Reverse Polarized Electrolytic Capacitors

Hi,

I did a search about the issue but I can not find any satisfying information about it.

What is the low (in 10uV - 100mV range) and reverse voltage biased electrolytic capacitors characteristics? In every datasheet it says that the applied reverse voltage should not be exceed 10% of the max rated voltage with some temperature dependent tables.
Like this,
not exceed 10% of rated voltage @20°C and max 1V
not exceed 3% of rated voltage @85°C and max 0.5V
not exceed 1% of rated voltage @125°C and max 0.1V

But I found this informations not sufficient.

I want to know, how the values which are listed below are effected with reverse biasing and without reaching the specified voltage limits stated in the datasheets.

• Capacitance
• Dielectric constant
• Frequency response (especially low(mHz) and high limits(MHz))
• ESR
• ESL

Since the manufacturers did not give the exact information I would like to hear your personal experiences about this issue.

Thank you for now

Since few people run an electrolytic with a reverse bias it likely will be difficult to find much info on that.

Under reverse bias, both the capacitance and dielectric constant becomes undefined.

Frequency response have to be determined on a case basis: it too will depend on the bias potential and the temp. In the low frequency range, the Imp vs log(freq) graph is expected to be linear.

Both ESR and ESL depends on the construction and need to be experimentally determined.

c_mitra said:

Under reverse bias, both the capacitance and dielectric constant becomes undefined.

Frequency response have to be determined on a case basis: it too will depend on the bias potential and the temp. In the low frequency range, the Imp vs log(freq) graph is expected to be linear.

Both ESR and ESL depends on the construction and need to be experimentally determined.

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Hi mitra,

I am little bit confused. Did you mean that even at the very low voltage levels, (uV to mV range) reverse biased capacitors does not behave as a capacitor. That is to say there is no charge stored at the capacitor plates.

I believe some of the questions in the original post can be answered by just thinking. E.g. ESL. Some can be probably answered by extrapolating known technical data. Depending on your definition of "satisfying answer", some will remain, requiring empirical measurements.

Under reverse bias, both the capacitance and dielectric constant becomes undefined.

Click to expand...

I doubt that you can substantiate the statement for mV bias.

darkdurrent said:

Did you mean that even at the very low voltage levels, (uV to mV range) reverse biased capacitors does not behave as a capacitor. That is to say there is no charge stored at the capacitor plates.

Click to expand...

No, I did not mean that. In this special case of electrolytic capacitors, the dielectric is basically a thin oxide layer and a electrical double layer formed on that.

I do not know exactly but at low reverse voltages (<1-5V, I presume) the oxide layer is intact and the electrical double layer undergoes changes and that affects the capacitance.

At high reverse bias voltages, the oxide layer develops faults (somehow it becomes leaky) and the defects apparently never heals.

In essence, if you have a 25V 10uF capacitor (Al electrolytic), it will not get damaged if you apply 1-2V in the reverse way. But 25V reverse voltage will kill the oxide layer and the capacitor will become leaky (not hold charge).

If you apply reverse voltage (low value; say 1-2V) and measure the capacitance it will find anything from 5-7uF and the readings will be unstable.

Of course high voltage electrolytic capacitors are more sturdy and they can perhaps take more abuse.

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FvM said:

I doubt that you can substantiate the statement for mV bias.

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No, I do not mean that with mV reverse potential. I do not recall accurately but the voltage drop across the electrical double layer is close to a volt and hence mV bias will not show much effect. But rarely a capacitor is used at mV potentials.

But rarely a capacitor is used at mV potentials.

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Not so unusual, I think. I have e.g. used electrolytic capacitors with "zero" (|Udc| < 10 mV) bias in AC coupled amplifiers.