Nominal Power misunderstood?

[(NoLongerRegistered#15675)]

Seems the phrase " nominal power " is open to various interpretations. In engineering terms it is quite specific. With Pedelecs it simply means max output ( named value) must not exceed 250w at the engine shaft but more current may well be consumed..This quote below is from wiki.





I suspect its wishfull thinking on many folks parts giving them freedom to uprade pedelecs or build bikes with over this limit.

 

[danielrlee]

Which Wikipedia entry is that from? This one suggests otherwise:

https://en.m.wikipedia.org/wiki/Real_versus_nominal_value

 

[anotherkiwi]

No it is very clear: the manufacturer must guarantee that the motor can provide a constant 250 W under certain operating conditions laid out in the norm EN15194. That norm is the basis for laws defining pedelecs in many European (and non-European) countries. The 250 W are nominal as defined by the manufacturer of the motor and either tested in an exterior lab or tested in-house if the company has the means to do so.

Simples!

The law is to stop companies from selling 250 W motors that don't provide 250 W and it is to stop them selling motors advertised as providing much more. It is at much a consumer protection law as it is a road safety law.

 

[trex]

it's not clear to me. Sure, if the manufacturer says he fitted 250W motor then that motor must be able to deliver 250W mechanical power without over heating but the specs don't say at which RPM. If he says he fitted a less than 250W motor, that bike satisfies still EN15194.
See how difficult it is to figure out the upper and lower limits of the capabilities of legal e-bikes' motors?

 

[Alan Quay]

Oh dear.

Firstly, in this context a motor does not provide a wattage, it consumes it. In nearly all pedelecs the power (watts) is controlled by the voltage (battery) and current (controller).

The rating of that motor is about how much power it can consume before it fails.

You can debate 'nominal' all you like, but that's irrelevant. 'Rated' is the important bit.

 

[(NoLongerRegistered#15675)]

A Watt is not only a unit of electrical energy, its a unit of performing "work".. Just as hp is...747 watts ...one hp...
250 w...about one third of a hp...output from motor.. Its quite simple really..

And we aren't talking about the philosophical meaning of nominal.. We are talking about the legal and engineering term.." Nominal output"...
Its 250w output. End of.No iffs or buts..its obvious. Not 600 watts overheating controlers, not 250 at 36v but with a booster battery added...Its 250w output. Just like legal learner in motorbikes is 11kw..not 11kw messed with..11kw..

 

[Alan Quay]

A Watt is not only a unit of electrical energy, its a unit of performing "work".. Just as hp is...747 watts ...one hp...
250 w...about one third of a hp...output from motor.. Its quite simple really..

And we aren't talking about the philosophical meaning of nominal.. We are talking about the legal and engineering term.." Nominal output"...
Its 250w output. End of.No iffs or buts..its obvious. Not 600 watts overheating controlers, not 250 at 36v but with a booster battery added...Its 250w output. Just like legal learner in motorbikes is 11kw..not 11kw messed with..11kw..

I understand all that, but you are missing the fact that it's about motor rating. Just for clarity I will say it once more. Motor rating.

Not motor output.

 

[flecc]

There are two problems with determining motor wattage on e-bikes. First is that measuring the motor shaft output is impossible on most without taking the units to pieces and measuring only the motor part. Arguably and correctly, that alters the unit's output so the finding is incorrect for the supplied unit.

The second is the EU's prescribed measurement methods. One is at the motor shaft as mentioned above, the second is by an acceleration time test. Since a controller can be programmed tro slow that, the result can be an artifically low one to get around the power limit.

The law says the manufacturer can specify what the power rating is, and that is what happens. In practice, virtually all e-bike legal motors have continuous output ability well over the limit, double being not uncommon. Motor only carefully measured hill climb performances prove that to be the case.
.

 

[(NoLongerRegistered#15675)]

There are two problems with determining motor wattage on e-bikes. First is that measuring the motor shaft output is impossible on most without taking the units to pieces and measuring only the motor part. Arguably and correctly, that alters the unit's output so the finding is incorrect for the supplied unit.

The second is the EU's prescribed measurement methods. One is at the motor shaft as mentioned above, the second is by an acceleration time test. Since a controller can be programmed tro slow that, the result can be an artifically low one to get around the power limit.

The law says the manufacturer can specify what the power rating is, and that is what happens. In practice, virtually all e-bike legal motors have continuous output ability well over the limit, double being not uncommon. Motor only carefully measured hill climb performances prove that to be the case.
.

If they do they are breaking the law. Nominal output means power output at the shaft. The rest is BS, to sell pedelecs to folk who think they need 600 w or over..
If my Haibike was capable of delivering anything well over 250w I could flatten my battery in well under an hour. Try as I might I cant.
The law says 250w..the numbers for battery usage say around 250w.
Like I,ve said before anybody who thinks any LEGAL pedelec can run continually at well over 250w go and flatten a 400 wh battery in under an hour..when you do let me know how... Nobody has yet told me how !!! The bike system is designed to limit the usage to under 250w let alone its output.
Do you really think firms such as Bosch and Yamaha could blatantly pay scant regard to the law ?? With all the litigation that would entail, ofcourse they cant. It would be exactly same as selling so called learner legal motorbikes capable of producing 25kw..they don't. Its not worth the risk.
Read the laws. Read the engineering meaning of those laws. Go out and try and flatten a 400wh battery in 35 minutes, then come back and talk sense.

 

[EddiePJ]

Flud, it is quite easy to flatten a 400wh battery as fitted to a Bosch Performance line motor in less than an hour. I have done so, in 10.9 miles of climbing, with an elevation gain of 6,362' Just because you can't do it, doesn't mean that others can't either.

 

[flecc]

Read the laws. Read the engineering meaning of those laws. Go out and try and flatten a 400wh battery in 35 minutes, then come back and talk sense.

Being ex trade, having over 65 years experience and knowledge of powered bicycles and following the development of the laws over all those years, I feel more able to talk sense than you on the subject.

Of course I fully understand that at double the legal rated output a battery could not last in the way you outline in opposition, but I have not said that everyone is using that up to double capability all the time since that would be unlikely anyway in practical circumstances.

What I have said is that these motors are capable of well over the legally specified output continuously when called upon to do so, and definitely do that. Unlike you I have actually measured that ability.
.

 

[soundwave]

i can drain my batt in a hour easy just keep going 30mph and its soon gone.

its says my motor is 250w on the frame but its not its 350w

 

[mike killay]

Flud,
Oh well, if you know best.
Problem is, there is no such thing as a 250 watt electric motor.

 

[soundwave]

there you go haha

 

[(NoLongerRegistered#15675)]

Only one person has mentioned how, soundwave is doing 30 mph on his, drawing zero current if legal..
And soundwave, what it says on your motor is totally irrelevant..
Climbing 6000 plus feet in 40 mins sounds most likely to get max current drain, but again I,d be interested to know details..ie cadence, gear and steepest incline.( so I could give it a go)
And to be fair that drain quoted is still only of order 400w per hour. Folk on here are claiming powers of 750 watts..and powered speeds of 32 mph !!!
Try as I might ( well try as bike might) my worst current drain has been 268 w/h..(over 30 mins) Which is about what you,d expect for a legal pedelec with nominal output of 250w..
As for claiming 65 years experience means you are right...well we could all list our experience and qualifications..but it would be pointless...my dad,s bigger than yours ??

 

[soundwave]

i have a dongle my cut off speed is 35mph.

this took over 2 bars off my battery in 15 mins

the faster i go the faster i drain the battery its as simple as that

 

[anotherkiwi]

Philosophy is fun. But out in the cold hard world norms have been fixed and ours is EN15194. If your bike or kit has that printed on it so be it! It is a legal pedelec. Can't climb hills? Sucker you bought a lemon. Climbs hills with ease? Well done! Enjoy your ride. EN 15194 is 250 W nominative, if it is on the sticker it is legal, end of story.

 

[(NoLongerRegistered#15675)]

Sou

i have a dongle my cut off speed is 35mph.

this took over 2 bars off my battery in 15 mins

the faster i go the faster i drain the battery its as simple as that

Soundwave..it ain't a pedelec..its illegal.
You cant compare current drain on a bike doing 30 mph with one doing 15 !! Its drag will be 4 times that of one doing 15...
I,m talking about LEGAL pedelecs. Yes the motor is capable of drawing more than 250w. Yes its capable of providing more than 250 w...but with a LEGAL pedelec I,m finding it impossible to put it in a situation to do either.
Folk keep saying they have bikes capable of delivering 600 w etc...( yes yours might be, not disputing that) but the bikes system with 15.5 mph cut off, high cadence low torque cut off, its almost impossible to put bike into a situation to draw over about 250w..
Yes I could keep my graphic high by abusing both bike and my legs.( ie falsely high gear, low cadence lowish speed) but moment I pedal " normally" ( correctly) current draw diminishes below the legal limit..
If folk know of a way to draw more than 250w ( without dongle mod) please tell..I don't think its possible on my yam haibike.

 

[soundwave]

it goes fast tho and i ride it past the police station all the time and they dont care either.

wait till i get my mobility scooter ill be putting a 170kw motor in mine and set the lap record round tesco

 

[(NoLongerRegistered#15675)]

I beat you to that !!!