Wanting to use poly caps

[Howie]

My mothers motherboard needs about 8 or 10 caps replaced around the CPU area. I want to swap these for poly caps, but not sure what specs to use with those.

The old caps are:

1000uf 16v & 1500 6.3v

What would be the values needed to replace these with poly's?

Thanks.

[mariushm]

Re: Wanting to use poly caps

I wouldn't bother replacing those 1000uF 16v capacitors with polymer capacitors. They're not THAT important to require very/ultra low ESR.

I'd use high lifetime capacitors like Panasonic FM for those.

As for the 1500 6.3v, you may get by with a voltage rating of 4v or even 2.5v but since I don't know the motherboard, let's say you should pick 4v rated polymers.
Usually you can go down in capacitance quite a bit by going with polymer capacitors.

Since you don't list the country and other stuff (sigh) I'm going to guess US and recommend going for some 1200uF 4v polymers that are cheap on Digikey:

http://www.digikey.com/product-detai...703-ND/2207239

They're Nichicon FPCAP so if that doesn't fancy your tastes, there's more expensive capacitors like this series:

http://www.digikey.com/product-detai...065-ND/1662451

Specs wise, not much difference as far as i can see.

[Howie]

Re: Wanting to use poly caps

Yeah its a US motherboard.. Asus ...I really like the low profile of the poly's as well so really just wanted to replace all them in that area with those because of the heat as well. That is what always confused me about the poly caps is how you can use a 4v on a 16v rated area..just never quiet understood that and wasnt sure what to use to be safe.

[mariushm]

Re: Wanting to use poly caps

It's not a 16v area.

The 16 v capacitors are indeed used on the 12v rail so you would have to use polymer capacitors rated for at least 16v. But for how those capacitors are used, it makes no difference if the capacitor is polymer or electrolytic.

The processor itself works at low voltages .. 0.9-1.4v, maybe a bit depending on architecture. So there's a bunch of dc-dc converters near the CPU which take energy from the 16v capacitors and produce those low voltages and the 6.3v rated capacitors store energy for when the cpu (and sometimes the memory and other things) have sudden demands of power.

As a poor analogy... those 16v capacitors are like cement trucks which just have to slowly unload cement in the pool from which a cement pump (the dc-dc converter) takes cement and pushes it up the building at high floors. They don't have to be any kind of special "truck", there just has to be a constant influx of cement to the pool.

The 6.3v capacitors have a more important role, giving the dc-dc converters time to react to more demand and increase their output and to prevent the voltage going to the cpu from dipping too low, so that's where esr and specs of capacitors is important..


Thing is... polymer capacitors rated for 16v are hard to find and expensive at such capacitance value. Most you'd probably find would be 270-330uF. But depending on what dc-dc converter chips are used on the board, this might be just too little and may make your board unstable.
You may also find some polymer capacitors that get close to that capacitance, but they may not be of the "low impedance/esr" kind - not all polymer capacitors are low esr.

[Howie]

Re: Wanting to use poly caps

Makes sense ..I appreciate your help and especially going the extra mile and throwing me the website link.