On 9 Sep 2009 at 22:44, Wayne wrote:
> Or should I be setting it so my points are just begining to open (my light
> will go out)?
And Oliver wrote:
> randall - correct me if i'm wrong...
I'm sure not Randall, and I see Randall and mjb have already answered
this. (It's nice to see mjb being an active participant.) But I'll
toss out some info anyway.
As already stated, the plugs fire when the points open. Here's why.
(Oliver, the front page of that How Stuff Works link shows only a
macroscopic view of the ignition.) The primary and secondary
circuits in the coil are not directly connected, so the current
through the points to ground is not a valve for the plug spark. The
coil is two separate circuits close together so that the fields
created by one will be felt by the other.
A magnetic field is created when current flows. A voltage is created
when a magnetic field *changes*, the faster the change the greater
the voltage. When the points close current starts flowing through
the primary circuit, and the buildup is slow for various reasons.
Its magnetic field builds up slowly too and creates a small voltage
in the seconrday circuit. When the points open however the current
just stops, right now, immediately (almost). A flawed but useful
analog is a water faucet. No matter how quickly you open it the
water starts coming out at its own rate. Slam it closed and you hear
the pipes bang as the water is forced to stop. So when the current
in the primary circuit stops suddenly its magnetic field decays
immediately, which induces a large voltage in the secondary circuit.
It's like life. The big event ain't the pace but the sudden stop at
the end.
--
Jim Muller
jimmuller@rcn.com
'80 Spitfire, '70 GT6+
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