Bypass the thermistor in a drill switch

TBirdUK

TBirdUK

TBirdUK

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Need some help from someone who knows about electronics please.

I have a few old 18v drills with no batteries which I want to use to power a couple of projects for my lad. My problem is that when I connect it up to a battery via the correct + & - terminals the light comes on but the drill motor doesnt charge - I have gone passed the drill switch and know the motors are fine but cant use it this way as I need the switch to allow variable speed control.

My thoughts are (from google) that as there is a white wire going down to a 3rd terminal on the battery that this is (again from google) a thermistor inside the battery - I dont have this, so how to a bypass this or make it think it is there and fine? My google skills to resolve this have failed me!

Many thanks
 
The thermistor in most NiMH cells is just used for charging purposes and has nothing to do with output.

Depending on what you are trying to achieve with the motors, wouldn’t a proper ESC (electronic speed controller) be more useful than a trigger?
 
yes but I have these drills - its to make a variable throttle on my lads 12v ride on car. I have read that some trigger switches take part of the voltage through the 3rd pin, others dont, and I dont know what polarity I would put on it as the drills didnt come with a battery.
 
seems the switch itself has a protection in it that wont allow any voltage through it unless the 3rd wire, a negative temperature coefficient (NTC) thermistor is connected - no idea how to get around this, anyone?
 
Sounds like you just need either a wire or a resistor going from wherever that white wire went into the drill, to either negative or positive terminals. Basically work out the original circuit, replace battery with 12V supply and thermistor with a fixed resistor.
 
I am just using the switch from the drill - I have tried it with 18v battery on the bench and it still doesnt work. The whole point of using the switch out of an 18v drill is it allows variable voltage control, its rated to 24v 15Amps so should allow for the extra draw, and when fitted to the car I can increase the volts without stripping the plastic gearboxes at the wheels on start.
 
possibly, usually it is faulty batteries and i think it unlucky if all the switches were the problem, I've got another couple to test but I think it is more likely that the 3rd wire in the actual drill does something (google failed me again on this model of drill). I have an older drill that only has + and - in the actual drill where the battery has 3 connectors for the charger, unfortunately I wired it up the wrong way last week and blew the switch (nice bang and smoke!!) which worked well until then.
 
another option is to buy a battery and strip it and use the connectors but this is prohibitively expensive - I would like to try and find a place to buy the 'dead' batteries but cant find anywhere that would sell them, anyone ideas of where to buy dead batteries, battery type BL1518-XJ?
 
That appears to be a lithium-ion drill.

If it is it should have voltage monitoring to stop you over discharging the battery. It's more likely that stopping it working than a missing thermistor.
 
so if its a voltage monitor any ideas how I bypass it?

Checking the instruction manual on line I get this:

Unit shuts off abruptly.

Battery pack has reached its maximum thermal limit. Allow battery pack to cool down.

Out of charge. (To maximize the life of the battery pack it is designed to shutoff abruptly when the charge is depleted Place on charger and allow to charge.

This suggests the unit (drill) has a thermal sensor of some kind for the battery.

Checked fleabay and its £35 and above for a battery, which for just the connector is not feasible (especially for 5+ of them)!
 
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I'll try connecting an 18v battery to the + and -, what should I connect to the 3rd pin?

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