Capacitor replacement

[debugtimog]

Hi,
I am trying to replace a defective capacitor the one on the left side, rated 47,000uF/7.5VDC with the one on the right rated 47,000uF 10V. The question is, the size is a big difference. The other one is humungus, the size of my fist, while the other one is slightly bigger than my thumb only. I know that through the years the size of the capacitors that shrunk due to technical advancement, but this is like time 10 shrinkage? i have seen half the size shrink, but this one, the replacement is so small I am thinking something will went wrong if I go ahead with the replacement. Any advice on this? Thanks.

[Hitto]

Re: Capacitor replacement

The big one is an ancient Computer Grade Capacitor.

The difference is that the big one handles much more current and its E.S.R. is very low.

The replacement is general purpose, quite a cheap brand and I'd bet it would not handle more than 1/10 of the current of the big one. It will fail to smooth properly the intended current of that circuit.

Look for some Cornell Dubilier high ripple capacitors.

[mariushm]

Re: Capacitor replacement

Have to agree, the small one may not be able to handle the current.

Look into capacitors rated for higher voltage, like for example 35v..63v.. the higher volume will give them the ability to handle higher current bursts.

[R_J]

Re: Capacitor replacement

A similar cap CDE CGR473U7R5V3C, 47,000µf 7.5v is rated 17.8A @120Hz .

[debugtimog]

Re: Capacitor replacement

"cant handle the current" means also it will blow at some point, or it can still be used but it will not filter the ripple properly as compared to the big one?

[stj]

Re: Capacitor replacement

cannot handle the ripple, and will potentially damage the device because of it.

[PeteS in CA]

Re: Capacitor replacement

That original cap looks like a super low ESR, very high ripple current type that Sprague and maybe Mallory used to make. The ESR will be less than 10 milliohms, probably less than 5 milliohms.

That Jackcon (a very poor brand, generally) cap would be spewing its guts, probably within minutes.

[Stefan Payne]

Re: Capacitor replacement

What device is that picture from??

[eccerr0r]

Re: Capacitor replacement

^ yes

Thing is, old computers that have these really huge old low ESR caps typically have the charging side with... 120Hz rectified mains, oddly enough. Switching PSUs were rare and in order to have the hold up, large capacitances were needed. So while the discharge side is same as always (though it tends to have little small bypass caps to help that) the charge side is very easy on the capacitor.

That being said, and still don't know what the capacitor came out of, and it very well may be switching. So, how did you determine the cap was bad?

[PeteS in CA]

Re: Capacitor replacement

^ yes

Thing is, old computers that have these really huge old low ESR caps typically have the charging side with... 120Hz rectified mains, oddly enough. Switching PSUs were rare and in order to have the hold up, large capacitances were needed. So while the discharge side is same as always (though it tends to have little small bypass caps to help that) the charge side is very easy on the capacitor.

That being said, and still don't know what the capacitor came out of, and it very well may be switching. So, how did you determine the cap was bad?

Boschert used a similar or that very cap for the output capacitor on their HL1500, a 5V, 300A, 1500W switching power supply. I do not know whether Boschert ever brought that model to market, though.

The capacitor in the picture has a 9121 date code, meaning it was made in the 21st week of 1991. Pioneer Magnetics is (was?) not a manufacturer of electrolytic (or any other) capacitors, but of switching power supplies.

[debugtimog]

Re: Capacitor replacement

The capacitor was from a power supply, it was determined to be bad using an ESR meter. Measured capacitance was 1000UF. Im planning to bank a few smaller capacitor to duplicate the big one. Advice are welcome.