[Vwdiesel] battery voltage etc.-info

Roger Brown r.c.brown at ieee.org
Tue Oct 7 20:22:56 EDT 2003

Mike & Coreen Smith wrote:
> Battery load tested OK, so I must not have pipped the throttle enough to get
> the RPM up and start the charging process before, during my multimeter test
> yesterday.  Perhaps this explains why sometimes I see the red charging light
> on when I first start the car until the revs are up, even if just for a
> moment...then the light goes out permanently.  Anyone know how this works?

That's normal, the Bosch/Motorola alts. are "self-exciting", they use the small current passing through the charge LED to
produce a small internal magnetic field, at about 2000-2500 RPMs, that field is sufficient enough to exceed the battery voltage
the then the regulator kicks in and the alt starts charging.  Once the alt. starts charging, the LED goes out since the voltage
difference is 0.


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