Battery Rebuild

[robbie77]

Hi All,

Maybe the wrong forum?
I am rebuilding my Nicad 18v snap on battery. I have bought the new cells with tabs on ready to make up but I have a problem with a wire that is attached at the top of the battery .

Maybe it is something to do with a heat sensor to tell the battery when its charged.
The picture hopefuly shows the wire. The problem I have is the little red part on the wire is missing on my battery, there are just two wires that were joined by this red "thing".

Can I just solder the wires together or order another wire?
If so where would I get one from!?

Help!

Untitled

• robbie77
• 10 Feb 2011
• 1

Untitled

• robbie77
• 10 Feb 2011
• 1

 

[robbie77]

Maybe better off in tools and materials?
Can it be moved?

 

[Schmill]

So have you lost the red 'thing' that was on your original battery?

It is probably a thermistor that lets the battery charging circuit know if the battery pack is overheating, although without knowing the characteristics of the original one I think you might be hard pushed to get a replacement...

 

[robbie77]

So have you lost the red 'thing' that was on your original battery?

It is probably a thermistor that lets the battery charging circuit know if the battery pack is overheating, although without knowing the characteristics of the original one I think you might be hard pushed to get a replacement...

No I haven't lost it exactly. Its another battery I am rebuilding, of the same brand that was rebuilt by someone else but with naff batteries. When I dismantled the battery that red thing was no there just some plastic coating joining the wires? There must be a reason for this join!

 

[bernardgreen]

If there are only two terminals on the battery and there is no printed circuit board ( or module ) in the battery pack then the red plastic is almost certainly a thermal trip and / or fuse which will go open circuit if the battery pack overheats or the current becomes excessive.

The pack will work if the two wires to the red trip are joined together but the battery would have no protection from overheating during use or charging.

Something like Thermal fuse Q82 self reset 55degC 2.5A from RS Components Stock No. 204-7382 MIGHT be suitable but best to check with the manufacturers of the cells as to the maximum safe temperature for the cells when packed together.

 

[robbie77]

Thanks. Bernard.

Would the thermal fuse be used to let me know when the battery is charged. I.e. red light on charger off or purely a safety thing do you think?

 

[bernardgreen]

It is normally only a safety device. With only two terminals on the battery there is no way for the device to get "information" out of the battery. Some two terminal chargers will monitor both the voltage on the battery and the current going into it and from those detect when the battery is charged.

Changing the type of cells in the battery pack may mean the charger cannot recognise a fully charged battery.

Only where the battery has more than two terminals can the charger read sensors in the battery pack and thus give a more accurate indication of the state of the battery.