Legality of power ratings

I'm in the process of considering an e-bike conversion & have been reading up as much as I can. I came across the thread from 2012 discussing the UK law & power ratings of motors.

I'm no expert but I think some are confusing the power rating of the motor with power consumption. Someone said that their 250 watt rated motor was reading 620 watts on the 'Cycle Analyst' display when they were going up hill using maximum power setting. As I understand it (40 years after leaving school where I should have learnt it!) the 620 on the readout was the consumption rate of the available power. A 36 volt X 10Ah battery = 360 watt hours of available energy so a reading of 620 indicates that that level of power consumption could be available for just 35 minutes. Remember there is a huge difference between maintaining a steady slow speed on the level, and climbing a hill quickly - try doing it without a bike! As a sufferer of ME / post viral fatigue I'm very aware that the weaker you are, the more noticeable the difference in energy requirement is between say, level walking & uphill running. The same applies to motors; a low voltage motor may not be able to drive up more than a gentle gradient but be capable of sustaining some distance on the level - think mobility scooters and vintage cars. A powerful modern car might be capable of spectacular acceleration and pulling power but it will not go further because it uses up more of its stored energy in the fuel tank.

The motor rating doesn't mean much. We now have a 25A version of the 250W Bafang BBS01. 25a x 40v = 1000w.

You are forgetting that E-bike power is governed by an overriding and universal physical law: Power cannot exceed 250W.

 

It acts a bit like the speed of light, a restriction which cannot be exceeded.

 

It's easy to prove mathematically:

 

25 x 40 = 250

 

(Smiley face, winking)

Edited June 20, 201510 yr by Alan Quay

The consumption is often expressed as Gross Power, the actual work output as Net Power. Motor efficiencies vary, but the net power at the wheel is generally about 75% of the gross.

 

So that 620 watts example you quote will give a little over 400 watts of power onto the road.

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You're quite right meman -people do confuse the two: our only legal duty, to my knowledge, is to use in public spaces, only those motors rated at 250w or lower by the manufacturer. This means simply that the manufacturer has to declare it capable of 250w or less (their duty is to not overstate, rather than to not understate the power). The fact it is capable of much more does not appear to be of any legal significance!

Edited June 21, 201510 yr by jonathan75

The motor rating doesn't mean much. We now have a 25A version of the 250W Bafang BBS01. 25a x 40v = 1000w.

 

They are labelled 500W, presumably 50% wasted in heat.

Apparently you can now buy 8-Fun BBS01 on aliexpress without the 8-Fun marking. Those are obviously more legal than the ones marked as BBS02 36V 25A 500W

They are labelled 500W, presumably 50% wasted in heat.

Apparently you can now buy 8-Fun BBS01 on aliexpress without the 8-Fun marking. Those are obviously more legal than the ones marked as BBS02 36V 25A 500W

No, they're not labelled 500w. They're labelled 25A 250w.

Will it take 48V (1200W)?

The motor rating doesn't mean much. We now have a 25A version of the 250W Bafang BBS01. 25a x 40v = 1000w.

Really? Where from? I only know of the 15A 250W ones, the 18A 350W ones and some early ones labelled 250W 18A. The 250 and 350 are the same unit with different programming. Mind you, I know some are starting to ship with a proper seal on the non-chainring side instead of the plastic washer to prevent water ingress.

 

Michael

Errrrrr, Bafang?

http://endless-sphere.com/forums/download/file.php?id=169742

 

 

Posted on Endless-sphere:

http://endless-sphere.com/forums/styles/prosilver/imageset/icon_post_target.gifby tahustvedt » Wed Jun 17, 2015 9:40 am

 

Custom adapted by Bafang for a norwegian distributor to perform the same as Bosch, Yamaha and Impulse "250 W" motors. It's limited to 15 A PAS, but the limit is raised to 25 A when a thumb throttle is pressed (which only works while pedaling).

It's a BBS02 but I didn't know they made any marked as 250W. The standard 250W BBS01 already has more pull than the Bosch or Yamaha units (don't know about Impulse). Good to see they are continuing to develop these motors.

that motor is an OEM job. If the OEM specifies 25A 250W then the factory produces exactly for that specs and marks the motor exactly as the OEM asked. It's the responsibility of the OEM to restrict what to send to that motor.

The 250 watt is a continuous rating on the motor, it can most likely run at 500w or so for a short term while climbing a hill but could not stand this all day - hence it is a 250w. Heinzmann quote wattage ratings for time periods - eg 30 mins, 5 mins, & 30 seconds.

In practice no one will ever check if you convert a bike yourself for your own use. A much bigger consideration is the terrain you will be riding (tough hills, moderate hills, or pretty flat like Norfolk & South Lincs) I would select my motor & battery system from this

Right but that continuous rating is a minimum, not a maximum, or?

Right but that continuous rating is a minimum, not a maximum, or?

 

The law says it's the maximum.

 

I don't agree with the conjectures that the higher figure is a short term rating, the issue is not that simple. Many of these "legal" hub motors are capable of running continuously without harm at well over the 250 watts rating. And I'm sure they can do that for the whole capacity of their battery, which is what counts in this respect of legality.

 

These higher powers came about through necessity, early true 200 and 250 watt motors being useless, prompting makers to stretch the interpretation. This just became a fait accompli over time, withthe EU technical requirement for testing making due allowance for that.

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Some law, which is so universally flouted!

 

I think the real thing to have a look at is the new directive, as if the UK legislation doesn't implement it properly then the offending section of the latter can be set aside just like that, shazam.

 

Edit - I think this is the case anyway.

Some law, which is so universally flouted!

 

I think the real thing to have a look at is the new directive, as if the UK legislation doesn't implement it properly then the offending section of the latter can be set aside just like that, shazam.

 

Edit - I think this is the case anyway.

 

In a sense the law is possibly being met, since there's a choice of how to test. One method inherently has room to get higher powers to pass, which is what I meant by "making due allowance".

 

I think we are adopting EN15194 which includes that testing method.

 

The national element comes into this, the very similar Japanese pedelec law has much stricter requirements to meet the 250 watts.

 

Personally I think lattitude is often sensible in laws relating to technical matters, since legislators are not designers, the latter better placed to know what is needed.

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Nor engineers and often not even users. In my book the latter is problem. We saw what happened when the judge knew a little about computers and programming in SCO vs IBM... Even a lot of "experts" are not users...

Some law, which is so universally flouted!

 

The law isn't being flouted. People are trying to interpret in in the way they think it's written, not the way it's actually written. It allows any motor that's rated at 250w continuous output. The three key words are "rated", "continuous" and "output".

 

If a Bafang engineer or any other person authorised and qualified to give a motor a rating decides to rate a motor at 250w continuous output for whatever reason, then it's allowed. Noone has to flout the law.

I may be quite wrong, but I get the impression that it is in fact the controller, not the motor that is important.

A controller set to deliver no more than 7 amps at 36 volts will allow the motor to develop 252 watts.

Up the amps and the wattage goes up.

There is no such thing as a 250 watt motor, simply a motor that will not burn out if run at 250 watts indefinitely.

I may be quite wrong, but I get the impression that it is in fact the controller, not the motor that is important.

A controller set to deliver no more than 7 amps at 36 volts will allow the motor to develop 252 watts.

Up the amps and the wattage goes up.

There is no such thing as a 250 watt motor, simply a motor that will not burn out if run at 250 watts indefinitely.

 

Which is why the EN15194 specified power tests are only for complete pedelecs, not just motors.

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And the only real problem with controllers is that they are not user tamper proof as per EN 15194.

 

When it comes to kits the only ones not playing the game are the people selling the kits. It is so damned easy to spec a kit for the European market - set the controller for one rim size and remove all posibility for the user to access the setup screens. Remove the throttle from the box and don't change the kit price would cover the cost of the above.

I may be quite wrong, but I get the impression that it is in fact the controller, not the motor that is important.

A controller set to deliver no more than 7 amps at 36 volts will allow the motor to develop 252 watts.

Up the amps and the wattage goes up.

There is no such thing as a 250 watt motor, simply a motor that will not burn out if run at 250 watts indefinitely.

You have the right idea, but it's much more complicated than that. You should be considering output power, which will be a lot less than what the controller allows.

 

Consider a typical 20 mph hub-motor with a 15A controller. The motor generates a back voltage as soon as it starts turning. At maximum rpm (20 mph), the back voltage is equal to the battery voltage, so no current can flow, even though the controller would allow 15 amps. You'd have to slow the motor down to something like 10 mph before you can get enough voltage difference to get 15A from the controller, but at that speed, efficiency is only about 60% is only giving about 320w of output power. Any slower and the efficiency goes right down, so you'll struggle to get 250w out of your motor when hill-climbing.

 

Once you get over 10mph, your efficiency starts to rise, but your current is ramping down because the net voltage is decreasing. You might only get 8 amps at 15 mph where the efficiency would be at its 80% maximum, so that's 36mx 8 x 0.8 = 230w output power.

 

If you were to measure continuous power, at what speed would you measure it? The power output is zero at zero speed. It ramps up to a macimum at about 50% to 70% of maximum rpm, then it ramps back down to zero at maximum speed. If you averaged it over the whole rpm range, it would be about half the maximum.

 

There's no test for maximum continuous rated power output because of all these factors. All the tests are to prove that the motor hasn't been over-rated, so they run it at the rated power continuously and check that it doesn't overheat.

 

These calculations are even more complicated with a crank-drive motor. It behaves the same as a hub-motor, but instead of the current and efficiency being related to bike speed, they're related to cadence.

The law isn't being flouted. People are trying to interpret in in the way they think it's written, not the way it's actually written. It allows any motor that's rated at 250w continuous output. The three key words are "rated", "continuous" and "output".

 

If a Bafang engineer or any other person authorised and qualified to give a motor a rating decides to rate a motor at 250w continuous output for whatever reason, then it's allowed. Noone has to flout the law.

 

I defer to you in all matters to do with engineering but everything you've said just doesn't hold, without reference to the precise wording of the legislation.

All I'm getting on this page is hearsay.

 

If you're right that rated, continuous, and output are the words used, then you're correct - but only partly.

 

Only as a matter of practice, seemingly, does 'rated' for pedelecs mean in law 'rated by any method', and for pragmatic reasons: if 'rated' were to mean, as flecc implies, 'rated by a justifiable method', then the consequence would be the destruction of the ebike industry, because people wouldn't want the puny bikes which would be all that were permitted. But the meaning of the word 'rated' will not be tested in court because all the bureaucratic parties are too sensible for that.

I'm in the process of considering an e-bike conversion & have been reading up as much as I can. I came across the thread from 2012 discussing the UK law & power ratings of motors.

I'm no expert but I think some are confusing the power rating of the motor with power consumption. Someone said that their 250 watt rated motor was reading 620 watts on the 'Cycle Analyst' display when they were going up hill using maximum power setting. As I understand it (40 years after leaving school where I should have learnt it!) the 620 on the readout was the consumption rate of the available power. A 36 volt X 10Ah battery = 360 watt hours of available energy so a reading of 620 indicates that that level of power consumption could be available for just 35 minutes. Remember there is a huge difference between maintaining a steady slow speed on the level, and climbing a hill quickly - try doing it without a bike! As a sufferer of ME / post viral fatigue I'm very aware that the weaker you are, the more noticeable the difference in energy requirement is between say, level walking & uphill running. The same applies to motors; a low voltage motor may not be able to drive up more than a gentle gradient but be capable of sustaining some distance on the level - think mobility scooters and vintage cars. A powerful modern car might be capable of spectacular acceleration and pulling power but it will not go further because it uses up more of its stored energy in the fuel tank.

 

As of 1st January 2016 REGULATION (EU) No 168/2013 states an EAPC as being exempt if under article 2 :

 

(h)

 

pedal cycles with pedal assistance which are equipped with an auxiliary electric motor having a maximum continuous rated power of less than or equal to 250 W, where the output of the motor is cut off when the cyclist stops pedaling and is otherwise progressively reduced and finally cut off before the vehicle speed reaches 25 km/h;

 

and defines maximum continuous rated power under article 3 as:

 

(35)

 

‘maximum continuous rated power’ means the maximum thirty minutes power at the output shaft of an electric engine as set out in UNECE regulation No 85;

 

UNECE regulation No 85 states:

 

5.3. Description of tests for measuring the net power and the maximum 30

minutes power of electric drive trains

The electric drive train shall be equipped as specified in Annex 6 to this

Regulation. The electric drive train shall be supplied from a DC voltage

source with a maximum voltage drop of 5 per cent depending on time and

current (periods of less than 10 seconds excluded). The supply voltage of the

test shall be given by the vehicle manufacturer.

Note: If the battery limits the maximum 30 minutes power, the maximum

30 minutes power of an electric vehicle can be less than the maximum

30 minutes power of the drive train of the vehicle according to this test.

 

5.3.1. Determination of the net power

5.3.1.1. The motor and its entire equipment assembly must be conditioned at a temperature of 25 °C ± 5 °C for a minimum of two hours.

5.3.1.2. The net power test shall consist of a run at full setting of the power controller.

5.3.1.3. Just before beginning the test, the motor shall be run on the bench for three

minutes delivering a power equal to 80 per cent of the maximum power at the

speed recommended by the manufacturer.

5.3.1.4. Measurements shall be taken at a sufficient number of motor speeds to define

correctly the power curve between zero and the highest motor speed

recommended by the manufacturer. The whole test shall be completed within

5 minutes.

 

5.3.2. Determination of the maximum 30 minutes power EN L 323/58 Official Journal of the European Union 7.11.2014

5.3.2.1. The motor and its entire equipment assembly must be conditioned at a temperature of 25 °C ± 5 °C for a minimum of four hours.

5.3.2.2. The electric drive train shall run at the bench at a power which is the best estimate of the manufacturer for the maximum 30 minutes power. The speed must be in a speed range, which the net power is greater than 90 per cent of the maximum power as measured in paragraph 5.3.1. This speed shall be recommended by the manufacturer.

5.3.2.3. Speed and power shall be recorded. The power must be in a range of ± 5 per cent of the power value at the start of the test. The maximum 30 minutes power is the average of the power within the 30 minutes period.

 

 

Edit: additional text for net power added

Edited June 24, 201510 yr by shemozzle999