Need to replace diff temp controller

[ric_barline]

Hi. My old 1970's solar solar circulating pump controller just went up in flames. This triac-based unit turns on a 3/4 hp circulating pump when the flat panel collector is warmer than the tank water and it also has a max temp setting potentiometer. The sensors (already installed in both tank and collector of roof) are 2-wire transistor types (not thermistors) and give a forward voltage drop as a function of temperature. I am having a hard time finding a replacement for my dead controller. I can find many differential temp controllers on the market but they all use thermistor-type sensors and I don't really want to have to replace the sensors if possible. Any suggestions? Attached is a photo of my old one. Thanks so much.

[LucMan]

All controllers are thermister based today.

[ric_barline]

OK, thanks. I guess I'll need to replace my existing ones. Not a problem.

[Amy@altE]

Your sensors are probably ready to die now anyways, replace everything while you are working on it and get a modern DTC.

[ric_barline]

Thanks for the advice.

[bcroe]

Hi. My old 1970's solar solar circulating pump controller just went up in flames. This triac-based unit turns on a 3/4 hp circulating pump when the flat panel collector is warmer than the tank water and it also has a max temp setting potentiometer. The sensors (already installed in both tank and collector of roof) are 2-wire transistor types (not thermistors) and give a forward voltage drop as a function of temperature. I am having a hard time finding a replacement for my dead controller. I can find many differential temp controllers on the market but they all use thermistor-type sensors and I don't really want to have to replace the sensors if possible. Any suggestions? Attached is a photo of my old one.

Perhaps your sensors are LM34 or LM35? A nice linear part; can easily be amplified to drive a temp display (voltmeter). I have a design for one
that is used to circulate fixture water the length of the house. It drives a 12V pump, but it could drive a relay to a big motor.

Or fix your old one. Bruce Roe