[Milsurplus] Can.military use of 14V/12V

[Bruce Gentry]

On 11/16/12 10:05 AM, Ralph Cameron wrote:
> I am told by former Canadian military staff that 14V was often stated on
> RCAF equipment because a fully charged 12V battery is 13.8V and that was
> close enough to call it 14V. At some point in time it was renamed 12V as
> being a nominal value and to conform to other services.
>
> Ralph
> VE3BBM
>
Calling it 14 volts is a compromise. A fully and recently charged 12 
volt lead acid battery will deliver about 12.7 to 12.8 volts under light 
load. This will decrease to about 12.6 and remain fairly steady until 
the charge nears depletion. Conversely, charging regulators adjust the 
voltage for battery temperature to insure full charging. A battery at -5 
degrees C. will need about 14.2 volts for a while. At about 5 degrees, 
13.8, dropping to about 13.2 at 30 degrees will assure a full charge. 
Because aircraft batteries tend to be in cold locations, they usually 
receive these higher voltages. Aircraft electrical systems were often 
set for 14 volts, and if the battery life was shortened, it was just a 
cost of operating the aircraft.  They tended to be at minimum size that 
would start the engine for weight saving, and had to be as fully charged 
as possible. It was a great source of batteries for me in high school, a 
battery that would not start a Beechcraft Bonanza (or a DC-3!) on a cold 
morning was still great for radios.

     Bruce Gentry