how efficent is your ebike

[geoff57]

Hi all
After seeing the term efficiency banded around everywhere I thought I would have a go at putting a figure to the name.
My best Idea is not given as a percentage maybe I can work out a formula eventualy for now just a number can be got from this concept.
If anyone has a better idea say.


Ok efficiency is the ratio of watts used to speed attcheved,this would be:-
watts /speed for comparison the speed should be in the same units mph or kmh.

The lower the number the more efficient the motor,for comparison the best readings should be on the level with little wind.
I'll start the debate with readings I have on my ebike resently.

speed 25mph, watts 850
using the formula I have proposed my eficiency number is 34
these readings were taken on the flat in little wind.
Try out the formula yourself and post a reply.
You could say I'm laying down a gauntlet.


Thats all for now
Geoff

[scottclarke]

Geoff,

Not so sure this is a very useful idea - way too many variables!

Anyway, my data....

At 38kmh - 24mph ish... I see 13-14A / 648W making my number...

27

I am running a lightweight alu framed full sus mtb with wide cut slicks. The motor turns 48kmh under no load. The complete bike weighs 32KG and I 78KG making a total of 110KG/242lb.

Has a range of 22 miles under ideal conditions. In the real world with stop start traffic it'll do 16ish miles and with hard core offroad running it'll do as few as 8!

Scott

[xyster]

Wind resistance is far and away the biggest inefficiency. So calculating efficiency as Watts/Speed will drown out all other lesser inefficiencies like motor/controller losses/friction etc...the most aerodynamic setup (or the person who tucks the hardest) should easily "win" this measurement, even if the rest of their system sucks.

FWIW, 25mph = 750-800 watts on my x5 @ 80 volts (hard to tell exactly with analog meters), upright position, no aero devices.

[jondoh]

I thought we were all going to use watt hours per mile?

like in this thread...

http://endless-sphere.com/forums/viewtopic.php?t=706

that was until randy ruined it...

watt hours per mile on an electric bike is like gallons per mile in a car. The smaller the number, the more efficient your bike is. Also like a car, your efficiency is affected by speed. The faster you go, the less efficient you are. I'm getting around 24 watt hrs/mile at around 20+ miles per hour.

[CGameProgrammer]

A better test may be to measure no-load efficiency. That would factor in controller, drivetrain, and motor inefficiencies while ignoring the highly variable wind, slope, and rolling (affected by rider weight) resistances.

[Lowell]

I like using Wh/km at various speeds, and since most readouts have a Wh number, it becomes easy to estimate your range.

Cruising at 33mph I can average 20Wh/km on level ground and get up to 45 mile range.

40mph = 31Wh/km

50mph = 35-36Wh/km

55mph = 38-39Wh/km

62mph = 20Wh/km (going downhill, DB reading only 2000W )

[eP]

Wind resistance is far and away the biggest inefficiency. So calculating efficiency as Watts/Speed will drown out all other lesser inefficiencies like motor/controller losses/friction etc...the most aerodynamic setup (or the person who tucks the hardest) should easily "win" this measurement, even if the rest of their system sucks.

So the best way to get wind independent values is measure efficiency at 10 mph also.
Then system which sucks will be no hard to find this way.

[geoff57]

Hi all
I had not seen the other thread using watt/hr per mile when I desided to start this thread.

I am not trying to find the efficency of the motors that are used but the actual ebikes rider and all including just how the riders sitting,a recumbent 2wheel fully flared will have a lower number than a mtb with the same person, motor ,overall weight and wind/gradent conditions.

There are not realy to many varibles, only the two used in the calculation, though on reflection road surface should be take in to account.

So again the commons are level, low to zero wind, level gradent and a good road surface eg tarmac no potholes.yYou can pedel to get there but once there the motor must do the work on its own as the watts used would be spread between you and the motor and you cant mesure how many watts you are using!

This is a mesure of you on your ebike not the motor on its own, so two riders on the same ebike taking readings over the same stretch of road one weighing in at 150lb the other at 200lb if the bike was given a topup charge in between then they would have different results.

Anyway that should clarify some points to make this a mesurment that can compare bike(and rider) to bike not motor to motor.

thats all for now
Geoff

PS

Wind resistance is far and away the biggest inefficiency. So calculating efficiency as Watts/Speed will drown out all other lesser inefficiencies like motor/controller losses/friction etc...the most aerodynamic setup (or the person who tucks the hardest) should easily "win" this measurement, even if the rest of their system sucks.

That is not the issue here the bike is on trial not the motor, my wife had a Powerbyke delta trike I dont know what the watts were as at the time i didn't have the meters I do now but once up to speed the meter showed 5 amps the battery pack was 36v so for arguments shall we say 180w @ 10mph this gives a figure of 18 using the watts/speed idea, but as far as an actual ebike is concered powerbykes are not very good at all![/quote]

[xyster]

Again FWIW, I posted this chart some time ago showing my x5's motor efficiency (pink line) and watt-hours per mile (blue line). The point of maximal total efficiency is at 10mph, where motor efficiency is 48%.
Riding 5mph is about as efficient as 20mph.

[eP]

Again FWIW, I posted this chart some time ago showing my x5's motor efficiency (pink line) and watt-hours per mile (blue line). The point of maximal total efficiency is at 10mph, where motor efficiency is 48%.
Riding 5mph is about as efficient as 20mph.

At flat ?
Or at some slope ?

BTW it is huge area for improvments i see.

[Drunkskunk]

At 22mph I pull 600 watts, so that gives me a 27
But that number is kind of meaningless unless someone else is going 22
At 16 I'm pulling 300 watts which gives me a 18.75

With my centertapped setup, this happens to be the max numbers at 48V for both motors on flat ground.

What eP said makes sense, there needs to be a common speed at which to do comparisons. 10 is too slow and boring, and for many motors thats down in the range were the motor is struggling and eating up power.

Why not pick 3 speeds to compare at? Say 15, 20, and 25?
Then have 3 values to compare with, or average the 3 together.

Personaly I prefer them watts per mile. Its easier to get my head around 13.65 watts per mile at 15mph. I can compare that much easier in my beer soaked brain than I can to an abstract like 27

[xyster]

At flat ?
Or at some slope ?

BTW it is huge area for improvments i see.

On the flat, no pedaling, sitting upright, calm wind. How would you go about improving this? Aero work -- fairings and such -- is the only significant way I see.

It's the nature of the ungeared motor to be inefficient at low speeds. On the plus side, popping out of the zone of less than 70% efficiency takes only seconds, and if I want to go slow, I can pedal, so overall losses are insignificant in practice. Besides, I rarely use even half the energy available from my 2,500 watt-hour battery pack. So what's a few extra wasted watt-hours here and there?

Efficiency is important, but I'm not going to go Nazi about it...

[eP]

At flat ?
Or at some slope ?

BTW it is huge area for improvments i see.

On the flat, no pedaling, sitting upright, calm wind. How would you go about improving this? Aero work -- fairings and such -- is the only significant way I see.

It is depend on the speed sector.
For low speeds the ultra low idle current is needed.
Coreless BLDC for example.
For high speeds fairings are much more important then low winding resistance.

It's the nature of the ungeared motor to be inefficient at low speeds. On the plus side, popping out of the zone of less than 70% efficiency takes only seconds, and if I want to go slow, I can pedal, so overall losses are insignificant in practice.

I don't like to say it (i'm not a troll) but you are wrong.
If you pedaling your motor operating at lower torque so it is much inneficient at low speed sector/area.

It is central point for the efficient assistance.
To lower idlle current as much as possible - and you could be the winner. Big gains waiting at that area.

At high speed you can also try to help for yours engine but at high power level you cannot help a lot.

Besides, I rarely use even half the energy available from my 2,500 watt-hour battery pack. So what's a few extra wasted watt-hours here and there?

You could get lighter/cheaper pack and get better performance at higer slopes as yours total weight will decrease.
And you also could gain more power source options.
Solar panels for example for low speeds.
This way you can gain greater flexibility how to configure power source for your bike.

Efficiency is important, but I'm not going to go Nazi about it...

So you will be punished
Yours pocket/batteries in fact.

[Lowell]

Some of us like speed and power, and don't mind spending a few extra bucks to get it. Obviously few people would go out of their way to waste watts for a given speed, but you can't have everything.

[geoff57]

Hi all
Looks like I have opened up a hornet's nest when I started this thread.
It still looks like there is confution as to the item on test, it's is not the motor that is on test but the whole bike with rider.
So as not to be a closed to other ideas could somone please explaine just what the term watt/hours is and how it is calculated so I can see if it is a statistic that should be used in this I am open to ideas.

[Lowell]

Don't worry about any hornets, they will be shot on sight if they come anywhere near. Constructive technical discussions are encouraged, but keep it clean and fun. If in doubt, read the FAQ at: http://endless-sphere.com/forums/viewtopic.php?t=152

"Posts, topics, reply, or profiles which go beyond simple expression of opinion and edge toward unfounded accusations will be removed. Repeated problems with a user will result in account termination. Everyone is entitled to their own opinion but don't take it too far."


Watt Hours is amp hours x volts, so a 48v 18ah pack would have 864Wh. Of course for an accurate measurement you have to measure real time voltage and current since high discharge rates lowers useful battery capacity due to voltage sag and cell heating.

Edit: forgot to add the hour part. fixed now

[Drunkskunk]

Hi all
Looks like I have opened up a hornet's nest when I started this thread.
It still looks like there is confution as to the item on test, it's is not the motor that is on test but the whole bike with rider.
So as not to be a closed to other ideas could somone please explaine just what the term watt/hours is and how it is calculated so I can see if it is a statistic that should be used in this I am open to ideas.

Opening up any topic of comparison 'round here is like stirring up a hornet's nest, but its all in good fun.
That is, untill someone forgets to sacrifice a hub motor to Volcano Boy, then it turns ugly.

A Watt hour is one watt for one hour. The reason its used most is because regardless of amps or volts, watt hours remains a constant. That's because 1 watt is 1 amp at 1 volt, and is figured at Amps X Volts.
that means 10 volts at 1 amp is the same watts as 1 volt at 10 amps. in both cases, its 10 watts.

[EbikeMaui]

Most of the watt hours per mile are figures given are unaccurate. Knowing the free spin watts help.Secondly the given figures on round trips WITHOUT pedaling and average trip speed on a given trip one can see most of the whole picture once the total weight is given. Trips up hill give the real figures to see how efficient the total system works.Once up hill figures are caculated the down trip frigures are free! unless your hub motor don't coast worth a dam.The average round trip speed in ANY hill grade or wind condition will tell the worst average round trip wattage used with excesive weight espaisally IF the motor performed many miles with a 100 lbs of battery weight UP HILL. These FACTS have been ttested for many more years than hub motors have been even available.So start testing with REAL figures to be somewhat creditable.All in good fun but honestly will help.Videos of the complete trip dont lie.

[TylerDurden]

Trips up hill give the real figures to see how efficient the total system works.

It is a good test of efficiency, but maybe not the whole story.

Most EVs for sale provide at least:

X max speed @ x range

Y max range @ y speed

0-Zmph @ z seconds

Vehicle weight @ test conditions

[EbikeMaui]

Trips up hill give the real figures to see how efficient the total system works.

It is a good test of efficiency, but maybe not the whole story.

Most EVs for sale provide at least:

X max speed @ x range

Y max range @ y speed

0-Zmph @ z seconds

Vehicle weight @ test conditions

Max contionus grade is a must if you don't want to get stuck with a burned up system.