setting the watt to make bike road legal

[Bike noobie]

hello peeps im having trouble setting my watts to make my bike (Smart Pie 4) road legal.
i've read I think from Bikemad that its calculated by watt/battery voltage x1.25 to account for effiency gives current otherwise known as Battery drawn current in the controller so with my 36 volt battery and 250 new uk law limit 250/36= 6.94 x 1.25 = 8.68. I tried input this value into my controller but I get an error message of unintelligible text and the number 10. I thought it might be to many decimal points so I tried 8.6 and I got the same message so I tried 8 and that didn't work either. am I doing something wrong or is the minimum supposed to be set to 10 ? if so wouldn't that mean I cant get the 36 volt battery ever road legal ?

thanks for reading

[Aeberbach]

The Magic Pie 4 is advertised as being a 500-1000W motor. I would not be very surprised to find that it cannot be programmed to less than 10 (and even that gives you less than 500W at 36V)

[Bike noobie]

i have the Smart Pie which is advertised as 200-400W its the smaller model

[Bikemad]

Hi Bike noobie,

You are correct in as much as the lowest setting that is currently available on the vector controllers is apparently 10A. Unfortunately the Battery draw current settings I suggested regarding setting the current cannot actually be entered. Perhaps I should have actually tried it out before posting.

I have been in touch with David at GoldenMotor in China and he has told me that the Smart Pie 4 with a 48V battery and the minimum (10A) setting produces a power output of 200W and a torque of 15Nm, so your 36V battery should theoretically be even less.

I presume that the maximum set current is probably higher than the actual current, either that or the efficiency of the motor is so reduced enough under high loads that it keeps the power output low enough to stay within the legal limits.

Also, the UK legal requirements used to be based on the continuous power rating of the motor not the peak power that it can develop, so I presume the new law will be the same.
This would mean that power in excess of the stipulated limit could be used intermittently as long as the stated power limit was not exceeded continuously.

I have a Vectrix electric scooter which is limited by the controller to a maximum top speed of 68mph (110km/h).
The motor produces 65Nm of torque and is rated as 7kW (9.4hp) continuous, but has a peak power output of 20.2kW (27.1hp).



Although the scooter weighs in at a whopping 210kg (460lb) without a rider, while carrying two people it will still accelerate as fast as a 400cc petrol engined scooter, yet it can apparently be ridden on "L" plates because the low continuous power output places it in the "up to 125cc" category. 
(The UK learner motorcycle specification is an engine size of up to 125cc and a power output of 11kw (14.6bhp))

So in the case of the Vectrix, the maximum power is almost three times as much as its continuous power rating, and because it's electric, I don't have to pay any road tax either.

Alan