Quote:
Originally Posted by Synchro909
With respect, I think you have it backwards. The resistance of the starter doesn't change when you put 12 volts through it. With double the voltage, double the current will flow.
Resistance (R) is calculated by dividing the voltage (V) by the current (I). R=V/I.
Clearly if you double the voltage, the current doubles to keep the resistance (R) the same.
The power of an unmodified starter on 12 volts is 4 times what it is on 6 volts.
Power (P) is V x I. If bother have been doubled, the P is increased by a factor of 4.
That is why an unmodified starter running on 12 volts will turn over the motor so fast, the fan would nearly pull the car along!!
I expect the cranking current on 6 volts to be about 180-220 amps and double that for 12 volts.
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12 volts needs less amperage to do the same job that's why the cables are smaller.
12 volts 250 amps is equal to 6 volt 500 amps.
When you double the voltage you only need half the amperage.
Bill