What do parameters like Torque (Nm), Power W (Watt), V(Volt), Ah (Ampere-Hour), Wh (Watt-Hour), mean and how do they affect the performance of electric bikes?

T:
Motor Torque is the characteristic which reflects the traction (thrust) and is important for climbing up hills. The more torque at the wheel gives you a higher grade-ability. The traction force equals Torque divided by wheel radius (F=T/R). The smaller wheel diameter gives a higher traction force or climb-ability with same motor torque.
The torque at the wheel for mid-drive motors should be calculated like this:
Max Torque at Wheel for crank motors = Max Motor Torque x Number of rear cog teeth / Number of Chain wheel teeth
W:
The amount in Watts shows the power (P) of motor. The power is important for riding faster both on flat or slope.
There is a rated power definition for electric motor which is the nominal power the motor is designed to work at which delivers a good efficiency and long life. Usually maximum or peak power is higher than the rated power. For example EbikeBC 350W geared hub motor can deliver up to 500W power at standard controller setting.
V:
Voltage has no mechanical effect on the ebike performance. This is a parameter which is set based on electrical characteristics of the motor/controller and wiring. Voltage in Li-Ion batteries is a matter of number of cells in series.
Power equals Voltage by Current, the higher the voltage the lower current is necessary to get the same amount of power (P=VI). The voltage should be managed by compromising safety and current rating of component. Having a higher motor or battery Voltage does not translate a higher performance or higher range by itself. Voltage alone doesn’t show any performance characteristics of the ebike unless you know the current rating for motor /controller or capacity of the battery in Ah.
Battery Voltage will not be constant and varies based on SOC (state of charge) a complete charged battery voltage is about 42V when it is nominally 36V and battery voltage is about 30V when the battery is considered complete depleted.
Ah:
It’s the current capacity of battery. The maximum current the battery can be discharged at continuously for 1 hour. For example; you can draw 10A continuously from a 10Ah battery for 1 hour or 5A for 2 hours. This is a parameter that gives you a range. However, the energy density of a battery should be measured by Wh(watt-hour) if you are comparing battery systems of different voltage. Ah increase when using higher capacity Li-Ion cells or using more Li-Ion cells in parallel in a battery pack.
Wh:
It’s the energy capacity of battery. Wh=Ah x V. For example a 48V, 8.8Ah battery gives you 48V 8.8Ah = 422.4Wh energy which ideally means you can draw 422W power for 1 hour. The equivalent battery in 36V standard will be about 11.7Ah.

By |2017-11-28T21:03:23+00:00November 28th, 2017|0 Comments

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