In a message dated 7/12/01 6:28:21 AM Eastern Daylight Time,
aribert@c3net.net writes:
<< I think that I will split the difference and do as one suggested
and install the 0.8 ohm ballast resistor and check that my output
voltage is in the range that Crane specifies. >>
I'm not sure if this was mentioned yet. The resistance of a ballast resistor
is dynamic depending on current flow. Think if it as a regulator for current
dependent on engine RPM.
When a engine is running slowly the points are closed for a longer period of
time allowing greater coil saturation. When the engine is running at high
RPM, the closed point time is less and the coil saturation is less. When we
add a _ballast_ resistor to the mix we are controling current flow at low RPM
inorder to prevent the points from burning up while allowing adequte coil
saturation at high speeds.
When the ballast resistor heats up due to high current flow ( low rpm )
resistance _increases_ limiting current flow. As the engine speeds up,
current flow drops, the resistor cools and current goes up.
My Formula Ford road race car ( 1.6L Kent British engine) uses a point
system without any ballast resistor and a coil designed "For use with a
ballast resistor". Since the engine is only operated under 3000 RPM during
warmup and typicaly sees 6800 RPM max, no resistor is needed.
It's been a 18 hour day, hope the above makes sense.
Harold
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