I know just enough about electronics that I think it's a wonder I haven't died from touching both ends of a flashlight battery, but here is my problem and I'm hoping someone out there can guide me.
I am restoring a 1957 vintage Chrysler dealer-installed air conditioning system in my 1957 Chrysler. The evaporator unit that mounts on the transmission hump has a little fan on it that has a two speed motor. But apparently there must be a short in the motor that causes it to run at high speed no matter which speed you switch it to. When you energize either one of the speed wires the motor runs, and the other speed wire also tests energized. Even if both speeds were working fine, you'd really want one somewhere between the two, so I want to go for a better solution than fixing what may be wrong in the motor.
My plan is to put what I understand is called a PWM in one of the speed wires and disconnect the other one. That way I will have infinite control of the range of speed for the fan. Now, all the info I have dredged up on PWMs says they are made to work on brushless motors. I don't know if brushless motors were even born in 1957 yet, but this certainly isn't one. And for the life of me I can't figure out if a PWM is supposed to work on a brush type motor as well.
This 12V motor is drawing about 8 amps on startup and 4 amps running.
Can I buy just any old PWM of perhaps 10-15 amp capacity and hook it up inline to this motor to control the speed?
Or do I have to use use a resistor type controller for this brush-type motor? What should I look for and where should I buy one ready to plug in?
Is it possible that the two wires you are connecting to are downstream of where the resistor packs would normally be?Cr0sh - I agree that double the current at startup sounds odd (but I guess it could it be a little "sticky" after all these years) in terms of practical application - can you treat a shunt motor in the same way as a permananent magnet motor in terms of PWM?
Finally - I want to re-iterate to you the importance of getting that motor fixed -first-; like I said, look into local vintage automobile clubs in your area, you might find a person who was a mechanic of the era (heh - maybe you'll find a "Gus Wilson" old-timer who knows exactly what to do!) who can help you out, and get it working right. You might also find somebody who can help you install or set up a motor controller with PWM or a resistor pack, and do it in such a way so-as not to ruin the value of the vehicle (especially if it is a show car).