Jim:
You have it correct.
The coil is an inductor, which means that energy is stored in the
magnetic field surrounding the core.
When the points open, the magnetic field collapses, and this stored
energy appears as a voltage across the output (*AND* the INPUT!!) The voltage
will go as high as it needs to in order to dump the stored energy in the form of
current. Hopefully this energy appears across the plug gap, and in turn ignites
the mixture in the cylinder.
Were it not for the condenser across the points, some (most?) of the
stored
energy would appear as an arc across the *points*. This would divert energy
from the
plugs (bad) and burn the points (also bad). The condenser prevents the energy
from
being wasted and breaking delicate stuff that we would like to keep around for
a while.
The ballast resistor, on the other hand, is used to make the car start
more
easily. It does this by allowing a 6 volt coil to be used. When the car is
cranking,
the battery is only delivering 6-7 volts. By using a 6 volt coil we get a hotter
spark than from a 12 volt coil (at least while cranking).
When the motor is running, a 6 volt coil would overheat, and deliver so
much voltage that you would have flashover, misfiring, etc. So the ignition
switch is wired to hook the ballast resistor in series with the coil after the
motor starts. This in turn drops the coil primary voltage down from the
battery voltage (now at 12 volts since the starter motor is no longer drawing
current)
to the 6 volts it is designed for. You get the best of both worlds with
a ballasted coil. Un ballasted coils deliver a weaker spark while cranking,
because they
are operating at half their rated primary voltage.
Cheers,
Vance
---------------------------------------
The most likely way for the world to be destroyed, most experts agree, is
by accident. That's where we come in; we're computer professionals. We
cause accidents. - Nathaniel Borenstein
-----Original Message-----
From: Jim Swarthout [mailto:jswarth1@tampabay.rr.com]
Sent: Monday, June 30, 2003 4:18 PM
To: 6pack@autox.team.net
Subject: RE: Ballast resistor question
Hmmmm,
I had always assumed that the ,(capacitor), condenser prevented a
current overload at the points? Current causing the pitting of the
points?
Occasionally I'm wrong!
Anyone care to describe how an ignition coil works? After-all we are
converting 12V to 25,000V
Jim Swarthout
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