Inverting SSR

Sunday, July 22, 2007 


This is part of a cooling system for the cabinet. This relatively inexpensive (on ebay) Watlow series 900 temperature controller has a single output and two alarm relays. The output and one of the alarm relays have snubbers inside and can trip fans on their own. The second output was NC and needed a relay to invert it. I used a solid state relay (SSR) to do it and it is currently controlling the halogen light. It turns on if the temperature goes over 81. Woo! Three more simple wiring harnesses to fabricate and then the whole mess to install in the cabinet. The concept is that a set of filtered fans will run full-time to drive fresh air into the cabinet (not quite working yet) to achieve ambient temp, say below 85 or 90 degrees. If the temperature goes above that, a single extraction fan will turn on. If it goes up another 5 degrees a second extraction fan will turn on, and 5 degrees above that a third, honking big fan will turn on. The extraction fans will probably suck in some dust, but better that than melting down.

Posted at 17:10:15 GMT-0700

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