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@aol.com
To: g8on@fsmail.net, donroden@hiwaay.net, amps@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@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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