Solar water heater pump controller.

Somewhere on the web I have seen a schematic for a differential temperature switch for controlling the pump on a solar hot water system. It can't be more than an op-amp and relay, but I can't find it. Does anyone on this newsgroup know where I can find such an animal? Commercial units start at about $75, and I think I could build one for no more than $5 with the stuff I have laying around.
Thanks
-- Mike Swift
Two things only the people anxiously desire�bread and circuses. Decimus Junius Juvenalls

Hi Mike;
Mike Swift wrote:

Somewhere on the web I have seen a schematic for a differential temperature switch for controlling the pump on a solar hot water system. It can't be more than an op-amp and relay, but I can't find it. Does anyone on this newsgroup know where I can find such an animal? Commercial units start at about $75, and I think I could build one for no more than $5 with the stuff I have laying around.

Maybe this is what you are looking for: http://www.redrok.com/misc1.htm#diftemp These schematics are for the sensors. These can drive a solid state relay to turn on the pump motor.

Thanks

Duane
-- Home of the $35 Solar Tracker Receiver http://www.redrok.com/led3xassm.htm [*] Powered by \ \ \ //| Thermonuclear Solar Energy from the Sun / | Energy (the SUN) \ \ \ / / | Red Rock Energy \ \ / / | Duane C. Johnson Designer \ \ / \ / | 1825 Florence St Heliostat,Control,& Mounts | White Bear Lake, Minnesota === \ / \ | USA 55110-3364 === \ | (651)426-4766 use Courier New Font \ | redrok@redrok.com (my email: address) \ | http://www.redrok.com (Web site) ===

Mike Swift wrote:

Somewhere on the web I have seen a schematic for a differential temperature switch for controlling the pump on a solar hot water system. It can't be more than an op-amp and relay, but I can't find it. Does anyone on this newsgroup know where I can find such an animal? Commercial units start at about $75, and I think I could build one for no more than $5 with the stuff I have laying around.
Thanks
you want the c.a.t book "solar water heating a d-i-y guide"

isbn : 1 89804911 4 contains p.c.b layout etc...
some times you see a 12v kit on ebay.co.uk
for a digital controler try this site : http://www.anotherurl.com/therm/Default.htm