What does the legal rating of 250w continuous actually mean exactly?
Posted by catboy519@reddit | ebikes | View on Reddit | 33 comments
I guess its defined indirectly as "if motor doesnt overheat from 251w continuous then its illegal"
But that doesnt make sense. Watts alone say almost nothing about how warm a motor will get. * RPM (going slow at 250 watts makes more heat than going fast with 250 watst) * Wind, * Ambient temperature
So 2 identical motors, one might overheat at 200 watts while the other can run at 500 watts continuously with no problem.
So then what does this law possibly mean, and how can it ever be enforced?
My bike is officially certified by the EU norms and it has the 250w sticker, placed by the manufacturer, too. But I know my motor can run more than 250 watt continuously. Not just peak power - It can run 300+ watt for an half hour long atleast in a row.
Does the law specify a specific testing condition for cops, where they need to test with a specific RPM/speed/weather/inside/outside ?
Ok-Reindeer5858@reddit
Watts is a power output, just like horsepower.
Just-Smart-Enough@reddit
Yeah, that's the easy part. Problem here is that the law generally stipulates nominal power, and there's a whole bunch of uncontrolled environmental factors that go into determining that.
Ok-Reindeer5858@reddit
None of those environmental conditions would increase the power output
Just-Smart-Enough@reddit
Re-read all of my words, especially where I reference steady state temperature. That takes much less power to reach when it's 40c out.
Ok-Reindeer5858@reddit
Have you designed a motor controller before?
Just-Smart-Enough@reddit
Yes.
Ok-Reindeer5858@reddit
Good so I assume that you understand it’s the controller limiting output power, not the motor. And since these are cheap, the mechanism of control is current feedback and back emf to determine rpm. From that, the controller can limit power to a specific number, which has nothing to do with the motor itself.
The law is enforced by an officer putting the bike on a dyno
Just-Smart-Enough@reddit
At the system design level, nominal power is constrained by thermal limits.
This is a fundamental property of an electric drive system.
Ok-Reindeer5858@reddit
Sure that’s one of the things that can constrain it. It can also be constrained by battery impedance, local laws, etc
Just-Smart-Enough@reddit
Cell impedance gives you voltage sag and heat, and if you increase current to maintain consistent power, potentially too much heat. Completely consistent with my earlier definition.
Manufacturers can choose to artificially limit power output below system nominal for any number of reasons, but that's a separate issue.
catboy519@reddit (OP)
Coolerweather = more power needed to overheat the motor.
Ok-Reindeer5858@reddit
That’s not how motor controllers work. It’s likely a current based controller since they’re cheap. So based off a maximum voltage and a controller current, you can calculate a maximum power.
catboy519@reddit (OP)
Thats peak power. We are talking about the nominal eating of the mooryor Mitot Motor I meant
Ok-Reindeer5858@reddit
Ok bud
catboy519@reddit (OP)
Yep!!
Just-Smart-Enough@reddit
Well, for starters, it's determined under specified lab conditions, not in the wild. I've seen it defined as the maximum power that will keep the max system temperature below 80C in 25C ambient still air. I've also seen it defined as max sustainable power for one minute- i.e. there's no standard, though I suspect one will come before too long.
catboy519@reddit (OP)
And ehat about the motor RPM? Coz that matters too.
Just-Smart-Enough@reddit
Under lab conditions, you shoot for the most efficient RPM, which would have already been characterized on a dyno.
Infinite_Ad_9106@reddit
Your mixing power watts consumption with power delivered by the motor. Also the law is clear that the limit is not peak power but rather what is produced continuously.
They way i read it, it's simple, you need to have an approved 250W continuous motor, which you claim you have. As consumer you just need to worry about making sure the motor is certified with the EN15194 standard. Provided that the system was not tinkered with, i don't see why the police would be questioning an approved vehicle.
This said, the law is very clear about the expected behaviour of such vehicle. The motor should work together pedal assistance and never exceed 25km/h. If you are caught at 40 km/h while not pedalling this will raise questions, the power the motor is making is not relevant here.
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 pedalling and is otherwise progressively reduced and finally cut off before the vehicle speed reaches 25 km/h;
catboy519@reddit (OP)
That answers my question. So if the ebike is certified by the norms in the factory, and a cop tests the motor which then runs at 300 watts for an hour, I should be good still?
Infinite_Ad_9106@reddit
EN15195 dictates the rules and conditions to have these motors tested and approved. It's hundreds of pages long. Unless the there is some visible after purchase manipulation I don't see how the police could even test it.
catboy519@reddit (OP)
Im just asking because ive seen some news where apparently the police tests power of ebikes and gives fines for it, which seems very strange.
4look4rd@reddit
I can output 400w or more in the rower for brief moment, but I’m closer to 180w continuously for any meaningful amount of time.
Motors are the same way, pretty sure my Bosch mid drive is outputting close to 1000w on my uphill climb, but it won’t do that continuously without lowering output.
Hungry_Orange666@reddit
EU norms specifie condition for electrical motor rated power, IEC 60034-1.
But they only mean that motor rated as 250W has to be able to deliver that much power without overheating.
There are no rules for sale of underated motor in EU laws, it's just uneconomical for manufacturers to offer stronger motor for price of weaker. Nobody though about motor power limiting laws, when motor power rules where created.
geekroick@reddit
It's a nominal, theoretical figure. We could describe a car or motorcycle as being able to travel at 60mph and that being its nominal speed. It doesn't really give us an indication of the maximum possible speed (or wattage, in this case) available. It's just a typical, workable figure that has become the default way to measure electric motor power.
A 250w rated ebike motor could easily top 600 or 700w at maximum assist levels. So you're right, it doesn't really make sense.
(The maximum amount of power going into the motor would be governed by the specific attached controller anyway - it's certainly possible to overwork a motor if it's connected to a more powerful controller.)
"250w continuous" is just that - it's deemed to be a figure at which that motor can run indefinitely without problems. Putting, let's say, 1000w through a 250w rated motor may increase the speed and torque of the motor for a while... But sooner or later it's going to burn out, because that motor just wasn't designed for that much continuous power.
How can this be enforced? Realistically, with great difficulty. What is far easier to measure is speed - so it depends on your local laws as to whether this is a factor in conjunction with motor power or not. (I don't think there's anything in legislation anywhere that specifies exactly how wattage should be measured.)
If the local requirements are that ebike motors are limited to 250w and 15mph, for example, is anyone going to care that you're actually doing 15mph using a 500w motor? Of course not. But they will if you're doing 30mph with it.
How would you be caught? It's all theoretical tbh - if you choose to use an ebike that is not legal in conjunction with your local laws then you only have a problem when... you have a problem.
Maybe your local police don't care about ebikes. Maybe they've been told they have to care about them. Maybe they do random checks where they pull over everyone on an ebike and see how fast their bikes will go. Maybe you just get stopped by a cop who hates ebikes. Maybe you never get stopped at all. 🤷
Keljian52@reddit
Continuously is a challenging thing to categorise - Long story short: a motor (and controller) that can sustain >250W output for over 10 minutes is fine, if it's only limited to 250W/10 minutes in most places of the world.
DonnPT@reddit
It doesn't mean anything, really. I mean, it does tell you that the motor can handle 250W, but they're all like yours, able to handle more than the power rating. It's just a number they arrive at arbitrarily.
The realest number, is determined not by the motor but by controller and battery. 48V battery × 20A = 960W (in principle - voltage will sag as you run it up there.) Very likely that can't be sustained for long, and that does depend on the motor.
Zenigata@reddit
The law has nothing to do with temperature and motors overheating, its all about the amount of power delivered to and put out by the motor.
I have an eu legal tongsheng tsdz8 motor which i believe is available in way more than 250w in much of the world. To be street legal in the uk however it had been governed down to 250. It could be hacked to deliver more than that without overheating as the motor is built for more.
Adorable_Wolf_8387@reddit
It's the power the controller delivers to the motor. A motor rated for 100kW could be limited to be run at 250W.
catboy519@reddit (OP)
Pretty sure its not that. The law says nothing about a controller and doesnt even mention the word controller.
DonnPT@reddit
Yes, but more importantly, the motor probably isn't limited to run at 250W.
Adorable_Wolf_8387@reddit
It absolutely is.
catboy519@reddit (OP)
Source? Because the law ive read mentions "the motor has a max power of 250 watt". Now since a motor doesnt necessarily have a peak power limit because thats controlled by the controller they must be talking about nominal. I believe thats even the explicit or implicit law too.