Ebike still legal if I run 36V motor at 48V and limit speed to 15mph?

[WheezyRider]

It's very complicated, but can be explained in simple terms. When you use 75% throttle, the controller reduces the power with its PWM, which effectively reduces the voltage supplied to the motor, so at 75% throttle, the effective voltage might be reduced from 48v to 36v, so the motor behaves exactly the same as it would at full throttle and 36v.

The controller doesn't reduce the voltage, it shortens the pulses, so the average current to the motor is lower (PWM = Pulse Width Modulation).

 

[WheezyRider]

They already do that. It's been going on for 10 years or more. The same motors can be stamped 180w, 250w or 350w depending on where they're sold. There have been many identical motors, but with different software in for different motors.

Just consider this. When Bosch started, they stated that their motor gave around 40NM and had a max speed of 25km/h. Their latest Gen 4 CX gives 75NM and has a max speed of 25km/h.

Power = torque times rotation speed. If they're both 250W, how can 40 x 25 = 75 x 25? Go figure! That's why they only ever mention torque in their list of performance characteristics. If they listed the actual maximum power output of around 600W, people might start asking questions.

It's probably to keep up with the Chinese manufacturers who are happy to print whatever numbers they can to sell their product.

 

[Gavin]

how do you define a 1KW motor?

how do you define a 1KW motor?

Well call me simplistic, but I would define it as 1kw delivered at the output shaft of the motor. But I suspect in the world of ebikes, it's not that simple!

Just consider this. When Bosch started, they stated that their motor gave around 40NM and had a max speed of 25km/h. Their latest Gen 4 CX gives 75NM and has a max speed of 25km/h.

An interesting point VFR. So as you all know the industry far better then me....How have Bosch managed to get the latest motor certified? Who does their certification? A third-party lab or do they do it in-house?

 

[vfr400]

Interesting fact that not a lot of people know. The Bosch motors are only run with 24v. The electronics somehow cuts down the 36v. If you remove the electronics and use a normal 36v controller, the motor's rotation speed increases by 50%, so instead of an optimal cadence of around 80 rpm, the optimum goes up to 120 rpm and maxes out at 180 rpm.

 

[WheezyRider]

Interesting fact that not a lot of people know. The Bosch motors are only run with 24v. The electronics somehow cuts down the 36v. If you remove the electronics and use a normal 36v controller, the motor's rotation speed increases by 50%, so instead of an optimal cadence of around 80 rpm, the optimum goes up to 120 rpm and maxes out at 180 rpm.

Interesting...you'd think that would introduce significant inefficiency. Do you think the dongles people sell for Bosch bikes bypasses the voltage step down process?

 

[Gavin]

"The DfT and Police are aware that electric bikes currently sold and used in the UK are fitted with 250W motors, they do not intend to become involved in prosecuting those that sell or ride them. The use of an "Off Road Button" however is strictly forbidden now and is specifically mentioned in documents appertaining to new and existing guidelines."

Note the word "use", not fitment.

Thanks for coming in @flecc, a useful addition to the debate. I note you stress the word "use" and see the point you're making.

However the link here....

UK electric bike usage law

Please note that the laws governing use of electric bikes on UK roads can be found here. In particular: Derestriction, ‘off-road’ switches or modes and dongles The Department of Transport say that electric bikes fitted with off-road switches or modes, that enable a bike’s motor to continue...

www.pedelecs.co.uk

....uses the phrase"bikes fitted with off-road switches or modes". Note use of the word "fitted", implying that the mere fitment of an off-road switch (even if you don't use it) renders the bike illegal.

I'd welcome your (or anybody else's) thoughts, 'coz I'm confused!

 

[vulcanears]

There's no flaw in your thinking. The 48v allows a higher speed and allows you to run with less current for the same power output. If you supply the same current to each motor, the 48v one will make more torque and power. If you select settings that make voltage x current the same, then they behave the same. That's a generalisation. At low speed, you have to consider efficiencies, and at high speed, the 48v will always have the advantage.

Thank you for your detailed explanation!
I will be going 15mph most of the time, so is there any way to quantify the "inefficiency" of a 48V system at a low speed?

 

[vfr400]

The controller doesn't reduce the voltage, it shortens the pulses, so the average current to the motor is lower (PWM = Pulse Width Modulation).

I said it "effectively" reduces the voltage, not "actually" reduces the voltage. I chose that word carefully because people argue both ways. With a 50% duty cycle, the average voltage is V/2 and current is constant, or you can argue that the voltage is constant and that the average current is I/2. In reality, its nothing like that because of capacitance, inductance, reactance and phase shifts. Sometimes we have to use simple explanations for simple problems.

 

[vfr400]

It's probably to keep up with the Chinese manufacturers who are happy to print whatever numbers they can to sell their product.

It's not the Chinese. Bosch, Panasonic, Shimano, Brose, Ultramotor, Bionx, Heinzmann and a load more are all at it.

Who can remember the 250W (might have been 200W) Heinzmann system with a 28A controller at 36V?

 

[flecc]

Thanks for coming in @flecc, a useful addition to the debate. I note you stress the word "use" and see the point you're making.

However the link here....

UK electric bike usage law

Please note that the laws governing use of electric bikes on UK roads can be found here. In particular: Derestriction, ‘off-road’ switches or modes and dongles The Department of Transport say that electric bikes fitted with off-road switches or modes, that enable a bike’s motor to continue...

www.pedelecs.co.uk

....uses the phrase"bikes fitted with off-road switches or modes". Note use of the word "fitted", implying that the mere fitment of an off-road switch (even if you don't use it) renders the bike illegal.

I'd welcome your (or anybody else's) thoughts, 'coz I'm confused!

Thanks for coming in @flecc, a useful addition to the debate. I note you stress the word "use" and see the point you're making.

However the link here....

UK electric bike usage law

Please note that the laws governing use of electric bikes on UK roads can be found here. In particular: Derestriction, ‘off-road’ switches or modes and dongles The Department of Transport say that electric bikes fitted with off-road switches or modes, that enable a bike’s motor to continue...

www.pedelecs.co.uk

....uses the phrase"bikes fitted with off-road switches or modes". Note use of the word "fitted", implying that the mere fitment of an off-road switch (even if you don't use it) renders the bike illegal.

I'd welcome your (or anybody else's) thoughts, 'coz I'm confused!

There are several relevant aspects:

First this is DfT guidance so not the law, and the DfT have been known to get their guidance wrong in the past. Note that this conflicts with their previous guidance saying use and not fitment and the use of button and/or switch is confusing

In a court only the law and its spirit of what parliament intended counts.

As a general rule in the UK it is not illegal for anyone to sell items which are illegal to use, hence we have sellers of various illegal vehicles like mini-motos and Segways, cars capable of speeds double and more our maximum limits. The UK legal custom is to specifically ban any item we really don't want sold, for example illegal drugs, certain types of guns and other weapons, and toys which are dangerous.

It follows that some thing legal to sell (despite being illegal to use) cannot of itself be illegal. Ergo, pedelecs with off road switches are not illegal and that DfT guidance is wrong. Someone must be caught riding the pedelec so equipped before they can be prosecuted. Then it becomes a matter for legal argument whether such a pedelec is illegal even when the defeat facility isn't used.

The outcome of that would depend in part on the wording of the 1983/2015 EAPC regulations and the wording of the exemption in 168/2013 EU (and now UK) law on type approval.

My opinion is that if sold as legal and legally compliant at point of delivery, a rider could not be successfully prosecuted if they hadn't used the defeat facility, since no intent is shown.
.

 

[vfr400]

There is no maximum out put in EN15194 for EPAC's. The motor must be rated for 250w continuous without overheating which is different from one running at a higher output.

EN15194 isn't a legal requirement. Under our law, overheating isn't mentioned, but it wouldn't surprise me if they could get you on reckless cycling or something like that if your over-powered DIY bike caught fire and did some damage. I can't see a situation where the police come along and stick a thermometer on your motor. "Ello, ello, ello! Your motor's running a bit hot sir. Contrary to The Road Traffic Act 1988 Section 28 that specifically makes it an offence to ride a bike in a condition that could injure someone, namely you if you were accidentally to touch the motor with your bare hand, I hereby arrest you".

 

[flecc]

EN15194 isn't a legal requirement.

It is in the UK. Oddly only two EU countries adopted this EU regulation, France and the UK, and it's now incorporated into UK law through the 2019 Great Repeal Bill to prepare for EU departure.
.

 

[vfr400]

Well call me simplistic, but I would define it as 1kw delivered at the output shaft of the motor. But I suspect in the world of ebikes, it's not that simple!




An interesting point VFR. So as you all know the industry far better then me....How have Bosch managed to get the latest motor certified? Who does their certification? A third-party lab or do they do it in-house?

They're is only one rule when it comes to rating a motor: When the motor is run at its designated rating it mustn't overheat. That means that there's nothing to stop a company under-rating their motor. The certification system only checks whether the motor is rated at 250w or below, not how or why it's rated at that.

To be fair, the rating has to take into consideration the worst case scenario. I think it's fair to say that if most motors were run under the extreme conditions of heavy rider and a very steep hill, the "250w" motors would overheat, which implies that they're over-rated rather than under-rated.

 

[Gavin]

There are several relevant aspects:

First this is DfT guidance so not the law, and the DfT have been known to get their guidance wrong in the past. Note that this conflicts with their previous guidance saying use and not fitment and the use of button and/or switch is confusing

In a court only the law and its spirit of what parliament intended counts.

As a general rule in the UK it is not illegal for anyone to sell items which are illegal to use, hence we have sellers of various illegal vehicles like mini-motos and Segways, cars capable of speeds double and more our maximum limits. The UK legal custom is to specifically ban any item we really don't want sold, for example illegal drugs, certain types of guns and other weapons, and toys which are dangerous.

It follows that some thing legal to sell (despite being illegal to use) cannot of itself be illegal. Ergo, pedelecs with off road switches are not illegal and that DfT guidance is wrong. Someone must be caught riding the pedelec so equipped before they can be prosecuted. Then it becomes a matter for legal argument whether such a pedelec is illegal even when the defeat facility isn't used.

The outcome of that would depend in part on the wording of the 1983/2015 EAPC regulations and the wording of the exemption in 168/2013 EU (and now UK) law on type approval.

My opinion is that if sold as legal and legally compliant at point of delivery, a rider could not be successfully prosecuted if they hadn't used the defeat facility, since no intent is shown.
.

@flecc- thanks for this. I'm sure you (and the others) have all heard my questions a million times before from other confused people but as it's all new to me, thanks for your patience...

 

[scott gaza]

Hi if you look at the simulator the wattage at 15mph on the 36 v is around 100w compared to the 700w on the 48v i changed the wheel size to 26" so i can verify with my own real-world set up
https://www.ebikes.ca/tools/simulator.html?motor=MG310_STD&cont=C25&hp=100&grade=0&wheel=26i&cont_b=C25&motor_b=MG310_STD&wheel_b=26i&grade_b=0&bopen=true&batt_b=B4816_GA&axis=mph&black=load&kv=6.33&kv_b=6.33

 

[flecc]

@flecc- thanks for this. I'm sure you (and the others) have all heard my questions a million times before from other confused people but as it's all new to me, thanks for your patience...

No problem, the questions keep me on my toes and brain working, important in my mid eighties.

You know the saying, use it or lose it.
.

 

[vulcanears]

Hi if you look at the simulator the wattage at 15mph on the 36 v is around 100w compared to the 700w on the 48v i changed the wheel size to 26" so i can verify with my own real-world set up
https://www.ebikes.ca/tools/simulator.html?motor=MG310_STD&cont=C25&hp=100&grade=0&wheel=26i&cont_b=C25&motor_b=MG310_STD&wheel_b=26i&grade_b=0&bopen=true&batt_b=B4816_GA&axis=mph&black=load&kv=6.33&kv_b=6.33

You left the throttle at 100%. If I adjust the throttle to get to 15mph on both systems, both end up at "Electrical power = 86W". Am I using this incorrectly?

"Using the Throttle Slider

Many people overlook the fact that there is a throttle slider and only bother looking at the full throttle output, and come to incorrect conclusions related to 'efficiency' and 'sweet spot'. If you want to see how a system behaves at slower speeds, which is achieved in practice by backing off on the throttle, then move the throttle slider to less than 100% or choose the "auto" checkbox and then click on the graph at the lower speed you want to simulate."

 

[vfr400]

Hi if you look at the simulator the wattage at 15mph on the 36 v is around 100w compared to the 700w on the 48v i changed the wheel size to 26" so i can verify with my own real-world set up
https://www.ebikes.ca/tools/simulator.html?motor=MG310_STD&cont=C25&hp=100&grade=0&wheel=26i&cont_b=C25&motor_b=MG310_STD&wheel_b=26i&grade_b=0&bopen=true&batt_b=B4816_GA&axis=mph&black=load&kv=6.33&kv_b=6.33

That's because system B is accelerating hard and sytem A is more or less at constant speed. Remember, both are at full throttle, but the 36v system is starting to max out and its current has already been cut down to 9.5A from 25A because of the back emf, while as the 48v one still gets 24.1 amps.

 

[scott gaza]

sorry the simulator is not real life unless you had true voltage control you would see a much higher current draw at lower speeds than they show. https://www.ebikes.ca/tools/simulator.html?motor=MG310_STD&cont=C25&hp=150&grade=0&wheel=27.5i&cont_b=C25&motor_b=MG310_STD&wheel_b=27.5i&grade_b=0&bopen=true&batt_b=B4816_GA&axis=mph&black=load&kv=6.33&kv_b=6.33&hp_b=150&throt=79&throt_b=79 your voltage fully charged is about 25- 30% more than it is when discharged and yes you are right 30v is the sweet spot on a 205rpm at 15mph total saturation

 

[vfr400]

sorry the simulator is not real life unless you had true voltage control you would see a much higher current draw at lower speeds than they show. https://www.ebikes.ca/tools/simulator.html?motor=MG310_STD&cont=C25&hp=150&grade=0&wheel=27.5i&cont_b=C25&motor_b=MG310_STD&wheel_b=27.5i&grade_b=0&bopen=true&batt_b=B4816_GA&axis=mph&black=load&kv=6.33&kv_b=6.33&hp_b=150&throt=79&throt_b=79 your voltage fully charged is about 25- 30% more than it is when discharged and yes you are right 30v is the sweet spot on a 205rpm at 15mph total saturation

The current is limited to 25A by the controller!.