On Thu, 9 Apr 1998, Tony Rhodes wrote:
> system exceeds the output of the alternator, should the ignition light on
> the dash
> definitely come on? I never really knew what it was that made the light
> come
> on/go off!
It's the bootstrap. <g>
One side of the light bulb is connected to your ignition switch. This
receives 12V when they key is at 'run'.
The other side is connected to the field outputs of the
generator/alternator. When the key is on, and the engine is off- the bulb
will glow, because there's 0V at the generator and 12V from the key.
After the engine starts, the electricity goes through the key-switch, the
bulb (making it light), and the generator fields, to ground. The fields
are just a big electromagnet, that perform the same function as the
permanent magnets in a model car motor.
The fields thus charged, the generator can begin charging. Without this
startup current, the generator is just a bunch of copper, lead, steel, and
varnish being flung around by the crankshaft belts. I could try to
explain what's *really* happening with the electrons, magnetic fields,
induced current, flux, etc. but it's a bit confusing and I'd have to write
it out carefully to avoid mistakes.
The light bulb goes out when the fields are 'up' because there's 12V at
both sides of the light bulb (for a total of 0V!)
One bad part of this system is that if your bulb burns out, the generator
is pretty much dead. (bunch of copper... etc). It may start charging
anyway if there's enough speed in the works to start charging internally,
but I doubt it. It's not something I usually experiment with :-)
Hope this helps
-Malcolm
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