... working with a friend on a project that wants to use a Nitro Plane Starter electric motor on a project that might have the motor running for several minutes. Typical use of these motors is 5 seconds every 2 hours or so, giving the motor plenty time to cool down.

These motors are basic, DC 12V brushed, no fan, and even worse, no ventilation slots whatsoever, totally enclosed. We plan to PWM the motor to give variable speed, but I am concerned the motor will accrue too much heat energy, bearing in mind the huge difference in duty-cycle...

What say you ?

 

5 seconds does not sound long enough to heat a motor, the PWM should not cause heat, why not size the motor adequately sized, there are several DC motors available, including ones found at auto wreckers that you could use/adapt maybe.
Max.

 

My gut reaction is - unsuitabe

 

My gut reaction is - unsuitabe

If so,why?
Max.

 

5 seconds does not sound long enough to heat a motor,
Max.

Yes , and 2 hrs is a ridiculously long cool off time .... 20 secs run and 10 mins cool off sounds more realistic

If you are PWM ing the motor , what's the problem , you are reducing the power so you can vary input so it doesn't get too hot ....

 

5 seconds does not sound long enough to heat a motor, the PWM should not cause heat, why not size the motor adequately sized, there are several DC motors available, including ones found at auto wreckers that you could use/adapt maybe.
Max.

Exactly my point, 5 seconds to start a nitro engine, then left alone for a while is what these cheap starters were (un) designed for, anything more and you are gonna be pushing them.

 

Exactly my point, 5 seconds to start a nitro engine, then left alone for a while is what these cheap starters were (un) designed for, anything more and you are gonna be pushing them.

I think you've miss understood max ... he's saying the motor can certainly run longer than 5 secs at full power ....

But you need not run at full power , just don't overheat it and it will be fine .

 

I think you've miss understood max ... he's saying the motor can certainly run longer than 5 secs at full power ....

But you need not run at full power , just don't overheat it and it will be fine .

I didn't misunderstand, I said that the "intended", as in *original*, application of said motor was to start Nitro model airplanes, and as such would have a very small duty cycle, say 5secs to start the plane, then it has oodles of time to cool down, if indeed it got hot at all.

My intended application of said motor could have it running for several minutes, and as it has no cooling fan, and no ventilation, I reckon it will get hot pretty damn quickly.

I've worked out we need to turn the motor at about 2200 rpm max, but we will need torque throughout the speed range, as it has quite a load on it (sorry I can't be more specific, but think of dragging a 2lb weight across grass for several hundred metres, you've got the actual load, plus the frictional load of the drag-line).

These starters hail from the far east, and there's absolutely no specs or rating plates on them, so have no idea of their no-load and loaded speeds and torque characteristics.... my WAG is they are pretty poor.

 

Well, it should be pretty easy to find out.

Try it at the full power you will need for increasing times and see how hot it gets.

Bob

 

Will do, just as soon as my PWM H-Bridge speed controller arrives - couple of days away....