Maker Pro
Maker Pro

Help to identify this component

Edward Grabczewski

Apr 1, 2018
4
Joined
Apr 1, 2018
Messages
4
Can anyone help me identify a component I found inside a battery pack which supplied dual voltages (7.2V and 3.6V). It has no markings to help.

upload_2018-4-1_15-2-50.png

[Mod Edited to resize huge image]
 
Last edited by a moderator:

KJ6EAD

Aug 13, 2011
1,114
Joined
Aug 13, 2011
Messages
1,114
It's probably a thermal sensor (thermocouple or thermistor) that tells the charger when to terminate charge. The pack is of the older nickel-cadmium type I guess.
 

davenn

Moderator
Sep 5, 2009
14,254
Joined
Sep 5, 2009
Messages
14,254
It's probably a thermal sensor (thermocouple or thermistor) that tells the charger when to terminate charge. The pack is of the older nickel-cadmium type I guess.

.... thermal fuse
 

KJ6EAD

Aug 13, 2011
1,114
Joined
Aug 13, 2011
Messages
1,114
Well, I thought of that too but it doesn't quite have the look I'm used to for that. If it is a thermal fuse, it's there to prevent a fire by stopping charging or discharging activity when the temperature is catastrophically high, meaning the batteries are damaged and should not be used further.
 

davenn

Moderator
Sep 5, 2009
14,254
Joined
Sep 5, 2009
Messages
14,254

KJ6EAD

Aug 13, 2011
1,114
Joined
Aug 13, 2011
Messages
1,114
Assuming that you're trying to rebuild a battery pack, I'd expect to be able to find design guidance from the cell manufacturers as to what temperature would be correct.
 

dave9

Mar 5, 2017
1,188
Joined
Mar 5, 2017
Messages
1,188
It's a bimetallic thermal breaker or switch. The significance is it has a much longer cycle life than your typical re-settable fuse. They are not used much for the planned charge termination, well they were in some poor designs but unless you are sure that's the termination method, I would double check that first.

Often they are more of a safeguard against damage for example running a tool full speed, slapping it into a rapid charger in a high temperature environment, or of course a fault in a cell(s) or the load short circuits.

An important question is what happened. Having one fail without some other fault will not cause it to char the wiring like that. Its failure is the result of some other fault.

This 7.2V/3.6V battery pack, is it one of the poor designs similar to that I've seen in old Black & Decker 2 speed cordless drills, where the Low speed just taps into half the cells in series, so any time it is used, it's unevenly draining the pack and contributing to cell damage if subsequently ran on high speed before recharging, but eventually contributing to damage even if only ran on high because the most used cells degraded in lifetime capacity sooner?


If the breaker is the only method of charge termination it is a reasonable choice, but since 45C is within a typical, acceptable NiCd charging temperature range, if it is used as a safeguard rather than charge termination, a little higher like at least 50C or 60C at most would be my pick.
 

Edward Grabczewski

Apr 1, 2018
4
Joined
Apr 1, 2018
Messages
4
An important question is what happened. Having one fail without some other fault will not cause it to char the wiring like that. Its failure is the result of some other fault.

This 7.2V/3.6V battery pack, is it one of the poor designs similar to that I've seen in old Black & Decker 2 speed cordless drills, where the Low speed just taps into half the cells in series, so any time it is used, it's unevenly draining the pack and contributing to cell damage if subsequently ran on high speed before recharging, but eventually contributing to damage even if only ran on high because the most used cells degraded in lifetime capacity sooner?

If the breaker is the only method of charge termination it is a reasonable choice, but since 45C is within a typical, acceptable NiCd charging temperature range, if it is used as a safeguard rather than charge termination, a little higher like at least 50C or 60C at most would be my pick.

You're very observant. I was astonished that all the wiring was charred. Nothing happened to the battery pack. I used it a few times and just left it for a few years before trying to recharge and use it again. It must have been the charger (which is a custom supplied one by the company that supplied the battery pack).

Thats was exactly what I was wondering. It's a wierd place to put the thermal switch if you want to to work for the whole battery pack. Why can't you put the switch on the black wire (negative) side of the battery? (the following diagram is a disassembly of the battery pack):

http://neathfilmmakers.org/images/Pro8mmClassicBatteryPack.png

Once again you're absolutley right. the component opened up (normally closed) at 55°C when I tested it in hot water. I can't see any markings on the old thermal switch but hopefully a KDS 9700 55°C (NC) equivalent will do the same job.
 
Top