Why 28V DC?

"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 :-)

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.

"Ron Natalie" wrote in message
...

"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 :-)


Ah well the systems I worked on had rather substantial batteries and the
real hazard was shorting something out rather than touching it. Some people
hated the feeling but unless I was sweaty I would just touch things to see
if they were live.

The 20 Hz ring was interesting because you can quite distinctly feel each
half cycle go by. The original systems I messed with used motor-generators
to make the 90 Volt 20 Hz and every so often when I am near an old elevator
the smell reminds me of those old dynamotors.

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...."

"S Narayan" wrote in message ...
The generation
of 3 phase power is also easy and I believe it may also be more efficient in
terms of the generator design.

That's probably why the alternators in your car and airplane both
are three-phase. A 60-amp alternator weighs less than an old 25-amp
generator.

Dan

Jeez...that's something I've never considered. You are RIGHT, internal to that
alternator there IS 3-phase AC that is regulated and rectified to produce the
DC...

And now with three small transformers and a little surgery on the alternator, we
could have 3-phase 115VAC to run those military gyros...I wonder...yeah, I know
the frequency is a function of engine RPM...but still...

Jim


(Dan Thomas)
shared these priceless pearls of wisdom:

- That's probably why the alternators in your car and airplane both
-are three-phase. A 60-amp alternator weighs less than an old 25-amp
-generator.
-
- Dan

Jim Weir (A&P/IA, CFI, & other good alphabet soup)
VP Eng RST Pres. Cyberchapter EAA Tech. Counselor
http://www.rst-engr.com

"Jim Weir" wrote in message news
Jeez...that's something I've never considered. You are RIGHT, internal to that
alternator there IS 3-phase AC that is regulated and rectified to produce the
DC...

And now with three small transformers and a little surgery on the alternator, we
could have 3-phase 115VAC to run those military gyros...I wonder...yeah, I know
the frequency is a function of engine RPM...but still...
\
You think that AC coming out of those inverters is all that stable? It tends to wander
with the input voltage. Of course the real problem is that if the alternator crumps, the
battery will not put out three phase.

"Ron Natalie" wrote in message
. ..

"Jim Weir" wrote in message
news
Jeez...that's something I've never considered. You are RIGHT, internal
to that
alternator there IS 3-phase AC that is regulated and rectified to
produce the
DC...

And now with three small transformers and a little surgery on the
alternator, we
could have 3-phase 115VAC to run those military gyros...I wonder...yeah,
I know
the frequency is a function of engine RPM...but still...
\
You think that AC coming out of those inverters is all that stable? It
tends to wander
with the input voltage. Of course the real problem is that if the
alternator crumps, the
battery will not put out three phase.


What?!? Your plane doesn't have 3-phase batteries? Call CBS!

On Sun, 18 Jan 2004 19:20:48 -0500, "Ron Natalie"
wrote:

"Jim Weir" wrote in message news
Jeez...that's something I've never considered. You are RIGHT, internal to that
alternator there IS 3-phase AC that is regulated and rectified to produce the
DC...

And now with three small transformers and a little surgery on the alternator, we
could have 3-phase 115VAC to run those military gyros...I wonder...yeah, I know
the frequency is a function of engine RPM...but still...
\
You think that AC coming out of those inverters is all that stable? It tends to wander
with the input voltage. Of course the real problem is that if the alternator crumps, the
battery will not put out three phase.

The voltage is pretty stable, and is a square wave clipped by the
battery voltage ... at least while charging. I think the regulator
shuts it off when not, but am not sure. Years ago, when construction
of auto alternators was less optimized, I helped a freind rig his full
kW ham rig ... we took the alternator output into a 3 phase
transformer to get plate voltage. MUCH better than the vibrators of
the day. And we needed very little filtration with the 3 rectified
phase.

FYI, one, and perhaps the main, advantage of 3 phase rotating
machinery is that in theory, the developed torque of a motor, and load
torque of a generator is constant. Only manufacturing tolerances and
real conductors and iron give ripple.

x-no-archive: yes

"G.R. Patterson III" wrote:

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.

Uh, yes. That's why I said it could feel pretty bad and juxtaposed it with the
relatively harmless 42 volts. BTW: that spark plug can knock you into last week, but
it has very few amperage and will not likely cause you any long term harm (unless you
bang your head as you back away fast