Date: August 19, 1998
I have been reading the various versions of the debate about ignition
circuits and I recalled that I had the manual for a Heathkit Ignition
Analyzer. I thought I would post what it says about the ignition circuit.
"Consider the breaker points as a switch. When the switch is closed,
current from the battery flows through the coil. The current flow causes a
magnetic field to be set up in the soft iron core of the coil. This
magnetic field builds up relatively slowly (it is not an instantaneous
occurrence). For this reason, the length of time the points remain closed
(called "dwell") is important.
"As soon as the switch opens, current ceases to flow from the battery
through the coil. The collapse of the magnetic field is practically
instataneous. As this field collapses, a voltage is "generated" which
tries to keep the current going. This voltage can approach several hundred
volts in the coil primary. It is the job of the condenser (or capacitor,
ed.) to absorb this surge of voltage across the points. At the same time
this voltage surge occurs in the primary, a surge is induced into the
secondary (which contains many more turns of wire). The net effect is to
"step up" the primary voltage to a level sufficient to fire the spark
plugs. This requires many thousands of voltage depending among other
things on compression, air/fuel ration and spark plug gap."
I hope this helps.
Bob Reisse
76 MGB
NAMGBR 8-3559
|