At 06:38 PM 10/1/2006, Randall wrote:
> > 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
Interesting. Just for grins I tried to power my fan from the charger - no
joy. But it spun right up with the battery! Who woulda thunk it. Good
call Randall!
J
--
Jim Hassall
Blacksburg VA
jhassall@blacksburg.net
'63 TR4 in autox preparation - 90% finished, 90% to go
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