Hot damn! I knew the expertise was lurking out there somewhere, given the
right challenge. Thank you, Charley Robinson.
At 10:51 PM 8/15/98 -0500, ccrobins wrote:
>.... this looks like the last post on the matter of breaker-point
ignition, ....
Sorry, Charley. On this list it's never the last question. <:(
>....
> When the points open current doesn't instantly stop flowing in the
primary windings of the coil. Current now flows through the condenser and
coil primary as the condenser charges up toward the 12 volt battery
voltage. As the condenser charge nears the battery voltage the current
thru it and the coil primary drop to the point where the magnetic field in
the primary collapses.
>....
> the condenser now discharges thru the coil secondary and the spark plug,
"powering" the spark.
This is the key to the whole spark trick. Current flows into one side of
the condenser and out of the other side, but it does not actually flow
_through_ the condenser. Internally it builds up a charge on the side
where the current is flowing in, and an opposite charge on the other side.
If you were the coil hooked up to that capacitor and only looking at one
side of it, it appears that you just crammed a big wad of electrons in
there, and then they come bouncing back out. At the moment of the big
spark, it is that wad of electrons that provides the current through the
secondary winding of the coil and that ultimately jumps the gap at the
spark plug. At that moment you have a circuit with current flowing out at
the spark plug, but no current flowing in on the ignition switch side of
the coil, because the charge has been stored halfway through the circuit in
the little capacitor. And as such, Charley's following comments:
> ....
> The condenser discharge current and the back EMF off the coil primary are
opposite in polarity to and greater than the battery voltage and block any
primary current from the battery.
>....
>.... hence the condenser to supply the current pulse to power the spark.
And the crowning answer:
>> 6.) Approximately how much current is flowing in the wire from the
ignition switch to the coil when the spark is happening ....?
>
> milliamps to 0.
Give that man an A+ and a hall pass for the rest of the period.
Now about that next question, ..... Charley, are you still out there in
the hall? How can a shade tree mechanic test a "condenser" for proper
function without fancy laboratory instruments?
And now for the follow up questions on a somewhat related subject:
a.) What is the source and nature of that "ignition noise" that bothers a
car radio?
b.) Why do high resistance spark plug wires greatly reduce that noise?
Take a break Charley. Let them speculate for a while. 0}:-)
Barney Gaylord
1958 MGA with an attitude
PS
I almost forgot. You may have noticed that the dual spark (waste spark)
ignition coil does not need a condenser to function. That "wad of
electrons" that fires across one spark plug to ground also comes from
ground via the other spark plug, so it does not need to be stored in the
ignition circuit.
BG
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