Re: [Amps] Solid State Relays Again

["Roger (K8RI)" <k8ri@rogerhalstead.com>]

On 2/10/2014 2:22 PM, TexasRF@aol.com wrote:
> 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?
Having worked with SCRs and Triacs I'd much rather switch on at peak 
power than switch off while drawing current.  The Collapse of the 
magnetic field can produce a tremendous voltage kick, or back EMF.
It's my understanding that even transformers that are low voltage, high 
current, if turned off while drawing much current can produce many times 
their regular input voltage.

73

Roger (K8RI)


> 73,
> Gerald K5GW
>
>
>
> In a message dated 2/10/2014 10:47:40 A.M. Pacific Standard Time,
> g8on@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@hiwaay.net
> To:  amps@contesting.com
> Cc:
> Subject: Re: [Amps] Solid State Relays  Again
>
> Quoting Peter Voelpel <dj7ww@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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