Continuous Rated Output

[Cuthy]

What is continuous rated output and how can it be measured? Who would be able to measure it?

 

[neptune]

I can only give you a vague answer. The official definition would probably be something like " that power at which an electric motor only rises x degrees above ambient temperature in y minutes." Try googling Continuous rated output power of electric motors. If the answer is needed for legal purposes, the tests would probably need to be done by a recognised laboratory.

 

[trex]

It's usually known as RMS, the maximum real world power rating within safety margins as specified by manufacturer.
With e-bikes, you also need to have an excellent battery & controller to reach the maximum output of the motor.

it's measured by a dynamometer like this one:
Inertia dynamometer for DC micro-motor - MotorLab Kit MLK-D - MEA Testing Systems Ltd. - Videos

Read also: Power rating - Wikipedia, the free encyclopedia

 

[Deleted member 4366]

The manufacturer decides what it should be for each of their motors, and then they mark them with the rating. There is an official measurement and test method, which is designed to stop manufacturers over-rating their motors, but there's nothing to stop them under-rating them, which is handy for ebikes.

 

[Cuthy]

Thanks for your replies.
So if the electric motor is a 250W motor then the maximum power it will produce is 250W, however this is not realistically achieved as there is loss of power through heat and actually maybe set lower by the manufacturer as a safety measure.
Does this mean that the an ebike with a 250W motor does not produce a continuous rated output of 250W - if it did it would soon fail?

 

[trex]

Thanks for your replies.
So if the electric motor is a 250W motor then the maximum power it will produce is 250W, however this is not realistically achieved as there is loss of power through heat and actually maybe set lower by the manufacturer as a safety measure.
Does this mean that the an ebike with a 250W motor does not produce a continuous rated output of 250W - if it did it would soon fail?

on the contrary, the specification takes into account heat loss and friction loss.

If the manufacturer specifies 250W continuous power, the motor should run perfectly at that power for its entire life expectancy - typically 20,000 miles + for e-bike motor.

 

[jackhandy]

No... A 250w Continuous rated motor is, as D8veh said, rated at 250w by the manufacturer & will provide anything from about 500w to 900w, depending on the restrictions imposed by the controller, provided it's fed by a strong enough battery. But some may not provide this amount of grunt for too long: All 250w motors are not born equal .

 

[flecc]

The most common continuously achievable output on todays e-bikes is around 400 to 500 watts. A very few produce less, to as low as 300 watts, but a select few in the other direction can be in the region of 700 watts or more.

 

[banbury frank]

Hi No such thing a s a rating on a motor it depends on the volt X amps you throw at it so throw 24 volts aned 10 amps 240 watts throw 72 volts at 30 amps same motor 2160 watts

Frank

 

[SRS]

Hi No such thing a s a rating on a motor it depends on the volt X amps you throw at it so throw 24 volts aned 10 amps 240 watts throw 72 volts at 30 amps same motor 2160 watts

Frank

Frank, if that is the case, why can I not run my bosch motor at 10 times the current and voltage that it is currently running.

I'd have loads of power with no ill effects on the motor. After all the motor is not rated so it will not burn out.

Are you not confusing power with rating?

Please explain your comments.

 

[flecc]

Couldn't on the Bosch, or the Panasonic and similar units, since the integrated controller/logic board couldn't take a very high voltage delivered and that board limits the current anyway.

 

[trex]

P = V * I is only true in special circumstances eg when the load is a resistor.
It is not true in cases of motor, whose real output depends on its Q factor, switching control, load etc.
This is because a motor gets pushed around its axle by solenoids, whose voltage across their terminals varies with time, the intensity of the current flowing through it is also a function of time, the output power is also a function of time with more variables than just V (voltage) and I (current Intensity). Each function has also its harmonics, the resultant P is a complex function which can only be analysed with something like MathLab. The power is usually measured while the motor reaches its thermal equilibrium in a room at 25 degree C.
The dynamoneter use a heavy wheel to average out the output, yielding effectively the RMS (root mean square) of the real P, a simple statistical answer to complicated situation. All motors will withstand 100 times its RMS but not for long.

 

[SRS]

Couldn't on the Bosch, or the Panasonic and similar units, since the integrated controller/logic board couldn't take a very high voltage delivered and that board limits the current anyway.

Was making a point, appreciate that it would be impossible in my example.

In my opinion is that a motor can have a max or cont rating. Any motor can be overdriven to the point of burn out.

 

[Cuthy]

Mmm! Confused now. So the legislation currently restricts ebikes to 200w continuous rated output but the most commonly rated output is 400-500 watts.
As you probably can tell I have no knowledge of electric motors and power ratings so was trying to understand how a 250w motor can produce the required output to satisfy the legislation or is it a case that there is no desire from authorities to act on this.
I am aware that some organisations run electric bike tours - are they exposing themselves to potential lawsuits if there is a tragedy and the bikes are not performing within the legislation.
Bit off topic but still related to continuous rated output.

 

[trex]

It's our fault really to be willing to pay more for a more powerful motor, forcing manufacturers toward a dodgy interprepation of EN15194 which gives conforming e-bikes their road legal pedelec status.

 

[Deleted member 4366]

There's effectively no limit in the European legislation EN15194, which is the standard most commonly applied. It's all about the words and test methods, neither of which pin it down. The rules are that the manufacturer must not label the motor with more than 250w and a motor with a 250w label mustn't overheat when running at 250w continuous.

You have to be careful about terminology and calculations. If you have a 20 amp controller and a battery at 40V, you can take as much as 800W from the battery, but at the low speeds where the controller will allow that current, efficiency will be as low as 25%, so the output power will only be 200W. When the motor is spinning fast enough to reach its 80% efficiency, the back EMF from the motor cuts down the current, so the maximum current from the battery might only be 10 amps max, so output power will be 10 amps x 40v x 0.8 efficiency = 320w.

 

[Geebee]

Until it melts, that is the kind of statement that could cost a noobie a lot of money.
Some motors will allow that kind of wattage a lot won't.

 

[flecc]

So the legislation currently restricts ebikes to 200w continuous rated output

There is a government intention to change UK law to 250 watts rating and meanwhile there is a DfT waiver in force allowing the 250 watts rating. Hence their open sale.

How the higher actual outputs are allowed others have explained.

 

[flecc]

Was making a point, appreciate that it would be impossible in my example.

In my opinion is that a motor can have a max or cont rating. Any motor can be overdriven to the point of burn out.

Agreed SRS, I was making the point to Frank since his statement was rather sweeping when so many "motors" now are integrated crank units.

 

[mountainsport]

on the contrary, the specification takes into account heat loss and friction loss.

If the manufacturer specifies 250W continuous power, the motor should run perfectly at that power for its entire life expectancy - typically 20,000 miles + for e-bike motor.

Hello Trex,

How could a person know when a motor, geared, gearless, brushless etc is on its way out even though they are still carrying you from point A to B ?

MS.