Jerry,
You state that the dwell time is the same at any RPM. I AGREE! But the
current flow through the coil is not linear. A post yesterday has an
excellent explanation of this. The instant the points close there is no
current flowing through the coil. The current flow increases as the
magnetic field builds. When the magnetic circuit saturates the current
flow will be the highest. At low speeds the coil saturates but the
points remain closed for a long period of time after that. The ballast
resistor heats up and increases in resistance thus limiting the current
to the coil. At high speeds even though the average time the points are
closed is the same, the points open soon after the magnetic circuit is
saturated. The maximum current does not flow for nearly as much time as
low speed operation. The ballast resistor cools down lowering the
resistance and increasing the current available to the coil. You also pointed
out the thermal mass of the system. I agree that there is some thermal mass
that must be taken into consideration. The world is not an ideal place, so the
mathmaticians don't get to have all the fun.
Comments welcome!
- - Mark = =o&o
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