Best Value Electric MTB

[Wisper Bikes]

d8veh has pointed this out for years, the wattage on the motor is what the manufacturer puts on the label.

For members who don't know much about e-bikes, how good the bike will climb up Park Street, Bristol depends on two factors: the power that the controller lets through and what type of motor it has. In this case, 15A and geared motors. Raise the maximum continuous output of the controller to 20A, the same bike will pull better. Change the type of motor to crank drive, the bike will also climb better.

There is no doubt that the more powerful the motor the easier the climb up Park Street will be. The question is whether a motor the can run continuously at 36V 15A is legal? Would a rider on such a vehicle be liable to lose their driving licence if caught? If they were involved in a
RTA and the bike was tested was more than 250 W continuous what would the legal position be?

 

[trex]

yes, if the manufacturer says it is.Ask d8veh.
Its assisted speed is of course legally limited to 25kmph.
All the rider has to do is to keep rotating the cranks to be legal, the rest can be done by the bike, no matter how steep the hill is.

 

[anotherkiwi]

My controller has printed on it "7 Amp nominal, 14 Amp peak" it is of course able to deliver peak Amps for a very long time... Especially with a 10.4 Amp battery that is 2C nominal and 3C peak. I think that is why the Ciclotek site mentions the kit as "Road legal", their quotation marks...

I am back to playing (illegally, naughty boy ) with top speed and have discovered that the sweet spot may be 33 kph for my motor. At 45 kph the motor was never drawing over 250 Watts. At 35 kph it draws up to 480 Watts and my previous testing at 33 kph it draws 540 Watts or "peak" power. At 27 kph (25 + 10% so a legal speed ), now that I am fit, the cut out comes just a little too soon. With the cut out at 35 kph I can pedal up to 40-45 kph with ease on the flat after motor cut out. I get strange looks from drivers who are now following me when the light goes green .

Next test: GPS verifying that the above speeds are not too optimistic on the LCD. I have a feeling that I may be 3-4 kph off which will also dampen my enthusiasm about distances achieved on a full charge...

 

[Deleted member 4366]

When the controller says 15 amps, that's normally the maximum. They would be rated at 7A, though they often don't have that written on them. Even though a controller allows a maximum of 15A, the motor only gets it when going slowly. The current to the motor in the top half of its speed range depends on its speed and the voltage because the current will be less than the controller's maximum.

To answer the question of the legality of a controller that would be supplying 15A continuous. It would be legal because there is no limit on the controller. The limits are 48v for the battery and a motor with a "rated continuous output" of no more than 250w. There is no specified method on how the motor is rated. Once rated, there's tests specified to determinewhether the motor can reach that rating, but no test to limit how far it exceeds it.

I'm pretty sure that the Dapu motor in both those bikes, and many others, could be rated much higher than 250w.

As I've said before, many people have in their minds that there's a 250w limit on motors' output. That's a wrong interpretation of EN15194. Nobody is cheating or deceiving anybody. It's allowed to have a high-torque motor running with whatever current you want provided that it won't catch fire or burn out.

 

[Deleted member 4366]

Atmosphere were certainly honorable and didn't try to push me in either direction.

That's nice to hear. Thank you for eliminating that as a possibility. Kudos to Atmosphere.

 

[trex]

I can think of one good reason why most e-bikes have 15A controllers. That's the best compromise for 10AH batteries. A 20A controller usually require 15AH battery and a BPM class motor to match, adding about 2kgs to the weight and about £200-£300 to the cost. The Oxygen MTB has the best compromise, a motor as powerful as the BPM, 13AH battery and 15A controller, not adding much to the weight and the cost.

 

[jonathan75]

I can think of one good reason why most e-bikes have 15A controllers. That's the best compromise for 10AH batteries. A 20A controller usually require 15AH battery and a BPM class motor to match, adding about 2kgs to the weight and about £200-£300 to the cost. The Oxygen MTB has the best compromise, a motor as powerful as the BPM, 13AH battery and 15A controller, not adding much to the weight and the cost.

Sorry if hijacking thread but while we're on the subject, will a motor run above 20a, say 23 or 26 or even 30, be OK with or would it damage a 14.5 ah with Samsung 29Es, and a 30a fuse? Same with 16a of 32As and 20a continuous discharge rating? Oops -looks like bmsb have taken latter off sale. Hope that doesn't bode ill for my recent purchase.

 

[trex]

battery makers tend to recommend 1.5C for maximum continuous discharge rate, eg 10AH = 15A continuous discharge rate. They are all capable of 3C.
Samsung 29E cells are usually recommended if you need 2C continuous discharge rate. Nowadays, Panasonic 3400 cell is gaining in popularity as leading quality cell.
TBH, because these cells are recent, not much track record to speak of.

 

[Deleted member 4366]

The 36v 14.5 Ah Samsung batteries are 10S5P, so should be alright up to 25 amps. I wouldn't go any higher.

 

[Wisper Bikes]

Thanks for helping clear this point up Dave,

So... we are saying that a 15A controller would actually be rated at or close to 7A continuous with a maximum output of 15A so the 500W plus would only be for start up etc when the motor peaks. If the motor were to continue to run at 15A and not melt down or cut out, the motor would not be acceptable under EN15195 which stipulates 250W continuous. If the Amperage drops to 7 for continuous running that would make the motor 250W and therefor fall within EN15194.

We have had 15A controllers for ages and I am constantly having this discussion with the motor and controller manufacturers as it seems to me we are too powerful to fall within the rules.

All the best

David

 

[Deleted member 4366]

No. You've not understood. The limit is on the selection of the motor, not how you use it; however, the motor must not fail when run at full power, though it's allowed to have temperature sensors or similar shut it down if it gets too hot.

There's no limit on controllers.

 

[Wisper Bikes]

So without looking at the manufacturers stamp, what governs the Wattage of a motor? The windings?

I was under the impression that if a motor can run continuously at more than 250W without burning out or triggering a temperature switch it is not a 250W motor.

It all seems to be more of an art than a science!

 

[Deleted member 4366]

That's an impression that's shared by many, but it's only an impression and bears no relationship to rules and regulations . Motors are rated by the manufacturers. They then have to be tested to meet that rating. As far as I can figure out, there's nothing to stop them exceeding the rating. For nearly every other use for electric motors, the problem would be overrating, which is what all the tests and standards are based on.

 

[anotherkiwi]

From my reading of EN 15194 once the motor has reached a steady temperature it has to be able to produce 250 W for several hours without temperature/power output variation within pre-defined tolerances.

All very voodoo gri-gri magical stuff performed in very expensive test labs by boffins in white coats.

 

[Deleted member 4366]

From my reading of EN 15194 once the motor has reached a steady temperature it has to be able to produce 250 W for several hours without temperature/power output variation within pre-defined tolerances.

All very voodoo gri-gri magical stuff performed in very expensive test labs by boffins in white coats.

That's correct. A 1000w motor would therefore pass that test, but it wouldn't be allowed if it was rated at 1000w.

 

[anotherkiwi]

The constructors wanting to make as large a profit as possible will of course make a motor that will pass that test with the cheapest components available to them. And of course a smaller cheaper to build motor will be lighter which also has its advantages.

Unfortunately some of our Chinese friends push the logic of using cheaper components a little too far which then brings up the reliability problems some motors experience... Heck even Bosch has its reliability problems all in the name of profit and happy stockholders...

 

[Wisper Bikes]

Does anyone actually know what the definition of a 250W motor is?..... Apart, that is, from a motor that is rated 250W by the manufacturer?

 

[soundwave]

mine says 250w on the frame but the motor is 350w with the dongle

 

[Deleted member 4366]

For EN15194 it has to be a motor with a maximum continuous nominal rated output power of 250w. Each of those words is important. Nominal means by stamping, listing in a catalogue, etc. Rated means what the manufacturer says its rating is, not the maximum it can produce or take. Continuous means exactly that. It should be able to run at that power all day. Output power means the motive power, not the power from the controller. Often, the output power is less than half the power from the controller. At high speed, the controller no longer limits the power because the motor limits it to less than what the controller can give. At maximum speed of the motor, the power is zero.

There's so many factors to consider in trying to pin down a motor's power that it's virtually impossible. The power when the battery is empty is 75% of that with a full battery. Power depends on speed, and so does efficiency. The varying efficiency changes the relationship betwen input and output power.

As I've said before, we don't have to worry about these things. As long as Bafang or any other manufacturer says it's a 250W motor, we're home and dry. We just have to restrict it to 25 km/h. Everything else is allowed.

The jury is still out on the voltage. EN15194 says it applies to ebikes up to 48v, but doesn't make it clear whether a 48v battery is allowed, which can be up to 56v fully charged, or whether the highest oltage sen in the system should be 48v. Different certifiers are interpreting it different ways. I've heard that Chinese SGS say 48v max, but Tuf say a 48v battery is OK. I've seen a Bafang motor marked by the factory as 43v 250W whatever that means. Does anybody know the voltage of the KTM. Is it 12S, which would still go over 48v (50.4v max) or the normal 13S (54.6v max)? It's getting even more confusing now where the latest cells can be charged to over 4.2v, so soon we'll have 36v batteries going over 48v!

 

[soundwave]

so im ok then as long as plod dont see me going 25mph on the roads then

tho even if i was stopped i could just take off the dongle and hide it, what could they do ?