Intro: Low Battery Motor Shut Off Circuit
This is a project I am working on now but I'm not quite done with it yet. This part of the circuit still works, and I think it is really cool so I'm posting a quick photo article about it now. Don't get all hung up on exact parts or values. As long as you use an N Channel Power MOSFET and NPN and PNP switching transistors (one I'm using is a 2N4250 or something? 2N2222 whatever you got) it should work. Even the resistors I used as long as you throw something close in value where they're at you should be fine. The value of the capacitor adds hysteresis to the circuit, so it doesn't oscillate on and off at its set voltage point. A larger value will make the circuit lazier, slower. Experiment!
OK I guess I should describe what this circuit does. The potentiometer (R1) sets a break point with the zener diode to switch the chain of transistors, when the input voltage of the circuit falls below the set value the motor shuts off. So your battery does not drain too much. I am making this because my solar pond pump controller died on me. It is a piece of junk!
All I want is my pond pump to come on when the battery is charged up enough, then shut down when the voltage falls off. I still have to make a charging circuit for it. This is the motor control half. When I'm all done I'll probably write up a whole step by step of the entire project. Until then this is fun to play around with.
The zener diode I am using is a 6.2 Volt one, but with the adjustment potentiometer it is adjustable so I don't think it's value is too critical either. Anything from 5 to 9 volts or so should work. 5 volt zeners are really common. I just happen to have a bag of 6.2 volt ones so I grabbed one of those. This is a total junk box project.
P.S. connect your motor to the connections named MOT-1 and MOT-2
P.P.S. The circuit is supposed to operate off a 12 volt battery, or somewhere around 12 volts.