Correct replacement electrolytic capacitor.

Thread Starter

John Czerwinski

Joined Jun 19, 2017
34
Confused on choosing the correct replacement electrolytic capacitor.

For example, on an Atari AR I board (built in the early 1980s), the parts list calls for two (2) 3300 uf Aluminum Electrolytic Fixed Axial-Lead 35V. The original capacitor PHYSICAL size are relatively large. When you go on modern parts suppliers, you can find capacitors that fit the capacitance and voltage specs, but their physical size can be significantly smaller.

I've read somewhere that you should choose a replacement that is exactly the same size, or very close, because the design is calling for the capacitor to support a high and constant ripple. A smaller physical size will get stressed out quicker and fail.

Is there another specification characteristics that I should be looking at on the datasheets that need to match to the original part?
 

shortbus

Joined Sep 30, 2009
7,920
I've read somewhere that you should choose a replacement that is exactly the same size, or very close, because the design is calling for the capacitor to support a high and constant ripple. A smaller physical size will get stressed out quicker and fail.
Your looking at this from the wrong prospective. That statement means to chose the electrical value, not physical size. Like many things, capacitors have gotten better over the years, and physical size has been able to be made smaller.
 

DickCappels

Joined Aug 21, 2008
6,580
Any way you do it, it's like a coin toss. You get the best odds with something that old is to find the specifications for the original part, if in a power supply or other high power stage, find the ripple freqency (or guess) and the ripple current rating. If you can't find the ripple current rating decide what is most important to you: Price, availability, or ripple current rating. Same for internal resistance, though they often track each other.
 
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