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[Amps] SSR snubbers

To: amps@contesting.com
Subject: [Amps] SSR snubbers
From: "John Lyles" <jtml@losalamos.com>
Reply-to: jtml@vla.com
Date: Thu, 29 Jan 2009 15:46:54 -0700
List-post: <amps@contesting.com">mailto:amps@contesting.com>
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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