capacitor blown

[perts]

i have relay that drives a inductive load of .6mH. The output of the relay also has a capacitor of 100n to ground.

i have noticed that after serveral switching the capacitor is blown (shorted)?

do you what could be causing this and why?

 

[Barry1961]

I would assume the coil is producing a high voltage spike when it is turned off. You should be able to bleed off the high voltage with an MOV.

Barry1961

 

[perts]

do you think the high voltage is blowing my cap?

 

[Barry1961]

I would guess there is a high voltage arcing through the insulation between the two conductors in the capacitor causing it to short.

Is this AC or DC?

Can you give a little more detail on the circuit? Voltage, components….

Barry1961

 

[perts]

its a DC circuit, with a 50 Volt Cap, the current is 6 amps steady state

in an inductor, the current cant stop instanteously, so who is suppling the current when the relay contacts open?

 

[ScottyUK]

The stored energy in the inductor is released trying to keep the current circulating. The voltage rises across the contacts causing an arc as it releases this energy. You need a diode, not a capacitor.


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One day my ship will come in.
But with my luck, I'll be at the airport!

 

[raisinbran]

Perts,
That attempt to suddenly stop the current flow is what generates a large voltage transient. If you can, you would be better off to place a diode across the inductor (called a freewheeling or flywheel diode) to suppress the voltage spikes. The diode should have a forward voltage rating of at least the maxmium voltage (preferably higher) of the circuit, and a minimum continuous rating of six amperes. This diode will allow the current to decrease based on the L/R time constant of the inductor. It should also minimize the arcing at the relay contacts. As the circuit response will be slower, make certain that the addition of this diode does not compromise any safety aspect of the circuit.
Hope this helps,
Raisinbran