Why oh why did my power consumption skyrocket?

[Russell]

I used to ride my E-bike and use a fairly low amount of power then I got a 48V LiFePO4 battery and my power use went up 46%. I was already using 48V by running my 36V/6Ah Fatpacks in series with a 12V/9Ah SLA so I didn't jump up in voltage. I always pedal with good effort so I can't understand why I use so much more power. I sifted through my ride data to pick out all rides done on the same bike over the same 31 mile course and here's the data.


Bike: Kona Smoke
Motor: 36V Bafang
Battery: 6Ah 36V Fatpack+9Ah SLA
Controller: Infineon 9-FET 15A


Date Spd Wh/mi

8/2 18.0 7.5
8/5 18.0 7.1
8/12 18.0 7.3
8/15 17.3 7.2
8/18 17.9 7.4
8/20 17.5 7.5
8/30 17.7 7.1
8/31 17.7 7.5
9/3 17.9 7.5
9/4 17.8 7.5
9/4 17.8 7.5
9/7 17.7 7.6

12 ride avg speed: 17.8 mph, avg Wh/mi: 7.4

As you can see I was super consistent. I tended to nurse the small battery for the first 20 miles then raise the pace the last 11 miles. Then I got the new battery and with the added capacity I didn't conserve power which increased my average speed a little (0.4 mph) however my power consumption increased far more, 46%! Even on days when I posted a comparable speed to previous results the power consumption was higher.

New 48V/10Ah LiFePO4

Date Spd Wh/mi

9/9 18.7 10.5
9/11 18.8 10.1
9/21 18.2 10.3
9/27 18.3 11.2
9/30 18.9 12.5
10/1 18.3 11.2
10/4 18.5 10.8
10/7 18.1 10.4
10/11 17.8 10.8
10/18 17.0 9.4
10/21 18.3 11.0
10/28 17.5 10.9

12 ride avg speed: 18.2 mph, avg Wh/mi: 10.8

When the hall wiring was damaged in the Bafang I locked the freewheel and switched to a 21A sensorless controller. Power consumption rose some but the weather was getting cold too which always slows me down.


Date Spd Wh/mi

11/20 16.5 10.6
11/21 17.4 12.0
11/22 17.7 11.9
11/28 18.0 12.2
12/1 18.1 13.1

5 ride avg speed: 17.5 mph avg Wh/mi: 12.0


For 2010 I started out with 1 less cell in my LiFePO4 battery (now 15). Here is the data for the last 8 rides covering the same 31 mile course with everything else the same as last fall.


Date Spd Wh/mi

3/23 18.2 10.9
3/24 18.0 11.1
3/29 18.0 11.5
3/31 18.4 11.2
4/1 16.8 9.6
4/4 17.0 10.5
4/5 19.2 11.9
4/11 19.3 12.2

8 ride avg speed: 18.1 mph, avg Wh/mi: 11.1

The power consumption now is only slightly higher (+0.3Wh/mi) with the locked freewheel and 21A controller compared to when the motor freewheeled and I used a 15A controller. This shouldn't be too surprising since I pretty much use the motor all of the time with a light hand on the throttle. However that still leaves me with the question as to why my power consumption rose so much after getting the LiFePO4 battery. Unfortunately I don't have the Fatpacks and SLA's any longer to try them again. I do have a freewheeling 24V geared motor I could try and perhaps with that I can pedal a little more effciently and use the motor a little less however I'm not sure I can ever get back to 7.4 Wh/mi at 17.8 mph :|

-R

 

[Demosthenes]

Then I got the new battery and with the added capacity I didn't conserve power which increased my average speed a little (0.4 mph) however my power consumption increased far more, 46%!

Well at least part of it you just said yourself. You took less steps to conserve power which led to an increase in power used. Average speed isn't necessarily going to increase linearly with power used. Run your trip the same as you would before.

 

[Russell]

Then I got the new battery and with the added capacity I didn't conserve power which increased my average speed a little (0.4 mph) however my power consumption increased far more, 46%!

Well at least part of it you just said yourself. You took less steps to conserve power which led to an increase in power used. Average speed isn't necessarily going to increase linearly with power used. Run your trip the same as you would before.

I should clarify what I meant by that; the only step I took to conserve with the small pack was to ride a bit slower the first 20 miles so I'd have enough power left to pick up the pace on the last 11 miles. I still basically ride the same and for the times now where I've made a real effort to conserve I still can't get anywhere near 7.4 Wh/mi, I mean not even close.

I did find some data that seems to point to the bike becoming less efficient for some reason. Back in August of last year when I was riding efficiently I went out for a ride where I barely pedaled (I estimated 15% of normal at the time). It's the only time I've ever done that and on that ride I averaged 18.0 mph and used 12.4 Wh/mi or about 5 Wh/mi more than when I pedaled normally. Now I pedal normally and almost consume that much power per mile. I think if I run that same route pedaling minimally again I should get a good indication if the efficiency of the bike has declined.

-R

 

[dogman dan]

Greased the hubs lately? I found on my commuters, that 5000 miles dried em up pretty good.

I still think the battery changed everything, without you being able to really feel it. With less sag the watts flow easy and you just naturaly reach a higher number for the most efficient riding that combination of motor, controller and battery is likely to do.

 

[Ypedal]

7~8 wh/mile is very very low consumption... those numbers only happen if you pedal alot with a very well setup bike, on good terrain and nice weather.

Add tire wear, and possibly lower tire pressure ( not sure how well you keep track of that, but it matters !! ) some wind, road conditions and body weight, used and dirtier connectors, meter calibration ( using the same meter ? ) .. factor all that in and in no time at all + 40 % difference in the bottom line !

Personally, i'm pretty consistent when doing my best, i average 10 wh/KM ( notice km.. not mile !! )

 

[icecube57]

I think dogman is right. Higher voltages and lower cell IR you tend to pull more current from the batteries even though your route or riding style never changed. The voltage is kept higher so your pull a fraction more wh out off your pack.

When you look at the fractionally higher voltage and speed higher speed and wind resistance, winding heating and other things plays a factor.

It goes against the law that you need a certain amount of watts to move a certain distance but unless you can control all the variables you can throw that saying out the window.

When you look at the Bosch/SLA setup you are looking at a 44-46v under load. With a good Lifepo4 pack it should be 48-50v under a 20A load. That difference is enough to make things add up at the end of the ride with the new pack.

Higher voltage results in higher waste/losses and i know this all to well. Its not linear it exponential.

 

[Russell]

I conducted a riding experiment today which shed some light on the subject. Last August while I was still riding with the 36V Fatpack+SLA combo I went out for a pleasant ride on my 18 mile course where I used the motor almost exclusively. It was fun however since I ride for fitness as well as fun it has been the only time I ever did that. Today was a beautiful sunny day here so I decided to repeat that ride but first I would ride the route while putting in a good pedaling effort. My goal was to ride the exact course at the exact speed as last August then repeat the ride using mostly the motor then compare the power used for all three rides.

On the first ride today with pedaling I made note of my average speed at key points along the route so that I could try to reproduce those times on the next trip. At 4.5 miles where I picked up the bike path west I averaged 16.7 mph, at 9.0 miles when I turned north the average was 17.3 mph and when I turned onto a frontage road back east at 13.7 miles I had hit the target 18.0 mph and just had to hold it until I arrived home. That turned out to be a little harder than I figured since I had a favorable wind which made riding without the motor easier. Thus while on my usual 31 mile trip I use the motor better than 95% of the time for this trip it was probably 80-85%. I also pedaled a bit harder than typical for the longer route though I didn’t bust a gut, I’d say half moderate and half heavy effort. After completing the 18.2 mile trip exactly where I wanted, 18.0 mph, I checked the WU meter in the rear trunk bag and the results were 3.149 Ah /152.1Wh for 8.36 Wh/mile.

I charged the battery back up then headed out for the second phase of the experiment, riding with little pedaling. Now I normally pedal at around 95 RPM but with the motor doing the work that’s difficult to do. If you ever have put your bike on a trainer and pedaled without the roller engaged you’ll know what I’m talking about. I also understand now why so many folks run big gears on their E-bikes since I often found myself in top gear so I could at least appear to be pedaling. For long stretches (when no one was looking ) I didn't even bother and simply enjoyed the ride. I did contribute a little more up grades to help the motor out as I didn't want to skew the results by having it bog down and draw excessive current. At the first checkpoint I was 0.2 mph behind the pace of the first “normal” ride though I closed that gap by the time I hit the mid point and once again when I turned home at 13.7 miles I was at the magic average speed of 18.0 mph. Again I held that all the way home letting the bike slow some on up grades and speed up on downgrades. At the end of the 18.2 mile ride then the average was spot on at 18.0 mph. The power consumed was almost double at 6.262Ah/298.4Wh for 16.40 Wh/mile.

Comparing all three rides then;

August 17, 2009 80F/light wind “mostly motor” ride, very light pedaling

4.63Ah / 226Wh / 12.4Wh/mi

April 14, 2010 72F/wind 10 mph, “normal” ride, med-heavy pedaling, throttle used 80-85% of the time

3.15Ah / 152Wh / 8.4 Wh/mi

April 14, 2010 76F/wind 12mph, “mostly motor” ride, very light pedaling

6.26Ah / 298Wh / 16.4 Wh/mi


The conclusions I draw from these three rides is kinda what I figured; first my pedaling contributes a good portion of the overall energy, second my E-bike today isn’t as efficient as it was last summer using 32% more energy to cover the same route at the same speed. Now I have to figure out why that is. :?

-R

 

[Russell]

I think dogman is right. Higher voltages and lower cell IR you tend to pull more current from the batteries even though your route or riding style never changed. The voltage is kept higher so your pull a fraction more wh out off your pack.

When you look at the fractionally higher voltage and speed higher speed and wind resistance, winding heating and other things plays a factor.

It goes against the law that you need a certain amount of watts to move a certain distance but unless you can control all the variables you can throw that saying out the window.

When you look at the Bosch/SLA setup you are looking at a 44-46v under load. With a good Lifepo4 pack it should be 48-50v under a 20A load. That difference is enough to make things add up at the end of the ride with the new pack.

Higher voltage results in higher waste/losses and i know this all to well. Its not linear it exponential.

I calculated the average volts for the rides above and it was actually higher for the "mostly motor" ride a year ago with the Fatpacks+SLA combo at 48.8V compared to the rides today with my 15-cell LiFePO4 at 48.3V for the "normal" ride and 47.6V for the second "mostly motor" ride. The LiFePO4 is the only battery I presently own so I can't swap that out but I do have a spare 24V GM Mini Motor to try.

-R

 

[dogman dan]

Well, if the volts is actually lower, including sag while riding not at rest, that pretty much leave just,,,, Greased your brearings lateley? Mabye one of those sealed ones in the motor hub? No drastic tire changes either?

Temperature definitely affects my range, but I don't think it really affects the watthours used. Just the capacity is less. But it isn't august weather yet.

And lastly, how old are you? Post 50, I find if I don't ride for 3 days, it hugely affects my pedaling output. Even a 48 hour break is noticed! In my thirties I could hold a condition for at least two weeks, now it's two days. Good reason to ride more though.

 

[Russell]

Well, if the volts is actually lower, including sag while riding not at rest, that pretty much leave just,,,, Greased your brearings lateley? Mabye one of those sealed ones in the motor hub? No drastic tire changes either?

Temperature definitely affects my range, but I don't think it really affects the watthours used. Just the capacity is less. But it isn't august weather yet.

And lastly, how old are you? Post 50, I find if I don't ride for 3 days, it hugely affects my pedaling output. Even a 48 hour break is noticed! In my thirties I could hold a condition for at least two weeks, now it's two days. Good reason to ride more though.

If you look at the data from the first post you will see when I'm riding the 31 mile course I am very consistent. The average power consumed for that ride rose abruptly when I switched from the Fatpack/SLA combo to the LiFePO4 battery, no other changes were made. At the time I chalked it up to riding faster and using the motor more but when I crunch the numbers my average speed was only 0.4 mph higher but power consumed was 46% higher. It would be easy to say I got soft with the new battery but actually that was not the case. Last fall we had exceptional weather and I rode a ton and put in strong effort. I have logged 740 miles already in the last 5 weeks and am essentially back to where I was last fall in terms of cycling fitness. I am using slightly more power (+3%) no doubt because of the locked freewheel and controller changes (15A to 21A) made late last fall.

The rides I did yesterday were a first attempt to isolate the issues affecting power use. Each ride took just about an hour (18.2 miles at 18.0 mph) and on the ride where I pedaled with moderate to heavy intensity I used 146Wh less from the battery than on the ride where the motor did most of the work. The ride yesterday using mostly the motor however used 32% more energy from the battery as the same ride last August. This ride comes as close as I can get to removing the rider as a variable and leaving just the E-bike.

I don’t have another battery to swap in however since the 36V Bafang does have almost 4,000 miles on it I figured I’d swap that out today. I removed the Bafang/Rhyno Lite wheel and installed the 24V GM Mini motor/Sun CR18 rim I last used on my Raleigh E-bike (which I converted back to pedal-only). This motor only has 200 miles on it. I like things to match so I changed out the rear wheel as well.

It was slightly warmer today at 78F by the time I got out on the road however the wind was blustery with gusts to 30 mph, not the best conditions to run a comparison test but tomorrow is supposed to be windy as well. Oh well the results may not be the best but I wanted to try the bike out anyway. Riding out of the parking lot I immediately noticed the bike was a little easier to pedal due to the freewheeling motor and 35mm tires (Vs 50mm before) however since this was to be a “mostly motor” ride the freewheel would essentially be locked most of the time.

Because of the wind I pedaled more than yesterday but I would still classify my input as “light” compared to “very light“ yesterday. I was able to hit the 18.0 mph goal at the 13.7 mile mark but with the wind behind on the way back my overall speed increased to 18.3 mph by the time I arrived home (Ok I also couldn’t resist blasting down the last grade at up to 38 mph). Anyway the end results from the WU meter was 5.943Ah/281.5Wh or 5.7% less than yesterday’s “mostly motor” ride. I’ll repeat this ride another (less windy) day as well as do a “normal” ride over the 18 mile course to better judge what difference the motor change made but so far it doesn’t look like it had much impact. After that I’ll install a 15A controller. Because I use a light hand on the throttle I don’t expect the controller to have much impact but I’ll have to try it. When I’ve tried all that and done my best to ride economically then all that will be left is the BATTERY.

-R

 

[Russell]

I thought long and hard about how I used to ride my E-bike in the “good old days” of early to mid 2009 when power use of 7-8 Wh/mi for average trip speeds in the 17-18 mph range was the norm and if I slowed a tad and pedaled even more on the perfect day I could hit 6 Wh/mi. In those days the freewheeling motor on a well set-up bike was easy to pedal therefore when conditions were favorable, a tailwind or downgrade, I would pedal the bike without the motor though overall I used the throttle to some degree perhaps 75-80% of the time. Even when I switched to a bike with bigger tires, moved to a hillier area and even augmented my 36V LiMn battery with a 12V SLA to give me a poor man’s 48V battery efficiency didn’t suffer much. The first post shows that I averaged just 7.4Wh/mi at 17.8 mph.

As soon as I received my 48V/10Ah LiFePO4 battery that all changed with power consumption increasing 46% to an average of 10.8Wh/mi at 18.2 mph. I know I’m not pedaling any less or contributing less power but something must have changed. I do know that after I got the bigger battery I tended to use the throttle all of the time. I still contributed with steady moderate or even heavy pedaling but thinking about it this must have had some effect on efficiency. By using the throttle most of the time the freewheeling motor never had a chance to freewheel and surely this could have been impacting my power use.

When after 3,000 miles of use, much of it at 48V, a hall sensor and some associated wiring failed on my Bafang motor I yanked it all out, locked up the clutch so it didn’t freewheel and switched to a sensorless controller. It worked perfectly and because I had been using the throttle most of the time leading up to the change I was essentially riding with the clutch locked most of the time anyway. It was no surprise then when I got my legs/lungs back into cycling condition this spring I was using only 0.3Wh/mi more power over the same course with the locked up motor running on a 21A controller instead of 15A.

I lost one cell group in my LiFePO4 battery over the winter and am now down to 15 cells (charged to 54.3V). With that reduction came a reduction in battery capacity too and while it is small (6.25%) it means I can’t ride further than my 31 mile loop. If I could get back down under 8 Wh/mi I could have assisted rides up to 50 miles with energy to spare.

Today I threw everything I could think of at the problem. I changed out the 36V Bafang with the locked up clutch for a spare 24V GM Mini Motor core with freewheeling clutch. The motor is really a Bafang and slips right into the old case easy as pie. I also swapped the sensorless controller for the original Infineon controller I used to use (now limits to 17.5A). I got the swap done this afternoon and went out for my normal 31 mile trip.

The plan for this ride was to try to reproduce the efficiency I enjoyed earlier last year by trying to ride the way I used to. When I used the 36V LiMn + 9Ah/12V SLA batteries the SLA would die at 4.7-4.8Ah which was my limit thus to conserve power I rode a bit slower than average for the first 20 miles then pushed hard the last 11 miles.

Today was a chilly day with the average temp during my ride of just 50F and a moderate wind out of the NE. When I rolled out on the street and headed south with the wind at my back the bike now with the freewheeling motor felt quite easy to pedal. I decided I wanted to exclusively use pedal power any time I could maintain at least 17 mph. For the first 4.5 miles this was much easier than I expected and I used the motor very sparingly indeed, perhaps 40% of the time. When I hit the bike path to head west my average speed was a fine 16.9 mph, just where I wanted it to be. This ride looked like it was going to be fairly efficient. The bike path was a mixed bag with the motor used about 70% of the time. Heck I even used pedal only power to pass a number of weekend riders! When I headed north the wind was now unfavorable so I used the motor much of the time, probably 95%. When I hit the 20 mile mark to head back east toward home my average speed was right at 17.0 mph. This is the point I used to speed up and use the motor more to reward myself for conserving the battery the first two-thirds of the ride. For a normal summer ride the wind is often favorable out of the west however today it was blowing in my face. I still figured with 11 miles left I could lift the average speed to the targeted 17.8 mph without too much trouble. I could have with enough throttle but today I also wanted to try to come in close to the old 7.4 Wh/mi power consumption and I no longer thought that was going to be too easy. I ended up a bit shy at 17.6 mph however given the cool temps I figured it wasn’t too bad; at 70-80F I would be good for at least the 0.2 mph difference.

Overall I figured had come close to matching the riding style of yore, I used exclusively pedal power when possible and kept my speed in check when on the motor. I was then understandably disappointed when I looked at the Watts-Up meter in the trunk bag and saw I had used 6.996 Ah/ 331.3 Wh for 10.69 Wh/mi or no improvement over the energy consumption of 11.1 Wh/mi at 18.1 mph I have been averaging this spring using the Bafang with the locked clutch, using the throttle almost all of the time and with the 21A controller. I didn’t think the controller would make much difference but I really figured I was on to something by staying off the throttle whenever possible. I figure overall I used the motor 80% of the time which is spot-on what I remember it being before getting the 48V/10Ah LiFePO4 pack.

I can’t get my head around the idea that I could have ridden sooooooo much more efficiently with the Fatpack/SLA 48V combo compared to the power I have used ever since on the same exact route using the LiFePO4 battery and frankly I’m out of ideas. A power consumption increase of 46%, or +105Wh over the 31 mile course has to have an explanation. :|

-R

 

[Russell]

To quantify my present cycling fitness I dusted off the indoor trainer and put the Kona E-bike on it. I didn’t use the trainer this year to get into cycling shape instead I preferred to simply wait until the snow melted and I could get outside and ride. Last year (2009) however before venturing out on my first ever E-bike ride on my newly converted Raleigh hybrid I tossed it on the trainer and used it extensively during the month of January. The first ride after a couple month hiatus is always the hardest as the lungs gasp for oxygen to supply to the heart and the leg muscles are put back to work. The first ride is actually something of an embarrassment as I averaged a granny-like 91W for all of 5 miles . My log shows I used the trainer 23 times that first month with an average power range of 91 to 148W. The log also shows I managed to get out on the inaugural trip for the Raleigh-E on February 6th, 2009, a momentous day indeed 8) . After that I continued to use the trainer but with my Cannondale flat-bar road bike. For February, '09 I used the trainer 18 times with a tight average power range of 143-153W. I continued using the trainer into mid-March recording a best average power output of 157W for 8.4 miles. I also believe that was my best average output ever, well for as long as I had the trainer anyway (~6 yrs I think). Ya, ya I could likely do 200W+ some 20-30 years ago but sadly no more . So how did I fare today? Well considering I had already put in 31 miles on the E-bike and I didn’t bother to unpack the fan I normally used to cool me down while on the stationary trainer, not bad at all. I managed to average 151W for 8.1 miles until I stopped because sweat was dripping all over the carpet. :|

-R

 

[Russell]

I DID IT, I DID IT!

7.37 Wh/mile over 31.0 miles at 17.5 mph, but boy it was work! The speed was lower than last summer by 0.3 mph but I gave myself credit anyway. Today was 58F instead of 70-80F where I ride faster, I was wearing a long sleeve drag-inducing jacket and the clutch is locked up on the motor so it doesn’t freewheel.



I conducted a number of tests to try to discover the answer to my original question and one of them was to test the E-bike as a whole under ideal conditions. While I had the indoor bike trainer out testing my performance I also decided to lock the front motor wheel in place on the trainer to get some hard numbers about the efficiency of the E-bike. Now I don’t know how precise the trainer “Watt” reading is but it tells me I output around 150W so it seems pretty close. I set the resistance level on the trainer so that the top speed of the motor was the same as on the road. I then ran the motor at various speeds and recorded the power in Watts displayed on the trainer panel, the power consumed as shown by the Watts-Up meter and the MPH as shown by the bike’s computer. The efficiency and Wh/mi figures were then calculated.





Train WU MPH Eff% Wh/mi

93 140 11.8 66.4 11.9

145 203 14.6 71.4 13.9

169 238 16.1 71.0 14.8

199 290 17.7 68.6 16.4

246 340 19.3 72.4 17.6

266 340 20.1 72.0 18.4

306 437 21.8 70.0 20.0

The really interesting thing about the data is the 16.4 Wh/mile at 17.7 mph power consumption figure with the bike on the indoor trainer is very close to the “mostly motor” ride I went on recently where I barely pedaled. On that ride I used the exact same 16.4 Wh/mi but at an average speed of 18.0 mph over 18 miles.

What the baseline motor power figures also drove home to me was if I wanted to get down to 7.4 Wh/mi at 17.8 mph (always have to include speed) I was going to have to be riding without the motor a lot more than I thought I used to. With that in mind on a ride two days ago aided by a strong tailwind I rode for a number of miles without the motor. Unfortunately on the way back I needed the motor more than ever to keep my speed up and while my power use of 8.99Wh/mi at 17.6 mph over 31.0 miles was the best this season it still wasn’t good enough. Today the wind was lighter so I set out even more determined. I not only used the motor less but employed the throttle so gingerly the peak amps as recorded by the WU meter (16.93A) never hit the maximum allowed by the controller (~20.7A).

In the end IT WAS all about my input and using the throttle oh so conservatively. When I employed the little Fatpack+SLA battery (yielding 48V/4.8Ah) I was fixated on the WU meter in front of me. I knew I had to conserve whenever possible in order to have power available at the end of the 31 mile ride. At the time I guess I thought nothing of it since that’s how I rode from the beginning starting with a 36V/9Ah SLA pack (5.4Ah max) which I would stretch out to over 30 miles also. The arrival of the 48V/10Ah LiFePO4 battery instantly spoiled me; I not only started using the motor all of the time but my cadence fell as well which reduced my power. Now do I want to work like a dog each outing to save a few cents of electricity, oh probably not I can ride by pedal-only bike for that, but the ride satiated my curiosity. Hmmm…I also used to regularly hit 6.0 Wh/mile, albeit at a lower speed, which I might try to match again. :wink:

-R

 

[dogman dan]

Well call me granny, Now that I have a cycleanalyst, I see I put out at most 80-100 watts with my pedaling, and often only about 50 watts. My watthours per mile is near 20. But that's at 25 mph or more.

Facinating once you can measure it, how really really hard it is to get from 20 mph to 30 mph. No wonder 15 mph is so efficient. Only takes about 200-300 watts to get that, and you can provide half of it.

Other really fit cyclists have complained that ebikes made them lazy, but for me I was so lazy and flab to start with that it has only helped me get and stay fit.
Trouble is, it doesn't take me all winter to lose it now. I go straight to square one if I don't ride for 7 days. Even 3 days without a 10-15 mile ride will make me feel pretty weak the next ride. Now I understand all those workout crazed 60-80 year olds. One day missed and you get to start over.

 

[mud2005]

nice work Russell, makes me think about building a super efficient road bike with a small motor and battery and seeing how far it will go.
maybe an astro 60 and one 6s lipo pack. with a top speed of 15-18mph you could get decent range.
if you wanted more range just carry more lipo packs in a backpack.
maybe we can start a "most efficient bike contest" thread

 

[liveforphysics]

nice work Russell, makes me think about building a super efficient road bike with a small motor and battery and seeing how far it will go.
maybe an astro 60 and one 6s lipo pack. with a top speed of 15-18mph you could get decent range.
if you wanted more range just carry more lipo packs in a backpack.
maybe we can start a "most efficient bike contest" thread

It's not the size, it's the efficiency of the motor that matters.

I would think going any smaller than an Astro 3210 would only result in worse w-hrs/mile.

 

[mud2005]

It's not the size, it's the efficiency of the motor that matters.

I would think going any smaller than an Astro 3210 would only result in worse w-hrs/mile.

good point the astro 60 is up to 93% efficient, but runs at much higher rpm so would lose efficiency in the gearing.

 

[dogman dan]

Zoot would win a most efficient bike contest, by peadling us all in the the dust on a cargo bike with an x5 and the motor off. :lol:

But most effiecient with no pedaling would be a very interesting contest, Isn't that kind of what they do in electrathons?

You'd have to have classes, one for recumbents and one for uprights. But to mean anything, the bikes would need to be in the same place at the same time since weather would have huge impacts on the watthours per mile.

 

[Russell]

nice work Russell, makes me think about building a super efficient road bike with a small motor and battery and seeing how far it will go.
maybe an astro 60 and one 6s lipo pack. with a top speed of 15-18mph you could get decent range.
if you wanted more range just carry more lipo packs in a backpack.
maybe we can start a "most efficient bike contest" thread

The lowest Watt-hour per mile for a given speed will of course be obtained by the rider who maintains a speed on their E-bike close to their capabilities before the conversion. I averaged 15 mph on my Kona Smoke before I converted it but with the added weight of the motor and battery plus the drag of the motor combined with the hillier area I live in now I figure I could average maybe 14 mph unpowered. The closer I ride to that speed then the less power I will require from the motor. A good compromise between energy consumption, speed, range and fun for me with this bike is to average about 18 mph. That’s an average speed btw which for me at 195 pounds and 51 years of age with about a 150W output is unobtainable on a regular pedal-only bike (though I've never tried a recumbent).

Power efficiency then for a rider and ebike for a given speed is always going to be different. If a cyclist who can already average 19 mph adds a small motor and lightweight LiPo battery to a road bike then they could no doubt obtain my average speed with zero Watt-hours used from the motor. On the other hand someone who can barely average 12 mph on a mountain bike before converting it who then adds a heavy motor and battery is going to need the motor running all of the time to hit an average trip speed of 18 mph consuming lots of power in the process.

Motor efficiency on its own then will play more of a role for the E-biker who runs their motor all of the time. The test I conducted with my motor-wheel spinning the indoor trainer showed it consumed 16.4 Wh/mile to maintain a steady 17.7 mph therefore if I replaced it with a motor which was 10% more efficient it would require about 14.8 Wh/mile. You can see however while that would make the bike more efficient under power it only helps a small amount to achieve really low power consumption because really low power consumption only comes with using the motor sparingly or not at all for a good portion of ones ride.



-R

 

[drewjet]

This has been an interesting thread Russell. I have been watching closer lately. On my 9.5 mile commute to work I have been around 10 to 12 wh/mile at average speeds of 17 to 19 mph, depending on the day. On my way home I am in a bigger rush to get home and am tired, so less pedling more throttle I am usually averaging 20 to 22 mph and around 20 to 25 wh/mile.

This is on a geared freewheeling rear hub at 48 volts hybrid bike.

 

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Just wish to add... air temp has been mentioned already, but this may be in relation to how it cools the battery. From 20 degrees celsius down to zero C for example, over this 20C range air density increases about 7% so even with an insulated and/or heated pack, no getting away from higher aero drag in the cooler months!
tks
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