Motor power restricting

[RichardT]

Hello Experts

If my motor is rated at 350w, how can i limit the power to 250w ?
Given the voltage of the battery and motor is 36v, I think one way , without changing the motor, is to limit the Current.
Is there a way to limit the Controller to output max 250w ?

Kindly could you give me some advice?

Thanks for reading.

regards
Richard T

 

[Drunkskunk]

Yes, it's done by current limiting. 6.94 amps @ 36 volts to be exact. There are various was of doing so. One would be with a Cycle Analyst. there are several versions depending on your controller, and so several different ways you would need to use it to limit the current.

Another would be to modify the controller it's self to limit the current. Some can be modified by software, others can be modified by changing either the resistance of the shunt, or the resistance of the trace from the shunt to the processor.

But ultimately, the question is why? Is this for legal reasons?
If so, this might not work, or might not be desirable. Normally, a 250w motor peaks out at around 700 watts , so limiting a motor to 250w would be seriously restricting it's usefulness. Other places do but maximum output ratings on the motor. Still others don't care what the maximum output is, only what the manufacturer's power rating is.

 

[RichardT]

Yes, it's done by current limiting. 6.94 amps @ 36 volts to be exact. There are various was of doing so. One would be with a Cycle Analyst. there are several versions depending on your controller, and so several different ways you would need to use it to limit the current.

Another would be to modify the controller it's self to limit the current. Some can be modified by software, others can be modified by changing either the resistance of the shunt, or the resistance of the trace from the shunt to the processor.

But ultimately, the question is why? Is this for legal reasons?
If so, this might not work, or might not be desirable. Normally, a 250w motor peaks out at around 700 watts , so limiting a motor to 250w would be seriously restricting it's usefulness. Other places do but maximum output ratings on the motor. Still others don't care what the maximum output is, only what the manufacturer's power rating is.

Hello Drunkskunk

Thanks for responding to my enquiry .
1. Yes, its for legal reasons. I live in a totalitarian state. You are forced to comply and rules are very strict.
2. When you say a 250w motor peaks out at around 700 watts, do you mean the physical rating of the motor , be it a brushless direct drive or brushless geared motor, is not the max it can achieve? So a 250w motor can easily output more than that by way of current control, that is , giving it more juice?

3. Yes, the new regulation is 250w max. Its highly impractical and silly. Safety is more about rider discipline than the power of the bike. Eg. a motor bike is countless times more powerful and heavier and more dangerous than a ebike and yet its legalised. The authorities are living in their ivory towers.

4. The Power rating limit seems to be on the motor.

Someone please adopt me to your country . I need to escape from totalitarianism.

 

[John in CR]

Don't wait to be adopted, just move. In the meantime get on the EE types about not taking proper advantage of the overly restrictive laws that limit output power. Power = torque X rpm, so at very low rpm you can actually have quite high torque and still be legal, but no ebikes are set up to limit actual power out to a fixed limit at any rpm.

 

[TroySmith80]

For what its worth, i'm not entirely happy with using my Cycle Analyst for power limiting, because it's a lurchy, unrefined limiting, kind of obnoxious.

 

[RichardT]

Don't wait to be adopted, just move. In the meantime get on the EE types about not taking proper advantage of the overly restrictive laws that limit output power. Power = torque X rpm, so at very low rpm you can actually have quite high torque and still be legal, but no ebikes are set up to limit actual power out to a fixed limit at any rpm.

Dear John in CR

Thanks for your response.

Pardon my ignorance, what is EE type?

A hub motor has a rating engraved on the shell or casing . So, that is the rating of the motor that i believe my gov is referring to as one of its criterias.

I believe this rating is in terms of the copper windings and gauge of the copper and the power of the magnet inside the motor?

While i accept that the actual power of a motor is not controlled specifically, a hub motor is nevertheless rated to a max (?) power rating at a superficial level?.

So , I can only limit the current by changing the shunt or use a Cycle Analyst?

Can i limit the power to 250W and yet still continue to use the same 350w rated motor (internally geared hub motor) by changing the shunt or using the Cycle Analyst? How can i prove i have limited to 250w ?

Thanks.

 

[danielrlee]

For what its worth, i'm not entirely happy with using my Cycle Analyst for power limiting, because it's a lurchy, unrefined limiting, kind of obnoxious.

In that case, you've not got it set up properly for your specific system.