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Old May 26, 2003, 10:45 PM   #1
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Join Date: May 2003
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Default The Thermistor terminal (T) on Canon NB-1LH

I want to connect an external 3.7V source to my Canon S400
It seems that the camera does not run with a connection to the plus and minus terminal only ( in the battery compartment).
There is the 3rd (middle) contact, which connects to the T battery terminal. How is it used, and how can I mimic it in an auxillary connection set-up :?:
Thanks in advance for any help.
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Old May 27, 2003, 6:02 AM   #2
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I went through this process with a mobile phone battery once. The thermistor is used for sensing the charge when complete. However like you, I found it has to be connected for the battery to work.

All I did was measure its resistance at room temp and replace it with a resistor. You'll need to find out which end of the thermistor is connected to the battery + or minus. Be careful your supply is regulated to the normal full charge battery voltage and fused, as there is rarely a voltage regulator internally after the battery pack. Also you may get strange processor things happen when you first connect the external supply as it might shut down and re-boot. So I'd make sure the cam was off before turning on the external supply.

However, if you were rebuilding a battery pack with say AA's, be careful plugging in a charger, if the thermistor is the only sense for charging, your batt will get hot and might explode!. In my case there was also delta V detection, so I assumed the thermistor was more of a safety device.
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