Same Motor, Different Power Rating

I keep looking at motors with different power ratings and I can't help but wonder - are they all actually almost the same motors with different labels and just minor differences?

 

For example Tongsheng TSDZTB... We can choose between 250W, 350W, 500W and 750W. I am guessing controllers must be different between 36V and 48V models, but is that it? Controllers and labels?

Edited December 18, 20232 yr by Az.

3.22 (EN15194 2009)

continuous rated power

continuous (or constant) output power specified by manufacturer, at which the motor reaches its thermal equilibrium at given ambient conditions

NOTE Thermal equilibrium: temperatures of motor parts do not vary more than 2K per hour.

Below is what I reckon although I am sure you will get other opinions.

I think the same motor can have different power ratings depending on its application as specified by the manufacturer e.g. A motor thats tested and rated to 250w continuous mechanical output at 25Km/hr could also be tested and rated to have a 350w continuous at say 30 Km/hr. (e.g in a different jurisdiction.)

With the TSDZ2. I think the controllers are the same but may (and may not in some cases) have different current settings and the user can change application with different speed limits which changes the intended application/rating.

The 36v has a different turn count/winding than the 48v and I think this is the only actual hardware difference.

PS I dont think I have ever seen the electrical input power (volts,amps,electrical watts) used to calculate the (mechanical) continuous output power ratings in documents.

Power (kW) = Torque (N.m) x Speed (RPM) / 9.5488

 

The most important three words in above is 'specified by manufacturer'.

Edited December 18, 20232 yr by Sturmey

For example Tongsheng TSDZTB... We can choose between 250W, 350W, 500W and 750W. I am guessing controllers must be different between 36V and 48V models, but is that it? Controllers and labels?

I concur with Sturmey:

The most important three words in above is 'specified by manufacturer'.

I order TSDZ2B from Tongsheng. I tell them what I want (48V, 250W), they make it and guarantee it. It may be the same physical motor that they make for other vendors who claim 500W or 750W but may differ in their settings. That's between Tongsheng and those vendors.

Another example - is the Bosh rear hub h400 series, the current version is the h405 - it is rated at 250, 350 and 500 w (usually but not always, depending what voltage you are running it at :36,43,48)

 

https://www.bafang-e.com/en/products/motors/hr-series/h405

 

https://www.bafang-e.com/en/products/motors/hr-series/h405

Edited December 18, 20232 yr by Peter.Bridge

As a punter, I buy a hub motor. It comes with a sticky label on it. How do I know who put it there? Was it the manufacturer or The middle man/supplier? Who can test the veracity of what it says?

My own AKM motor now has a label stating 250W which is absolutely bloody meaningless - yet makes it legal, apparently.

It came with a label that was stuck on over some etched print that contained no info as to the wattage rating, as far as I can see.

 

How is continuous rated power tested? Can it be done outside of an engineering lab?

Surely a motor that does not overheat at 250w may also not overheat at 350w, or 500w, but if it's labelled 250 (by the manufacturer [or supplier?] ) then it's legal in the UK. Is that right?

It seems to me that a manufacturer could put any label on a motor they like, so long as it doesn't cause the motor to be used in overload conditions.

So I manufacture a motor with windings capable of taking 22A at 36v (800w) put a 250w label on it and alls hunky dory.

It seems to me that a manufacturer could put any label on a motor they like, so long as it doesn't cause the motor to be used in overload conditions.

When I learned for the first time that the tests were rubber-stamped, I was flabbergasted like most members.

the motor rating needs to be understood in the context of actual use.

the tests are done when you are not climbing a hill or having a gale blowing in your face.

They can be made on real road or in a lab, in which case, 10% allowance is given to compensate for the absence of road friction.

So, on a flat road without headwind, your and your bike's weight add up to 100kgs, respecting 25kph speed limit, all motors will pass.

A motor thats tested and rated to 250w continuous mechanical output at 25Km/hr could also be tested and rated to have a 350w continuous at say 30 Km/hr. (e.g in a different jurisdiction.)

 

The way I see it motor rated 350W should be automatically rated 250W as well.

I am surprised though to find out all motors across the power range might be identical. After all when you visit shop and you see many different products on sale you expect they are different.

I was assuming higher power motors are bigger, have more copper inside, better thermal dissipation etc

 

With the TSDZ2. I think the controllers are the same but may (and may not in some cases) have different current settings and the user can change application with different speed limits which changes the intended application/rating.

 

You can buy five different controllers for TSDz2 on PSW, so they might be different after all, but is that all? Controller and label is the only difference?

 

https://www.pswpower.com/products/bare-controller-for-replace-36v-250w-350w-or-48v-500w-750w-tsdz2-electric-bicycle-central-mid-motor-1

 

The most important three words in above is 'specified by manufacturer'.

 

Specified by manufacturer means sticker put on? They must have a good laugh there.

I concur with Sturmey:

 

I order TSDZ2B from Tongsheng. I tell them what I want (48V, 250W), they make it and guarantee it. It may be the same physical motor that they make for other vendors who claim 500W or 750W but may differ in their settings. That's between Tongsheng and those vendors.

 

So technically, what would be the difference between TSDZ8 750W sold by PSW and TSDZ8 250W sold by you? A sticker?

BTW, did you get them already or still waiting?

As a punter, I buy a hub motor. It comes with a sticky label on it. How do I know who put it there? Was it the manufacturer or The middle man/supplier? Who can test the veracity of what it says?

My own AKM motor now has a label stating 250W which is absolutely bloody meaningless - yet makes it legal, apparently.

It came with a label that was stuck on over some etched print that contained no info as to the wattage rating, as far as I can see.

 

How is continuous rated power tested? Can it be done outside of an engineering lab?

Surely a motor that does not overheat at 250w may also not overheat at 350w, or 500w, but if it's labelled 250 (by the manufacturer [or supplier?] ) then it's legal in the UK. Is that right?

It seems to me that a manufacturer could put any label on a motor they like, so long as it doesn't cause the motor to be used in overload conditions.

So I manufacture a motor with windings capable of taking 22A at 36v (800w) put a 250w label on it and alls hunky dory.

EN15194, the standard for electric bicycles, specifies the standard to be used for motor power rating. I can't remember the number, but it clearly describes the method. First you find the rpm for optimum efficiency, then you run the motor at the rated power in the band of optimum efficiency. To pass, the temperature must stabilise and not burn the motor.

 

Any motor that can run at 2000w at its optimal rpm without overheating will pass the 250w rating test.

 

Any motor will overheat when running at rpm substantially below its optimum rpm. In that case, the engineer, who decides the size or maximum power, has to take into account the inefficiency when climbing hills with heavy riders, so it's not surprising that peak power would be substantially above 250w.

They should specify also the controllers.

They should specify also the controllers.

All the parts of the system have to work together. If the controller doesn't give enough power, the motor might go too slow and burn either the controller or the motor. Some systems include temperature sensors, but that's a bit dangerous to cut the motor when you need it most or when you don't expect it.

 

To me, the most sensible solution would be to make it more simple: just a 15 mph powered speed limit, everything else allowed. In France, you can drive a 45 km/hr quadricycle without a licence at 14 years old! They don't care.

 

To me, the most sensible solution would be to make it more simple: just a 15 mph powered speed limit, everything else allowed.

I couldn't agree more plus the need to have the pedals turning for assistance.

 

With those two simple criteria law enforcement officers could enforce the rules - that is if there are enough of them to do so plus the political will of course.

To me, the most sensible solution would be to make it more simple: just a 15 mph powered speed limit, everything else allowed.

 

Would you not then get those who would interfere with the speed controller!!!

Would you not then get those who would interfere with the speed controller!!!

Yes, definitely, but it's not as bad as people, who beat their partners, park on yellow lines, shoot their neighbours and things like that. People will always break rules. Somebody needs to catch them and hold them to account for it.

..........How is continuous rated power tested? Can it be done outside of an engineering lab?.......

I think the test its simple enough as far as I can see.. I would think the motor is loaded with a 250W mechanical brake + 15% allowance for errors etc and ran until temperature equilibrium is reached as explained in document below. The actual max temperature is supplied from the manufacturer. Its an old test and I think there is a lot of leeway which I think is an advantage.

The test is described in document IEC 60034 which attached below is the only copy I can get for free and may be outdated. The test is duty type S1 page 8 or 13pdf. If anyone has an update or more info on this test, please let me know.

motorPower.60034.1.2004.pdf

Edited December 19, 20232 yr by Sturmey

PS If you think about it, it seems from above that it may not be too difficult for say a 36V motor with a 14 amp controller to pass the test. Although the electrical input may be 500w, if the test is done at say a slow cadence or say the 55 -60% area on the efficiency curve, then the actual mechanical output could be 275- 300 watts. EN15194 allows for an extra total 15.5% on top of the 250W which brings the figure to 288W.

Furthermore, the motor manufacturer may allow a lot of headroom in terms of his quoted maximum temperature figure which probably means that many motors in reality can take a fair bit more, especially peak current, than the motor is certified for.

This is not unusual with electrical components. For example, the typical rcd will carry 40% more amps than its rated amount for over two minutes.

So from the above, I can see how a motor may easily have 700w electrical peak power and still be rated as 250W continuous mechanical output power.

Edited December 19, 20232 yr by Sturmey

But this still leaves us in the place where, so long as the motor has a 250w label, it's legal. Mainly because there is no roadside test the authorities can do to check this. Input power does not equate with output power, but that's not what the regulation states. I believe the wording is 'maximum continuous rated power'. That is not output power.

But this still leaves us in the place where, so long as the motor has a 250w label, it's legal. Mainly because there is no roadside test the authorities can do to check this. Input power does not equate with output power, but that's not what the regulation states. I believe the wording is 'maximum continuous rated power'. That is not output power.

I don't know why this gets discussed again and again. We've known that's how it's been for many years, but people (not you, in case you think this is directed at you) keep spouting the same old shite. What's written is all very clear and simple, but somehow people make their own invention about what's in the standards and or what the guy, who wrote it, might have been thinking about on his day off, then they complain about it.

.....But this still leaves us in the place where, so long as the motor has a 250w label, it's legal. .......

But I think this is no different than say with a motor car. The engine power/cc/bhp/emission rates is what the document or label on the engine says. Most people buy cars and never question the rating. We leave the rating and certification to the civil servants and the car manufacturers to worry about.

PS. My first car (1975) was a Ford Escort and was rated at 8 horse power. I suppose I could have borrower eight horses and tried some type of tug of war to see if the rating was correct. But I never worried. If eight horsepower was on the registration book, the so be it, its eight horsepower.

Edited December 19, 20232 yr by Sturmey

The power rating, continuous or maximum of our cars is however unlike our e-bikes not currently embedded in its usage legality.

The power rating, continuous or maximum of our cars is however unlike our e-bikes not currently embedded in its usage legality.

Exactly so.

They are also capable of going far faster than the national speed limit, but non has ever been confiscated because of the ability to do so.

My Ezee conversion in level 5 and on the stand, wil register 19mph. But that's on a cycle computer who's speed registration is dependant on wheel size setting and this is not precise. Also, if roadside tested, this would be without any resistance, so what would the actual road speed be?

As there's no legal requirement to have one, maybe we should all just remove speedo's.

'Was I speeding officer? The only way I can tell is by how much the wind is making my eyes run, it's very windy today isn't it?'

How is continuous rated power tested? Can it be done outside of an engineering lab?

By the way, there was a way proposed that could test and rate the output power without a lab or any special equipment. I dont think it will work with a torque sensor but will certainly work with a hub motor.

You need to take the chain off the bike and fit a pannier rack as you need to add ballast (e.g. drums of water) to bring the overall weight of bike + rider+ ballast = 150Kg.

A calm day, a marked level piece of ground and an assistant with a stop watch is all else that is needed.

The calculation/formulae is based on applying good old Newton's physics to a short standing start. It averages the power over a range of speeds.

Take note that the instantaneous peak power is never measured in all these tests. This is because the power output curve of a motor is considered as 'parabolic' shaped ((EN15194) and some means has to be used to apply a 'mean' or average value.

This is common with electrical measurements. For example, the UK main voltage has a maximum instantaneous peak value of about 320V. However, this higher peak value is found not to be useful so they came up with the idea of using the notional Root Mean Square value which comes to 230V, which give the mains AC voltage the equivalent DC heating value (or something like that). i.e actual 320V peak = notional 230V rms.

 

Brilliant ! Not many unquantafiable variables in there !

For every day use, the power of the motor is what the sticker says it is.

Buy a resonably sized geared hub and put on a label that says ' 250w' and 'Hoofrungdung Motor Corp' on it and enjoy it, 'cos the only thing practically measureable is the speed.

If mid drives are your thing then who knows? Where is the power measured. At the crank, at the wheel? What gear's it in? How much is attributable to the rider? What's the frontal surface area of the rider? Where does half the moon go twice a month?

Think I'm goin' out on my bike now

...... How much is attributable to the rider? ......

I specifically said above that 'You need to take the chain off the bike'. This solves that problem.

Sturmey, mate, take the chain off a mid drive and the level piece of ground and stop watch aren't gonna be much use .

Buy a believable motor and sticker it accordingly.

Here's one I did earlier. Take out the bleedin obvious, put in the 'yeh, I can believe that'

https://www.pedelecs.co.uk/forum/attachments/dscf3353-jpg.53861/