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Old 24th May 2005, 06:15 PM   #1
K-amps is offline K-amps  United States
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Default Containing Back EMF in a large relay's Coil

I am planning to power up my system with a nice set of 30A relays that will be rigged to go off one after the other. The coils are 120v and will be driven from an Isolation transformer such that each end of the coil will see 60vac and not 120v plus 0v.

Question, what should I use to contain the back EMF from teh Coil as it is turned off? I am planning a 1A diode in series with a 300ohm resistor, any ideas on the values of the Back EMF containment for a 120vac coil?

See pic: Thanks!
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Old 24th May 2005, 11:08 PM   #2
moamps is offline moamps  Croatia
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Default Re: Containing Back EMF in a large relay's Coil

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Originally posted by K-amps
.....Question, what should I use to contain the back EMF from teh Coil as it is turned off? I am planning a 1A diode in series with a 300ohm resistor, any ideas on the values of the Back EMF containment for a 120vac coil?

Hi,
AC driven relay doesn't need any back EMF suppression, IMHO.
However, using snubber RC might be a good idea.

Regards,
Milan
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Old 24th May 2005, 11:51 PM   #3
K-amps is offline K-amps  United States
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Thanks for your input, What values do you suggest?
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Old 25th May 2005, 03:21 AM   #4
jcx is offline jcx  United States
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Old 25th May 2005, 02:28 PM   #5
K-amps is offline K-amps  United States
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Thanks JC,

In my case the Relays will be housed in a separate Enclosure ala the Adcom ACE 515. But point well taken,

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