[Amps] Solid State Relays Again

peter chadwick g8on at fsmail.net
Mon Feb 10 13:47:11 EST 2014

If you switch at zero voltage, there is no EMF to drive a current through the load impedance. A quarter cycle later, when there is EMF across the load, the current will lead or lag by a factor depending on the phase angle and magnitude of the impedance. So there's a difference between the transient condition existing for the first part of the cycle - probably somewhere between 5 and 10 degrees -  and the stabilised condition. But the initial switch of zero volts must be with zero current.


Peter G3RZP

 Message Received: Feb 10 2014, 06:24 PM
 From: donroden at hiwaay.net
 To: amps at contesting.com
 Subject: Re: [Amps] Solid State Relays Again
 Quoting Peter Voelpel <dj7ww at t-online.de>:
 > I guess with transformers the relay should switch in on the peak voltage.
 > As current peaks 90 degree behind that should be the best moment with least
 > surge current.
 > 73
 > Peter
 But if you switch at zero voltage, the current is at zero 90 degrees later...
 So you have at least 1/4 of a cycle where there is minimum IxE  
 supplied to the load.
 Don W4DNR
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