When using a Modified 6V nicad (use to be 4.8V) it becomes very hot.. probably about +70C. the system it drives is designed to automatically shut down when supply voltage drops (Unsure what to) recently tested and found the drop from the 6V was as follows
- Fully Charged = 7.55V
- Shut down voltage = 5.89V
However i have not modified the system in which it is used for so how is it that it is shutting down before the standard nicad voltage of 4.8V ?
Have placed the Nicad in the freezer to see if dropping the temperature will allow me to re use the nicad in the system.
NiCads in general electronic applications are typically designed to NOT get hot, since the heat destroys the NiCad battery, can damage electronics and causes lawsuits when users get burned from the hot battery. Some devices like radio-controlled cars are high-drain applications that generate a lot of heat, so the batteries for these devices are designed for their specific use.
Batteries get hot when they charge due to the high current going into them. The faster they charge, typically the hotter they get. When the battery discharges during use, the same thing happens, the battery gets hotter as more current is drawn from the battery.
Without knowing anything else, my guess is that high current draw from the battery cells is causing them to heat up. This can be due to a defective battery, a battery not designed for the way you are using it or your modification damaged the battery or is otherwise causing excessive current drain.
Also, increasing the supply voltage can drive more current through the device, so it may just be that the higher voltage is drawing more current.
I’m not sure how the device is shutting down, so I can’t say why it’s doing that. Note that the voltage at which a device stops working is the voltage seen by the device itself. If you remove the battery from the device and measure the voltage, you will get a different voltage than if you measure the voltage at the precise moment the device shuts down. This is especially true for high current drain applications, which appears to be what’s happening with your batteries.
Placing the NiCad’s in the freezer won't help. They’ll have to warm up to work properly anyway.