Power supply construction question

bushroot · 20th October 2006, 03:04 PM

I'm using some huge Mallory computer grade capacitors. They are rated for 200VDC. Previously, I had them wired between V+, V-, and Chassis Ground. I'm curious if it will hurt anything to wire them between V+ and V-. I am running 160VDC rails. I know the caps will be fine, but will it have any adverse effect not being tied to ground? I have another filtering stage after these caps that will be connected in the conventional manner. I'm not sure if I'm making myself clear here, so I'm attaching a diagram.

Minion · 20th October 2006, 06:11 PM

In all Power supplies I have ever seen or built the Negitive end of the Caps on the positive rail were allways tied to ground and on the Negitive rail the Positive end of the caps were allways tied to ground and I"m sure it is like that for a Good reason....

Probably has to do with the fact that the Ground is also 0V....

Also if you Tie a cap between + and - if that cap ever fails and become an open circuit you will Cause a Short and Fry your PSU and maybe even your whole Circuit....

So I wouldn"t do it if I were you ......

Cheers

AndrewT · 20th October 2006, 06:20 PM

Hi,
I think the impedance from ground to either rail will not be improved by the rail to rail caps. The ground connection is still between the second level of filtering and this determines the PSU output impedance relative to ground.

I do not understand this

Quote:

if that cap ever fails and become an open circuit you will Cause a Short and Fry your PSU

please explain.

Minion · 20th October 2006, 06:32 PM

Well, It seems pretty logical to me....If you Take a positve wire and connect it to a Negitive wire with nothing in between then bad things will happen...

The last time I stuck a Hair pin an an electrical outlet bad things happened, like it blew out the circuit breaker and I had to go to the Hospital.....

Would this also not effect a circuit if it was not protected by a Fuse?? Like when a Caps fails and allows DC to pass through??

Hey your the expert(Well more than me anyways) , Please show me the error of my ways...

Cheers

Stocker · 20th October 2006, 06:50 PM

Capacitors from rail to rail keep the rails quieter relative to each other. From one rail to ground keeps them quieter, period.

If you were considering it, don't use tantalums from rail to rail. The bang is much louder than rail to ground, and the common mode of failure for tant. caps is short.

bushroot · 21st October 2006, 06:06 PM

Because the voltage rating on the big mallory caps is so high, I can have twice as much capacitance rail to rail as I would from rail to ground. That's why I was considering it.

20th October 2006, 06:50 PM	#5
Stocker diyAudio Member Join Date: Dec 2003 Location: Austin	Capacitors from rail to rail keep the rails quieter relative to each other. From one rail to ground keeps them quieter, period. If you were considering it, don't use tantalums from rail to rail. The bang is much louder than rail to ground, and the common mode of failure for tant. caps is short. __________________ Jesus loves you.

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20th October 2006, 06:11 PM	#2
Minion diyAudio Member Join Date: May 2006	In all Power supplies I have ever seen or built the Negitive end of the Caps on the positive rail were allways tied to ground and on the Negitive rail the Positive end of the caps were allways tied to ground and I"m sure it is like that for a Good reason.... Probably has to do with the fact that the Ground is also 0V.... Also if you Tie a cap between + and - if that cap ever fails and become an open circuit you will Cause a Short and Fry your PSU and maybe even your whole Circuit.... So I wouldn"t do it if I were you ...... Cheers

20th October 2006, 06:32 PM	#4
Minion diyAudio Member Join Date: May 2006	Well, It seems pretty logical to me....If you Take a positve wire and connect it to a Negitive wire with nothing in between then bad things will happen... The last time I stuck a Hair pin an an electrical outlet bad things happened, like it blew out the circuit breaker and I had to go to the Hospital..... Would this also not effect a circuit if it was not protected by a Fuse?? Like when a Caps fails and allows DC to pass through?? Hey your the expert(Well more than me anyways) , Please show me the error of my ways... Cheers

21st October 2006, 06:06 PM	#6
bushroot diyAudio Member Join Date: Oct 2004 Location: The high-five state	Because the voltage rating on the big mallory caps is so high, I can have twice as much capacitance rail to rail as I would from rail to ground. That's why I was considering it.

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