The reason DC power systems in vehicles and aircraft used 28 V or less historically is that that was the highest DC voltage that could be switched mechanically without excessive arcing. (Has to do with the energy required to pull electrons out of metals, I believe.) With the solid state switching devices now available, of course, higher voltages could now be used.

OT, I know, but I always thought that was interesting.


Scott  K9MA

On 10/15/2016 19:46, ab2tc wrote:

Well, as I remember it there was once a push to move to 48V for automotives
but that never happened (so far).

I was always skeptical on the wisdom on moving to FET finals at the 12V
level. Generally bipolars work better at this low voltage. FETs come come
into their own at higher voltages (24-75V).

In general I still think it is silly to make modern radios compatible with
the old 12V car power system. For portable use there are plenty of ways to
provide higher voltages. (Eventually power supplies manufacturers will make

AB2TC - Knut

David Gilbert wrote
There was a major initiative at least 15 years ago in the automotive
industry to go to 28 volt systems in order to reduce the cost and weight
of the heavier wires that were needed to cope with the expanding current
drain as more things in the car went electronic. Not sure what happened
to that since I've been retired, but I assume ways were found to make
the new electronics more energy efficient in the first place.  As I
remember, one of the issues holding back 28 volt systems was the higher
breakdown voltages that would be needed for the various semiconductors
involved ... not everything gets more efficient or cost effective as
voltages go up.

Dave  AB7E

On 10/15/2016 12:49 PM, Ron D'Eau Claire wrote:
And therein lies the reason for using 12V. It would have been easier had
gone from 6V automotive power to 28V as is used on many aircraft so
manufacturers were encouraged to build generators and equipment for that
voltage, but that didn't happen.

73, Ron AC7AC

Scott  K9MA

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