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Spitfire Spitfire Ballast Resistor

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J

JPrisbe

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The ballast resistor on my '70 Spitfire gets hot to the touch with the key on and the car runningor not.

Should it be getting hot?
 
Yes, a ballast resistor will certainly get hot when the ignition is on and the engine isn't running. It should be a little less hot when the engine is running.

Worst case, the resistor is passing 4 amps (12v / (1.5 ohm ballast + 1.5 ohm coil) = 4 amps). One power formula is simply Watts = V x amps. So, there will be six volts across the resistor and 4 amps = 24 Watts (6x4=24). Turn on a 15 or 20 Watt light bulb and try to grab it, that will put things in perspective.

With the engine running there isn't current flowing all the time (reduced duty cycle) so the resistor will have time to cool a bit. It will certainly still be warm.
 
It very well may not be original.

I just got the car and am learning things everyday. Like about voltage stabilizers and creative wiring by POs.
 
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