When you increase the temperature of a conductor, you increase the resistance. When you increase the resistance of the windings in a motor, the motor becomes less efficient.
So here’s where I’m going. If a motor is loaded and starts heating up, the windings heat up and the motor becomes less efficient. Your range drops, your speed drops- essentially, the load gets higher on the motor for a maintaining a given speed. So the motor heats up more. And things get progressively worse.
It would seem that cooling a motor isn’t just about keeping from burning itself up- it’s about keeping it running as efficiently (due to minimizing resistance buildup due to heat) as possible. More speed, more range.
How ‘m I doin’?
The big question seems to me to be, how much effect does this have, real world? I’d guess a great deal- considering the cooling fan on the Enertia and the water cooled motors we’re seeing. I’ve got to think that the overhead of the cooling system pays for itself in maintaining higher efficiency.
The thing about it that gets interesting is the motor size issue. If you’re running a motor at, oh, say, 85% load, it’s going to run hotter than a motor that can do the same work at, oh, say 50% of it’s load. Am I right? If so, it changes the way I was thinking about motor size in general… in terms of real world range.
First, run a bigger motor at a lower load. It stays cooler, it’s not working as hard. It runs more efficiently- maybe not on the bench, but in real-world.
Second, look into active cooling.
Interestingly, back a couple of years ago when I first started asking about this, I got no answers. Then I noticed Brammo was running a cooling fan on the Enertia. Efficiency really didn’t come into the discussion, it seemed it was more about keeping things from blowing up. As of last night, and hearing Azhar Hussain talk about the swell of innovation and development that has been happening with the TTXGP bikes, it seems there’s one common thread where motors are concerned- liquid cooling is trumping air cooling.
Had a look at the Brammo Empulse specs? The motor? Liquid cooling.
Think racing technology and development doesn’t trickle down to the street? Think again.