I am thinking of replacing some aluminum electrolytic capacitors on a 1980's vintage computer board. While I know that caps must be replaced with same or higher voltage rating, I was wondering if there are any negative effects or reasons NOT to bump up capacitors' voltage ratings. The original cap I was thinking of replacing is very messy looking and has probably leaked out onto the board. It is 16v, but I found some 25v caps for a cheap price. Considering dieletric, plate separation, internal resistance and the like, are there really any negative effects that could result from using a higher voltage rating?

 

Higher voltage caps will be larger than the lower voltage caps of the same value.

Be careful about cheap caps, they might be counterfeit or be of lower quality.

 

I wouldn't worry one wit about a change from 16V to 25V. But be careful about the footprint dimensions and the lead diameters. It may not be a deal breaker but it can be a pain to drill new holes or try to squeeze in a can wider than the spot it needs to fit.

 

The biggest problem with choosing new aluminum electrolytic capacitors for old applications is that there are so many types to choose from and the types vary significantly in their characteristics and performance. More on that later. As a general rule of thumb, within a single product family from a single manufacturer, capacitors of the same uF value but higher voltage rating have higher internal resistance and lower ripple current capability. The change between adjacent voltage ratings is not much, but can be a problem if the circuit must withstand a specified ripple voltage value. In case you can't tell, I got burned once by a ripple current issue. Using a 25 V part in a 16 V design probably is no big deal. Using a 100 V part might be.

A much harder thing to determine is if the new cap (at whatever voltage) has approximately the same leakage current, ESR, and ripple current ratings as the old one, and is in fact a good drip-in replacement. For an audio coupling circuit, probably not a problem. For a switching power supply regulator or input/output filter, it could change the circuit performance enough to fail EMI testing or radiate noise into an adjacent sensitive circuit.

ak

 

Higher voltage caps will be larger than the lower voltage caps of the same value.

Be careful about cheap caps, they might be counterfeit or be of lower quality.

Like this fake capacitor!