Low Battery and Circuit Breakers and Cold Weather

 I am planning an article for the Comanche Flyer which explains a few items regarding batteries.  

1)  Charging voltages for cold batteries

Batteries require a high voltage to charge when cold.  Many Comanches have the battery in the fuselage away from the engine and these never warm up if it is very cold outside.  However, the regulator is in the engine compartment.  These will allow a higher charging voltage when cold but will soon warm up and lower the voltage.  Therefore, it is quite possible that cold battery will NEVER charge up in cold weather.

2)  Current draw for the gear motors

The current drawn by a shunt wound motor (the gear motor) varies inversely with supply voltage.  If the supply voltage is low the current needed for a given torque is high.

3)  Take off is the highest current draw

The current on an airplane is highest during takeoff.  The battery is charging, the gear motor is running, the landing lights are on, the fuel pumps are running, and all the other items are also going.

4)  Torque produced varies with the square of the voltage

Low voltage means the motor is weaker.  Much weaker.

Therefore a low battery in cold weather may never really charge up.  This means that during takeoff a 35 amp generator will lower its voltage until the current draw is ok.  This can be so low that the gear motor cannot actually do its job and will stall.  This leads to the gear motor circuit breaker popping.