Running a power tool without a battery.

Thread Starter

pawelp

Joined Feb 19, 2020
5
Hi,

I have a 10.8V Bosch battery which is standard for power tools. It has 5 terminals:
+
-
C1
C2
T

I'd like to power the device without the battery using a DC power supply. When I apply just the right voltage to + and - it doesn't work.

How am I supposed to mimick C1,C2 and T interfaces?

Thanks
 

BobTPH

Joined Jun 5, 2013
2,254
That’s a tough one. The C1 and C2 leads are for balancing while charging, so it is unlikely the tool would be using them.

The T is for thermistor, which gives an indication of the temperature of the battery. The tool might have a cutoff for when the battery gets too hot, do this is promising.

I worry about suggesting anything, because I would hate to be responsible for ruining your tool.

But, with that caveat, here is a relatively safe way to check this:

Get a 10K pot. Add a 1K resistor in series to each of the outer terminals, and connect these resistors to battery + and - terminals. Then connect the slider of the pot to T. Hopefully, the tool will run with the pot in some range of positions. If that works, you could replace the pot with two equivalent resistors.

Bob
 

Thread Starter

pawelp

Joined Feb 19, 2020
5
@BobTPH Thank you for your answer! Could you maybe draw a diagram of what you mean. I am not sure I get it, I am not especially good with electrics/electronics.

Thanks
 

BobTPH

Joined Jun 5, 2013
2,254
Yes, acually, that would work. But you have to know whether the other end of the thermistor connect to + or -.

Here is what I had proposed, it would handle either case:

1582122896673.png

If you want to go your way. Measure the voltage between the + terminal and the T, if it is approximately the battery voltage, the resistor would have to go between T and -. If it is zero, measure it with the - terminal. If that is the battery voltage, the other end of the thermistor has to go to the plus. If each reading gives you something less than the battery voltage but not 0, then you have to do it my original way.

Bob
 

Thread Starter

pawelp

Joined Feb 19, 2020
5
@BobTPH That's awesome, thank you for your instruction!

I guess I was lucky and between + and T there is the battery voltage. Resistance between T and - on the battery is 6.2k Ohm.

So I just added a 6.2k resistor on the PCB board between - and T and it works.

Is there any requirement in terms of the power of the resistor? I have those tiny 1/4 W resistors. Will this work fine in the long run?

Thanks
 
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