PTC Thermistor for nicad battery pack

[A. Kay]

I am looking for a PTC thermistor, epoxy coated with approximately these
characteristics:
6.8k ohm at 45 degrees celsius

I have an old nicad battery pack with a thermistor that failed during
charging and one of the battery cells split along with the thermistor. The
thermistor is inside the battery pack and connected in series with the
charging circuit. The numbers on the thermistor are 6K8K. After searching
the internet I deduced that the numbers meant 6.8K ohm with 10 percent
tolerance. The 45 degrees celsius was the upper recommended
charging/operating temperature for the batter pack stated in the manual.

I took the battery pack to a Batteries Plus to rebuild it and their
suppliers could not find a replacement. I figured that this thermistor isn't
that unusual.

Maybe someone can suggest a replacement, at least an electronics store that
I can buy only one or two and not a hundred.

 

[Ross Herbert]

:I am looking for a PTC thermistor, epoxy coated with approximately these
:characteristics:
:6.8k ohm at 45 degrees celsius
:
:I have an old nicad battery pack with a thermistor that failed during
:charging and one of the battery cells split along with the thermistor. The
:thermistor is inside the battery pack and connected in series with the
:charging circuit. The numbers on the thermistor are 6K8K. After searching
:the internet I deduced that the numbers meant 6.8K ohm with 10 percent
:tolerance. The 45 degrees celsius was the upper recommended
:charging/operating temperature for the batter pack stated in the manual.
:
:I took the battery pack to a Batteries Plus to rebuild it and their
:suppliers could not find a replacement. I figured that this thermistor isn't
:that unusual.
:
:Maybe someone can suggest a replacement, at least an electronics store that
:I can buy only one or two and not a hundred.
:

Most battery packs I have opened don't use a thermistor, they use a thermal
protector switch.

http://www.sensata.com/files/battery-4mm.pdf

If it looks like the ones in the pdf then it isn't a thermistor. Find a supplier
for the Klixon/Sensata device and use that.

 

[A. Kay]

Thanks for the advice. My device looks nothing like the thermal protector
in the pdf. Mine looks similar to an epoxy coated tantalum capacitor. So,
this thermal switch might be a viable replacement. Do you know of a
supplier?

 

[Ron(UK)]

Thanks for the advice. My device looks nothing like the thermal protector
in the pdf. Mine looks similar to an epoxy coated tantalum capacitor. So,
this thermal switch might be a viable replacement. Do you know of a
supplier?

Sounds like a polyswitch perhaps?

Ron

 

[William Sommerwerck]

I'm curious as to what this pack powers. A classic Vivitar electronic flash,
perhaps?

I still have a 283 that runs only from a wall wart. But it's a nice flash,
if only because it has a remote sensor with _continuous_ settings.

 

[A. Kay]

The battery pack is a 13.2 volt sub C pack for a Freud cordless drill. The
protective case on one of the cells was actually pealed away and one leg of
the thermistor was welded (not soldered) to the cell casing.

 

[Franc Zabkar]

I am looking for a PTC thermistor, epoxy coated with approximately these
characteristics:
6.8k ohm at 45 degrees celsius

I have an old nicad battery pack with a thermistor that failed during
charging and one of the battery cells split along with the thermistor. The
thermistor is inside the battery pack and connected in series with the
charging circuit.

If the device is in series with the battery, then it must be a thermal
and/or current limiting protector of some kind, possibly a polyswitch.
Elsewhere you state that the application is a cordless drill, so I
would expect a charging current of up to 1A or more.

Alternatively, if your battery pack has a third terminal, then your
mystery device could be a temperature sensing thermistor.

- Franc Zabkar

 

[Ross Herbert]

For the Sensata Klixon device I don't know of a reseller so if you specifically
want that item you should enquire from Sensata. Sensata say that theie USA/Canda
distributor is Component Concepts http://www.componentconcepts.com/ but to see
whatthey have you have to click on the Thermal products tab and select Texas
Instruments from the menu. Apparently, Klixon came unddr the TI company at one
time and CC haven't updated their catalog yet. One product which has been around
in their range is the 7AM and this is also made by a number of companies ie
Thermtrol http://www.thermtrol.com/

There are other manufacturers of similar devices which have been around for a
long time. ie Pepi http://www.pepiusa.com/modn.html
Electronic Goldmine sells a pack of 3 for $1 each
http://www.goldmine-elec-products.com/prodinfo.asp?number=G14366

Hope this helps.



:Thanks for the advice. My device looks nothing like the thermal protector
:in the pdf. Mine looks similar to an epoxy coated tantalum capacitor. So,
:this thermal switch might be a viable replacement. Do you know of a
:supplier?

 

[Jimmie D]

For the Sensata Klixon device I don't know of a reseller so if you
specifically
want that item you should enquire from Sensata. Sensata say that theie
USA/Canda
distributor is Component Concepts http://www.componentconcepts.com/ but to
see
whatthey have you have to click on the Thermal products tab and select
Texas
Instruments from the menu. Apparently, Klixon came unddr the TI company at
one
time and CC haven't updated their catalog yet. One product which has been
around
in their range is the 7AM and this is also made by a number of companies
ie
Thermtrol http://www.thermtrol.com/

There are other manufacturers of similar devices which have been around
for a
long time. ie Pepi http://www.pepiusa.com/modn.html
Electronic Goldmine sells a pack of 3 for $1 each
http://www.goldmine-elec-products.com/prodinfo.asp?number=G14366

Hope this helps.



:Thanks for the advice. My device looks nothing like the thermal
protector
:in the pdf. Mine looks similar to an epoxy coated tantalum capacitor.
So,
:this thermal switch might be a viable replacement. Do you know of a
:supplier?

I have seen some batery packs with thermistors. They look like a two wirres
with a tiny drop of epoxy on the end, smaller than a mtch head. These were
used in the battery packs of some aviation radios when they used lead acid
batteries. Since they switched to using nicad the thermistor is no longer
used.

Jimmie

 

[A. Kay]

My batteries are definitely nicads. Do you think if I used a thermal
protector switch instead of a thermistor (which I think I have) will it
damage anything? I could check the resistivity of the thermistor out of the
circuit and if it is zero at room temperature then I think it will probably
work since a thermal protector switch is basically on or off.

 

[A. Kay]

The battery pack does have a third contact, hence I suspect it is a
thermistor. I am considering using a thermal protector switch to replace it
because when disconnect the thermistor from the pack, the charger does not
charge. I am guessing the thermistor is zero or close to zero resistance at
room temperature. Hence, the thought that I could replace it with a thermal
protector switch which is basically on or off.