Ballast Resistors Again
> Well, we don't have 400V available. But we do have 12V.
> And we can choke it down to 6V with a resistor, so the
> coil doesn't burn up. However, at the moment when we
> first connect up the coil, and it looks like an open
> circuit, the RESISTOR DOES NOT DROP ANY VOLTAGE WHATSOEVER,
> AND WE HAVE A FULL 12V ACROSS THE 6V COIL. Remember,
> resistors drop voltage by the virtue of current flowing
> through them ( V=I*R ). No current flowing through, no
> voltage drop. This makes the coil "start to charge" much
> faster.
> It's common to have a solenoid terminal that shorts out the
> resistor during starting. Heck, the battery voltage drops
> down to 9 or 10 volts anyway then. Especially when you're
> trying to crank over a big V8. You do lose the benefit of
> the "current source", but the engine is turning so slowly
> that it doesn't matter.
> Bet everybody's *really* confused now :-).
It's really not all that complicated --
With any coil, the higher the input voltage, the higher the
output voltage.
When the starter is engaged, the resistor is shorted and the
coil sees the full battery voltage, therefore the spark plugs
get a hotter spark.
Once the car is running, and the starter circuit is no longer
active, the resistor limits the current to the coil, preventing
it from overheating and dying.
Ballasted coils will fail quickly if they are forced to run at
12V for very long. This means the manufacturer can provide a
hot spark for starting without the cost of a heavy duty coil.
Obviously, resistors are cheaper than beefier coil windings.
That's all there is to it. Charge rates, magnetic flux, back-EMF
and photon-plasma discharges are not the main consideration here,
cost is. This is a (relatively) cheap way to provide a better
starting capability.
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