[time-nuts] Where does 28V come from?

[Brooke Clarke]

Hi Hal:

Automotive electrical systems are said to be "12 Volts" (or "24 Volts" for 
military vehicles).  That's the voltage of a six cell lead acid battery when 
it's discharged.  It's fairly common to run down a car battery by say using a 
ham radio while the car is parked.  The rated voltage of a rechargeable battery 
is the discharged value.

But the same electrical system when installed in an aircraft is called a "14 
Volt" system ("28 Volts" for military aircraft).  In aircraft the engine is 
always running and the generator is always charging the battery.  You don't 
park an airplane in the sky.

The 12/14 volt system can see a range of 10 to 15 Volts and the 24/28 volt 
system will see a range of 20 to 30 Volts.


Have Fun,

Brooke Clarke
http://www.prc68.com

Hal Murray wrote:
>> 	That said, the modules also appear to be powered by 28VDC, add some
>> regulation, you could use the chassis to power the Thunderbolt, and
>> mount it in one of the blank panels. 
> 
> Lead acid batteries are close to 2V per cell.  For cars/trucks, they come 
> conviently packaged in 6V and 12V units.  The phone company works off 48V.
> 
> But where does 28V come from?