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what is the best protection of ac coil

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ZeleC

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ac coil

hello i know that for dc coil the besst protecton against overvoltage is a reverse diode, but what about ac coils example a ac valve what is the best protection , itried a series RC parallel to the coil but it didnt work
anything else
 

wrong values

You probably did not use the right values of R and C. The C is chosen to set the ringing frequency in conjunction with the coil L and the R is chosen to make it critically damped with the inclusion of the coil resistance.

Another thing to try is a zero voltage switch IC which will turn the load on and off at the zero crossings which will reduce the transients.
 

thx flatulent
do u have some links and documents on these to subjects
i tried also to put a varistor in series with a 10R it worked but not that much, so back to RC so help guys if anyone have documents or links on how to calculate these two values
 

Hi ZeleC,

The energy stored in the coil has to be distroyed in the protection circuit.
If you use a diode (DC coil) the reverse voltage will be low (0.7 volts) and
the time the current flows is relatively long. If you allow the voltage to
go higher (e.g. with a varistor), the same energy can be distroyed in a
much shorter time.
A lossy RC-network has to be designed correctly, so no swings will occur.
But normally also for AC coils a correct adopted varistor is a good choice.

Bye
 

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