What's the ebike wattage rating? 750W = 1 horsepower? or is it simply the consumption of electricity.

[Timpo]

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

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?

 

[Johnny]

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

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.

 

[Stefan Mikes]

Watt or horsepower are the units of power, that is, the energy spent during a time unit. If your motor is 1 HP, it can deliver 750 W power or - in other words - 750 Joules of energy per each second. Power is the energy rate.

If power is delivered over some time, the energy delivered will be power * time. If the motor delivers 750 W, it will deliver 750 Wh or 645 kcal or 2700 kJ of energy during one hour operation.

Now, to deliver 750 W of power, the motor has to draw far more energy because there is the factor of mechanical and electrical efficiency; nothing is perfect in this world. Let us assume the overall efficiency is 70% or 0.7. To deliver 750 W of power, the controller has to deliver 750/0.7 = 1071 W from the battery. Let us assume (for simplicity) the battery is 48 V. As electrically 1 W = 1 V * 1 A, the controller will draw this current from the battery: 1071 / 48 = 22.3 Amperes.

Now. We know our 48 V battery is say 600 Wh capacity (the amount of energy stored). We already know that the controller power demand is 1071 W. The time during which the motor will work in throttle-only operation will be 600 Wh / 1071 W = 0.56 h = 33 minutes 36 seconds.

Does it answer your questions Timpo?

 

[Stefan Mikes]

So if you say this light bulbs consumer x amount of horsepower, it is technically not wrong?

Technically it is correct. Specifically, Mr Joule the brewer determined that work and heat were equivalent long time ago. Energy rate / work rate / heat rate is the power. The power was later redefined with electrical terms of Volt and Ampere. That is why the SI system of units is such logical.

 

[Stefan Mikes]

yeah, it does, kind of.

So you're saying that in the perfect world (100%) efficiency, any motor can produce 1hp as long as 750W (48V x 15.6A) of electricity was sent to the motor?
If Bafang hub motor and Dapu hub motor, different magnet, different design, different material, etc.. but had no power loss, they will be identical?

If the 100% of efficiency, then yes, in the power terms. Different motor differ in other aspects such as torque that translates to the acceleration capability of a wheel-driven vehicle.

If it is a mid-drive motor, the derailleur acts as a torque multiplier (low gears) or divider (high gears). This is why mid-drive motor is better on climbing than the hub-drive one at the same rated power. Mid motors typically have higher torque than the hub ones, too.

James Prescott Joule made this experiment in 19th c: He was delivering a controlled amount of work to an agitator that mixed water. He measured the water temperature increase and found out the work and heat were two forms of the same property: the energy. You can put an electrical heater in the Joule's vessel to see the electricity is the third form of the energy and all forms of energy are equivalent. That is why you can say you deliver some horsepower to a light bulb.

 

[Mike_V]

zEnergy is Fun!
"thanks for the explanation but now it is getting beyond my comprehension"
Watts power, we want torque.

 

[Trail Cruiser]

That's where the confusion arises.

Chinese ebikes: 750 watts rating equals 750 "maximum" watts coming from the controller into the motor (volts x amps).
Non-Chinese brands : 750 watts equals 750 "sustainable" watts, plus it is measured as a mechanical watts at the output shaft (work / time or force x distance / time).

I remember Justin from ebikes Canada measured a 350 watt Bosch motor producing peak electrical output of 800+ watts.

Ideally, electrical watts is equivalent to mechanical watts. In reality, there is efficiency loss from friction and heat. And that is calculated as delta. Efficiency of electric motor is usually at the 80% (give or take) depending on load and speed. Additional efficiency loses occur at the drivetrain (gears, chains, derailer, etc...)

If you compare apples to apples between Chinese ebike and German ebike, the 750 watt Chinese ebike may not be as powerful as the 350 watt German ebike.

The power rating becomes moot between the 2. The more significant way to compare is actual riding experience and battery range.

 

[Alex M]

That's where the confusion arises.

Chinese ebikes: 750 watts rating equals 750 "maximum" watts coming from the controller into the motor (volts x amps).
Non-Chinese brands : 750 watts equals 750 "sustainable" watts, plus it is measured as a mechanical watts at the output shaft (work / time or force x distance / time).

Ah, that notorious "continuous vs peak" confusion... Yeah, Chinese ebikes do this, and sometimes RAD ...

Normally ebike motors are specked in electrical wattage, not mechanical shaft output as the latter is more complicated. Wattage on display is also electrical and (I think) is measured as input to the motor before any losses - not the output, though I might be wrong on this one.

 

[Trail Cruiser]

Ah, that notorious "continuous vs peak" confusion... Yeah, Chinese ebikes do this, and sometimes RAD ...

Normally ebike motors are specked in electrical wattage, not mechanical shaft output as the latter is more complicated. Wattage on display is also electrical and (I think) is measured as input to the motor before any losses.

Ebike motor output is measured at the output shaft using a dyno just like a car engine. Watt display is electrical measurement but roughly corelates to actual power to the wheel (minus the efficiency lose).

 

[Ebiker33]

V X A=W/746=HP

However some use 1000W as a divider to compensate for all types of things that can impact the final number like heat, voltage drop and so on.
That is how you can get different ratings, that why a 48 volt battery is allowed with a 20 map controller for 960 watts, ultimately that 250 watts is in flux effected by other variables.

Factoid: George H Bush decided Ebikes should be 1HP during his presidency and that is why we have the 750/1000W rating we have today.

 

[Trail Cruiser]

It all started as a law in the US (EU have different laws). Motorized bicycles in the US canot have more than 1 horsepower (750 watts) in many states. It does not matter if the power comes from internal combustion engine or electric motor. The horsepower rating is measured at the crank (or drive shaft) using a dyno.

The most likely explanation for using inflated electrical wattage (for Chinese ebikes) is to hype the power rating to attract more buyers.

However, back to back testing showed very close sit-on-the-pants power delivery between my 350 watt Raleigh Tekoa and my 1,000 watt BBSHD.

There was also another person who measured a 350 watt Bosch producing 800+ electrical watts from the controller.

 

[Trail Cruiser]

The 800W electric watts was from the controller, so once you put the motor on dyno, it will probably lower due to energy loss.

The actual mechanical power will be lesser. On the other hand a professional athlete that is pedaling at 750 watts, the measurement of the power is also done at the pedal crank. An ebike motor power measurement is also done at the pedal crank. It's different on a hub motor since it is measured directly at the wheel.

 

[highpockets]

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

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?

You lost me, I can barely do math using numbers.

 

[steve marino]

Okay so National Geographic did a documentary (it's on YouTube) on Bugatti Veyron.

They said that Bugatti Veyron produces 3,000 horsepower, however most of them will be lost in forms of heat, so it only produces 1,001 horsepower.
Is it similar to that?

If I understand correctly, you're saying that 750W in electricity is same thing as 1 horsepower.
Is it interchangeable? Just like cm and inch, meter and feet, lbs and kg?

So if you say this light bulbs consumer x amount of horsepower, it is technically not wrong?

Not quite. A car engine that produces 1001 hp actually produces 1001 horsepower. The power is measured at the crank, it's exactly what you get. An internal combustion engine's horsepower is determined by many, many things, including friction, design, fuel, altitude, etc, but not heat. To my understanding, electric wattage has nothing to do with horsepower.

I love the idea of a light bulb producing horsepower though! Might want to trade in the Ford for a string of Christmas lights.

 

[Stefan Mikes]

To my understanding, electric wattage has nothing to do with horsepower.

Your understanding is not correct.

The lightbulb uses the horsepower, not produces it. Watt and horsepower are just two different units of power, of which the HP has more historical meaning nowadays. A car manufacturer gives the car power in kW today, followed by horsepower for easier understanding.

 

[Ebiker33]

To my understanding, electric wattage has nothing to do with horsepower.

Not true, every major stationary power tools is rated by horsepower, and has been for decades.
Just one example Table Saw

 

[Stefan Mikes]

Not true, every major stationary power tools is rated by horsepower, and has been for decades.
Just one example Table Saw

Not in Europe. Nobody uses hp for power tools here.

 

[Smong]

Curious about the Bafang to Bosch comparisons...how does torque play into it?
I tried Bosch and Yamaha commuter bikes and they felt pretty zippy until I tried a 1000 watt Bafang Ultramax on a fatbike. I think the numbers always tell a different story than the actual ride. I understand that the Bosch, Brose and Yamaha were rated lower power than the Bafang but the dealers assured me that they were better, stronger, more efficient than the Bafangs and perform better than the higher rated Chinese motors. In real life riding, the 80NM torque bikes felt about 1/2 as 'zippy' as the 160NM bikes, as I would have expected.

 

[Johnny]

Curious about the Bafang to Bosch comparisons...how does torque play into it?
I tried Bosch and Yamaha commuter bikes and they felt pretty zippy until I tried a 1000 watt Bafang Ultramax on a fatbike. I think the numbers always tell a different story than the actual ride. I understand that the Bosch, Brose and Yamaha were rated lower power than the Bafang but the dealers assured me that they were better, stronger, more efficient than the Bafangs and perform better than the higher rated Chinese motors. In real life riding, the 80NM torque bikes felt about 1/2 as 'zippy' as the 160NM bikes, as I would have expected.

The big brand names may run smoother but I don't think the claim about efficiency is right. It may even be the opposite and Bafang ultra maybe more efficient at outputs >= 500W.