MAH per mile?

[recumpence]

Hey Guys,

I am curious to know how much power is typically used in an e-bike over a given distance.

I get 24 miles out of 8AH 48 volt pack on my bike (if I am careful). That is averaging 20 mph without any pedalling at all.

That equates to 333 milli-amp-hours per mile.

What would be the norm? This is my first e-bike. So, I am unsure if this is good or not.

What do you think?

Matt

 

[slayer]

without any pedaling ...i think it is great ...i can get close to that with lot pedaling on a 36 volts 15 ah nimh and 5404... just by memory i usualy get around 30 km for about 11 ah ... so 396 watt hours for 30 km wich is worst than you without pedaling ... you would be getting 384 watt hours for 38 km

 

[recumbent]

I also have a 48 volt battery that only seems to get 10 AH according to my Cycle Analyst meter, but can go 45 km (28 mi) before it dies.
No peddaling and combination terrain including trails.

 

[recumpence]

This is a recumbent. So, it looks like (for a recumbent) this is about right.

My bike as a 4,000 watt bike. There are alot of driveline losses due to being a high power setup. So, considering that, it looks like I am doing alright.

The best range I have seen (calculated over about 8 miles, then extrapolated out) is 25 miles on 8AH (10 AH lipo pack leaving 20% capacity in the pack) averaging a touch under 18mph. The worse was 17 miles distance on that same 8AH. That was done over very hilly roads at full throttle 37mph the whole way.

I guess my setup is fine, then.

Matt

 

[slayer]

I DONT KNOW HOW TO PUT IT IN MAH

me =13.2 w km
recumpence = 10.10 w km
recumbent = 10.6 w km

 

[michaelplogue]

Just took my electrified Diggler kick scooter (no pedals) out for its maiden voyage today.

20" wheels
36V, 16.4AH - Li(Ni-Mn-Co)02
Xlite 5303 w/ 3640 controller
Top speed 23.2 MPH
Average speed 18.5

On hilly terrain for about 10 miles I ended up getting about 980 mA per mile.

.

 

[recumbent]

The best range I have seen (calculated over about 8 miles, then extrapolated out) is 25 miles on 8AH (10 AH lipo pack leaving 20% capacity in the pack) ...

Hey, that's no fair because our LIFEPO4 batteries, BMS kicks off at about 40 volts, if we disconnect the BMS we can go MUCH further. edit: maybe not because the cells will reverse polarity or die if we do that.

BTW, thanks to "Slayer" for reminding me to check my Cycle Analyst meter, it says I get 9.8 Watts per KM.
8) I'm pushing for first place, wonder what i can do to get better performance next time.

 

[monster]

i get about 850mah per mile with gentle pedaling on X5 at 36v NiMh

 

[recumpence]

The best range I have seen (calculated over about 8 miles, then extrapolated out) is 25 miles on 8AH (10 AH lipo pack leaving 20% capacity in the pack) ...

Hey, that's no fair because our LIFEPO4 batteries, BMS kicks off at about 40 volts, if we disconnect the BMS we can go MUCH further. edit: maybe not because the cells will reverse polarity or die if we do that.

BTW, thanks to "Slayer" for reminding me to check my Cycle Analyst meter, it says I get 9.8 Watts per KM.
8) I'm pushing for first place, wonder what i can do to get better performance next time.

Well, for this discussion, you are definately in first place.

I did some more calculations. My MAH per mile is closer to 400 when you look at other factors such as needing to get on the throttle hard once or twice in a run. Also, the 333 mah per mile was letting off throttle down hills and getting back on it only when the road flattened back out, etc. I was pushing for absolute maximum distance. However, again, I have a super high power drive setup using a 3 stage reduction from the motor to the rear wheel. That drive sucks up power just to turn it. My idle current is also high because of the motor I am running. So, all that considered, I am pleased with it!

I know I can increase my efficiency, though. The primary belt I am running from the motor to the jackshaft is a 15mm wid3, 5mm pitch toothed belt. The belt gets planty warm running. I have tried 9mm wide and I was able to shred that belt when abused heavily. But, my efficiency was noticeably better with the 9mm belt. Maybe I will have a custom 12mm wide belt made. That should give me about 10% better efficiency for the drive system and should be enough to tolerate the load I put on it under heavy acceleration.

I love this stuff!

Matt

 

[Drunkskunk]

Saying .333 amps per mile only works if you compare it at 48V. Converting it to watts lets us compare your power useage at other voltages. You're getting ~16 Watts per mile at 20mph.
Not bad! My gearless hub mountian bike gets around 20 watts per mile at 20mph.

 

[safe]

I've got a 48 volt 18 ah setup and can go 10 miles at 30 mph average. So that means I'm using about one "usable" amp hour of the 18 (since Peukert takes the rest) per mile.

But it's better to think in terms of Watt Hours because that combines volts and amp hours into a single figure. (it's a unit of energy that needs no more dimensions to it)

And your top speed should matter too.

So for me I'm using something like 1000 watt hours per hour or something like 350 watt hours per ride or 35 watt hours per mile. (something like that)

And you also need to ask:

" Can I survive a high speed sweeper turn when the rear wheel drifts out slightly without crashing." :lol:

(my bike is all about "sport" and not efficiency)

 

[recumpence]

It looks like my rolling resistance and great aero (being a low recumbent) is helping me alot.

Again, if I run it full throttle 37mph on a very hilly road, I still see 480 mah per mile. Hmm, I definately think it is my aero and rolling resistance because the 333 mah I was seeing was 20 mph average while doing alot of coasting. The 480 mah per mile I just mentioned is 37 mph full throttle the whole way (maybe a small amount of coasting down hill).

I love R&D.

I am at the shop today machining a piece of medical equipment I designed (invented) for a local doctor I know. Fabrication is fun!

Matt

 

[TylerDurden]

Just to add context:

Bill's WAW velo got 15.79Wh/mi @ ~30mph

My Citicar got 333Wh/mi last week @ ~25mph

 

[safe]

The 480 mah per mile I just mentioned is 37 mph full throttle the whole way...

So if you take the voltage times the amp hours you get:

48 volts * 0.48 Ah / mile = 23 watt hours per mile.

The guy that did the ePower Challenge was getting roughly three times the efficiency as I do with about the same SLA configuration. However, that's "steady state". When asked about real world riding with starts and stops and hills he would probably be closer to mine. (he claimed his best real world average speed would be about 20 mph average compared to my 30 mph)

One of these days I'll have to find some sort of oval to test what my efficiency could be ... I've never tried it... my tests tend to revolve around my "thing" which is performance. (turns, hills, braking, etc) I think if you actually saw the speeds I'm carrying through tight turns you would appreciate my unique sport idea. (the bicycle road racer concept)

Recumbents definitely are best suited for efficiency contests...

 

[recumpence]

Just to add context:

Bill's WAW velo got 15.79Wh/mi @ ~30mph

My Citicar got 333Wh/mi last week @ ~25mph

Cool, so I am right in line, then.

Matt

 

[safe]

Bill's WAW velo got 15.79Wh/mi @ ~30mph

Cool, so I am right in line, then.

Yeah you're in the running no doubt about it. (23 Wh/mi vs 15.79 Wh/mi so far...)

What's needed is a perfectly smooth and flat oval so that you (or I) could actually test for steady state conditions. There's a huge difference between racing around verses steady state. I would not be surprised that with your RC motor that you could compete head to head with the ePower challenge machines. My bike has all kinds of inefficiencies in it, so I could improve my score a little, but never get near these efficiency records. (I'm not expecting it to compete on that level)

After all... I'm running a brushed motor, a transaxle between two worn out chains and almost 4,000 miles of wear and tear... (it's still a lot of fun, but "elite" efficiency it is not)

 

[recumpence]

I did some more testing and found my front tire was low (35 pounds of air) and my rear was at 48 pounds. They are now up at 90 pounds. I pulled 120 pounds of weight in my trailer over my normal riding course (but at 14 mph instead of 20 mph) and averaged 19.23 WH per mile. I will do some more testing, but it looks like I can get it around 17 or 18 WH per mile at 20 mph without the trailer.

Matt

 

[safe]

...averaged 19.23 WH per mile.

You need to find some smooth flat oval to test on. Ideally if there was a school nearby you might be able to circle the track if it's made of cement. You need to maintain a 30 mph+ speed and seek to get your energy usage down to 15.79Wh/mi.

Your ePower competition is an SLA battery powered, fully fairing covered, pure efficiency machine... so you're up against something that was designed specifically for this sort of thing. But come next year you might start to think about attending the event... it's a good place to demo your work. (you might even get on tv)

My efficiency is nowhere in the ballpark, so for me to do the test it would be more of me just wanting to know how efficient my machine can be in ideal circumstances.

You would think that in order to get such efficiency that you would need Lithium, but the ePower guy used SLA.

 

[EMF]

If you can do that without pedalling, that is quite impressive. If I average ~22 mph on my bike, it uses between 21 and 23 watt hours per mile, and I pedal a little bit. A recumbent like yours will certainly help with the wind resistance factor as compared to mines sit up in the wind design. If I go over 22 mph on my regular bike, the watt hours really start to climb. I keep the tires filled with the highest amount of air they are desinged for.

If I were to stay under 15 mph, I'm sure i could get 17 - 18 watt hours per mile. (especilally at these speeds, it's easy to pedal along) But, I can't do it, I like cruising around 20 or so.


EDIT: Rats! I meant watt hours, not amp hours. I fixed the post :?

 

[paultrafalgar]

Watt Hours per mile seems to me to be the way to compare our bikes. We're about producing efficient means of transport compared with gas/petrol/diesel cars/motorbikes. The only factor that should be taken into account in compensation is perhaps rider weight. Assuming that's not amendable (by slimming); the bike weight is part of the challenge (make it as light as possible). I suppose hilliness of terrain might be included. If you wanted to compensate for that you would have to include "height gain" for the trip on which you measured the watt-hours. You could use Fugawi, or some such to give you that figure. So, I propose an Ebike Efficiency Index:
Ebike Efficiency Index (EEI) = Watt-Hours per mile (WH/M) less (Rider Weight (RW) * Height Gain (HG))

Tests to be done in negligible wind conditions.
Speed should be should be incorported as a parameter in the following way:
Use the average speed for the test trip...

Subtract the power (watt-hours) used in climbing from the watt-hours/mile figure.
Calculate the power used in climbing as follows:

Say the climb is 200 feet and my weight is 220 lbs = 44000 lbs-feet
Say my average speed was 7 mph and the test trip was 14 miles.
That's 120 minutes or 7200 seconds for 44000 lb-ft = 6.11 ft-lbs/ sec
1 Horsepower = 550 ft-lbs /sec
6.11/550 HP = 0.01111 HP = 8.33 watts for 2 hours = 16.66 watt-hours
= 16.66 watt-hours for 14 miles = 1.19 watt-hours per mile

So, if my CycleAnalyst (if I had one!) reads 18 watt-hours per mile for the trip, my

EEI = 18 - 1.19 = 16.809 watt/hours per mile.

Please criticise this a) as a strategy for scientific analysis of efficiency and
b) incorrect maths/reasoning

 

[Miles]

Paul,

Wouldn't a "there and back" trip be an easier way to handle this?

 

[TylerDurden]

HG is kinda tough... I'd suggest testing be done on flats, with separate testing for hillclimbing ability.

Reason: averaging the hills won't balance the difference in grades.

:?

 

[paultrafalgar]

Paul,

Wouldn't a "there and back" trip be an easier way to handle this?

Don't understand that at all, Miles. If you were measuring speed, yes, you could average over both directions. To get a measure of motor efficiency, you need to test how much power the bike uses; the components of that are:
1) Working against wind resistance (which we are ignoring)
2) Working againt rolling resistance (differences of surface friction eg tarmac vs cycle path - ignoring)
3) Working against gravity (which varies with rider weight - which we need to eliminate as it's irrelevant to ebike performance)
Now, explain what you meant, please, I don't understand :?

 

[paultrafalgar]

HG is kinda tough... I'd suggest testing be done on flats, with separate testing for hillclimbing ability.

Reason: averaging the hills won't balance the difference in grades.

:?

For this forum, most people could, if they had a CycleAnalyst, test on the flat, I agree. But, to get efficiency figures that differentiate between hill climbing ability (eg between Hub and Chain-driven motors) you need to include hill-climbing ... but exclude the difference in rider's weight. I have tried (probably with errors ) to work out and subtract the power needed to raise the rider (weight x height gain) from the efficiency index. Tell me where I'm going wrong.

 

[Miles]

Using average speed could give quite large errors, depending on the speed range.

I proposed "there and back" as a simple way to neutralise the height element on relatively flat terrain.

Surely we want to measure the total system efficiency, no? Measuring the motor efficiency is more easily done by calculation and verified on the workbench.