Barry,
Two electronic rules. Ohm's Law I=E/R or R=E/I, and Kirchoff's law of sum of voltage's in a loop = 0. How to apply here to your question: With a 12V Power supply that means that the voltage developed across a resistor and the voltage across the coil will = 12V. On motor 1, the coil voltage for 4V means the voltage across the resistor will need to be 12V-4V = 8V. The coil current for the coil at 4V @ 4.1 Ohm = .975A (I=E/R) so the resistor will be (R=E/I) 8v/.975A = 8.2A The resistor power is E*I or 8*.975 = 7.8 Watts or greater (typical would be 10W). This is assuming you will be using two resistors, one in each center tap.
Phil, Still too many interests, too many projects, and not enough time!!!!!!!!
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