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power supply filtering questions

post #1 of 9
Thread Starter 
I didn't know if this would have any effect on the motherboard here but I was curious on adding an extra cap in parallel with the 12v plugins if it might help with voltage stability and reduce any noise that might be on the lines.

I just didn't know exactly if this could cause any problems even more so being with active PFC that I believe this PSU has.
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post #2 of 9
Quote:
Originally Posted by rx7speed View Post
I didn't know if this would have any effect on the motherboard here but I was curious on adding an extra cap in parallel with the 12v plugins if it might help with voltage stability and reduce any noise that might be on the lines.

I just didn't know exactly if this could cause any problems even more so being with active PFC that I believe this PSU has.
err....

First off, PFC is on the primary (AC) side of the PSU and you're talking about filtering on the secondary (DC) side.

Also, if the ripple and/or noise is anywhere near justifying having to put an additional cap on the line for filtering purposes, the PSU is bad and needs to be thrown out.
post #3 of 9
Thread Starter 
thank you for the clarification. I was not sure where the PFC part was in the circuit as I don't know much about it or how it works . if it is on the AC side then there is no point it trying anything with that.


as far as ripple on the line I haven't tested it myself as I don't have a scope but just a cheap DVM. being a cheapy the response time is long enough that I can't read any ripple using it on the DC setting and on the AC setting it can't read that low so still can't verify there is a ripple or noise problem. only indication I do have of one is by your own review of the supply in question showed it was out of spec at higher loads (which I know my load is not even that high).


this is more of a question of curiosity on IF it could be done and also if there is any chance of it possibly making for a more stable power delivery to the computer? Being that I have a bunch of caps lying around it wouldn't put me out any real addition expense at least. figured ask before I try though and see if it is even worth the effort.
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post #4 of 9
Quote:
Originally Posted by rx7speed View Post
thank you for the clarification. I was not sure where the PFC part was in the circuit as I don't know much about it or how it works . if it is on the AC side then there is no point it trying anything with that.


as far as ripple on the line I haven't tested it myself as I don't have a scope but just a cheap DVM. being a cheapy the response time is long enough that I can't read any ripple using it on the DC setting and on the AC setting it can't read that low so still can't verify there is a ripple or noise problem. only indication I do have of one is by your own review of the supply in question showed it was out of spec at higher loads (which I know my load is not even that high).


this is more of a question of curiosity on IF it could be done and also if there is any chance of it possibly making for a more stable power delivery to the computer? Being that I have a bunch of caps lying around it wouldn't put me out any real addition expense at least. figured ask before I try though and see if it is even worth the effort.
Ripple can never be measured by a DMM. And anything that IS measurable with a DMM (like poor regulation) can't really be fixed by caps.

So if you have poor regulation or excess ripple and/or noise, like I said, it's time to just chuck the PSU. Caps aren't going to help and the problem is only going to get worse.
post #5 of 9
Quote:
Originally Posted by jonnyGURU View Post
Ripple can never be measured by a DMM. And anything that IS measurable with a DMM (like poor regulation) can't really be fixed by caps.

So if you have poor regulation or excess ripple and/or noise, like I said, it's time to just chuck the PSU. Caps aren't going to help and the problem is only going to get worse.
Just to add.... ripple occurs too rapidly for a multimeter to detect. The reporting period of a multimeter is just to slow (and you couldn't read that fast anyways). You need a oscilloscope to measure ripple since it provides a graph and variable polling periods.
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post #6 of 9
Thread Starter 
sorry if I sound as though I'm trying to be arguementative I'm not. I just don't know if you are quite understanding what I was getting at as you keep refering to problems with the psu and what I'm trying to get at it not quite fixing a problem. If I'm just having some issue with understanding what your trying to say just tell me to drop it your not changing anything.

wouldn't the AC section of a dvm be able to at least read the ripple on the line if it is able to detect a low enough voltage or is that something that would need a blocking cap in place to make it readable? I know trying to read DC would be pointless as my meter has around a .5-1 second update speed. much slower then the 60hz ripple (not counting harmonics). this actually brings up another question not quite related. anyone know of any semi decent hand held scopes? I know there are some on ebay for around 100 bucks or so that I was looking at made by valeman or something like that but not sure yet on how bad I really want one.

also I don't see any reason to chuck the PSU as I have no indication yet at least of any problems with regulation or noise that I'm aware of and is working fine as is and is within spec. this was more of a hope of making the product work better then spec.


I do not know a lot of about digital electronics or switching power supplies as I'm sure you can see. I know though that most any ac to dc converter is going to have some rippled adn I believe that the ATX specs say what 100mv is allowable. so even if this design is within the 100mv it wouldn't be considered defective correct? my thinking was more along the lines of lets say the ripple is only at 60mv peak which should still be considered within spec but if I could reduce the amount of ripple to lets say 30-40mv by using a either a cap or a LC filter would that make any improvement to the operation of the psu even though both are within the normal operating range?
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post #7 of 9
Quote:
Originally Posted by rx7speed View Post
wouldn't the AC section of a dvm be able to at least read the ripple on the line if it is able to detect a low enough voltage or is that something that would need a blocking cap in place to make it readable? I know trying to read DC would be pointless as my meter has around a .5-1 second update speed. much slower then the 60hz ripple (not counting harmonics). this actually brings up another question not quite related. anyone know of any semi decent hand held scopes? I know there are some on ebay for around 100 bucks or so that I was looking at made by valeman or something like that but not sure yet on how bad I really want one.
There are some REALLY expensive DMM's with 450KS/s sample rates that can report RMS noise ripple.. but for the money you could buy a decent scope!

You're going to want to sample AT LEAST every 0.05 seconds (5ms), 0.02 seconds preferred.

Quote:
Originally Posted by rx7speed View Post
also I don't see any reason to chuck the PSU as I have no indication yet at least of any problems with regulation or noise that I'm aware of and is working fine as is and is within spec. this was more of a hope of making the product work better then spec.
If it aint broke, or you don't know if it's broke, don't fix it. Spec is spec for a reason. If it's in spec, it should provide zero-problem service. If it's out of spec, it's a piece of crap to begin with and you know what they say about polishing turds.
post #8 of 9
Thread Starter 
fair enough and thank you

do you have any cheapo hand held scopes that might work?
I was thking one of these, but don't know if I could do better for the money.
http://cgi.ebay.com/VELLEMAN-HPS10-P...QQcmdZViewItem

most my uses would be either auto or novice audio circuit work or other misc.
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post #9 of 9
For $100 jump all over that Velleman.
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