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

Chuck Harris cfharris at erols.com
Tue Jul 21 12:19:32 UTC 2009


28V is a nominal voltage, not an exact voltage.  It is derived from the
system voltage of a 24V battery that is being continuously charged.

The typical lead acid battery, as used in vehicles, wants to be charged at
a voltage that will quickly return it to full charge after the high starting
load has been removed.  That requires about 2.3V per cell, which leads to
28V nominal.  Your car works this way too, and if you measure the voltage
on your battery while the car is running, you will find your 12V is really
13.8 to 14.5V

-Chuck Harris

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?
> 
> The Isotemp OSCO 127-10 data sheet says 27 V, but that's +3, -6 or 21-30V 
> which straddles both 24V and 28V.
>  
> 



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