powersupply recapping question.

[aidynphoenix]

hello.
i have a nice powersupply that has 7 buldging caps and about 13 total,,

i had replacements for the smaller caps already and replaced them..
however there is 6 tall and skinny caps 4700uf 10v smack in the middle of all the 12v, 3v, and 5v outputs.
these need replacement pretty bad..

now my question is.. how important are the UF ratings of these caps????
(are these caps used as noise filters for the power rails?)

i dont know the rules of capaciator's used as filters. (assuming these are filters)

is it fine if i go up or down with the UF rating of these because i dont have any 4700uf caps in anything higher than 6.3v

[aidynphoenix]

bump

[scutzi128]

If used in a filter then yes the uF rating does matter. See here for info on RC filters. http://en.wikipedia.org/wiki/RC_circuit

[NEOAethyr]

Capacitance(uf) can some times determain the switching freq of the mosfets that drive the line.
The biger the uf, the faster and smoother the mosfets switch.
Within there range and the range of other parts.

If the "giant" caps fail btw, don't go to big with them otherwise you could blow some parts if your psu sucked...
800uf or 1200uf total should be fine.
They can be wired up diffrently though but usually the single ones are running at eur voltages and don't split the capacitance in half in favor for high voltages.

Caps in general can add a slight charge, or smooth the output a bit of dc generated signal.
The higher the better kinda...
As long as you have decent coils.

You can replace 10v with 6.3v.
The 16v volts, you can either check with a dmm or get 16v caps.

I never buy lower quality then rubycon or samxon.
It's rubycon mbz, mcz, zl and zlh models.
Samxon, whatever the goods ones are I can't remember off hand, I think gd, ga and whatever, can't remember.

4700uf, samxon defently, getting a rubycon of this size for zl or better zlh is about impossible, at least for me.

The diameters of the caps are (this is important):
8mm, 10mm, 12.5mm and 16mm.
8's are skinny.
10's are what you normally used to see on board's for there cpu.
12.5 are usually used on 12v caps, if not 3.3v and 5v as well.
"Sometimes" you'll see 16mm caps on those rails instead.

10mm's "can" fit into 12.5mm holes if you wanted, I've done it.
The bigger the better kinda, it's what you got to work with.

If the orignal's were 16, then you got space.
If 12's, then good.
If you psu is using 10mm caps..., well, then you're gonna have a hard time sqeezing in 12.5mm caps.

Height, max you wan't to play around with is 25mm.
Or close to that.
You run the risk of bumping into stuff...


To put it simply.
Rail caps, like 12v and 5v and 3v, 5vsb, get the best you can and the biggest you can.
As long as you have enough coil's.... if you don't you'll get a high pitched noise coming form the mosfets that sounds like a tv or a vcr when they are turned on that some people can hear (which is not good, for 1 it's noise in your line, and it's radiation.., and it's probably not good for your ears even if you can't hear it).

For tiny caps, best not to mess around unless you know what you are doing, get exact replacements otherwise(brand name replacements).

Edit:
Oh... and you do know how to discharge a psu correct? (there's a reason why they say don't open...)
If you don't you shouldn't be touching it...
When unpluged from the wall either press the power button on your board while it's hooked to the psu, or jump start it when it's not hooked to anything other then a fan.
That will discharge the psu.
Make sure it's completely dead...
Fans stops, it's good.

[aidynphoenix]

thanks very much guys.
i rigged up a few caps.. they are too big to fit in the origional places. so i ran some wires on the ends of the leads to make it work..
i am going to order a 10pack of the caps i need. but i will have to wait for shipping in the meantime..
i could go to radioshack but they are charging $6. a cap!!!!!! its less than $6 online for ten of them..
so i will just do some waiting.. but these caps will be temporary untill i get the proper replacements..
btw i only had a few 4700uf caps to use. so i had to doubble up several others to make the right rating..
i'l take some photos of it when i can.

[SexyMF]

Always replace capacitors with same or high capacitance and/or voltage rating.

The capacitors you are referring too are on the output side of the switching transformer. It is very important to get low ESR capacitors. The crap you get at your local store are likely to be standard electrolytic capacitors. Capacitors have a resistance which change with frequency. The ouput of a PSU runs at high frequency. Normal caps will get hot, dry out and fail.

Only use a single cap. In theory you can follow the rules for series/parallel caps and what it does to the capacitance rating and voltage - but this isn't the time to do that.

[aidynphoenix]

i replaced a few of them. and tryed it on my multimeter the voltages are jumping up and down pretty crazy. i have seen it at 3, 7, 11, 1, volts..
does that sound like what a regular electrolyc non low ESR caps might do?
i guess will order all new caps for the psu..

[SexyMF]

i replaced a few of them. and tryed it on my multimeter the voltages are jumping up and down pretty crazy. i have seen it at 3, 7, 11, 1, volts..
does that sound like what a regular electrolyc non low ESR caps might do?
i guess will order all new caps for the psu..

No. The caps will work just that they won't go the distance. There should be no AC component to the voltage.

I would recommend you replace the the PSU. Otherwise you do risk damaging your PC if your repair doesn't hold up.

[aidynphoenix]

thanks sexy i will definetly not use one unless the voltages are stable. like they should be..

all those bouncing voltages were on the 12v rail..

i did also replace 2 small caps that were not one of the 6 large filter caps.
i dont know the purpose of these two.
but i will completely recap it and see if the voltages are still moving..

can you shoot me some posible reasons why the voltages might be changing like that..

also there was no load on the psu when i tested the voltages.. so maybe that has something to do with it,, idk..