Wattage per mile or kilometre

Stefan Mikes

Well-Known Member
Since I've got interested with e-bikes, the battery range has become one of my greatest interest. Now, having read big claims of Bulls about their new "super-range" e-bike, I started thinking in terms of "watts per distance unit". There are several factors affecting the range per battery charge:

On the input side:
  1. Your own legs input
  2. Battery capacity [Wh]
On the output side:
  1. The motor and drive-train efficiency​
  2. The pedalling support level​
  3. Rolling resistance depending on the rider's weight, tyres used, tyre pressure and quality of the terrain surface​
  4. Air resistance related to speed, face area of the rider/bike and wind direction and speed​
  5. Elevation change (the potential energy change when riding uphill) - most of e-bikes cannot recover energy on downhill ride or the recovery is minor (regenerative braking)​
  6. The season: It is clear batteries are less efficient at low temperatures​
Hopefully, all factors have been taken into account (if not, please correct me so I can edit the post).

Now, there is a universal factor that integrates all the factors specified above: the wattage per covered distance unit [Wh/mi or Wh/km]. By analogy, it is similar to fuel consumption figure for cars.

Said the above, let me give you the energy consumption figures for my e-bikes:

I weigh 107 kg (236 lb). I ride in comfortable upright position. The terrain I am usually riding is good tarmac, poor tarmac, lower quality local roads (gravel etc) and a little bit of forest paths. There are no dramatic hills here, the terrain is almost flat.​

  • Under ideal summer conditions and very light breezes, my rear-hub-motor e-bike unrestricted, with speeds kept at 30+ km/h (up to 19 mph) uses 6.19 Wh/km (9.93 Wh/mi)
  • Under the same conditions, the same e-bike restricted to 25 km/h (15.5 mph) uses 4.27 Wh/km (6.84 Wh/mi)
  • My Vado 5.0 during cold Autumn conditions (temperatures 5 C or below, 40 F or less) with strong winds uses as much as 12.84 Wh/km or 20.68 Wh/mi.
I must admit I have used mostly Sport mode on my Vado during Autumn rides and of course I tried to keep higher speeds than on Lovelec, the other e-bike, where I tend to ride in Eco mode. I have to add that Vado cuts the power off at 5% battery while Lovelec allows emptying the battery. I put corrections in my calculation to get true figures.

Your own experiences with watt-hour consumption per distance unit?
 

JRA

Well-Known Member
What you get for wh consumption only pertains to how what you ride, how you ride and where you ride. That said 15wh/mi has been said to be about the average for most people. Which yours would be if you rode your Vado an equal amount in the winter and your other bike in the summer.
 

Manu

Active Member
Many variables influence this, but one of the most common is the type of wheel and its width and weight, a 700x 25 wheel can consume 20 w , a 700 x 45 wheel = 30 watts if you go to mtb 27.5 + example minion = 40w but that is ...... a wheel ... multiply x2 Then there is the disk multiplier and cassette, on a flat terrain with a 44 x 11 vs a 20 x 11 who has less pedaling cadence is a 44 x 11, understand this is very important to have a cassette of something gear and two plates high and under gear,only one plate when it is mtb


a 20w x 2 = 40 watts but a minion mtb 27.5 40 x 2 = 80 watts, twice the effort to move it


you exceed 25km / h without wind and spend more watts the more speed you want. = wasted money
 
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Stefan Mikes

Well-Known Member
Watts and watt-hours are two different things ;) Watts are units of power (work done in unit time) while watt-hours are units of work (energy). These two should not be confused.
 

Manu

Active Member
Same energy what changes is the value of time unit, watts second ..... watts hour, watts monthly, a very important factor is the weight especially climbing the hill.A conventional human is in 150 / 200w a professional It can have 400w peaks. If your wheel weighs a total of 800 grams it is much easier to roll than a wheel that weighs 1600 grams, especially climbing the hill because you have not one, 2 wheels, 1600 grams more, you will spend more time and energy up the hill, be it human energy or drive unit or both.


1000 grams more up the hill = 6 seconds per kilometer + watts consumed,having less weight on the wheels is easier to roll is that you add inertia and kinetic energy, in addition to reaching top speed before.
 
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Stefan Mikes

Well-Known Member
I feel you mix two different quantities. A watt (W) is joule per second (J/s). It means that if the motor draws 200 W at a moment, it uses 200 Joules on every second. If this power is drawn for an hour, the motor has used 200 watt-hours which means 720 000 Joules (720 kJ).

Let us assume, your battery capacity is 600 Wh and the efficiency is 100% (which is not a fact but let us keep things simple). If the rider only used the throttle, the ride would last 3 hours (600 Wh / 200 W = 3 h). Let us also assume that the constant speed was 25 km/h. During those 3 hours, the rider covered 3 * 25 = 75 km. Dividing 600 Wh by 75 km gives wattage figure 8 Wh/km. 8 *1.604 = 12.83 Wh/mi.

Now, if you want to calculate energy consumption per meter of elevation (riding up), the formula is Potential Energy change = m*g*h where m is the total mass of the bike and the rider, g is gravity and h is the elevation change. Let us assume the rider and the bike weigh together 100 kg, and the elevation change is 1000 m. The potential energy change requires at least 100 * 9.81 * 1000 = 981 000 Joules (981 kJ). Translated to the energy stored in the battery it is at least 272.5 Wh of the battery consumption. This figure assumes no other resistance than climbing so it means the climbing is very very slow. Now, let us assume the rider was negotiating a 5% grade. The rise is 1 km, the run is 20 km. In practice, the slope length (distance ridden) is about 20 km. Now, the wattage will be 275.2 / 20 = 13.76 Wh/km or 22 Wh/mi.

Manu, you say 1.6 kg of wheels means much. I will say it is a negligible factor. The potential energy change will be 1.6 * 9.81 * 1000 m = 15.7 kJ = 4.4 Wh. Completely negligible. What matters is the weight of the rider and the bike (which is over 60 times greater than the weight of the wheels alone).

I do repeat: a watt is not a watt-hour. (You can trust me, I'm an engineer).
 

harryS

Well-Known Member
I have been tracking AH used on our rides for two years now. I use Tenergy Wattmeters, either on the battery during a ride or during recharge,

On our folding bikes, 20 x 2.0" tires, at 132-13 mph, I burn 9-10 WH/mile while my wife uses 6 WH/mil. I'm 195 vs her 135 pounds/ I pedal continuously, while she goes on for a few seconds, off for a few seconds, so that duty cycle probably works in concert with the weight difference.

I'll get the same number on my 26" bikes at the same speed.

Since the above depends on pedaling effort and no one knows how much the rider puts in, I've seen 20 WH/mile at 16-18 mph with throttle only on my BBS02 mid drive. Kind of boring to ride 15 minutes w/o pedalling.
 

Manu

Active Member
I feel you mix two different quantities. A watt (W) is joule per second (J/s). It means that if the motor draws 200 W at a moment, it uses 200 Joules on every second. If this power is drawn for an hour, the motor has used 200 watt-hours which means 720 000 Joules (720 kJ).

Let us assume, your battery capacity is 600 Wh and the efficiency is 100% (which is not a fact but let us keep things simple). If the rider only used the throttle, the ride would last 3 hours (600 Wh / 200 W = 3 h). Let us also assume that the constant speed was 25 km/h. During those 3 hours, the rider covered 3 * 25 = 75 km. Dividing 600 Wh by 75 km gives wattage figure 8 Wh/km. 8 *1.604 = 12.83 Wh/mi.

Now, if you want to calculate energy consumption per meter of elevation (riding up), the formula is Potential Energy change = m*g*h where m is the total mass of the bike and the rider, g is gravity and h is the elevation change. Let us assume the rider and the bike weigh together 100 kg, and the elevation change is 1000 m. The potential energy change requires at least 100 * 9.81 * 1000 = 981 000 Joules (981 kJ). Translated to the energy stored in the battery it is at least 272.5 Wh of the battery consumption. This figure assumes no other resistance than climbing so it means the climbing is very very slow. Now, let us assume the rider was negotiating a 5% grade. The rise is 1 km, the run is 20 km. In practice, the slope length (distance ridden) is about 20 km. Now, the wattage will be 275.2 / 20 = 13.76 Wh/km or 22 Wh/mi.

Manu, you say 1.6 kg of wheels means much. I will say it is a negligible factor. The potential energy change will be 1.6 * 9.81 * 1000 m = 15.7 kJ = 4.4 Wh. Completely negligible. What matters is the weight of the rider and the bike (which is over 60 times greater than the weight of the wheels alone).

I do repeat: a watt is not a watt-hour. (You can trust me, I'm an engineer).
1 watt is an instant energy of 1 second = 3600 joules, we only use watts hour referred to the multiplicative consumption for 3600 seconds (60 minutes x 60 seconds), they are 2 different time concepts,
the total weight is decisive in that we agree, for professional cyclists where their races and performances are measured in watts, the kilogram of weight that I told you is decisive because the factor is human only and when they tell you that 1000 grams is 6 seconds of loss in ascent of the hill spending the same watts they know what they say, structurally the bicycle has a part that is immobile and another that is mobile, the wheels are applied inertia and kinetic, you can have 2 bicycles of the same weight but the wheels of one are 20000 grams and structure of 4000 grams and the wheels of the other 2000 grams and structure of 22000 grams, the bike that you can move easily is the one with the lightest wheel, it is easier to move a light weight with movement than a heavier weight and the only thing that moves on a bicycle is the wheels.

Example mont veloux 30km uphill = 6 seconds more /kilometer = 180 seconds with human



Even if you have a 100% charged battery, a drive unit does not convert 100% energy every watt in motion,% of watts becomes heat, efficiency 80/85%, the system will not yield 100% of your total battery 20% is converted into heat that is not moving, therefore less kilometers than the real ones, I have a battery of 2000 watts, 400 watts will be converted into heat and not moving by the drive unit.
 

Stefan Mikes

Well-Known Member
As long as you are talking human power only and racing then every single watt matters @Manu, I concur. Several athletes compete among one another and the strongest and best equipped wins. However, we are talking e-bikes that are already heavy and mostly ridden by seniors who do not put as much human power in pedalling and rely a lot on the motor and battery. Therefore, we are talking battery watt-hours per distance unit figure.

I also agree nothing is 100% efficient. When talking about fuel consumption, nobody talks about internal combustion engine's or transmission efficiency but people say: "My car uses 6.5 liter of diesel oil per 100 km" or "my car can go for so and so many miles on a gallon of gas". The same way we can say "my e-bike can cover so many mi/km per watt-hour" or "my e-bike uses so and so many watt-hours per km/mi".


My bike will go at least 50 miles on a charge. That is as technical as I get.
Then the only question remaining is what capacity your battery has.
 
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Manu

Active Member
As long as you are talking human power only and racing then every single watt matters @Manu, I concur. Several athletes compete among one another and the strongest and best equipped wins. However, we are talking e-bikes that are already heavy and mostly ridden by seniors who do not put as much human power in pedalling and rely a lot on the motor and battery. Therefore, we are talking battery watt-hours per distance unit figure.

I also agree nothing is 100% efficient. When talking about fuel consumption, nobody talks about internal combustion engine's or transmission efficiency but people say: "My car uses 6.5 liter of diesel oil per 100 km" or "my car can go for so and so many miles on a gallon of gas". The same way we can say "my e-bike can cover so many mi/km per watt-hour" or "my e-bike uses so and so many watt-hours per km/mi".



Then the only question remaining is what capacity your battery has.


W / hour that's the measure, how far does it travel? less than people think 80/85% motor efficiency not 100%, and how is that limited energy spent? in watts / hour converted into mechanical movement at a given place the wheel, when a human says that wheel It consumes 20w / hour is energy or watts spent either by a human, by a drive unit or by both, but all bicycles carry 2 = multiplier x2 = 40 watts, therefore to operate the 2 wheels of 20 watts you need 40 watts mechanics for one hour, if the wheel is 40 w and multiply x 2 = 80 watts of burned energy to move that wheel for 1 hour, it is twice the energy consumption for the same distance traveled, if you give it 80 watts / hours spent in the 40-watt wheel the 20-watt wheel can be 2 hours, double the distance with the same energy spent .

If you want to guarantee that these wheels rotate the 60-minute time knowing the real watts you have to add 20% more watts in battery capacity to the calculation by the efficiency of the 80% drive unit in the worst case and all this in conditions optimal, flat terrain, no wind, no more weight, asphalto,

not exceed 25km / h /dont up hill gravity negative
etc


those watt hours you spend on the wheels is an automatic and mandatory expense and therefore the weight there is decisive, not only the overall weight, but the partial weight on the wheel, the lighter the better, the less wattage expense
for the same distance


For 20w wheels x2 = 40w + 20% = 8w more,40+8= 48 w, for 40w wheel x 2 = 80w + 20% = 16 watts = 80 +16 = 96 watts / hour


Eye this is just the wheels we don't include the rest of the structural weight ...... +++++ more W/hour


Look at a detail, the wheel moved by a human for an hour is 20w / 30w / 40w depending on the model, but in the case of the drive unit it is the human w / h + 20% by 80% efficiency
 
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Stefan Mikes

Well-Known Member
I refuse to talk with someone who says "watts spent".
You do not understand this simple concept Manu. You cannot spend watts. You might as well "spend" volts or amperes (same wrong).


It is the voltage, not the battery capacity. The battery capacity is expressed in Wh.
 
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Manu

Active Member
I refuse to talk with someone who says "watts spent".
You do not understand this simple concept Manu. You cannot spend watts. You might as well "spend" volts or amperes (same wrong).



It is the voltage, not the battery capacity. The battery capacity is expressed in Wh.


In a battery the consumption or watts/ hour that can be stored is determined by voltage and intensity, both voltage x intensity of delivery, when you have discharged all the battery you have burned those watts, converted into mechanical movement and heat, example 48 volts x 10 amps = 480 watts/hour of battery storage, 36 volts x 15 amps = 540 watts/hour ,90 volts x 5 amps =450watts/ hour ,10volts x 50 amps= 500watts/ hour, a human at rest 24 hours spends 200 watts = 8.333 watts spent per hour .

In a human, no voltage is applied by intensity, kilocalories spent per hour are applied by their body temperature.


energy is not destroyed, it is transformed into mechanical/magnetic movement and heat.


energy cannot be destroyed, only transformed into other types of energy
 
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PaD

Well-Known Member
I refuse to talk with someone who says "watts spent".
You do not understand this simple concept Manu. You cannot spend watts. You might as well "spend" volts or amperes (same wrong).



It is the voltage, not the battery capacity. The battery capacity is expressed in Wh.
His battery capacity is ”at least 50 miles” :D Distance is the important unit for many of us.;)
 

Stefan Mikes

Well-Known Member
If you stored 500 Watts Manu, it probably took 10 seconds to charge the battery, Manu, didn't it. (Joke, in any case).

You do not store "watts" in the battery. You store watt-hours. If you were unloading a 576 Wh battery, you might get electric current of 250 W / 36 V = 6.9 Amperes and this current flows through the motor circuits, disregarding the battery capacity. However, since you are drawing energy from the battery, and you are drawing 250 W, your battery will work for 576 / 250 = 2.304 h or roughly for two hours and eighteen minutes.

Also, the fact Wh (not W!) are measure of energy stored is the charging process. Assuming your charger is 4 A and the voltage is 36 V, you push 36 * 4 = 144 Watts or 144 Joules per every second. Your battery capacity is 576 Wh, so charging would take at least 576 / 144 = 4 hours. It is because you are storing energy (Wh) not power (W).

Still, it is hard to talk to someone who mixes pears (Watts) with apples (Watt-hours). Both are fruit, true. Both are engineering units. For different physical quantities.


His battery capacity is ”at least 50 miles” :D Distance is the important unit for many of us.;)
Good joke @PaD ;) So I can tell you the tank of my car is good for at least 900 km :D How many liters per Swedish mile does my car use?
 

Mr. Coffee

Well-Known Member
His battery capacity is ”at least 50 miles” :D Distance is the important unit for many of us.;)
The point is that number is meaningless if you are riding in variable terrain, variable temperatures, and variable road surface. It becomes even more challenging when you are riding someplace you never rode before.