high voltage capacitors for low voltage applications?

[SArepairman]

Is there anything special to know about using those nice HV (100V+ ) electrolytic capacitors for low voltage applications, such as smoothing after a bridge rectifier at low voltage (3-50V)?

how about 50V parts in a 5V circuit? Is there any rules?


other then they are over sized

[Rerouter]

generally none, but I believe the esr will be higher for higher voltage units,

[Conrad Hoffman]

Crap, my fat fingers just trashed my brilliant reply. Have to settle for this one- If you look at the data sheets for a given cap series, the higher voltage parts will have the lowest dissipation factor, at least to a point. I often take advantage of this and use 35-100 volt parts in much lower voltage circuitry. I've seen no downside whatsoever. That said, I'm not fully convinced that it's a good idea to use high voltage parts, say 250-500 in low voltage circuits. I've seen old caps that can't support any more voltage than what they were run at for decades, without large and destructive DC leakage. Of course, you could just call them bad caps that have reached the end of their lives. There's also the size and expense issue, and they don't have the performance advantage that you get with a moderate voltage increases when working under 100 V. There seems to be a sweet spot with capacitor performance between 35 and 100 volts, but above that you might see the dissipation factor stay the same or even increase. Always check the data sheets for the specific behavior.

[calexanian]

Depending on chemistry and production some caps if never run up in voltage may never fully form properly and leak and fail early in life. I recall seeing a minimum spec for pre forming them. Generally speaking you are fine from then out. Best practices I recall is 70% to 80% rated voltage is ideal for maximum cap life after having been formed at peak voltage (Typically just above DCWV) I believe however than most caps are pre formed nowadays.