Do caps with a higher max voltage have lower ESR?

Question

Does a capacitor of a higher max voltage, all other factors the same, have a lower ESR? If so, is the any relationship between the voltage and ESR differences?

Answer 1

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.

Answer 2

There's no reason to think so. ESR is primarily a function of how the conductors (wires, plates, etc.) are constructed, while the voltage rating is primarily a function of the dielectric thickness. There's no correlation between the two; they are independent parameters.

Leakage (parallel) resistance would be related to the dielectric, however.

Answer 3

High voltage capacitors do not generally have low ESR.

The importance of low ESR is that it is critical in low voltage and high current ripple filtering, and a high voltage capacitor will often have no ESR specification at all (there's other 'dissipation' or 'Q' measures used), both because it is unusual for HV supplies to have a tight voltage tolerance, and because at few-watts power levels, a HV capacitor handles low currents.

An 80 watt CPU that is powered at 1.8V can exceed ten percent terminal voltage tolerance if the ESR of its filter capacitors is over 0.004 ohms. The same 80W from a 200V capacitor will exceed ten percent terminal voltage if the ESR is over 50 ohms.

Capacitor construction technologies differ greatly in their character, and only electrolytic capacitors are likely to bear an ESR specification. Many HV capacitors which are not electrolytic would have low ESR.