# Factors Causing a Capacitor's Insulation Resistance to Decrease over time

## Summary:

I am trying to understand factors that cause a capacitors insulation resistance to decrease over time
I am lookin designing balancing resistors for series capacitors and understand that I need to consider the leakage current from the capacitors. I am trying to determine factors that would case the insulation resistance to decrease over time so I can design around that.

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I should add that I do realize heating and aging are two factors. Is there some way to estimate the percentage the leakage current would increase based one either of these factors? I'm not sure how I would use them in the design stage.

I know that a capacitors lifetime is reduced as you operate closer to the rated voltage. How does this effect it?

Tom.G
Is there some way to estimate the percentage the leakage current would increase based one either of these factors?
Some of the US manufacturers show graphs of leakage current for some products. I don't recall which particular ones, so you will have to search around a bit.

Here is an online calculator to help for lifetime:
https://www.illinoiscapacitor.com/tech-center/life-calculators.aspx

Also try this search, and look at the suggestions at the bottom of the results page.

Cheers,
Tom

Ntip
Well think of other materials and how heat can age them?

Also - when voltage is applied - this applies a mechanical stress to the material at the molecular and bonding levels - so that is why as you approach the rated Voltage they also age faster.

Keep in mind - the capacitor by design wants the thinnest dielectric possible to increase the capacitance.

Look at how the manufacturer defines the lifetime - the leakage current they give MAY be the EOL leakage. So as long as you stay within the aging parameter limits and time - you should be fine.

Ntip
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I am lookin designing balancing resistors for series capacitors and understand that I need to consider the leakage current from the capacitors. I am trying to determine factors that would case the insulation resistance to decrease over time so I can design around that.
You have not specified the capacitor technology you will use. Are you using electrolytic capacitors?

I think of electrolytic capacitors as being more like living things that must be cared for, and that can chemically learn about operating voltages, or die in a hot environment. In many respects, other types of capacitors are more robust.

We discussed various aspects of resistive balancing for chains of capacitors in a recent thread.
https://www.physicsforums.com/threa...-my-high-voltage-circuit.994058/#post-6396764

hutchphd
You have not specified the capacitor technology you will use. Are you using electrolytic capacitors?

I think of electrolytic capacitors as being more like living things that must be cared for, and that can chemically learn about operating voltages, or die in a hot environment. In many respects, other types of capacitors are more robust.

We discussed various aspects of resistive balancing for chains of capacitors in a recent thread.
https://www.physicsforums.com/threa...-my-high-voltage-circuit.994058/#post-6396764
I was thinking about electrolytic because it seems like I can get a high value capacitance pretty easily.