuff in front of us so we can nail down the reason.

 

[apolon34]

you should use a separate diode bridge for each transformer and then tie together the + output of one bridge with - ouput of the other. This'll be your gnd point.

il your transformers ac voltage are the same, the dc will be the same too.