On a wound coil armature and a wound coil stator any residual magnetism can
induce a current into one of the coils and excite the other one. With motion
energy applied this can feed itself (self excite), as if the battery was
there, once in motion.

Without two sets of windings this doesn't happen.

---------------

"BobH" wrote in message ...
That is not strictly true. I drove a 72 AMC (with a Motorola Alternator)
for months without a battery in it. The alternator retains enough
magnetism to self excite enough to fire the coil. This was a carburated
straight 6. I lived and worked in a hilly area. If I killed it in
traffic, I was hosed.

A newer fuel injected vehicle requires enough current to run the fuel
pump and the computer in addition to the coil, so you be walking now.

BobH



On 03/09/2011 04:26 PM, wrote:
A wound alternator needs some DC to start up, one reason you can't
push start a car with an alternator and a totally dead battery.