What's a safe temp limit for motor windings?

Edit, I think I got false readings from a multimeter with a dieing battery. This looks to be a false alarm. I think my actual motor temps are in the 65 C range.
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I just got back from riding, lots of slow crap city stop and go, 90 degrees F outside, and the temp sensor in my Mac read 94 C (201F). I spun it no load for 30 seconds then it dropped to 68 C.

I should be able to use my cell meter that I use to check lipo to get a voltage reading which translates to temperature. Right now I can only check it with a multimeter and sticking the prongs into the hall connector.

The outside of the motor cover felt to be about 110 F, by comparison. I was running 1200w limit on this 8T mac with 48v.

I'd also like to know what a safe temperature is. I think someone once said they are good up to about 200C?

It depends on the thermal rating of the insulation used.

Hall sensors cook at around 150-160 depending on which ones are used. I would say 100 is the absolute max I'd ever like to see again but prefer it to be around the 75 I see now on 60V, 1300W.

I've oil cooled mine and there is information about magnets starting to permanently lose their magnetic power from around 80 celcius..... hence why I don't want to have temps above the 75 I see during most riding.

No doubt Andy is talking degrees C as the world does. Us doofus Yanks think in F, so I always try to say so.

Depends on the intended use. I consider the safe limit for a hubmotor intended for reliable transportation to be pretty low. Say about 180F, maybe 200f briefly inside the motor. At those temps, you won't even discolor the varnish on the winding wires. It should be pretty easy to stay below 150F if you have the right setup, and aren't trying to travel much faster than typical ebike legal.

So if your use is to commute farther than you'd care to pedal home unpowered, or make it through 100 mile crosscountry days, Sub 200F is my recomendation.

Racing, stunting, dirt riding, etc the limit is much higher. Some say 300F is fine. I've sure had a few motors much hotter. But at 450 you start to ingite anything combustible inside and you will be quickly done.

On my dirt bikes, I like to try to keep them below 200F as much as possible, but if the hill is long and steep enough, I'll get into the 250F ballpark easily. At that point, I want to cool off if I can, and coming to a dead stop at that temp can cause it to spike even higher. Best thing when that hot is to do some cool down riding at low wattage on the flat, or a mild downhill. A steep downhill actually heats the motor, but will still beat a dead stop because you at least get some wind cooling.

If my 8t Mac can't reliably handle what I did yesterday then I'm going to say ebikes suck and be really pissed off. i was stuck at 15mph due to traffic and a cop right next to in a 15mph zone. Had a small climb and some stops. then finally got to 25mph for the last half mile home. I had done about 4 miles of this city riding. 94 c motor when I got home. If I can't ride at 17mph average speed in stop n go in 100 degree heat then its useless.
and in my other threads some are telling me I should run my 6t Mac.... Which would heat up worse.

Not happy.

Erm.... that's an oddly high temp for such a low speed.. then again it is stop & go.
..not that i have ever measured my MAC motor's internal temps!
Most hubbies can handle around 150C / 302F.. which is the point where the insulation and halls start protesting for better working conditions.

Electric motors have a point where they can run continuously at a certain load, shedding X amount of heat. That is actually how they get their wimpy little 500w rating. Maybe that temp you're seeing is the continuous temp it likes to hang out at. I think you need to do more research.

Doesn't help that it is hot and most likely humid outside where you are. Your motors have always ran a bit hot, haven't they?
I remember you talking about the little MXUS motor running hot on the stock controller.

I have a similar problem with my Fusin front geared hub: I can easily run it at faster speeds like 20MPH probably all day long; certainly for at least an hour for a 15-17 mile trip, with about 10 miles of it non-stop 20MPH and the rest 20MPH cruise between more frequent stops. The motor gets very warm, but not dangerously so, even after it's been stopped long enough for heatsoak to get thru the outer casing.


But if I ride it at only 8-12MPH, especially in stop-and-go, it'll overheat and cook, so hot that the halls stop responding. It's happened a couple of times, with and without a big load on the bike, so it isn't the load, it's the speed.

AFAICT, it's because at some speeds, depending on the wind of the motor, and the voltage it's running at, the motor is much less efficient and more of the power fed to it is wasted as heat. I don't know if this is at *all* lower speeds than the top speed, or if there are specific ranges that are worse than others, but definitely for the Fusin motor I have (which is wound for 36V to get ~20MPH, IIRC), it happens at that medium speed range but does not at the faster speed.

When i ran the motor at 36V with the old NiMH pack, I didn't have this problem that I can recall. (though I did blow caps in teh controller twice from the high Phoenix heat and partial throttle). That's why I think it has to do with the voltage it's at, too, but that might not actually have anything to do with it.



So, it may well be possible that your other MAC with different windings would work better in a different speed range (but I don't know if it would be higher or lower speed).

http://ebikes.ca/simulator/

Check out how "well" the 8T ( BMC 'speed' wind ) performs at lower speeds..
The DD hubs suffer as well in these situations.

What would help you a lot is shifting to a lower gear on the bike at a stoplight and pedaling very hard until you hit speed.
Cars have this problem too. #1 situation for overheating a car with a weak cooling system is during stop and go traffic or climbing a hill.

Welcome to why I'm a dd kind of guy. I don't think you are making that much extra heat, but you are experiencing poor cooling off typical of gearmotors once warmed. The stop and go lets the hub bake with no wind cooling causing a heat soak. Kinda warm early this year eh?

EDIT:
Ahh crap. Well actually this is good. My multimeter seems to be off by 50%. Hence 100 = 66 or so......

Yeah, I tested my 36v battery and it said 54v...........wtf.....haha.

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Yeah, my mxus geared motor got hot last year when it was 100 and I had some laundry in my panneirs, going 20 minutes across town, no actual hills either. That's at 15mph too. I'd guess the windings got a lot more than 100C based on how much hotter the casing was then the Mac is right now. The casing on the mac isn't even hot IMO.

Good to know. BTW, you get a closer to real time idea of the inside of a hubmotor's temps by taking the temp of the axle, rather than the cover. This is particularly true for gearmotors. That axle is physically part of the stator, so it will warm up faster. I learned this back when I had a functioning IR thermometer.

Nowdays I tuck a thermometer sensor under the axle inside the dropout to get a guesstimate of motor temp inside. The readout is not used so much for telling my limit, so much as for detecting conditions when the temp is rising fast so I can stop what I've been doing to cause that in time.