Vance,
Fantastic explanation!
I would like to add a bit more...kind of on the mechanical side for all
to get a visual.
An ignition coil actually consists of two different coils of copper
wire. The primary coil is made up of, let's say, 100 turns of copper
wire of a certain gauge. The secondary is made up of 2000 turns of a
smaller gauge wire.
Amps X Volts = Watts
12V X 3amps = 36 watts
At the time the points close the primary coil is momentarily energized.
When the points open the magnetic field is transferred, (collapses), to
the secondary coil of fine wire consisting of many more turns.
This results in a low current, high voltage output...i.e. "spark"
There are losses or perpetual motion would be the norm of the day!
Result...24,000V X 15 milliamps = 36 watts.
We've just converted a low voltage high current source to a high voltage
low current Spark...which makes fuel ignite!
Jim Swarthout
-----Original Message-----
From: Navarrette, Vance [mailto:vance.navarrette@intel.com]
Sent: Monday, June 30, 2003 7:39 PM
To: Jim Swarthout; 6pack@autox.team.net
Subject: RE: Ballast resistor question
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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