Hi.
At the photo you may see a small dent on the aluminum shell of a run capacitor type cbb65 (metalized polypropylene film capacitor/"self healing").
The dented aluminum shell is probably squishing the insulator (PP) and the metal film inside.
My question are:how will this condition affect the capacitor function now or in the future?
Can it cause a leakage to the ground through the metal shell?
May it cause a premature fail?
Thanks.

 

My question are:how will this condition affect the capacitor function now or in the future?

The dent didn't rupture the can, but I'd still be concerned about reliability.

This is from a Cornell Dubilier application guide. The dent could be causing some plates to be closer together which could decrease the working voltage in the vicinity of the dent.


This is from Rubycon.

 

So,do you mean that the decreasing in the working voltage in the vicinity of the dent can cause the PP insulator(in this vicinity)to break-down and make a short between the metal film?
Can the short leak also to the aluminum shell,so it will leak current to the ground?
Can i make some test to verify whether the dent does or doesn't make damage?

 

If the motor still runs, you’re good.

 

So,do you mean that the decreasing in the working voltage in the vicinity of the dent can cause the PP insulator(in this vicinity)to break-down and make a short between the metal film?

Essentially.

Can the short leak also to the aluminum shell,so it will leak current to the ground?

I'm not an expert in capacitor failure. Caps might be able to recover from "small" shorts or fail catastrophically.

Can i make some test to verify whether the dent does or doesn't make damage?

Not without taking the cap apart.

You could opt to run it until it fails. I've never had a run capacitor failure cause any problems that a replacement capacitor didn't fix.

The bottom line is that the dent doesn't help reliability.

 

Essentially.
I'm not an expert in capacitor failure. Caps might be able to recover from "small" shorts or fail catastrophically.
Not without taking the cap apart.

You could opt to run it until it fails. I've never had a run capacitor failure cause any problems that a replacement capacitor didn't fix.

The bottom line is that the dent doesn't help reliability.

I undertand,thanks for your help.

If the motor still runs, you’re good.

Yes,it may run okay at first,but the question is how long? will the dent cause a premature failure later in the long run or it won't affect its longevity at all?
So,that was the main concern.
Thanks.

 

The motor run type capacitors are pretty rugged, oil filled Paper usually and can take some abuse without failure in my experience.

 

Try it. What can you lose?

 

I agree with dl324 that this dent doesn't help reliability
and i understand that it can decrease the working voltage etc.But,as he adviced and also,you all adviced,i will give it a try,i will use it as an experiment and see how long it will run.The problem is that it may fail in the future due to other reasons and not necessary this reason.Can i determine,after it will eventually fail,whether the dent was the reason for the failure or not?

 

Can i determine,after it will eventually fail,whether the dent was the reason for the failure or not?

Maybe. If the cap doesn't explode, you could disassemble and see if there was a hot spot near the region of the dent.

The manufacturer would be most qualified to do this, but they probably wouldn't bother to investigate unless there were a lot of failures, and you were a high-volume customer. Still, it wouldn't hurt to ask. You could also ask them about reliability concerns with a dented can.

 

Maybe. If the cap doesn't explode, you could disassemble and see if there was a hot spot near the region of the dent.

The manufacturer would be most qualified to do this, but they probably wouldn't bother to investigate unless there were a lot of failures, and you were a high-volume customer. Still, it wouldn't hurt to ask. You could also ask them about reliability concerns with a dented can.

Thanks for your advice,as at least there is a way to check it in the future in the case of failure,as you explain.
Though i hope it will be way way in the future.
Thanks you all for your help.