I am considering increasing the torque output of the Mars bldc motor by increasing the voltage to 144V, while keeping max current at 300amps. Will this increase the torque constant higher than the quoted 1.2 lb-in/amp or would the torque remain the same with only an increase in motor RPM?
Question, Does higher voltage increase the torque constant?
- Thread starter cycleguy
- Start date
Voltage does not affect the torque constant.
If you're limiting the motor current to 300 amps, and assuming the lower voltage does put out 300 amps at the start, you won't notice a difference in torque at the start. However, a higher voltage will increase the range of speeds which the motor current will be limited, so the torque will remain higher at a higher voltage after you get past the speed which the motor current starts to drop for the lower voltage.
So, in essence, you'll get more torque with a higher voltage somewhere in the middle of your speed and past that speed (The speed at which the motor current starts dropping for the lower voltage), but you'll get no difference in starting torque.
If you're limiting battery current to 300 amps, the higher voltage will have a higher torque since the motor current and, thus, torque will be greater.
If you're limiting the motor current to 300 amps, and assuming the lower voltage does put out 300 amps at the start, you won't notice a difference in torque at the start. However, a higher voltage will increase the range of speeds which the motor current will be limited, so the torque will remain higher at a higher voltage after you get past the speed which the motor current starts to drop for the lower voltage.
So, in essence, you'll get more torque with a higher voltage somewhere in the middle of your speed and past that speed (The speed at which the motor current starts dropping for the lower voltage), but you'll get no difference in starting torque.
If you're limiting battery current to 300 amps, the higher voltage will have a higher torque since the motor current and, thus, torque will be greater.
cycleguy said:
Usually, the max current rating is due to copper heating and the highest temperature it can take, however, it takes time for the temperature to rise so the max current should be defined in reference to the amount of time involved. Assuming there isn't a "fuse" or something with fuse-like properties, you can usually exceed the specified current rating, but only for a period of time shorter than the specified period of time.
Does it define it as 300 amps for 10 seconds? 300 Amps for a minute? 300 amps period?
I'm looking for 1000 lb/ft rear wheel torque, through dual motors. Yes you can gear it for more torque off the line but you end up over speeding the motor at higher speeds, at which point torque falls off dramatically and prevents you from going any faster. So far the best solution is two AC-15 AC induction motors at 96V - 108V and 550amps, however this is an expensive set-up requiring two controllers. My thoughts were to use brushless DC motors to save on the controller cost, however it looks to me that large brushless DC motors in this torque range don't exist, unless you use specialized motors by companies like UQM or Calmotor, these are $40,000 setups.
vanilla ice
1 MW
How come the ebikes.ca sim says torque increases with higher voltages? Is it because the example I'm looking at there is battery current limited? I kept everything the same except voltage. Specifically I used 20a controller, 18ah nimh batteries, and different voltages of course.
I agree, higher voltage would extend the torque range but not enough. Consider a theoretical top speed of 150mph, this is approx 2000 rear wheel RPM with a 190/55/17 inch tire. Lets assume a 144 volt system and 500 amps, this would provide 50 lb/ft of torque per motor (100 lb/ft combined)and a max RPM of 10,000 rpm. Final drive gearing would need to be 10/1 ratio to obtain 1000 lb/ft wheel torque. At this ratio the motor would have to spin at 20,000 RPM to achieve the theoretical speed of 150 MPH. The 10,000 RPM motor limit would only get to 1/2 that speed or 75mph.
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