On Tue, 5 May 2009 19:38:34 -0700 (PDT), Half-Nutz
wrote:
On May 4, 3:46*pm, jeff_wisnia wrote:
I'm thinking that all else left alone, it probably doesn't matter which
way the shaft of an automobile alternator is rotated since the machine
produces ac which is then rectified to create a polarized dc output.
Am I right about that?
The question came up just now when eldest son and I were kibitzing about
this week's "Car Talk" puzzler:
http://www.cartalk.com/content/puzzl...918/index.html
Thanks guys,
Jeff
--
Jeffry Wisnia
(W1BSV + Brass Rat '57 EE)
The speed of light is 1.8*10^12 furlongs per fortnight.
A former poster on this group....
Told a tale of parking his car Many miles into the wilderness, and
leaving on foot for several months.
Upon his return, the battery would be dead, and a few ( 50?) miles
from any passing help.
What he used was an old propane tank, and AIR (80's style smog) pump,
and some lines.
He'd fill the old propane tank with water, throw it on the fire, and
the line ran to the old AIR pump, which was rigged to run backwards
and act as a "turbine" spinning the alternator and charging the battery
to allow his escape in the fall.
That was his story. It was Just crazy enough to work.. Maybe.
Agreed - Just crazy enough that it might work.
But the efficiency would be abysmnal, AFAICT those were carbon-vane
pumps and weren't very efficient going forward, reverse would probably
be worse.
Now an air drill motor, that has far better possibilities...
And as has been brought up, there has to be enough power left in the
battery to excite the field windings on the rotor. Or the alternator
won't start alternating - chancing enough residualk magnetism after
several months of sitting is asking a lot.
If he thought far enough head to disconnect the battery when he left
the car, and the battery was in good shape, it's possible.
If he left in a hurry, he's screwed - "several months" and the
battery will be dead just from the clock and memory drains. Even 5 to
10 milliamps will kill a battery if you let the car sit over two
months - one month is about the limit without a trickle charger or
disconnecting the battery.
-- Bruce --