Barney Gaylord wrote:
> When engine is running the points are closed less than half the time, and when
> the points are open the coil is drawing no current and generating no
> heat.
>
> Take the mathematical average of the current flow(s) when running,
> assuming the points are closed 40% of the time. (3.9a x 0.4 + 0.0a x
> 0.6) = 1.56a That's pretty close to the 1.4 amps noted in your book.
There is actually a little more to it than this.
The coil primary is inductive. This means it resists changes in
current flow. If there is current flowing, it wants to stay flowing,
if the current is NOT flowing, it will fight to prevent it.
The numbers might work out either way depending on a lot of
things. However, the important nugget is that the instant the
points close the current will not be 3.9A. The coil primary will
develop a voltage across it to resist current flow, and it will
be somewhat less.
After some time it will rise or oscillate depending on
a myriad of things.
The numbers might actually average out, but it is important
to note that because inductance is present no first order
function will describe the system.
--
Trevor Boicey
Ottawa, Canada
tboicey@brit.ca
http://www.brit.ca/~tboicey/
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