5 cell Lipo or lithium battery detect and cut out for electric drill or similar with MOSFET. Untried yet

665

07:57:30

A 18v lipo battery (5 cells) nominal voltage, cell voltage must not drop below 3v (3v x 5 = 15v)or damage can occur. The switch simulates voltage drop to danger level and operates a relay to switch off the main power to the relay which will power the motor. (Replace the green LED with a 12 to 20 volt relay). 
The variable resistor is set to 33% wiper position.
The comparitor is used in conjunction with a zener diode voltage reference point. The diode is to stop back EMF caused by a relay.
Can be used with 3 cells which would make a 11.1 volt battery (near enough 12 volts) with a cut off set at 3 x 3 cells = 9 volts.
I used a 36v Bosch cordless lawnmower lithium battery to convert a nickel metal hydride battery in a good quality drill.
I used a multi charger bought on ebay for £15 used in radio controlled models to charge it. The critical thing is not to over-discharge it.

published 12 years ago

afinchum

12 years ago

Cool! Also the type of circuit found in laptop batteries :D

creeek

12 years ago

Yes, they are usually in parallel, to give required current and capacity. It's giving the necessary current that could be a problem. That's why I chose a lawn mower battery. If you try take too much current, then you want the motor to cut out. Also a cordless Dyson does this. So you don't get the vacuum slowing down, it just cuts out.

ppedovic

10 years ago

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