Jim Adney wrote:

On Sat, 16 Jul 2005 22:10:12 +0100 "Dave Plowman (News)"
wrote:



In article ,
satellite_jim wrote:


I actually have some experience with backwards batteries. I grew up in
my fathers auto repair shop in the sixties. Back then if you hooked up
the jumper cables to a generator equipped car you could start the car
and the generator would reverse polarity and you could go on your merry
way with a positive ground American car.


I don't see how, as the cutout wouldn't pull in. That only happened when
the generator started producing more than battery volts which it couldn't
when reverse connected.



I guess I'll have to think about the WHY of this, but I've seen it
happen. I agree that it's odd. The time I saw it, the owner had
installed the battery backwards, then realized his mistake and put it
in correctly. When I got to it the battery was correct, but I
eventually determined that the generator was polarized backwards.

Now I have to admit that it never occurred to me to wonder why putting
the battery in backwards would reverse polarize the generator while
putting the generator in forwards wouldn't correct it.



I think the key to an explanation is that the cut out relay senses
current direction as determined
by referencing the magnetic field of the current to the magnetic field
of a voltage fed electromagnet.

Since both were reversed the cut out relay didn't have a clue as to the
polarity.

I hope I explained my thinking clear enough.

Bill K7NOM