Jim
My thinking on solid state relays has not changed in the over quarter
century I have been invested in factory automation and industrial control
These trinkets first arrived on the scene about mid 70's, a product of the
"we can do anything with electronics" gadgeteers
At that time it was proclaimed that mechanical relays and contactors would
be obsoleted by the solid state relays. The market for electomechanical
relays today is larger than ever. Must be a reason.
They are only useful when switching highly cyclic resistive loads---theatre
lighting comes to mind
If an inductive load is involved---use a real relay with contacts
You can be stubborn and persist it making them work but why do that. I want
my transformer really off when I think it is off, not sitting there with
leakage current ready to turn on due to any number of reasons from line
noise to failure
Another misconception is that zero crossing relays switch at the minimum
point. Only true for a resistor. ELI the ICE man has his rules and they
will be followed. The turn off surge is what kills many solid state relays.
SSR websites are a good source of this information
I don't think we are stuck in the dark ages here. We use our share of solid
state motor control up to some pretty impressive power ratings and have
designed and manufactured some ac soft start soft stop controls. A bit of a
different animal for sure than the typical SSR. But for just switching
something on and off a simple relay works very well and lasts "forever".
Costs less too. I certainly have replaced my share of failed SSR's in
industry with "just a relay". Plenty of other real high tech opportunities
out there.
Just my take on the subject.
Paul
--------------------------------------------------
From: "Jim W7RY" <w7ry@centurytel.net>
Sent: Sunday, February 09, 2014 9:13 PM
To: "amps" <amps@contesting.com>
Subject: [Amps] Solid State Relays Again
I just had a solid state relay in my 8877 power supply short during the
RTTY contest this weekend.
I use 2 relays, one to short out the step start resistor, and the other
one for the other leg of the plate transformer. Both are controlleed by
the WD7S triode board.
The one that shorted is was NOT the step start resistor shorting relay.
They are both Crydom D2440. They have been around a while because the
defective one has a date code of 9425.
Just trying to do some research and thinking of switching to mechanical
relays.
I looked at the archives and read a debate between Ian and Paul about this
exact subject. Any new thoughts?
73
Jim W7RY
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