Electrolytic capacitors: capacitors vs. batteries
Capacitors are expected to obey ${\displaystyle C={\frac {Q}{V}}}$ very closely, so computations in RCL-networks can be done assuming impedance to be $j\omega C$.
On the other hand, batteries (rechargeable or not) are assumed to keep up the same voltage as long as possible.
It looks to me like electrolytic capacitors are somewhat in the middle of these, some designed to follow the capacitor equation as close as possible, others focused more on energy storage.
Is that true, and how to describe it? Sure in professional engineering there are criteria (unknown by name) to me.
2 answers
The following users marked this post as Works for me:
| User | Comment | Date |
|---|---|---|
| watchmaker | (no comment) | Oct 11, 2025 at 03:59 |
It looks to me like electrolytic capacitors are somewhat in the middle of these, some designed to follow the capacitor equation as close as possible, others focused more on energy storage.
Not as far as I am aware. Even Ultracaps tend to fairly rigorously follow the capacitor equation. Some ceramic capacitors "lose capacitance" with their applied voltage but, this is a well-known phenomena and nobody would realistically use then for timing applications that are reliant on the capacitor equation.
Is that true, and how to describe it?
It's not true.
0 comment threads
Electrolytic capacitors are still capacitors. Of course no physical capacitor is ideal.
The charge as a function of voltage is reasonably linear for most electrolytic capacitors. If it were not, I'd expect the datasheet to make that clear and provide some guidance about what to expect at different voltages.
Datasheets might express the non-linear nature of the charge as a function of voltage as the apparent capacitance as a function of voltage. That's another way of expressing the same thing, although you have to be clear about whether that's the total effective capacitance, or the differential effective capacitance at each particular voltage.
Some ceramic dielectrics store less incremental charge at higher voltages. That is often specified as a minimum guaranteed capacitance at the maximum voltage, or the drop in capacitance from 0 to full voltage. Datasheets don't usually go into much detail because such caps are intended for applications, like bypassing the power feed of digital chips, where some variation in capacitance doesn't matter.
As always, read the datasheet for the details.
0 comment threads
0 comment threads