When looking at electric bikes you may come across information on the watts that an electric bike is rated for. Understanding how many watts you will need for an electric bike can be confusing.
The following is guest post by Ed Benjamin about the common sizes of electric motors found on electric bikes and some background on the what will suit your electric bike riding needs the best. Ed Benjamin is the founder of the Light Electric Vehicle Association (LEVA).
What is the Difference in Motor Power 250w, 500w, 750w, By Ed Benjamin
2. How that power is measured. An argument can be made to measure power in these ways:
- A. Electric current into the motor.
- B. Mechanical power output at the “shaft”. (but if it is a hub motor…do we measure at the hub flange or the rim / tire?
- C. Power in, less the efficiency losses of that motor. (Complicated.) And 2A: Whose machine and which method do we use to measure that power? In the EU, there are detailed regulations about how to measure power. In the USA, it is pretty much what the maker says it is, with no testing method described or required.
4. How much power can the battery support? There is a balance of cost, weight, and energy storage in the decisions about the motor power, battery size, etc.
This is not a simple subject. But I will offer my advice:
- Most 250 watt systems are satisfactory for pedelecs (where the rider is pedaling and thus adding in his energy / effort).
- For throttle controlled, or power on demand systems where the rider is not pedaling 350 to 500 watt systems are a better choice.
- 750 watts seems attractive, but this requires a big battery – and the combination of cost and weight is not that attractive. This will get better, but at this time, 500 watts may be a better choice in many cases.
Climbing hills on any of these will require the rider to add in some muscle power – but not a lot.
In all cases, the rider will enjoy the ride, sweat a lot less, and have less fatigue and go farther, faster.
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