Power Supply capacitors

5 replies [Last post]
Witchy's picture
Offline
Joined: Aug 6 2016
Posts: 13

Hi folks,

Looking at the PSU of my Lisa's ProFile after it died gracefully not so long back and it obviously needs new caps since one of the 1000uF 16V ones has bulged badly. While I'm replacing that one I'll do the 47uF 250V ones too. And the mains filters but I've got a stock of spares for them already.

When it comes to cap replacement I know I can go up a notch if the required capacitance or voltage isn't available so 25V and 400V is ok, but what about physical size? I can get the correct capacitance but they're physically much smaller than the ones I'm replacing. If I go up to 25V I can get 15mm diameter which is the size of the old ones.

Am I worrying for nothing?

Cheers

Witchy

__________________

--
www.binarydinosaurs.co.uk, UK home computer history

Comment viewing options

Select your preferred way to display the comments and click "Save settings" to activate your changes.
Witchy's picture
Offline
Joined: Aug 6 2016
Posts: 13
Re: Power Supply capacitors

Sorted! Nothing to see here, move along now....

__________________

--
www.binarydinosaurs.co.uk, UK home computer history

gsmcten's picture
Offline
Joined: Oct 4 2005
Posts: 2616
Re: Power Supply capacitors

"These are not the Caps you're looking for...Move along."
lol

Steven Smile

__________________

Steven (gsmcten)

"Apple ][.....It's ALIVE!!!!!"

CWJ_Wilko's picture
Offline
Joined: Jun 3 2015
Posts: 272
Re: Power Supply capacitors

Glad you sorted it out! AFAIK capacitor technology has improved over the decades, so physically smaller capacitors can perform just as well as their older counterparts that had a larger footprint. But in my Apple II PSU I specifically went for capacitors that had a larger footprint at the same capacitance, with a much higher voltage rating. It was purely an aesthetic choice for me.

For posterity, you should have no problem using capacitors with a higher voltage rating, no matter the difference - it's just a max limit. But capacitance should be closely matched when possible, with capacitors of a slightly higher capacitance preferred when a match can't be made.

Witchy's picture
Offline
Joined: Aug 6 2016
Posts: 13
Re: Power Supply capacitors

Quote:

For posterity, you should have no problem using capacitors with a higher voltage rating, no matter the difference - it's just a max limit. But capacitance should be closely matched when possible, with capacitors of a slightly higher capacitance preferred when a match can't be made.

yep, that's exactly what I'm doing. I talked to a couple of electronic engineers who said the main issue with the smaller modern caps in old circuitry might be heat dissipation in instances of high AC ripple. 25V and 400V caps at the right capacitance are winging their way to me as I type, and I've just realised one of my ][+ needs new caps too, dammit Smile

W

__________________

--
www.binarydinosaurs.co.uk, UK home computer history

Offline
Joined: May 27 2013
Posts: 794
Re: Power Supply capacitors

If one is going to be replacing caps, one needs to make sure that components like the resistors are not overheating or all your work will be for nothing.

Hey, if you want to blow up your apple, that's fine but maybe it would be better on the 4th of July.

At night.

With everyone watching.

There's a video somewhere which explains this from the people who run ultimateapple2.

The principles are the same.