# dyno chart



## major (Apr 4, 2008)

Hi ronis108,

Electric motor performance curves are drawn for a particular applied voltage (V=144v-.03I in this case) with torque as the X-axis because torque is the independent variable, the load. The motor will behave in a manner shown by the curve for the particular load applied, or torque opposing shaft rotation. So for any given torque, one can read the resulting current draw, RPM, horsepower and efficiency of the motor at that applied voltage.

You ask the effect of doubling the amps. Again, assume the specified voltage. Then to double the amps, you will have to increase the torque load. This changes the X-axis point and that is where you read the new resulting RPM, hp and eff. The RPM will certainly fall off and the torque may not exactly double, so the hp is not going to double.

You say it is strange it all starts above 3000 RPM. The other way to look at it is: It all starts below 700 amps. Which is probably a recommended current limit.

I think you are missing the fact that if one wants to operate the motor below 3000 RPM at loads less than 160 lb.ft. (in this case), one must reduce the applied voltage to the motor. Hence the need for a motor controller. The performance curve shows the motor characteristic for only the specified voltage, full or max voltage in most cases. At any load, you can operate at speeds lower than the curve shows by reducing the voltage, even down to zero RPM.

The shape of the power curve above 700 amps will likely be determined by the controller, battery pack (voltage with sag) and the motor. Chassis dyno tests can be difficult with EVs. I've tried it a few times. Always seems like by the time you get it figured out, the battery is dead.

Hope that helps,

major


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