Electronic – Does an electrolytic capacitor degrade each time it receives reverse voltage


I know that I mustn't connect an electrolytic capacitor reversely. It will explode if I apply the reverse voltage long enough.

But, what happens if the reverse voltage is applied for a short time? For example, a fault occurs in the circuit and the capacitor becomes reverse biased or exposed to AC voltage for a short time, but it still looks OK from outside. Does the internal physical and chemical structure of the capacitor change permanently? Would it still have the rated capacitance, voltage and life time? Is it okay to keep it using if it doesn't explode? I feel that the answer is "no", but I'm looking for an explanation for it.

Best Answer

There are many types and subtypes of electrolytics, I will concentrate on those most common for hobbyists: the liquid electrolyte aluminum one.

Most details can be read in the corresponding wikipedia article but in short:

  • The cathode oxide layer can withstand up to 1.5V of reverse voltage
  • it can receive permanent damage earlier, but 0.5V is deemed safe

When applying too high reverse voltages for too long, one of two things can happen:

  • gassing makes the cap explode
  • dissolving of the oxide layer shorts the cap

These numbers and probability of failure mode can greatly differ when going far outside of what is considered "room temperature".

Even short application of too much reverse voltage can permanently damage the capacitor. Sometimes the self healing abilities can reverse this a bit over time, but there will be permanent damage.

Some ways to see the damage is:

  • increased leakage current (due to partly dissolved oxide layer)
  • decreased capacity (due to self healing of oxide layer holes)

Other types of electrolytics have different kinds of behaviour, but most people deem short exposure of up to 0.5V reverse voltage ok. This is why a lot of LCR meters measure capacitance with 0.5V AC regardless of any polarity.