what is that and why is it there? (at the battery pack of my drill)

Batteries and Chargers Rechargeable Batteries
1

Hello guys,

I’m sure you can help me with a battery pack question.

Short backround story: the battery packs of my cheap drill are dead, so naturally I opend one up to take a look inside. Was thinking about replacing the batteries if possible, but now I kind of want to understand the batterypack first.

I understand what I see except the additional shiny silver “thingy” in the negativ wire.

It is in prarallel with another negativ wire, both going from ground to the same battery of the battery pack with 15x1,2V NiCd batteries in series for 18V.

closer picture of that thingy

and a diagram UPDATED

It’s reading “JRM 45” with this symbol between.

Clearly I’m no expert, but maybe you guys know what this is and what’s it doing.

Thanks for the help!

2

That looks like a thermal fuse.
But if your diagram is correct it is bypassed by the minus wire.

3

thanks Jerommel, reading your comment (and wondering about the bypass myself) I took another look and it turns out the fuse only connects to the charger. The drill makes no connection to the ground where the thingy/fuse connects to.
I updated the diagram above.

The charger has connections to both ground.

Do you know (or can you guess) if that is a “one time” fuse? as a last saftey meassure or is that part of the charging process?

(the charger has an LED that switches vom red to green to indicate a full charge)

4

Searching for JRM 45 i found this PDF:

Page 7 is about this one

In this case it seems to stop the charging when it gets too hot.

5

Thank you so much Jerommel!

6

thermal switch.
the fast charger runs till it opens to signal end of charge.
make sure you install it as it was.
it must be in good contact with one or more cells to work correctly.