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Why the 250W motor is a Myth

Adoption of the 250W EN Standard

All through Europe and many parts of Asia including Singapore, regulators have adopted the EN 15194 standard as their de-facto electric bike certification baseline.

This is especially annoying to users and enthusiasts as this certification shows 3 things: 1. Lack of technical knowledge of how power is transmitted in a DC motor 2. A complete lack of understanding of use case requirements and user needs. 3. Lack of understanding of classification of motor.

We shall explain.

Enter the underpowered 250W motor

The max power of the motor (no matter the rating) is determined by the voltage put out by the speed controller and the max current the controller can supply to the motor. For a 36V 250W motor, a 36V 15A controller can easily push out more current such that the motor can be “over-driven” to output more power.

The simple math of finding out the power can be done by multiplying the Voltage and Current (36V x 15A max). You can see that its clearly more than the rated “250W”.

A 250W motor can easily be fed more power by the controller to drive beyond the 250W. So what really determines the actual operating power is not the power rating of the motor, but the controller. A non-limited controller can feed a 36V 250W motor and drive the motor up to 500W.

User Needs

A majority of e-bikes are used for commuting purposes so these commuting e-bikes are designed to be lightweight and smallish. A 250W motor fits that criteria perfectly.

However, for doing anything else other than going on a flat road, a 250W motor sadly underwhelms. 250W of electric power is the equivalent of a rider pedalling on a normal road bicycle at 25 km/h continuously. Professional cyclists can easily put out 400W of power on a road bike.

However, not everyone is built like a professional cyclist so 250W of motor power is clearly not going to cut it on hilly places or even moderate inclines.

In other words, 250W is measly for e-bikers looking to travel on any kind of terrain other than flat roads.

Classification of Motor Power

When a motor is classified as a 250W motor, it could mean different things, none of which are inaccurate.

250W of continuous power output means that the nominal discharge for a motor running continuously at cruising speed is 250W. However, more power can and will be drawn if the motor is to reach maximum rpm.

250W of peak power output means that the maximum discharge to reach maximum rpm is 250W. Peak power will plateau at the rated power specification and no more power will be discharged from the controller.

These 2 classifications are both accepted in the e-bike industry so it is hard to say if a 250W motor is rated at peak power or continuous power.

If you are looking for a bunch of 250W peak powered e-bikes that comply with regulations, please check out the ebikes listed here.


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