35v caps on 286 board?

[Moogle!]

I've got a 286 board I want to recap, but it has 35 volt tantalum caps all over it. Is there a reason they would have used these over 16 volt caps, other than maybe they got a good deal on 35 volt ones?

 

[NeXT]

Likely they just got a good deal, but also using tants with a higher voltage rating is fine as it just means they are less likely to blow on inrush spikes, plus tants REALLY do not like going over their rated voltage for any amount of time.

 

[T-R-A]

Yep, common practice. In fact, we have an assembly at work that I work on that normally comes in with 2000µF 35v electrolytic filter caps on the output of the 12v power supply. Another assembly we have uses 2200µF 50v capacitors. To save from having to stock 2 different values, it's cheaper for me to use the 2200µF ones.

 

[KC9UDX]

There's no upper limit to the voltage rating selection of most capacitor types, except electrolytics. When the voltage rating of an electrolytic is too high, normal "formation" is conversely affected.

 

[eeguru]

Caps start to significantly de-rate as they near their max rated voltage. The common rule of thumb is to use caps rated twice the voltage as normal steady state voltage. Capacitance is never static and always a function of voltage. Always check the data sheet for C vs V curves.