Same Motor, Different Power Rating

[saneagle]

I think its the other way around. A motor running at its rated value of 250W will be close to its specified maximum temperature or for the temperature class it falls into( if this is applicable). If its running cool at 250W its over rated. Ideally for the test, it should run close to its specified maximum temperature because its the safe maximum continuous power figure we are looking for.

You can't make up your own rules for rating and testingt. The engineer responsible for the product decides the rating, and government departments decide on the tests, not you.

The test only covers running at optimal rpm, but the motor has to run at a lot of different rpm during use in an ebike. The engineer needs to allow for that. The test is at optimal rpm. The efficiency at optimal RPM is typically around 75%. At 3mph, the efficiency of a hub-motor could be as low as 20%, which would make more than three times as much heat. Other rules in the EN15194 standard say that the motor must't burn in use, which includes climbing a hill at 3 mph.

 

[Benjahmin]

So where are we?
The thread title is, 'Same motor, different power rating'.
Seems that motors are given a power rating that will not cause them to overheat at optimal rpm. However there must be headroom in there to allow the motor to run at lower rpm and therefore operate less efficiently so producing more heat. The rating here depends on the demonstration of a negative, i.e. not overheating. This is not definitive in the way that a measured length or diameter is.
Further, the latest motor I bought was 'rated' at 800w, but it has the same physical dimensions as a 350/250w one. Wether there are internal differences, winding size/amount, I don't know. All I know is that it is the same physical dimensions as a 250w and has been labelled as such making it a legal motor.

Are there different ratings given to same motors? Certainly looks like it. Is it a cheat? Well no, I don't think so, afterall the power a motor consumes (and therefore it's output allowing for inefficiencies) is governed by it's controller. It would be wrong if a 250w motor overheated on a hill climb - guess it wouldn't be on the market long.

It's like the old story:
A copper approaches an old guy hanging around in Trafalger square and wants to know what he's doing. 'I'm stopping elephants from coming into the square' says the old guy. 'That's ridiculous' says the copper. The old guy replies,' Well, have you ever seen an elephant in the square?'.

 

[Az.]

So where are we?

After checking spare parts sold for TSDZ2B my conclusions are:
Tngsheng is using two motors. One for 250W and 350W motors and one for 500W and 750W. The same case is used for all of them, so dimensions must be the same. What are the differences between them then? I have no idea and I hoped somebody wiser would know the answer.

Here you can buy one bare motor for 36W and one for 48W. Pictures and price are identical... so it still can be the same motor across whole range.

TSDZ2 TSDZ2B TONGSHENG Bare motor for replace 36V 250W/350W or 48V 500W/750W TSDZ2 or TSDZ2B electric bicycle central mid motor

TSDZ2 TSDZ2B TONGSHENG Bare motor for replace 36V 250W/350W or 48V 500W/750W TSDZ2 or TSDZ2B electric bicycle central mid motor

www.pswpower.com

There are few available controllers and there is no surprise there:

tsdz2b tsdz2 tsdz8 tongsheng controller for replace 36V 250W/350W or 48V 350W/500W or 48V 750W electric bicycle central mid motor

tsdz2b tsdz2 tsdz8 tongsheng controller for replace 36V 250W/350W or 48V 350W/500W or 48V 750W electric bicycle central mid motor

www.pswpower.com

So it is likely all differently rated motors are in fact the same motor with different controllers or only settings are different.

My TSDZ2B motor has no label stating rated power at all. I know motors sold by Woosh have proper stickers, but I guess only because Woosh requested it.

 

[saneagle]

This thread and the many others like it are all based on the false premise that there is some sort of regulation that limits the power a motor can make.

 

[AGS]

I have thought for some time that motor manufacturers label the same motor differently depending upon the market. I have a Bafang SWX02 and I’m pretty sure the 250w 350w and 500w motors are the same. You can buy them with different numbers of windings, but they will still operate at 250, 350 or 500 watts quite happily. I am even running one at over 1500 watts with oil cooling and it runs perfectly at that level.

They have to build plenty of redundancy in them, so they don’t spontaneously combust as soon as you pump 251 watts through them.

 

[flecc]

So where are we?

Does it matter? Look at i.c vehicles which are often just as vague but nobody frets about that. For example 50cc Mopeds, just a cubic capacity specifying the vehicle class with no idea of how powerful any one actually is.

Cars were similar for many decades. From 1910 there was the RAC rating of HP which was determined by the piston diameter and number of cylinders. At first that compared well with the actual BHP, but as engines developed in the 1920s and '30s, they diverged widely, so by the late 1930s that was expressed in the model numbers, for example Wolseley 14/60 (RAC rating and actual Brake Horsepower).

it's still confused now, with engine powers given in both kW and BHP. That's meaningless to most ordinary mortals so more meaningful numbers are are also given, the 0 to 62 mph (100km) acceleration time and maximum speed.

Still less than useful though, since with today's traffic ones best acceleration is that of the slowest car in front and the maximum speed is that on the white roadside sign with a red surround.

If all that vagueness is good enough for other vehicles, it's good enough for us.
.

 

[Benjahmin]

Does it matter?

Well no, not really.
I think the outcome is, just make sure you have the 'right' label on your kit motor, then you're less likey to get it taken away from you.
'Cause that's all with the caveat that you aren't hooning around at 30mph whilst going uphill and not peddalling.

 

[flecc]

Well no, not really.
I think the outcome is, just make sure you have the 'right' label on your kit motor, then you're less likey to get it taken away from you.
'Cause that's all with the caveat that you aren't hooning around at 30mph whilst going uphill and not peddalling.

Most importantly on the wattage power question, any pedelec that complies with the rules is a bicycle in law and specifically ruled to be NOT a motor vehicle.

Other than that for bicycles, they have no law on construction and use, the laws on those that exceed 15.5mph assisted, exceed the 250 watt rating or getting motor vehicle power without pedalling are solely motor vehicle laws which only apply to motor vehicles that are specifically not EAPC pedelecs.

Ergo, legal pedelecs / EAPCs do not need any power rating.
.

 

[RollingChunder]

Well no, not really.
I think the outcome is, just make sure you have the 'right' label on your kit motor, then you're less likey to get it taken away from you.
'Cause that's all with the caveat that you aren't hooning around at 30mph whilst going uphill and not peddalling.

What about 17mph up a hill while pedalling without a sweat?

 

[flecc]

What about 17mph up a hill while pedalling without a sweat?

No problem.

The DfT have confirmed that the usual 10% tolerance on speed limits applies here to, so up to 17.05mph is legal.

It follows that the motor can be assisting that pedalling at 17mph.
.

 

[Nealh]

One will have to put in a good bit of pedal action to manage 17mph up hill .

 

[Sturmey]

I came across an abridged amended copy of EN15194 (Nov 23) which at least clarifies the position for me and that I can now show on paper. The position seems to be more or less what Flecc and saneagle are saying. ( I think).

The paper defines

3.20 continuous rated power as 'output power specified by manufacturer, at which the motor reaches its thermal equilibrium at given ambient conditions' P12 (14pdf)

On page 10 it states

This European Standard is intended to cover electrically power assisted bicycles of a type which have a maximum continuous rated power of 0,25 kW, of which the output is progressively reduced and finally cut off as the EPAC reaches a speed of 25 km/h, or sooner, if the cyclist stops pedalling. P8 (10 pdf)

(my emphasis above in bold)

Interestingly then, if you take into account the actual definition of 'continuous rated power' and substitute this phrase with its defined meaning as in 3.20 above, you could state for clarity that

"This European Standard is intended to cover electrically power assisted bicycles of a type which have a maximum output power specified by manufacturer, at which the motor reaches its thermal equilibrium at given ambient conditions of 0,25 kW, of which the output is progressively reduced and finally cut off as the EPAC reaches a speed of 25 km/h, or sooner, if the cyclist stops pedalling."

 

[RollingChunder]

One will have to put in a good bit of pedal action to manage 17mph up hill .

Not if the 250w rated motor is able to draw on 1 kW+

 

[flecc]

I came across an abridged amended copy of EN15194 (Nov 23) which at least clarifies the position for me and that I can now show on paper. The position seems to be more or less what Flecc and saneagle are saying. ( I think).

The paper defines


On page 10 it states

(my emphasis above in bold)

Interestingly then, if you take into account the actual definition of 'continuous rated power' and substitute this phrase with its defined meaning as in 3.20 above, you could state for clarity that

"This European Standard is intended to cover electrically power assisted bicycles of a type which have a maximum output power specified by manufacturer, at which the motor reaches its thermal equilibrium at given ambient conditions of 0,25 kW, of which the output is progressively reduced and finally cut off as the EPAC reaches a speed of 25 km/h, or sooner, if the cyclist stops pedalling."

Agreed. I actually published a 2009 full version of EN15194 in my Pedelec Law - The Details thread back on 21st May 2020:

Pedelec Law - The Details

I think many of you will be aware of what a complex subject electric assist bicycle law is and pitfalls in trying to second guess it. As a result, and with my knowledge of it since joining the trade 70 years ago, I'm often called upon in here to give answers on the subject. But of course I...

www.pedelecs.co.uk

In that the continuous rate power definition is on Page 15 of it below:

http://www.flecc.co.uk/m/EN15194%20document.pdf

.
.

 

[RollingChunder]

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[Sturmey]

Agreed. I actually published a 2009 full version of EN15194 in my Pedelec Law - The Details thread back on 21st May 2020:

Thanks. The one thing I do notice is that there has been some additional restrictions listed in the 2017/2023 document index that are not in the 2009 documents. For example, there appears to be an extra section 4.2.17 'Anti-Tampering Measures' which makes me wonder precisely what these measures are?

 

[saneagle]

I came across an abridged amended copy of EN15194 (Nov 23) which at least clarifies the position for me and that I can now show on paper. The position seems to be more or less what Flecc and saneagle are saying. ( I think).

The paper defines


On page 10 it states

(my emphasis above in bold)

Interestingly then, if you take into account the actual definition of 'continuous rated power' and substitute this phrase with its defined meaning as in 3.20 above, you could state for clarity that

"This European Standard is intended to cover electrically power assisted bicycles of a type which have a maximum output power specified by manufacturer, at which the motor reaches its thermal equilibrium at given ambient conditions of 0,25 kW, of which the output is progressively reduced and finally cut off as the EPAC reaches a speed of 25 km/h, or sooner, if the cyclist stops pedalling."

Too complicated. The only relevant bit is "specified by the manufacturer". It's not for us to guess, interpret or other way try to understand the manufacturer's methods or intentions, nor what the motor can or can't do. When the manufacturere specifies it as a 250w motor, you're home and dry - nice and simple!

 

[flecc]

Thanks. The one thing I do notice is that there has been some additional restrictions listed in the 2017/2023 document index that are not in the 2009 documents. For example, there appears to be an extra section 4.2.17 'Anti-Tampering Measures' which makes me wonder precisely what these measures are?

I don't know the precise details, but as so often is the case, I'm sure these were motivated by EU protectionism, making the market tougher for China et al.

Basically they are as said, defeating such as dongles by recording such uses making it much more difficult to break the basic rules without admitting to it. Canbus likewise makes upping battery voltage for more speed difficult, all these protections built to the German crank motors.
.