Hi.
I have found an old article for driving a temp controlled pump. The circuit is pretty good the way it is but I need to make a few changes.
Firstly, it calls for a mosfet which would cost about 8 dollars at Jaycar. I want to swap that for a bc548, a high power relay with a coil resistance of 160 ohms with a 1A protection diode.
Except the mosfet, all of the parts above I have here and would prefer to use them if I can. I want to use a relay to both isolate the circuit from the pump and also there is a chance I may need to run a 240v pump in the future.
A further problem is I'd like the pump to stay on for an adjustable time period of 0-20 seconds. And this is where I'm stuck. I need help and suggestions for a simple circuit between the output of the comparator, the delay circuit between it and the base pin on the transistor. If I start adding capacitors, wont it stuff up the hysteresis? Can I somehow incorporate the unused 2nd comparator? How would you do it?
The problem is the pump would turn off too early since the water tank is quite far from the solar collector. I want it to keep running for a few seconds while the pipe is still hot.
Here is the original circuit:
And here is the article:
http://www.siliconchip.com.au/cms/A_30610/article.html