Hello.
Would a 12V automotive starter motor be capable to run non-stop a few hours if fitted with forced ventilation to keep it under ~80 Celsius, or there is more considerations to make it work reliably ?

 

That's kind of a tough question. They are fairly cheap at the junkyard, might be better to experiment. They aren't built for continuous running, or for long durations, just a quick burst of high torque. What sort of load are you planning? I've heard stories of using them for go-carts, but don't know if there was any truth in it, or how well it worked out. Search the internet, I'm sure there have been many attempts to use the motors for other things. Lots of torque, cheap and easy to get/replace... Seems like an ideal toy.

 

They are designed for very intermittent duty. You might have to use LN2 to keep one from frying after a few minutes. Unless you need the rotational speed, a gearhead motor producing high torque would be a better choice.

 

Starter motors are designed to be operated for a maximum of about 30 seconds, with a 1 to 2 minute cool-down period between operation cycles.

If you try to operate them continuously under load, you will wind up with melted down rotor and stator windings.

The housing is generally made out of steel, stampings, castings and perhaps even plastics nowadays. None of those materials are really efficient at conducting heat.

Starter motors don't have much in the way of clearances inside the housing. It would be rather difficult to provide clearances for the amount of air that would be necessary to provide sufficient cooling without seriously affecting the performance of the motor.

If the loading is very light, you may be able to get away with running the motor for extended periods. However, you should add in provisions to monitor the motor's temperature, and shutting it down if it gets too warm.

 

Back in the 50s we used Ford starter motors to drive cable reels holding a half mile ofhalf in. cable. Motor had 2 in dia. leather wheel driving 24 in. rim. Pick up was at about 15 mph. I replaced motors about every two years. Finaly went to ball bearing front ends. Est 2 hp. Never had one burn up; justbearings commutators & brushes.