On Mon, 11 Jan 2010 16:45:22 -0600, Peter Laws wrote:
>Well, I mean not "really" as in "you don't know what you're talking
>about" but as in "wow, the SAE types spend a lot of time getting those
>rise-fall times just right so that the car meets the applicable
>standards for fuel consumption and emissions" ... Although not
>mandated, there are also drivability concerns as well ...
I can't comment on the automotive aspect of the design problem, but the
electronics and EMC part is solid and well known.
>Just how much would chokes change that?
That's hard to predict. It will certainly vary with the plug circuitry
and the ferrite part(s) being used. HOWEVER -- it is also well known
that rather small changes in the switching waveform can make a large
difference in harmonic content. If I were working on the problem in a
vehicle, I'd have a scope with a piece of wire attached to its input
set up next to the engine and watch the waveshape as I worked on the
plug wires. Even better, a spectrum analyzer.
>And how does this compare to the old "resistor plugs" that were sold
>to make the ticking on the car radio go away?
Same fundamental idea, except that a ferrite part has much less effect
at DC and low frequencies than does a resistor, and has more effect at
high frequencies. In other words, ferrites can probably provide more
suppression with less effect on motor performance.
Jim Brown K9YC
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