Electronic – Do caps with a higher max voltage have lower ESR

The answer is "it depends"...

Most cheapo general purpose capacitors (ie, not specified for very low ESR) will have a lower ESR with higher voltage rating. Let's have a look at this datasheet. It gives \$ DF = \tan \delta \$ instead of ESR, but you can get it with:

\$ ESR = DF*Xc = DF/(2 π f C) \$ (with f = 120 Hz).

Now, the datasheet dives DF=0.2 for a 10V cap, and 0.1 for a 50V cap, so the 50V one will have lower ESR. Notice as DF (and ESR) climbs again at much higher voltages like 200V.

You can use this formula to calculate the ESR of your caps if it is not specified. Remember it is not an accurate spec and depends widely on temperature.

However if you measure by physical volume of cap, a lower voltage cap will have more capacitance in the same physical size, so if you are space-constrained and need lower ESR, adding more µF is a solution too.

The rule kind of applies to low-ESR non-polymer caps, too. When in doubt, check the datasheets...

It does not apply at all to ultra-low ESR polymer caps because these are designed specifically for low voltage applications (ie, PC mobo, CPU decoupling, etc). Higher voltage ratings (like 25V) for this kind of product are still relatively new, therefore less optimized. You can get a 5 mOhm cap for 6.3V but for 25V it would be much harder...

Now, remember liquid electrolytes don't work well at cold temperatures. Electrolytic caps have much higher ESR at -20°C.

ESR of other types of caps (like solid polymer, ceramic, etc) is much less (or not at all) affected. So watch your temperature range.