Electrolytic Capacitors Leak Current

Electrolytic capacitors leak current, even new ones. How do I know? It says so on the datasheet for the capacitors. Here is part of the datasheet for a typical aluminum electrolytic capacitor:

The leakage current is calculated by the formula 0.01*C*V but is a minimum of 3uA. A film capacitor will have essentially no leakage under the same conditions.

Larger capacitance values have higher leakage and so do caps with higher rated voltages. Leakage is also temperature dependent, and increases with rising temperature.

An example of how this can be a problem is if the electrolytic capacitor is on the input of the pedal circuit, where the leakage current can cause popping when the pedal is switched on and off. It would be better to use film capacitors at the input and output terminals whenever possible.

Another potential application that could be problematic is in timing circuits where leakage could change the expected performance of the circuit. Once again, film capacitors or other low leakage types would be better.

As capacitors age, the leakage can increase and may even result in reduced volume, hum, distortion, poor filtering or other unwanted noise. Even long periods of storage will increase the leakage of an otherwise good capacitor, and it may take 30 minutes or more after power is reapplied for the device to recover.

There are some aluminum electrolytic capacitors that are specified to have low leakage. A reduced leakage type that I have used is specified as having a leakage current not more than 0.002*C*V or 0.2uA whichever is greater. This is much better than a standard electrolytic but still not on par with a good film capacitor.

Electrolytic capacitors are essential parts for use in pedals, but should be good quality and applied where the small leakage current will not be a problem.

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