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GRutter · 12-05-2020, 08:55 PM

Yup. There is a formula for that.
E (Voltage) = I (Current) x R (Resistance)

What happens is 6 volts are 'dropped' across the resistor when the points are closed, so that the coil sees 6 volts rather than 12 volts.
E (6 volts) = I (4 amp Current Thru Coil) x R (1.5 ohms of ballast resistor)

12-05-2020, 08:55 PM	#4
GRutter Senior Member Join Date: Sep 2017 Location: Mint Hill, North Carolina Posts: 386	Re: 12 volt system on a Model A Yup. There is a formula for that. E (Voltage) = I (Current) x R (Resistance) What happens is 6 volts are 'dropped' across the resistor when the points are closed, so that the coil sees 6 volts rather than 12 volts. E (6 volts) = I (4 amp Current Thru Coil) x R (1.5 ohms of ballast resistor)