Why 28V DC?

Jim Weir wrote:

So why was there 12 volts to begin with? Because Detroit started making cars
with a much higher compression ratio and to turn the starters over, the old 6
volt batteries weren't cutting it. Bingo. Two 6 volters in series gives 12
volts and that was close enough for Detroit gummint work.

Actually the auto industry is moving to a 42 volt system in the future to handle
increasing electrical requirements, plus more accessories (e.g. oil pump) may be
electric in the future. Where can you find more information on this? Why
http://www.42volt.org of course.

In article , Tiffani wrote:

Jim Weir wrote:

So why was there 12 volts to begin with? Because Detroit started making
cars
with a much higher compression ratio and to turn the starters over, the old
6
volt batteries weren't cutting it. Bingo. Two 6 volters in series gives
12
volts and that was close enough for Detroit gummint work.

Actually the auto industry is moving to a 42 volt system in the future to
handle
increasing electrical requirements, plus more accessories (e.g. oil pump) may
be
electric in the future. Where can you find more information on this? Why
http://www.42volt.org of course.



Just what we need in a car -- an electric oil pump! That would be fine
for pre-oiling, but for regular operation? It degrades reliability by
making the lubrication system dependent on another system.

"Tiffani" wrote in message ...


Jim Weir wrote:

So why was there 12 volts to begin with? Because Detroit started making
cars
with a much higher compression ratio and to turn the starters over, the
old 6
volt batteries weren't cutting it. Bingo. Two 6 volters in series
gives 12
volts and that was close enough for Detroit gummint work.

Actually the auto industry is moving to a 42 volt system in the future to
handle
increasing electrical requirements, plus more accessories (e.g. oil pump)
may be
electric in the future. Where can you find more information on this?
Why
http://www.42volt.org of course.


A 42V DC? shock could be pretty bad. The new Toyota Prius uses 273V for the
traction motor, but that is very local to the hybrid system. Maybe a low
voltage higher frequency AC system might be a solution as someone suggested
earlier in the thread. Conversion efficiencies are pretty good these days
with more advanced controllers. Then individual components could step up the
voltage and convert to higher DC voltages as needed.

"S Narayan" wrote in message
...

A 42V DC? shock could be pretty bad. The new Toyota Prius uses 273V for
the
traction motor, but that is very local to the hybrid system. Maybe a low
voltage higher frequency AC system might be a solution as someone
suggested
earlier in the thread. Conversion efficiencies are pretty good these days
with more advanced controllers. Then individual components could step up
the
voltage and convert to higher DC voltages as needed.


I've worked on a lot of 48 Volt systems and it is more like an unpleasant
tingle than a bad shock.

Higher voltage means thinner wiring, cutting weight.

"Peter Gottlieb" wrote in message . net...
I've worked on a lot of 48 Volt systems and it is more like an unpleasant
tingle than a bad shock.

It is until ringing voltage is applied :-)

"Peter Gottlieb" wrote in message
. net...

"S Narayan" wrote in message
...

A 42V DC? shock could be pretty bad. The new Toyota Prius uses 273V for
the
traction motor, but that is very local to the hybrid system. Maybe a low
voltage higher frequency AC system might be a solution as someone
suggested
earlier in the thread. Conversion efficiencies are pretty good these
days
with more advanced controllers. Then individual components could step up
the
voltage and convert to higher DC voltages as needed.


I've worked on a lot of 48 Volt systems and it is more like an unpleasant
tingle than a bad shock.

Higher voltage means thinner wiring, cutting weight.

I meant if things got wet, it could be quite a tingle. Considering the
highly litigous public in this country, I can see the lawsuits if poeple got
even slightly "hurt". Agree about the copper savings. I grew up with 240VAC
power and that is something you don't fool around with. I have also had
shocks from the flyback transformer in TVs and ignition systems in cars, but
those are likely to get you physically hurt (uncontrolled muscle reaction)
than the shock itself.

S Narayan wrote:

"Tiffani" wrote in message ...


Jim Weir wrote:

So why was there 12 volts to begin with? Because Detroit started making
cars
with a much higher compression ratio and to turn the starters over, the
old 6
volt batteries weren't cutting it. Bingo. Two 6 volters in series
gives 12
volts and that was close enough for Detroit gummint work.

Actually the auto industry is moving to a 42 volt system in the future to
handle
increasing electrical requirements, plus more accessories (e.g. oil pump)
may be
electric in the future. Where can you find more information on this?
Why
http://www.42volt.org of course.


A 42V DC? shock could be pretty bad.

Not really. Touching a spark plug could feel pretty bad. Touching 42 volts
might give you a bzzz! However you wouldn't normally become part of the
circuit, anymore than you would with your domestic 120 volts or your telephone
(about 53 volts on hook, maybe double while ringing). Remember even if you did
get a shock, it's DC not AC. AC is worse for shocks because it can cause the
muscles to hold on to the conductor. DC tends to do the opposite. And it is
the amps that are most damaging to humans, not the volts.

Lisa Hughes wrote:

Not really. Touching a spark plug could feel pretty bad.

Spark plugs run on extremely high voltage. The 12v battery power is fed through
a step-up tranformer (known as a "coil" on most systems) to increase the voltage.
Voltage at the plug will be anywhere from 40,000 to 100,000 volts.

http://www.howstuffworks.com/ignition-system2.htm

George Patterson
Great discoveries are not announced with "Eureka!". What's usually said is
"Hummmmm... That's interesting...."

Bob Martin wrote:
I'm working in the avionics integration test facility at Gulfstream...
one of the engineers had a question for me (being an airplane person
instead of an electrical/computer guy) that I couldn't answer... why
do airplanes use 28V DC systems (or 14V)? He says most industrial
applications use 24V DC. I tried googling on it but nowhere did it
suggest any reason why, just that it is.

Lead-Acid chemistry batteries need 13.8 to 14.4V for "charging". The
voltage regulator on the alternator is usually set to a "compromise"
setting of 14.25V, which causes the bus voltage of the aircraft to be
near this voltage all of the time the engine is running.

All of the avionics and instrumentation is running off said 14.2V for
the duration of the flight. Double all of the above voltages if the
airframe has a 12 cell battery instead of a six cell.

What happens if the alternator fails in flight? Almost immediately, the
battery voltage sags down to under 12.6V, so the avionics has to work
over a voltage range of 11.5 to 15V...

MikeM