Page 1 of 1

Auto starter motor

Posted: Sun Jan 19, 2003 11:14 am
by Erik Seyler
I'm still thinking about a simple EV.What about car starter motors ? How can you vary the speed? I think because they have brushes they would burn out any mosfetpower transistor control or am I wrong ?

Re: Auto starter motor

Posted: Sun Jan 19, 2003 12:52 pm
by russlk
The starter motor is series wound, it looks like a short circuit at startup, so yes it would destroy the switch transister unless you have a way to limit the maximum current. The series motor has no top speed limit (in theory), so you would control it by turning it on & off. If you use a series inductor to give a controlable current ramp, the series motor could work.

Re: Auto starter motor

Posted: Sun Jan 19, 2003 8:36 pm
by Chris Smith
Keep in mind that the motor wants to draw upwards of 600 amps depending on size, but pulse width will work with the motor and you will need at least 400 amps worth of Fets. <p>Once spinning with lesser load the motor will peak out at around one hundred plus amps, with a reasonable load. <p>Running the starter at high amps will smoke it if run too long, but they are durable.<p> The starter is not designed as full duty cycle motor so it will wear out prematurely. <p>Also polish the commutator as smooth as possible to keep brush wear to a minimum and have good condition bearings on each end. <p>Bushing type starters should be avoided or modified to use bearings. <p>You also dont need the internal type solenoid starters as this only gets in the way.

Re: Auto starter motor

Posted: Mon Jan 20, 2003 10:03 am
by Dimbulb
In theory a pwm dc speed controller could drive
10 IRFZ48N power hexfets each rated at 64A each

Re: Auto starter motor

Posted: Tue Jan 21, 2003 6:59 pm
by Chris Smith
The "fan out" for Fets is almost infinate because they dont draw current at the gate, they merely require a voltage present at the gate.

Re: Auto starter motor

Posted: Wed Jan 22, 2003 12:29 pm
by Crowbar
A better bet would be to use a compound wound or a stab shunt field motor. That would give you good speed control and torque with only tach feedback.

Re: Auto starter motor

Posted: Wed Jan 22, 2003 7:58 pm
by Gary
Starter motors are ment for short-term use at their rated voltage. A method around this I've seen is a 12v starter motor coupled with a 6v deep-discharge battery.