Physical size of cap's

[Ric]

I have a cap on a board that is 405v 47uf 105'c and is 50mm long by 10mm (2" x 3/8").
Can I replace it with a cap of the same value but physically smaller ? Half the size.
It is in a switch mode psu.

 

[(*steve*)]

Generally speaking, a physically smaller cap with the same voltage and capacitance is likely to have worse specs in other areas.

Is the new cap 105C or 85C? They typically operate in a warm environment.

Another important rating is ripple current. The smaller cap is likely to have a lower rating.

However, in most cases this cap is, relatively, under lower stress than other caps (especially for 220V operation), so it may be OK.

I had to replace a pair of calls in my oscilloscope. The original caps were unobtainable. The replacements we physically smaller. I do note a slightly higher amount of residual ripple, but it's not significant.

 

[Ric]

Thanks. I was wondering about the ability of the smaller one to dissipate any heat that might be in the larger cap.
I will look for one that is closer size to the original.
Hard to find here.

 

[davenn]

Thanks. I was wondering about the ability of the smaller one to dissipate any heat that might be in the larger cap.
I will look for one that is closer size to the original.

It's not a hugely major issue
More modern manufacturing techniques have also meant that the physical size has shrunk for a given value and voltage rating

Dave

 

[(*steve*)]

Yeah, I should have mentioned that. The relationship exists (roughly) for a cap you purchase today. The older the equipment the less it applies.

I guess I should have asked about the age of the equipment.

In more direct answer to your question, newer caps generally have lower internal losses, so the self-heating, and hence heat to dissipate is lower.

 

[Ric]

I will give the smaller ones a chance this time.
Thanks for the replies.