Building the most efficient electric bicycle possible

[auraslip]

Who has the most efficient ebike here in terms of Wh per mile? What's your setup?

I want to build an electric bicycle. As in, 23 mph top speed, and built to be pedaled. This will suit my commuting much better than my other 50 mph bike that will overheat or give me range anxiety if I'm not careful. Also, at stock power levels I'll have much less reliability issues!

I'm thinking a vintage steel road bike frame might be good platform or a newer $200 AL cross frame paired with a geared hub motor.

Lastly, I'd like to have the battery pack at less that 40v. Why? Because I want to build some of the components for the bike myself such as on board charger, DC/DC, and startup circuit. Above 40v the ICs to make these components are non-existent or very rare! Also, less packs in series are MUCH simpler to monitor. I'm stilling having nightmares about the 50 feet or so of 20awg wire I used to make the balance harness on my last bike.The perfect setup would be an 8s battery pack made from 4s hard case lipo bricks, but I'm not aware of anyone running their bikes on a voltage that low.

So I guess I'm asking: what sort of efficiency can I expect from a geared hub at lower voltages like 8s, 10s, and 12s?

 

[Hillhater]

you should look at Keplers Eboost or Adrians "commuter booster" , for low voltage , high efficiency drive packages.

 

[Sunder]

The great thing about this forum, is that so many of my questions are answered without having to ask them!

I was thinking about an 8S pedal assist bike as well. My 12S2P 1000W bike is a bit of a nightmare. I built it without guidance from anywhere (Didn't even find this site until after my first ride). I really don't need 1000W - in fact, for 10-15 minutes, I can actually go faster on my carbon road bike, than full throttle on my 1kw steel framed clunker.

My thoughts were something like the MXUS motor, small, light, 24V controller over driven with an 8S pack on an alloy/carbon frame. Possibly even only pedal assist, but from my experience and what most people say here, it's very unreliable, and front brake kill switches are an absolute must. So given that, I'm thinking of twist throttle and no electric kill switch in the brakes, as long as there is a master kill switch in the throttle.

 

[neptronix]

10t mac motor on 36 volts. Use at least 10ah of lipo so that you minimize the voltage drop to get the maximum WHr/mi.

On 36v, that will get you a little over 2 miles per amp hour if you pedal.

Or if you want ultra efficiency, you want a tiny geared hub that does about 15mph, aka european spec. On 36v, you could get 3 miles per amp hour on 36v.

I don't have a cycle analyst so WHr/mi. is a bit foreign to me, thus the amp hour per mile at 36v measurement.

 

[StudEbiker]

I don't have a cycle analyst so WHr/mi. is a bit foreign to me, thus the amp hour per mile at 36v measurement.

Do you have a Turnigy watt meter? It shows whs used . I just use that number with my cycle computer for dist. traveled to get wh/mi.

 

[auraslip]

Oh, hell yeah. I'm going for range. Probably 15ah or 20ah. Near a KWh fully loaded. This is gonna be my "go to school, work, the store, and to the bar with out charging once" bike.

10s would be fine, but 5s packs are more expensive. And at that point I'm over 40v and might as well go to 12s.

Are there any hub motors that would run at 8s? Perhaps a faster geared motor in a 700c wheel?

 

[neptronix]

I don't have a cycle analyst so WHr/mi. is a bit foreign to me, thus the amp hour per mile at 36v measurement.

Do you have a Turnigy watt meter? It shows whs used . I just use that number with my cycle computer for dist. traveled to get wh/mi.

That's a really good idea and i do have a turnigy watt meter.
But my bike computer cuts in and out ( occasionally reading 0mph ), so for calculating mileage, i don't trust it.


Auraslip: 5s packs are not that expensive. $42 for 5AH 5S 20C from hobbyking..

http://www.hobbyking.com/hobbyking/store/uh_viewItem.asp?idProduct=15008

But you know what would be boss? a cell_man MXUS geared kit on 12S. Should hit 20mph on that voltage. Smaller gears and transmission than the MAC will make for a pretty low parasitic drag, so it could very well be more efficient. I sold mine to veloman, now he's hooked on the MAC motor like me these days, probably has the kit lying around, and lives in Texas as well.. might be a good setup for you, besides the wheel + motor is like ~8-9lbs and can hide behind a rear disc brake and freewheel with a 30t gear very well... stealth mode, son!!

So like i do with my build.. falconEV bag on a hardtail.. you can stuff 20AH into that sucker no problem.

 

[Hillhater]

........I want to build an electric bicycle. As in, 23 mph top speed, and built to be pedaled.
........Are there any hub motors that would run at 8s? Perhaps a faster geared motor in a 700c wheel?

I dont see your problem ...
If you want to pedal, and only need 23 mph then any old 350W , 24v ( 6s) hub with a 30a controller , will do what you want.
Efficiency (as always) will depend on how much you pedal ! :wink:

 

[cwah]

I've a 250W motor at 36V with a direct drive motor and 25kg bike (from Conhismotor). It reaches 33Km/h at 12Ah and use 12wh/km without peddling.

I think most of the bike will consume around 12 wh/km for this speed if you don't pedal. I'm keen on hearing any better configuration.

------------------------------------------------------------

The only bike that can go below 12 wh/km are:
- The one where author is peddling at the same time. But in that case you're not really measuring motor efficiency, but rather the motor and the author efficiency together. To make comparison easier, I think we should only compare motor efficiency without peddling
- The bikes slower than 30km/h. But this is not an acceptable speed. In that case we just have to buy a light road bike and that's enough
- The RC configuration bike. But author has to peddle to start. So I'm not sure how to compare.
- And the Bent bikes. Wind seems to be a huge factor.

 

[parabellum]

Isn't DD motor more efficient the geared when used? I would only use geared motor if pedaling with no assistance is in mind. Remember, you get 1-5% back on regen with DD.

 

[veloman]

I'm currently building that mxus geared motor into a rigid steel mtn bike, either as an ultra distance bike or something for my gf to ride. I even thought about selling this bike, but have doubts I could get my money back on it in the local market.

It is very efficient, but I think that's due to going so slow on 36v - 17mph-ish. You can easily get 10wh/mile on it if you pedal a bit. But you need to go 23mph, so that will need like 15s.

What you want it is a Currie geared my1018z set up as a crank drive. That would give you incredible range and hill climbing. My 2nd -4th builds used this. Noisy and complicated.

aim for light weight and low power.

 

[Hillhater]

Isn't DD motor more efficient the geared when used? I would only use geared motor if pedaling with no assistance is in mind. Remember, you get 1-5% back on regen with DD.

First line of the OP ..

........I want to build an electric bicycle. As in, 23 mph top speed, and built to be pedaled.

 

[parabellum]

First line of the OP ..

My bad, I understood he wants to pedal helping the motor to extend range, not just pedal. Just pedaling and lycra makes it the most efficient setup, why putting all the heavy electric stuff on it?

 

[Drunkskunk]

Pedaling is way less efficient that Ebikes. it takes around 40watts to get1 watt of food from the seed to your table, and your body burns that at about 25% efficiency. So 160W of fossil fuels to get 1 watt of pedal energy.



DD is the way to go if you have long stretches at constant speed and plan to use the motor assist all the time. I can get 11wh/mi easily on a MTB with fat low pressure tires and modest pedaling, and thats on a Clyte 408. A 9C would bump the efficiency up 5% or so. And regen to boost your numbers (slightly) even more. You're also more efficient at higher voltages, and more efficient still if you don't use any DC/DC converter, and run a separate pack

 

[parabellum]

I actually pedaled once after 15 years brake, with 3 shorted phases in the hub, no joy, no more pedaling for me for at least 15 years more.

 

[neptronix]

Yeah, on a long & steady speed, a DD will have 3-5% better efficiency in the absolute best case scenario where you have no wind, stop and go, or hills to deal with.

In anything other than perfect conditions, a

Does regen even the playing field in a flat area? i don't know. But owning 1 bike with a MAC and 1 bike with a DD, the MAC always wins in acceleration ( steadier, flatter torque band ), and goes a bit further on the same charge in my hilly, stop and go sort of terrain.

 

[jmygann]

I thought direct chain drive was the most efficient ... maybe a 3 speed hub on 24 volts

 

[Jason27]

I pay about 4 cents to go 15 miles on my electric bike. I used a killa watt meter along with san francisco electricity rates to get this conclusion. It doesn't get much more efficient than that.

 

[Hillhater]

I pay about 4 cents to go 15 miles on my electric bike. I used a killa watt meter along with san francisco electricity rates to get this conclusion. It doesn't get much more efficient than that.

What is you kWhr charge ?..10c /kWhr ?
so you used 400whrs to do 15 miles... = 27 whrs/mile
... thats not very efficient when guys are getting under 10whrs /mile

 

[Hillhater]

I actually pedaled once after 15 years brake, with 3 shorted phases in the hub, no joy, no more pedaling for me for at least 15 years more.

That is one good reason NOT to go DD hub !

 

[neptronix]

I pay about 4 cents to go 15 miles on my electric bike. I used a killa watt meter along with san francisco electricity rates to get this conclusion. It doesn't get much more efficient than that.

What is you kWhr charge ?..10c /kWhr ?
so you used 400whrs to do 15 miles... = 27 whrs/mile
... thats not very efficient when guys are getting under 10whrs /mile

Well he does live in San Francisco. Ever been there? i know i shaved some serious life off the clutches of my cars driving there. 0%-12% grades and drops every 2-3 blocks. It's no wonder that the shops over there seem to specialize in selling MAC/BMC motors. I'd think a DD would overheat from being outside of it's efficiency band out there on those crazy hills.

 

[amigafan2003]

My Trek FX 7.5 built with a 190rpm Tongxin hub on a Lyen controller limited to 13amps and 44.4v 10ah Lipo pack does 11watts/km @ 32km/h no peddalling.

 

[dogman dan]

FWIW, my experience leads me to believe that 23 mph on the flat, on similar frames, takes just about the same wh/mi regardless of whether the hub motor is dd or planetary gear. Even motor windings make little difference if there are not excessive hills or stops involved. All the real differences in wh/mi numbers for a given speed are more the result of how much or how hard you pedal, your weight, grade of hills, and the areodynamics of a particular bike and rider.

If I'm not mistaken, your commute is fairly flat? So on the flat, once going 23 mph it's simply going to take x watts regardless of the type of motor.

So you want excellent wh/mi numbers for a given speed? Improve your aerodynamics, likely with a bent, and pedal your ass off.

You won't find the magic hub motor that is noticeably more efficient. It's quite possible that a chain drive setup with gear shifting could be more efficient, but that might be mostly a result of having the ability to dial in the optimum motor rpm. But even with a hubmotor that isn't the ideal winding, it won't do much worse on the flat, once at speed. Only when bogged down on a hill will it matter so much.

I'd say for 23 mph, running a 9c or muxus 2807 at 10s would be about optimal.

Build your pack easy to remove from the bike, then you won't need permanent paralelling of balance wires.

 

[veloman]

There is no need for a heavy DD motor if he's only interested in a 23mph top speed. Just overvolt one of the little geared motors.


My efficiency has gotten worse the last month or so, with long pants and a jacket. I also think I'm pedaling less / not as hard, and I'm on a full suspension now. It took 230watt hours to go 9.5 miles over nearly all flat terrain with about 14 stops. My top speed is only about 27mph instead of 28-29mph too. I hate losing efficiency but I had to go to a full suspension. and it's impossible to find decent looking, affordable, form fitting cool weather clothes.


All these wh/ mile figures mean very little. We are all going different speeds, have different riding positions and different conditions and roads. Speed is the biggest thing by far though. Like I said, I got 6 watt / mile on my first ebike ride this year since I pedaled the entire time, was limited to 500w peak and 17mph top speed. This morning I got 25wh/mile riding mostly about 24mph, 800w peak, more frequent stops, and pedaling much less, on a 12lb heavier full suspension with a larger geared hub.


Why avoid weight so much? Weight costs you a lot more than what it looks like it does on paper. It adds rolling resistance too, so it is slower on the flats. You can't ride as narrow tires with more weight. It's like a snowball effect. Ever ride a road racing bike? Try one out at the LBS. See how you can endlessly coast at 10mph.

My point is that if you are going for efficiency, a 10-14lb hub motor may not be the best bet. It's my rule of thumb that weight has DOUBLE the effect it does on paper. When are you *not* accelerating? If you think about it, even steady riding involves tiny accelerations half the time.

23mph is fast enough to make aero a big deal. Wear tight clothes. My regular fit jeans cut my speed down by at least 1mph compared to gym shorts at 28mph. Get low, get narrow. The average ebiker is a brick, by far the least aerodynamic object for it's speed and weight.

But the easiest way to improve range is to lower your amp limit, if you have such a controller or CA. I got 13wh/mile on my current setup, but at 14amps limit. At 21amps I'm getting 22-25wh/mile because I pedal a LOT less.

 

[jmygann]

Most efficient with pedaling ..... Josh should know .....

http://endless-sphere.com/forums/viewtopic.php?f=28&t=34595