[Amps] SSR snubbers

[Paul Kraemer]

Sounds like John and I have had similar experiences along the industrial 
road of life.
For one of our products we designed that was used in auto assembly plants 
had ssr input modules that would not false on from leakage current picked up 
on thousands of feet of field wiring in conduit or from being energized from 
some other triac output on a controller. They were good and outperformed any 
that could be purchased comercially. They had a snubber on input and a high 
electronic threshold in the circuit. They were actually less susceptable to 
false on than some small magnetic relays.
As far as using SSR as contactors---why bother? It isn't safe by itself and 
costs a lot more than a plain old magnetic contactor.
Some things just don't need the solid state fix, unless you are a 
tech-a-holic.
Paul K0UYA
----- Original Message ----- 
From: "John Lyles" <jtml at losalamos.com>
To: <amps at contesting.com>
Sent: Thursday, January 29, 2009 4:46 PM
Subject: [Amps] SSR snubbers


>I cannot find info on the snubbers we used at BE Inc. on the transmitters, 
>to keep the chatter from occuring in the SSRs when inductive loads switched 
>in the system on the same power line and caused them to false on. Looking 
>at their current design (8 years old) they replaced all the SSRs with 
>homemade devices they called OCRs, for Optically controlled relays. 
>Apparently someone didn't like the use of commercial SSRs or they had a lot 
>of trouble with them, as the new units appear to fit the same mounting 
>screws. They have a real relay on the output, and still have a 0.03 uF and 
>560 ohm 1/2 watt R for snubber. This is actually for relay contact 
>lifetime. And they are only used to switch the primary power to the coils 
>on large AC contactors that switch the real power to transformers and fans. 
>The capacitor pass the high frequency components of transients while the 
>resistors dissipate it. You find it in most of the old databooks for SCRs 
>and TRIACs as Paul suggested. If you make
>  the C
> too large, you suffer excess AC leakage current, and there is an empirical 
> or prescribed way of figuring it, i just cannot remember 20 years. But 
> others here apparently haven't seen the effects using SSRs. I would 
> definitely not depend on them for safety, nor would I depend on contactors 
> or relays for that matter. Pull the plug.
> 73
> John
> K5PRO
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