Introduction: Low Battery Motor Shut Off Circuit

Picture of 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.


rimar2000 (author)2012-06-14

This seems a very useful project. Sadly, I dont know electronics to follow the circuit.

pfred2 (author)rimar20002012-06-14

Sad? You're bringing me down! All I used in order to make this project was a few things. I used a multimeter. Everyone Needs a multimeter.

But I'm going to take it 2 steps further than even Phil did.

I used a power supply. They're essential in this day and age too.

I also used a little piece of breadboard.

Then with a handful of junk parts and a schematic you're as much of an electronics expert as I am. I mean the first few dozen times I put this circuit together different ways it really didn't work for me. But when it finally worked I was so excited I slapped this photo article up about it. With a working schematic.

rimar2000 (author)pfred22012-06-15

The true problem is that I am too lazy to study...

pfred2 (author)rimar20002012-07-24

What study? I practice electronics like I'm cooking. I either follow someone Else's recipe, which sometimes I may try to spice up. Or rarely I whip up my own concoction, with varying degrees of success. When anything works no one is more amazed than me.

Lectric Wizard (author)2012-06-14

Hope it's a big battery, you're still drawing about a milliamp, just thru the pot...

pfred2 (author)Lectric Wizard2012-06-14

4.5 amp hour gel cell.

lemonie (author)pfred22012-06-16

Yes, that should supply a milliamp for half a year I reckon.


Lectric Wizard (author)lemonie2012-06-18

If you have a fully charged battery & don't use the pump...

lemonie (author)Lectric Wizard2012-06-20

Yes, the pump makes the pot's consumption  insignificant, and the battery gets a regular solar-charge.


Lectric Wizard (author)lemonie2012-06-23

30 years of elecrtonics engineering vs smurff porn... I stand corrected

lemonie (author)Lectric Wizard2012-06-24

I'm pleased someone actually looked at that site (I don't), was there anything more interesting?


schumi23 (author)2012-06-13

To quote IRC:
"[21:39] its cool!"

And I agree :)

pfred2 (author)schumi232012-06-13


About This Instructable




Bio: I was pfred1 but moved, changed my email address, and lost my password. I suppose worse things could happen.
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