[Amps] Solid State Relays Again

[peter chadwick]

I think that there is a very good argument in favour of Gerald's (K5GW) suggestion. If the relay went short on switch on, would you know? Not until you tried to turn it off and found that it wouldn't! If it goes at switch off - which, from the argument on V and I relationship when turned on seems probable, you wouldn't know if it failed at switch ON or switch OFF.

32 years in the semiconductor industry makes me very dubious about the vaunted semiconductor device reliability....After all, who would have believed 50 years ago that semiconductor devices could exist that, even when unused, inherently have a shorter life than most tubes?

73

Peter G3RZP




========================================
 Message Received: Feb 10 2014, 07:22 PM
 From: TexasRF at aol.com
 To: g8on at fsmail.net, donroden at hiwaay.net, amps at contesting.com
 Cc: 
 Subject: Re: [Amps] Solid State Relays Again
 
 Additionally, the step start R will alter the phase relationship as the  
 load is primarily resistive when it is in the circuit.
  
 So, perhaps the more critical scenario is at switch off?
  
 73,
 Gerald K5GW
  
  
  
 In a message dated 2/10/2014 10:47:40 A.M. Pacific Standard Time,  
 g8on at fsmail.net writes:
 
 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.
 
 73
 
 Peter  G3RZP
 
 
 ========================================
 Message Received:  Feb 10 2014, 06:24 PM
 From: donroden at hiwaay.net
 To:  amps at contesting.com
 Cc: 
 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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