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"
<[email protected]>
To: "Discussion of precise time and frequency measurement" <time-
[email protected]>
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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