An electrolytic capacitor charges by itself?

In summary, the conversation discussed the observation of an off-the-shelf electrolyte capacitor charging without being connected to a current supply. The potential across the capacitor ranged from 10-100 mV depending on the surroundings. The effect was identified as "dielectric absorption" and was further explained in a related article. An individual also shared their experience of charging the capacitor in a lab and then measuring the voltage, which rose slowly. However, when they measured the voltage again at home, it did not increase as much, possibly due to time passing and shorting the capacitor multiple times.
  • #1
Philip Koeck
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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?
 
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  • #3
Lord Jestocost said:
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.
 
  • #4
Most likely electrochemical. Electrolytic capacitors rely on the formation of an oxide layer on one plate. Hence you have one plate that is essentially metal and another that is highly oxidised, so it's not hard to imagine there will be some sort of battery action. Especially given that electrolytics become leaky and have to be re-formed after a period of storage, which implies that the oxide layer is vulnerable to attack by the electrolyte.

Anyway, the chemistry is bound to be a bit more complicated than just forming a simple oxide - for a start, the oxygen would have to come from water, leaving some hydrogen to be mopped up somewhere, or perhaps some other metal than aluminium being plated onto the "metal" plate. One way or anothert is very likely that highly-reduced species will be formed on the "metal" plate and hyper-oxidised ones on the "oxide" plate.
 
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Related to An electrolytic capacitor charges by itself?

1. How does an electrolytic capacitor charge by itself?

An electrolytic capacitor charges by itself through a process called self-healing. This occurs when the capacitor is connected to a power source and the electric field within the capacitor causes a chemical reaction to take place, resulting in the buildup of charge on the capacitor's plates.

2. What is self-healing in an electrolytic capacitor?

Self-healing in an electrolytic capacitor is the natural process of the capacitor charging itself when connected to a power source. It occurs due to the chemical reaction within the capacitor, which results in the buildup of charge on the plates.

3. Can an electrolytic capacitor charge itself without a power source?

No, an electrolytic capacitor cannot charge itself without a power source. The chemical reaction that causes self-healing and the buildup of charge on the plates requires a power source to initiate.

4. How long does it take for an electrolytic capacitor to charge itself?

The time it takes for an electrolytic capacitor to charge itself depends on several factors, including the capacitance of the capacitor, the voltage of the power source, and the resistance of the circuit. In general, it can take a few seconds to a few minutes for the capacitor to fully charge itself.

5. Is it safe to leave an electrolytic capacitor charging by itself?

It is generally safe to leave an electrolytic capacitor charging by itself, as long as the power source is within the recommended voltage range for the capacitor. However, it is always recommended to monitor the charging process and ensure that the capacitor does not overheat or exceed its voltage rating.

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