Watt rating on motors

Kurt

10 kW
Joined
Apr 21, 2008
Messages
962
Location
South Australia
I have been finding it interesting when looking at ebike kits most kits are given a rating like 600w, 200w, 1000w the ratings seem to slapped on like they are rating a cheep set of car stereo speaker. Personally I only see it as some kind of guide to the size of the motor /controller the kit has. for example the izip/ezip bikes are rated at anywhere between 200w and 450w depending what country you buy them In but they all use the same geared motor.They all have at least a 25amp speed controller and some of them come with a 35amp controller so that is 600w to 840w peak. I know you would have to take some off for heat loss and so on .

I guess what I am getting at is it would be nice to have some kind of to the wheels /ground power rating on ebikes or even if sellers just gave the max amp rating of the controller and the engine efficiency at that rating .
 
I find the watt ratings kind of ambiguous, even though I sort of relied on them when I first began searching for a hub motor.

Even now, there's the question of "wattage, at what current would this motor draw and at what voltage? Is it peak or RMS? etc.". I've noticed the "wattage" of a motor tends to go up as a function of voltage, so it seems the voltage and reference point for the power(peak? RMS? average?) needs to be defined for there to be any meaning(And efficiency for determining "useful" power, but that's a bit much for mere merchants and novice e-bike customers. It's like Intel during the late 1990's: "It's the frequency, not MIPS, that counts!" It's clear that frequency doesn't matter without additional information like how effective the pipelining is, etc., that leads to the more comparable standard of MIPS. But general customers just want to see one figure to simplify and expediate their comparison-shopping, however misleading it is. Linux users might demand a little more. :) ).
 
Best way I know to judge em is to multipy the controller amp rating by the voltage. Most of the hub motors can take 1000 to 2000 watts, but the battery and controller may not.

Example , WE BL36. 50 amp controller x 36v = 1800 max wattage. I belive this motor kit is sold as a 600 or 700 watt. Whether it's controller can actually provide 50 amps from the battery its connected to I have no idea. But in cruise mode, full speed on flat ground, the setup is likely to be running at about 600-800 watts. Going to 48 v with the same stuff likeley gives you 900 watts when cruising.
 
I basically just ignore any wattage rating on the motor. I just have a look at the motor physically and can judge fairly well that, yeah, that could take a 1kW controller, or whatever.

As for the wattage of the actual system it's in, I think pretty much everybody just multiplies nominal battery voltage by controller amp limit, since there's really no better (easy) way to do it.
 
Kurt says,
the ratings seem to slapped on like they are rating a cheep set of car stereo speakers ...

No kidding. I'm really a newbie to the scene, my bl36 is only about a month old. But before reading this forum (and others) I confess to being "taken in" by the claims, like swbluto.

But there is a possible usefulness in these ratings -- if my ride should ever be scrutinized by the authorities, I can just point to the advertising. 600/750 peak is well within legal guidelines.


Dogman says,
Example , WE BL36. 50 amp controller x 36v = 1800 max wattage. I belive this motor kit is sold as a 600 or 700 watt. Whether it's controller can actually provide 50 amps from the battery its connected to I have no idea.

I actually question that 50a rating. I put an automotive ammeter in line and it would pull no more than 25a full throttle. The gauge is not very precise, just by the way the numbers are printed and the width of the needle it's probably no better than +-5, but the reading was far from 50.

My guess is that it actually limits current at 25 amps. This is consistent with the range I get -- 12AH is good for about half hour and full throttle.
 
The limit is more likely the battery, wiring, connectors, etc. The 50 amp rating most likely means, hopefully won't fry below 50 amps. Excluding the big crystalites, most motors don't draw much above 20 amps for most of the time. To get the thing to actually draw 50 amps, find a hill steep enough to make the motor just about stop. Just before the controller trips, you may see 50 amps or more, but that is when the motor is stalling. I don't know what battery you are using, but most of the guys actually seeing more than 50 amps on a cycleanalyst are running homemade A123 packs with heavy wires and and big motors. Since WE upped the amps on the bl controller, I have heard no reports that the kit is faster, so I figured it's more like making it less likely to blow than actually putting out 50 amps from the stock batteries. If it did put out 50 amps, you would have like what, 4 mile range on 12 ah slas?
 
Thanks dogman. My batteries are the stock SLAs. 3x12v.

One vendor (electricrider) has chosen to not advertise in terms of watts. Instead they publish performance charts and graphs for their various products. That kindof makes sense to me, and is probably the closest to the notion of "to the wheels /ground power rating".

Without actually having the experience of driving a 600 watt setup, it's hard to understand what it really means in terms of experience. We all know what a 100watt lightbulb will do, by experience, but that's hard to equate to kinetic energy. So when they say "30 MPH in 13 seconds" -- that is something I can relate to. And dream of.

Mine is not that fast BTW, but I'm very pleased with the performance. 20mph is easy on level or slight grade and in a good mood she'll do 25. A cycleanalyst might be in my future. I'm sure it would help me relate the abstraction of volts and amps into concrete terms like bags of groceries per mile/hour.
 
I run 800 watts uphill in a Bafang powered trike that weighs 300# with me (230 lbs of pure muscle :) ) and it really is nowhere near enuff juice. I prolly need 1200-1500 watts uphill but my batts wont deliver it! These motors are very under rated and can pull many more amps. Sometimes they really need to! But that is a factor of controllers and batts, not the motor!
otherDoc
 
nutsandvolts said:
Obviously some motors can use a lot more power than others, but I think every hub motor around can handle at least 800-1000 watts, probably more.
IMO, the issue is not how much any of these motors can take; but how much, for how long.
 
How true, my normal use of a WE brushed motor only lasted 400 miles in abnormal temperature. Ok, maybe the use wasn't exactly normal since the setup is designed for use with a battery that would drain in a half hour, and I put a big ol Ping on it. So the how long, was definitely not for 1 hour continuous.
 
Storm said:
Yes where can I get a sticker from?? :lol:
I vaguely remember AussieJester photoshopped some really nice looking "official" ones! :) :) :)
otherDoc
 
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