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Why some NIMH battery packs got three wires.

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dilan2005

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hi,
i got a NiMH rechargeable battery pack from local market. well knows a cordless phone battery pack.the product Model is HGB-15AAx3 an it says "Ni-MH battery 3.6v 1500mah" & it's a green colored battery pack consisting 3 outputs wires.black ,red an white wire.

My question is why there are 3 wires out puts of the battery pack?

i measure the voltages of the battery pack and i noticed that only black and red wire gives the reading. The white wire give no any output.

Thanks!
 

White wire is thermistor terminal which is needed for battery temperature sensing during fast charging.
You should measure white wire voltage against black and red. White wire have some voltage against one of other two wires if a thermistor for temperature sensing is build in.
 

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    dilan2005

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Thanks borber.
so if need to build a charger for this pack how could i use the temperature sensor.
Do u have any idea what is the type of the sensor on the battry.

Anlog -->variation in resistance
--->variation of voltage

or

Digital-->SMB bus type temp sensors


Thanks!
 

It should be usual thermistor and cold resistance can be from 10k to 50k. Simply measure resistance between white and the wire that has no voltage against it to be shure.
 

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    dilan2005

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Thank u very much for all your help.

I am wondering whether i could make a Fast Charging circuit to charge
this NIMH pack!

Any Ideas! Circuits! Application Notes!

Thanks[/b]
 

Dilan,

I'm not an expert on high-performance battery charging, but here a lecture note type material for charging Ni batteries **broken link removed** The rest of that web site is very informative as well.

- Nick
 

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    dilan2005

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Well, that third wire is for temperature monitoring ...once the battery is almost or fully charged there is steep change in temperature curve, which is read my charging controller to stop any further charging.

Sensor so used is basically reverse biased diode or thermistor followed by current limiting resistor.
 

A lot will depend on the quolity of the nicad pack but i have striped a battery pack down from a battery powered drill and the thired connection went to a heat swich that opened if the charger battery was to hot
 

Thanks every one for support this thread.following is measurements i get from the battery pack.

Normal resistance between Negative and Thermostat 40.4k
when after charging and gets heated the resistance is about 15k


i will add a temp vs time when charging .Very soon


again thanks for the support.

Rgds
dilan
 

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