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

[Neville Michie]

In the early days of radios, there were A and B batteries. A were 2,  
4 or 6 volt. B were 90 to 120 volts
in glass accumulators.
These were taken back to the radio shop to be recharged when flat.
This is where the 6.3 volt filament voltage for vacuum tubes came from,
the voltage of a 3 cell accumulator on discharge, the A battery.
When radios were to be used with motor generator sets, particularly  
the military,
the standard was for 7 volts, the voltage on a 3 cell accumulator on  
charge , and there as even a
series of 7 volt filament valves for military use.
As more power was required, particularly to power genemotors, battery  
banks were
  doubled and doubled to give 14 volts and then 28 volts. At this  
stage with genemotors
any voltage could be made to order, and voltage was regulated with  
carbon pile series regulators
at the 28 volt level. A genemotor with 28 volt input could produce  
-150 V for bias and 250V
and  600V for seriously powered radio transmitters.
Aircraft also came into the picture, also with generator supported  
accumulators.
Car radios used vibrators and transformers to transform 12v to 260  
volts.
It was not until 1960 onwards that solid state power supplies began  
to appear.
The telephone industry used higher voltages around 50 I think, from  
accumulators
under charge.
So that is where these standard voltages came from.
Cheers, Neville Michie

On 21/07/2009, at 5:17 PM, phil wrote:

>
> ----- Original Message ----- From: "Hal Murray"  
> <hmurray at megapathdsl.net>
> To: "Discussion of precise time and frequency measurement" <time- 
> nuts at febo.com>
> Sent: Tuesday, July 21, 2009 2:59 AM
> Subject: [time-nuts] Where does 28V come from?
>
>
>>
>>> 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.
>
> Hal,
> Where did you find that Isotemp OSCO 127-10 data sheet ?
> Any other data on that unit?
> Phil
>
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