> My car has no battery, among other things, so I'm using a 10A battery
> charger and a fused lead to apply power to the fan. I'm using a 15A
> fuse, and Dan Master's TR6 book says the fan motor draws 6A. I'm
> testing the motor directly, so the fan switch is not the problem.
Tom, my suggestion would be to first check that the fan spins freely, and then
repeat your tests using a real battery rather than a battery charger.
DC motors normally have a very low resistance when they are not running; and
draw a lot more current when power is first applied than when they are running
normally. What happens is that, as they spin, they effectively generate a
voltage that opposes the input voltage and thus reduces the current. Depending
on the motor, the startup current can be several times the running current.
Also, battery chargers generally don't put out a constant 12v, but rather an
ugly mix of AC and DC. On mine, if you put an oscilloscope on the output with
no battery connected, it varies from 0 to about 18 volts. I don't know that
this is your problem, but it seems worth eliminating to me.
Randall
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