An electrolytic capacitor charges by itself?

[Philip Koeck]

We've observed that an off the shelf electrolyte capacitor (330 μF) charges when it isn't connected to a current supply.
Depending on the surroundings we get something between 10 and 100 mV potential across the capacitor.

Does anybody know what's happening?

 

[Lord Jestocost]

To my mind, this effect is known as "dielectric absorption".

https://passive-components.eu/capacitors-capacitance-dipoles-and-dielectric-absorption/

 

[Philip Koeck]

To my mind, this effect is known as "dielectric absorption".

https://passive-components.eu/capacitors-capacitance-dipoles-and-dielectric-absorption/

That makes sense. I charged the capacitor in the lab, then shorted it and then measured the voltage, which rose slowly to about 100 mV.
Then I took it all home and measured the voltage during the weekend, never getting more than about 20 mV.
I thought it was due to a change in the environment (such as electromagnetic background), but I guess it was just because more time had passed since I charged it and I had shorted the capacitor several times in the mean time.