I am assuming that electric motors are faster and stronger (more torque) when it's cold? On a cold morning, I can hit 35mph constant while on a normal morning, I can only get 32-33mph with the same wind condition on the same stretch of road. Is this true? If so, maybe DoctorBass should carry around liquid nitrogen tank to cool his motor so he can hit 100mph or whatever the goal is. : )
Electric Motor faster when cold?
- Thread starter mvly
- Start date
Dave Sloan
100 W
- Joined
- Jun 22, 2009
- Messages
- 128
Probably it is because the air is less drag = thinner. As far as cooling goes - there is not much difference - less air to take the heat away.
TylerDurden
100 GW
Resistivity of copper rises with rise in temperature.
Your motor loses efficiency/power as it gets warmer.
Cooler ambient = slower rise in motor temp = higher efficiency = higher power output.
Your motor loses efficiency/power as it gets warmer.
Cooler ambient = slower rise in motor temp = higher efficiency = higher power output.
liveforphysics
100 TW
Dave Sloan said:
You know that cold air is more dense, cools better, and the higher mass per volume for the same viscosity means higher drag. Cold air only gets to be thin when you're cold because of going up in elevation, so the pressure is dropping with temperature, and you end up with lower density air (which has less drag). If you're at the same elevation each time, the hotter the air, the lower the drag.
TylerDurden said:
Yep.
The Temperature Coefficient of Copper (near room temperature) is +0.393 percent per degree C. This means if the temperature increases 1°C the resistance will increase 0.393%.
So, if your motor is 20degC colder, it will have roughly ~6% less copper loss, which means ~6% higher output.
Yup confirmed. I rode my bike in the rain today and getting solid 34mph. If you take into account water resistance of the road and the water drops hitting me and my bike, it is definitely a faster motor when cooled (water was on it). Yeah DoctorBass should find a way to liquid cool his motor during his run. : )
So if we could keep it at liquid nitrogen temperatures, it would be up to 60% more efficient?
Well, at least until you hit that first bump, and the bike shatters.
:lol:
Well, at least until you hit that first bump, and the bike shatters.
:lol:amberwolf said:So if we could keep it at liquid nitrogen temperatures, it would be up to 60% more efficient?
Well, at least until you hit that first bump, and the bike shatters.
well I was hoping that you guys will be feeding it 20KW or more into the motor to counter that cooling effect of the liquid nitrogen. Either that, or have a temperature sensor that feeds the nitrogen only when it's needed to keep the motor really cool but not too cold. : )
Pure
10 kW
http://endless-sphere.com/forums/viewtopic.php?f=3&t=33254
dogman dan
1 PW
Any other pilot will definitely confirm that the density altitude of the atmosphere is lowest in cold weather. It's why one passenger and one fuel tank got kicked out of my balloon in summer. Density altitude is a combination of temp and barometric pressure, and in any season, typically is at it's highest for the day at dawn.
The hot weather slowdown could be just that your wiring is hotter, and resisting more at noon. So the problem may be more on the bike, than in the motor itself. Not saying a cool motor doesn't run better, it does, just that your wiring harness may be the thing more affected by the cooler air in the morning. Cold enough, and the bikes external wiring gets affected the other way.
The hot weather slowdown could be just that your wiring is hotter, and resisting more at noon. So the problem may be more on the bike, than in the motor itself. Not saying a cool motor doesn't run better, it does, just that your wiring harness may be the thing more affected by the cooler air in the morning. Cold enough, and the bikes external wiring gets affected the other way.
The Mighty Volt
1 MW
@OP
Something else to consider is the temperature of the surface you are riding on.
Hot days can make for slower trips as the tyres get increase traction on the tarmac which softens in the heat.
I noticed this once during the Summer when my X5305 BMX seemed to lack its usually acceleration.
I checked everything and then found that the tyres were themselves quite warm, despite a short trip.
As for the motor, the hotter the copper in the motor becomes, the less efficient it becomes.
So its a double whammy. You lose efficiency, so it runs hotter, so you lose efficiency.
Something else to consider is the temperature of the surface you are riding on.
Hot days can make for slower trips as the tyres get increase traction on the tarmac which softens in the heat.
I noticed this once during the Summer when my X5305 BMX seemed to lack its usually acceleration.
I checked everything and then found that the tyres were themselves quite warm, despite a short trip.
As for the motor, the hotter the copper in the motor becomes, the less efficient it becomes.
So its a double whammy. You lose efficiency, so it runs hotter, so you lose efficiency.
