itchynackers wrote:Hopefully your data will include empirical evidence like actual temperatures & temperature changes, not just "warm", "warmer", "better", etc...
Sorry, but I've never bothered with a temp sensor since I've never burned up a motor. That's despite running faster and with heavier loads than the vast majority who have. A 5mm wider stator is not the explanation. I've done my research homework into air flow systems, and I've crunched the heat transfer numbers. Then I actually try different things and share what works, and share explanation of what doesn't.
I'm into results more than the numbers behind them, and our biggest problem has been creating a big enough load to test the limits of my centrifugal cooling approach, and have yet to get a ventilated motor close to hot. Those who have is due to 2 factors, improper approach combined with pushing motors past saturation. We don't have enough controller to push these low turn count motors into saturation.
Here's some empirical evidence for you though, and far better than simple temperature measurement of one unknown spot on a stator. Through research and calculation, I came up with a reasonably conservative estimate for heat dissipation above 350rpm (about 21mph in the 20" wheels we run) of 2-2.5kw for a common 20cm stator motor using my approach to ventilation. At 75% assumed efficiency under heavy load, that's 8-10kw input. The most we've managed using a steep 3.75 mile hill and some extra weight in a backpack is to push 1kwh through the motor in right at 7 minutes. First we rode around for a couple of miles with plenty of hard launches to make sure the motor was at a decent operating temperature before attacking the hill. The motor wasn't noticeably warmer at the top of the hill than at the bottom, and after a 2min wait it didn't feel any warmer, so there wasn't a lot of heat stored at high temp in the stator. That 8500W average input with the far heavier load in the top half where it's much steeper, proved to me that my calculations and estimates were valid and on the conservative side, though we still don't know the limit.
FWIW, I also came up with an estimate for the oil bath approach of a sealed DD hubbie using the same methodology, and even with covers reaching 100°C (a temp I don't want my magnets reaching), the max heat it could dissipate was less than 1000W. No doubt that it would be helpful for those running less than 4kw average with higher turn count windings and pushing the stator into saturation in short bursts or other intermittent low efficiency situations, but not for the continuous power I require to tackle long steep hills or to hit highway speeds in excess of 60mph. More surface area or some kind of radiator is required.