Do cooler motors run quicker?

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speedyebikenoob   100 W

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Do cooler motors run quicker?

Post by speedyebikenoob » Sep 22 2020 10:38am

If the efficiency of an e bike motor at 2500 watts is 85 percent for example, that means 15 percent of the power is going to heat and being wasted right? If you cooled the motor somehow, wouldn't the efficiency increase so more power would be used for making the bike go instead of being wasted into heat? So wouldn't this make the bike quicker without actually increasing the power level? I don't really have any background with this kind of stuff so please correct me where I'm wrong :)

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E-HP   1 MW

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Re: Do cooler motors run quicker?

Post by E-HP » Sep 22 2020 11:18am

speedyebikenoob wrote:
Sep 22 2020 10:38am
If the efficiency of an e bike motor at 2500 watts is 85 percent for example, that means 15 percent of the power is going to heat and being wasted right? If you cooled the motor somehow, wouldn't the efficiency increase so more power would be used for making the bike go instead of being wasted into heat? So wouldn't this make the bike quicker without actually increasing the power level? I don't really have any background with this kind of stuff so please correct me where I'm wrong :)
Yes, you could recapture that 15% by cooling the conductors to absolute zero, where the resistance goes to zero. With zero resistance, no energy is wasted in heating the conductors. If you go the opposite direction, as the motor heats up, resistance of the conductors increases, causing even more energy to go towards heat, so cooler is betters. Good luck on the supercooling!

speedyebikenoob   100 W

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Re: Do cooler motors run quicker?

Post by speedyebikenoob » Sep 22 2020 11:32am

E-HP wrote:
Sep 22 2020 11:18am
speedyebikenoob wrote:
Sep 22 2020 10:38am
If the efficiency of an e bike motor at 2500 watts is 85 percent for example, that means 15 percent of the power is going to heat and being wasted right? If you cooled the motor somehow, wouldn't the efficiency increase so more power would be used for making the bike go instead of being wasted into heat? So wouldn't this make the bike quicker without actually increasing the power level? I don't really have any background with this kind of stuff so please correct me where I'm wrong :)
Yes, you could recapture that 15% by cooling the conductors to absolute zero, where the resistance goes to zero. With zero resistance, no energy is wasted in heating the conductors. If you go the opposite direction, as the motor heats up, resistance of the conductors increases, causing even more energy to go towards heat, so cooler is betters. Good luck on the supercooling!
Lmao maybe supercooling will be my next project! :D But am I correct in that the cooler the motor is the more power I would gain back? So if I strapped a dry ice pack to my motor just for fun, it would accelerate a little quicker?

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pwd   1 kW

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Re: Do cooler motors run quicker?

Post by pwd » Sep 22 2020 12:24pm

A cooler motor will run "better" but depends on the temperature differences and motor setup etc... here is a basic example:
https://www.ebikes.ca/tools/simulator.h ... &temp_b=90

10 C vs 90 C initial motor temperature - click on the "Show Advanced" to adjust
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john61ct   100 GW

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Re: Do cooler motors run quicker?

Post by john61ct » Sep 22 2020 3:00pm

More practical to say, just avoid getting too hot, and the motor will have a much longer life.

Balmorhea   100 kW

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Re: Do cooler motors run quicker?

Post by Balmorhea » Sep 22 2020 3:16pm

Even more practical is to say that if you're making your motor hot, you're doing it wrong. Use more motor or abuse it less.
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AngryBob   1 kW

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Re: Do cooler motors run quicker?

Post by AngryBob » Sep 22 2020 5:08pm

Cooling the motor just sheds the heat you are making quicker, it does not in and of itself make it "better".

However, a hot motor does run less efficiently, so preventing extreme heat build-up is a good thing.

If the heat build-up is not extreme, then no real need for extra cooling.
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speedyebikenoob   100 W

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Re: Do cooler motors run quicker?

Post by speedyebikenoob » Sep 24 2020 12:44pm

So if I were to run a 1500 watt continuously rated motor at 3000 watts instead but figured out a way to cool it down significantly, it would still be much more inefficient than if I was running only 1500 watts through it?

speedyebikenoob   100 W

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Re: Do cooler motors run quicker?

Post by speedyebikenoob » Sep 24 2020 12:48pm

AngryBob wrote:
Sep 22 2020 5:08pm
Cooling the motor just sheds the heat you are making quicker, it does not in and of itself make it "better".

However, a hot motor does run less efficiently, so preventing extreme heat build-up is a good thing.

If the heat build-up is not extreme, then no real need for extra cooling.
What exactly do you mean by "efficiently"? Do you mean if a motor is running hot, the amount of watts being produced by the motor compared to the amount of watts being inputted would be lower than it would during normal running temperatures?

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E-HP   1 MW

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Re: Do cooler motors run quicker?

Post by E-HP » Sep 24 2020 12:54pm

speedyebikenoob wrote:
Sep 24 2020 12:48pm
What exactly do you mean by "efficiently"? Do you mean if a motor is running hot, the amount of watts being produced by the motor compared to the amount of watts being inputted would be lower than it would during normal running temperatures?
Read my first post. As the motor heats up, the resistance of the windings go up. When that happens, more power is diverted to heat rather than motion, hence efficiency decreases.

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dogman dan   100 GW

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Re: Do cooler motors run quicker?

Post by dogman dan » Sep 29 2020 6:02am

I get in trouble every time with this stuff, I'm not an engineer.

But yes,, if your motor is actually overheating, then as it starts to melt its winding resistance increases, and you do start to feel it in the power, just before the flames shoot out the holes you drilled in the cover to help it cool slightly faster. You feel it lose power as it gets flaming hot. If you drilled cooling holes in the cover, you smell it before the flames shoot out the holes. But in these cases, you were never running at 85% efficient. Melting the motor starts either with overloading the motor, or over powering it with more watts than it can handle for long.

My experience though, after melting quite a few motors, is what really helps your motor is to stop in time. I found even a tiny 1/8 inch hole drilled in the cover let just enough smell out, to let me know its time to stop and let er cool down.

The short answer is don't overcook your motor too much, and it runs cool enough to keep its resistance down. What matters is time to overheat. Not overall efficiency. I did a lot of real world testing of time to overheat, which I needed to be at infinite, to make it 60 miles or more in the rocky mountains. The key thing was hitting an equilibrium temperature, vs running so inefficient that you had a one hour, or half hour time limit. Example, 500 w rated motor running 4000w had a time limit shorter than a 30 min race. The motor flamed with a lap to go. Wouldn't have won with 3000w, but would have finished in the top 5. Bigger motor would have lasted long enough.

Much depends on your needs, but whether you want a one hour ride or an 8 hour ride, you need to make the copper in the motor big enough to last the time you need, even if less than 85% efficient. To get infinity, its more a matter of making the motor big enough to be at high enough rpm to stay in that max efficiency zone where the motor will cool as fast as it heats, and reach equilibrium temps that don't roast the winding. Its matching the motor size to the load, and or the power level you plan to push.

Typical 500w DD motors common in cheap kits handle 1500w with ease, unless you weigh way too much. My eventual solution to infinite time to overheat was the old clyte 5300 series motor running only 2000w. It was plenty to get me and my cargo over the mountains at 15 mph, remaining efficient. So the 100 pound bike, my 200 pounds, and 100 pounds of cargo never even got warm at the top of a mountain pass in the rockies. Even when the day was 100F! I had plenty of copper in that motor to push 400 pounds up a mountain, and remain in its maximum efficiency rpm. Hard to improve on max efficiency, and the motor covers would never even feel warm, let alone hot.

I overkilled the motor, but then ran only what I needed to get up that hill. Sure, I could have run 4000w, and got over the hill faster. But at 15 mph I was running max efficiency, which is what I needed to cross 50 miles of desert on the other side of that mountain.

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Matador   100 kW

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Re: Do cooler motors run quicker?

Post by Matador » Sep 29 2020 6:12am

AngryBob wrote:
Sep 22 2020 5:08pm
Cooling the motor just sheds the heat you are making quicker, it does not in and of itself make it "better".

However, a hot motor does run less efficiently, so preventing extreme heat build-up is a good thing.

If the heat build-up is not extreme, then no real need for extra cooling.
Totally agree with this. Unless heat is so high the magnets in the BLDC lose their magnetic field (around 120°C), cooling is just masking the heat the motor is producing anyways. You might notice it less, but the power loss is still there and the same.... Unless you are using supraconductors, which only start to work at very low and impractical temperatures for ebikes.

Unless it's to avoid motor damage for excessive heat, I see no point in cooling the motor.

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Last edited by Matador on Sep 29 2020 6:24am, edited 1 time in total.

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Matador   100 kW

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Re: Do cooler motors run quicker?

Post by Matador » Sep 29 2020 6:23am

Cooling the motor doesn't make the motor loose less energy in heat, it just hides the fact that the motor is loosing the same amount of heat.

Overheating can
1) Demagnetize the neodynium magnets of a BLDC
2) Melt the winding. P=RxI², meaning if you double current, the power loss in heat quadruples. If you triple current, heat power loss is x9. So if the windings get too hot, the insulating varnish from the copper strands melt. Thus the windimg stands loose their insolation an touch each other creating a short circuit. When a short circuit occurs, resistance is zero, or relatively close to zero. So when you short out motor windings by overheating it, thr resistance is VERY LOW. However, if you also melt the copper metal (temps much higher than for melting insolating varnish) then you can interrupt the circuit and resisyance become infinite.

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john61ct   100 GW

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Re: Do cooler motors run quicker?

Post by john61ct » Sep 29 2020 12:59pm

Ref my post #5

John in CR   100 GW

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Re: Do cooler motors run quicker?

Post by John in CR » Oct 01 2020 12:19pm

Cooler runs a bit faster and less efficiently. Here's a graph of a nice cool motor vs a hot one.
Cool vs hot motor.JPG
Cool vs hot motor.JPG (156.28 KiB) Viewed 266 times

markz   100 GW

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Re: Do cooler motors run quicker?

Post by markz » Oct 02 2020 1:10am

Not a matter of speed but how long you can ride at what slope, thats why there is Statorade by Grintech.

https://www.ebikes.ca/shop/electric-bic ... orade.html

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Re: Do cooler motors run quicker?

Post by John in CR » Oct 02 2020 8:05pm

markz wrote:
Oct 02 2020 1:10am
Not a matter of speed but how long you can ride at what slope, thats why there is Statorade by Grintech.

https://www.ebikes.ca/shop/electric-bic ... orade.html
Never used the stuff and the motors on my performance rides run cooler. The highest I've seen is 103°C at the stator, and that was accelerating hard to over 80kph out of each switchback up a mountain road built to get wind turbine parts to the peak with a 20% continuous grade with gravel at the switchbacks that forced very low speeds every few hundred meters. Air cooling with blades on the exhaust side to create real flow is the king of hubmotor cooling.

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