What effects capacitor resistance

[bosskardo]

Hi
I have had a problem with ceramic capacitors shorting out (voltage peak too much over rating). I found out that I can easily detect a it by measuring resistance and if its some ohm then its shorted.

But my question would be what effects the resistance reading of the capacitor? Sometimes I get a fluxuating resistance that settles at 28kohm after some seconds (measurng both ways), other times I get it measuring one way but get 5kohm measuring the other way. Sometimes i get infinite resistance. I don't get why it has so many possibilities.

 

[malli_1729]

I didn't understand you question. If you are using capacitor with voltage exceeding it's max rated voltage--> capacitor will damage. Why you want to measure the resistance of capacitor...? did you mean ESR?

 

[bosskardo]

I know that I can measure if the capacitor is damaged by measuring its resistance.
What I'd like to know is what effects the measured resistance of a capacitor because I've gotten different results from same capacitors.

 

[LvW]

I know that I can measure if the capacitor is damaged by measuring its resistance.
What I'd like to know is what effects the measured resistance of a capacitor because I've gotten different results from same capacitors.

I suppose, you are referring to the DC resistance of the cap, correct?
How did you measure? You should know that the dc resistance is very large and will be - probably - in the order of the input resistance of your measurement device. Thus, the whole measurement is rather problematic and will be influenced by contact properties of the measurement probe also.

 

[bosskardo]

I suppose, you are referring to the DC resistance of the cap, correct?
How did you measure? You should know that the dc resistance is very large and will be - probably - in the order of the input resistance of your measurement device. Thus, the whole measurement is rather problematic and will be influenced by contact properties of the measurement probe also.

Yes, DC resistance. Measured with a multimeter.
But I don't get why I get different results (same component in the same place, different items):
fluxuating reading that steadies at 5kohm after a few seconds
fluxuating reading that steadies at 28kohm after a few seconds
infinite resistance
resistance of 1-5 ohm (the capacitor is shorted)
resistance of 200-300 ohm (I think the capacitor is shorted but not sure)???

 

[Audioguru]

A ceramic capacitor has a resistance of many Megohms. My digital multimeter shows infinity when measuring the resistance of a good ceramic capacitor and its maximum reading is 40M ohms.

 

[LvW]

Thus, the whole measurement is rather problematic and will be influenced by contact properties of the measurement probe also.

...and don´t forget your own body (in case you are touching the device under test) during the measurement.

 

[dick_freebird]

A good capacitor will have high resistance. The resistance
of a defect, t=0 or introduced by overstress, will be lower,
not necessarily stable or linear with voltage. Dielectric
ruptures evolve over time, charges local to it come and go,
conductive filaments can be created or destroyed and so
on.