- #2

First of all, I’m not an engineer and I am a complete amateur when it comes to this topic.

So I have seen several posts here on EBR how 750W ebikes make approximately 1 horsepower because 750W can be converted into 1.01972 hp.

But is this actually the case?

If so, from engineering perspective, your 100W light bulb in your room = 0.13 horsepower light bulb?

I did a quick Google search and came across this website, it doesn’t seem to be the case.

There are different types of wattage, and they do not seem to be interchangeable.Power vs Energy Explanation — Clearing up the Confusion

cleantechnica.com

I went to Wikipedia, and there are different types of wattage.

Object’s velocity

Electromagnetism

Ohm’s Law

So, the wattage shown on ebikes are simply the Voltage x Amp = W and has nothing to do with the horsepower generated by the motor. (or so I thought)

One thing was Ohm’s Law, it says that unit conversion can be done by Ohm’s law. https://en.wikipedia.org/wiki/Watt so I guess they are interchangeable?Bolton Ebikes posted a YouTube video how two different motors could both drain 750W of electricity and still get different result because of the power difference due to the efficiency of motor.

They are both rated at 750W, but one had more heavy duty construction and better magnet, just because they could both drain 750W of energy, didn’t mean the power (output of motor) was equal.So what this told me was that 750W in ebike world, wattage was figured out by battery voltage, amperage transferred by the controller and not the horsepower generated by the motor itself.

Can anyone clarify this?

-Watt is a unit for measuring power which is the rate of change in energy.

-Energy can take different forms, mechanical, electrical, chemical etc. it can be transformed from one form to the other. What you write are not different types, they are simply examples which 1 watt of power is produced.

-Electrical motors are rated by their ouputs. 750W refers to the measured mechanical power at the crank of the motor.

-Your battery stores energy in chemical form then it transforms it into electrical form. Your motor takes this electrical form and converts it to mechanical form and that moves your bike. In an ideal world to produce 750W of mechanical power motor would use 750W of electrical power. Unfortunately conversions are not perfect, there are by products such as heat. So some of the electrical energy transformed into heat for example instead of mechanical power.

-Efficiency is the rate at which the desired conversion is achieved. In this case it is the proportion of the electrical energy converted into mechanical energy. If your electric motor has efficiency of %80 then to produce 750W output at the crank you need 937W of input in the form of electrical power which is what you will measure by multiplying potential difference (measured in Volts) by the current (measured in Amps) at the terminals of the battery.