Not mine, plagarised from another forum for old boxer bmw's





Knowing how something works always makes it more fun to work on, and
helps in the diagnosis. Electricity doesn't give up its secrets
easily, so here is a short explanation of what happens in the
ignition system.

The ignition system produces a lighting-sized voltage of some 40,000
volts from a 12 volt input. It is the coil's job to produce the
voltage multiplication. Coil is a bit of a misnomer, it is an
inductor, a sort of transformer with two coils of wire: a primary
set with some 12 volts running through it initially, and a secondary
set of wire. The coil (more correctly an inductor) performs its
magic by having the system voltage (12 volts) applied to the primary
coil of wire almost all the time. Like any coil of wire with
electricity running through it, it becomes an electromagnet. The
points (short for breaker-point assembly) are a switch that
interrupts the voltage to the primary coil of wire. When the flow of
electricity stops, the magnetic field that the primary coil of wire
had created collapses. The magnetic field is really pissed because
the only place for the energy stored in the magnetic field can go is
into the secondary coil of wire. The secondary coil of wire is wound
with thousands more turns than the primary, and this difference,
like a transformer, increases the voltage in the secondary set of
wires. The collapsing magnetic field's energy races into the
secondary wiring, out of the secondary wiring at a very high voltage
(an low current) and is forced to jump an air gap at the spark plug
in the engine, igniting any gasoline vapor that was sucked into the
cylinder.

With all the electrical instability created by creating and
collapsing magnetic fields in the coils, there is some electrical
energy that thinks it can sneak back across the breaker-point switch
assembly. To prevent this, our antiquated ignition systems have an
electric shock absorber as part of the system. The condenser is the
shock absorber. It is a capacitor, it doesn't condense anything. It
is constructed from a strip of aluminum foil sandwiched in with a
sheet of insulation that is rolled up like a sleeping bag and put
into a little metal can. The capacitor stores electrical energy in
an electric field (not a magnetic field like a coil). The condenser
soaks up a couple hundred volts trying to jump back across the
breaker-point assembly. This prevents the metal on one side of the
points from acting like an electric welding rod and being deposited
on the other side. When the breaker-point closes again, it gives up
its energy stored in the electrical field back into the primary
winding of the coil.

:beer:beer:beer:beer:beer:beernn[ Edited on 29-6-2005 by koolkarmakombi ]

A truly excellent explanation!

Could you please fix one of the bits of plagiarism though. It kind of gnaws at me.

This bit.

lolol done!

isnt it a bastard when even plagarism is wrong?

Mistakes just make it look more authentic.