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varistor + ceramic capacitor problem

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catur_3414

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ac varistor

Hi everyone,
I have a problem with a power supply, the varistor and ceramic capacitor is oftenly burnout. I have replace it with the same type its working normally, but not in along time (2 - 3 days), then its burned again.
can everybody tell me the cause of capacitor and varistor burnout.
thank you. sorry for my english.
9_1201009564.jpg
 

varistor for 230v supply

Hello,

basically your supply lines apparently conduct transients of higher energy than your varistor could absorb without damage. You either should use a "stronger" type (bigger in size) or a higher voltage type, if transient voltage isn't very high and the protection purpose would be still served. Regarding the capacitor, you should be able to find a higher voltage type that could be fully protected by the varistor. I wonder if 100 pF has an effect at all, if the value is printed correct.

You should also be aware that some voltage transients, e. g. from direct and indirect lightling effects could be hardly handled by small varistors. At best they protect the downstream devices by shortening the overvoltage irreversibly.

Regards,
Frank
 

ceramic capacitor burn out

thank u FvM.
The 220 V ac input is an output of an ac voltage stabilizer, do you still think that this is an over voltage?
 

capacitance-voltage relation in varistors

catur_3414 said:
thank u FvM.
The 220 V ac input is an output of an ac voltage stabilizer, do you still think that this is an over voltage?
Click to expand...

FvM might still be right, what sort of voltage stabilizer ? There were some old designs where they used relays to switch between tabs to control the voltage. Another design uses a servo motor, you might have a worn out brush running over the VARIAC windings.
These two situations can be source of spikes.
 

servo burned capacitor

Could anybody explain me why Varistor is required?

What is mean by surge protection?

Why we use it across the AC Supply ?
 

varistors for small motors

I tend to go with expalnation of FvM , but to add to it what is the tolerance level of your 220VAC(even tough it's from stabliser) .there is no other way than high AC voltage or very high transient .

For explanation of varistor, i personaly like this application note ;
 

problem of capacitor

what is the tolerance level of your 220VAC(even tough it's from stabliser) .there is no other way than high AC voltage or very high transient .
Click to expand...
As previously discussed, in some situations, considerable overvoltages may be present at a 230V AC mains. To my opinion, standard electronic equipment can't be operated in this case without additional protection means, e.g. magnetic (transductor) voltage stabilizers. Of course, you can increase the varistor voltage rating above 275V standard value, but than damage of the connected equipment must be expected instead of damaged varistors. So I don't think, it's a meainingful suggestion. If the equipment can stand high voltage transients, e.g. electrical motors and similar, you don't need varistors at all.
 

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