Newbie considering an e-conversion. But what.

[vidtek]

That's not true at all. There is no limit on output power for ebikes in the UK. It's a myth based on a misunderstanding of the rules. The standard specifies that the motor must be "rated" at no more than 250w. How much power you put through it is up to you, and there is no rule as to how the motor is rated other than that it mustn't burn at 250w. There are very few ebikes on the road in the UK that don't produce more power than 250w. 400w to 500w is typical of most legal ebikes. Some (legal) are much higher.

@vfr400
No. As far as the authorities are concerned, the motor must be rated at 250w with a stamp or sticker on the motor certifying that fact.
Any spin you put on it does not alter that.

 

[danielrlee]

@vfr400
No. As far as the authorities are concerned, the motor must be rated at 250w with a stamp or sticker on the motor certifying that fact.
Any spin you put on it does not alter that.

It's easy to become confused by conflicting opinions on the matter, but VFR is correct. The 250W rating as defined by EN15194 refers to a motor's 'maximum continuous rated power'. However, there is no limit placed on the actual power supplied to the motor from the controller.

 

[vidtek]

It's easy to become confused by conflicting opinions on the matter, but VFR is correct. The 250W rating as defined by EN15194 refers to a motor's 'maximum continuous rated power'. However, there is no limit placed on the actual power supplied to the motor from the controller.

You try telling that to the authorities after an accident on an e-bike with 1000w motor without a 250w sticker---good luck with that one.

 

[vfr400]

@vfr400
As far as the authorities are concerned, the motor must be rated at 250w with a stamp or sticker on the motor certifying that fact.

You've just copied what I said. "Rated" was missing from your previous post. "Rated" power is independent of actual power. It just means mustn't burn at that power. A motor capable of and running at 1000w will pass any 250w rating test. Rating is an arbitrary engineering term. Engineers can decide how much safety margin they allow when they rate something. Ebike motors have very difficult circumstances to deal with, so any self-respecting engineer would rate at 50% of peak power or lower, which AFAICS is about what they choose.

 

[danielrlee]

You try telling that to the authorities after an accident on an e-bike with 1000w motor without a 250w sticker---good luck with that one.

Sorry, I do not understand the point that you are trying to make, or who you are arguing with. A 1000W rated motor is not permitted under EN15194. A 250W rated motor being supplied 1000W by the controller is perfectly legal, as long as it conforms to all the other rules stipulated by EN15194.

 

[vfr400]

Let's make it as clear as I can, as this is about choosing a motor for an ebike conversion. You can use any motor that has a manufacturerss' label or stamping of rated power 250w or lower. They normally leave off the "rated", so it'll just say 250w, but everybody accepts that as the rated power. You can also choose any other motor from a listing that says 250w or has a certificate from the manufacturer that says the rated power.

Once you have the motor in your hand, you can do what you like with it regarding how much power you feed it and get out of it. there is no legal requirements covering that other than it needs to be safe.

Some manufacturers supply motors or kits with very powerful "250w" motors if you know where to look. Two examples are the 48v hub-motor kit from Woosh and the "high torque" version of the 250w BBS01 (actually BBS02) sold by Brighton Bikes.

The thing about ebikes is that you generally want a nice balance of weight, power, handling and convenience, otherwise the bike can be unpleasant to ride. For a hub-motor it's most important to get one with the right Kv rather than a high power one. A middle-sized hub-motor with 48v and 15amps will give enough power for most people's needs, yet still allow the bike to have a weight of under 20kg with a battery that can give a decent range.

 

[Bikes4two]

• At the risk of being boring, can I dwell a bit more on the 250w thing please?
• The wording in EN15194 is or is similar to "The maximum continuous rated power of the electric motor must not exceed 250 Watts "
• Can it be assumed from this that if a motor can deliver more than 250w continuously, then that motor is outside the legal limit of that EN? I assume this because of the wording "must not exceed"
• So a rating label on a motor can say anything the printers want it to say (and 250w labels are easy to buy from ebay) but if that motor can by virtue of its design sustain (as in continuously) deliver more than 250w without burning out, then its not within the EN legal limit surely?

Stands back for the comments .............

 

[Nealh]

Lets put it another way if the rating was max continuous 250w and no more then 250w what so ever then practically every ebike sold will be illegal that includes Bosh, Yamaha all mid drive bikes and all hub bikes

 

[Bikes4two]

Lets put it another way if the rating was max continuous 250w and no more then 250w what so ever then practically every ebike sold will be illegal that includes Bosh, Yamaha all mid drive bikes and all hub bikes

No, not 'what so ever' but continuous rating.

The wording is about not exceeding a continuous power output, not peak/occasional/now and then.

I agree that if you stick the extra (above rated) volts in then the power out is much more than the nominal rating, but would such a motor maintain continuous operation under such conditions? If it would then its continuous rating is more than 250w and thus above the EN limit.

Then of course, what is the definition of continuous as in time duration, ambient temperature etc?

Plus which enforcement authority is going to be checking it anyway!

Just trying to tease out a better understanding here.......

 

[Nealh]

Continuous or the rating is what ever the manufacturers put on the label. 250w/350w are identical 99.9% only the rating is different for the markets.
In the UK/EU and a lot of other countries esp down under 250w is the mark for the US esp then 350w is the mark.

 

[vfr400]

No, not 'what so ever' but continuous rating.

The wording is about not exceeding a continuous power output, not peak/occasional/now and then.

I agree that if you stick the extra (above rated) volts in then the power out is much more than the nominal rating, but would such a motor maintain continuous operation under such conditions? If it would then its continuous rating is more than 250w and thus above the EN limit.

Then of course, what is the definition of continuous as in time duration, ambient temperature etc?

Plus which enforcement authority is going to be checking it anyway!

Just trying to tease out a better understanding here.......

You can't leave out the word "rated". Rated means what the design engineer decides and orders to be put on the label or listing. When the engineer does the rating, they have to take into account the durability of the motor as well as the temperature stability, so any self-respecting engineer would leave a sizeable safety margin. For buildings and structures, it used to be 300%, but that's probably come down now that computers can anayse better. If I were designing a motor, I'd leave at least 100% safety margin.

Incidentally, the standards used to mention maximum continuous output power, but they changed it to add the word "rated" because max continuous power cannot be defined without specifying the conditions. You have to remember that ebikes have to go up hills, sometimes with heavy people on them, and they have to work at different speeds, and efficiency changes with speed, so would you say maximum continuous power when going slowly up a hill, at a steady 12 mph, at 15.5 mph or all of them.

Also, there is no test for "maximum continous rated power". What would be the pass criteria?

All this is academic. Nobody needs to understand it. All you need is a 250w manufacturer's label on the motor.

I was recently involved in a case where the police seized an e-trike from a larg fleet owner after they did some ad hoc power measurement and came to the conclusion that the motor was more than 250w. I wrote a letter for the owner, which was given to his lawyer and then presented to the police. He got his bike back immediately with an apology. The motor was capable of driving a milk float, but it had a manufacturer's label that clearly stated that it was 250w and 25km/h max speed. In this case, the manufacturer considered durability to be more important than temperature when they did the rating, as the trike was designed for fleet owners commercial use rather than occasional/leisure use.

 

[Bikes4two]

@vfr400 -

All this is academic. Nobody needs to understand it. All you need is a 250w manufacturer's label on the motor.

You're right, it is just academic as knowbody has defined the 'continuously rated' parameters and how to measure them and I absolutely agree with the label notion.

The law is often an ass and this pedelec parameter (of 250w) is another example. But hey, wouldn't a perfect world be boring?