72V efficient city commuter ebike - build log

[mlt34]

This build is going to be my first foray into voltages above 60V. I'm planning a 72V ebike with the main requirements being:

• top speed: 30 mph (48 kph)
• range at top speed: 20 miles (40 kph)
• highly efficient for city driving
• capable of occasional light off-roading (shortcut through park, curb hopping, etc)
• regenerative braking
• cruise control
• accessories: car horn and airzounds horn, powerful 12V front/rear lights, phone charging, and more to come...

More specifically, these are the parts I plan to use:

Motor: Nine Continent 2810 (slow 6x10 wind)
Controller: Greentime 15fet 4410 72V 45A to eventually be replaced with 72v Infineon 12 fet 4110 (and CA limited to 20A)
Battery: 72V 11.4AH custom pack from LG 18650 2850mah cells and BesTechPower D131 BMS
Bike: Haro Vseries V2, aluminum frame, 26" wheels

The bike:
The bike isn't my first choice, especially not the aluminum frame. But in Israel, good bicycles cost at least double what they do in the US, and so this was a decent used bicycle with lots of room in the triangle and most importantly, affordable. I'll use a torque arm obviously, and so the aluminum isn't too big of a problem. I'm also not going to be running high current, so it should be fine as far as the dropouts are concerned.

The motor:
I love the 9C 2810. Many people find it too slow, but when run at high voltage it makes for a very efficient, torquey and powerful setup - all while minimizing current draw and increasing range as compared to faster winds at the same voltage. Genuine 9C 2810's are rare these days. This particular one was purchased years ago from ES user methods and spent a year on a previous bike of mine before going on sabbatical (i.e. spending nearly three years under my bed). Now it's time to dust it off and return this motor to its former glory.

It's a bare hub so I'll have to lace it myself. No biggie, it's just a royal pain in the ass to cut and roll all those spokes. I live in Israel where buying custom cut spokes is crazy expensive. So it looks like me and my Cyclo spoke forming tool are going to get intimate again.

(image from the future, after I cut the spokes)

The controller:
I'm starting with a greentime controller because a) I've never used one and wanted to try it out, b) it has all the features and functions I need, and c) it was cheap and fast from aliexpress. The 4410 fets are not ideal, but again I'm not going to be running high power so it should be fine. Eventually I may replace it with an inineon - or not, depends on how I like it.

Because I don't need huge power, I'll be CA limiting to 20A. 1400 watts will be plenty for 30 mph.

The battery:
I couldn't find any sources for good 72V lithium packs. The only 72V complete NMC pack I could find was from calibike, and it was recently revealed that they use UltraFire cells to build their packs, which is about the same as building a car out of PVC pipe in terms of quality and longevity. It can be done, but it ain't going to be good.

I also considered lipo but I decided against it for the following reasons:

• with lipo I can't lend the bike to a friend without worrying about safety
• I want a plug and play solution for easy charging, even on the go (balancing never required)
• I don't want a cheap lipo charger and I don't want to spend the money on a good one right now (one day...)
• I want a removable battery for when I park in public places - and not one that looks like 8 small improvised bombs

Sure, the charging one isn't as much of an issue, but still, I just want a simple plug-it-and-forget-it battery on this bike. So in lieu of finding a good vendor or going lipo, I'll just build my own from 18650's.

More to follow.

 

[upek]

My advice - don't use these cells at that current!
If you want to have long life from this pack use up to 5A/per cell. I know that these are rated at 8.5A burst, but number of cycles will be much lower and cells will be getting warm.

Use at least 20s8p or choose real high current cells (LG HE2, Samsung 25R or similar)

 

[mlt34]

You are absolutely right, I forgot to mention that I'll be CA limiting the current to 20A, which will be just under 5A per cell, their near maximum.

The 25R's are awesome but a bit out of my price range right now

 

[upek]

You can also "hunt" for high current cells with little less capacity like Samsung IMR18650-20Q or 20R, Sanyo UR18650R, UR18650RX. These are widely used in many packs, so second hand cells could be pretty cheap.

 

[999zip999]

I ran that 2810 @ 72v30a 2,200 watts 29mph doesn't get hot. I did burn it up in soft wet sand 4 days ago. My fault, but it was my low tide beach motor after a couple yrs 5,000 plus miles. I was being lazy. I loved that motor and want one more.

 

[mlt34]

The pack I'm building from LG cells I got from tumich's thread here: http://endless-sphere.com/forums/viewtopic.php?f=31&t=61608
I almost don't want to advertise it because I want all his cells for myself. But I can't afford all his cells, so maybe someone else can make some nice packs too. I highly recommend it if you're looking for new, affordable name brand cells.

Anyways, I picked up two packs that were already welded for 10s4p. The welds look great. Apparently the plastic cases failed QC, but the cells were fine, so these are brand new, ready to go packs. Woohoo!

I'm using a D131 BMS from BesTechPower. It is perhaps the nicest BMS I've ever seen. Hell, it's probably nicer than I need. But I know I won't have an issue with it, so I don't mind paying more for a black box that I don't have to worry about.

The packs are getting wired in series, giving me a 20s4p for approx 72V11.4AH in the end. Not bad for $300.

 

[arkmundi]

This build is going to be my first foray into voltages above 60V. I'm planning a 72V ebike with the main requirements being:

• top speed: 30 mph (48 kph)
• range at top speed: 20 miles (40 kph)
• highly efficient for city driving
• capable of occasional light off-roading (shortcut through park, curb hopping, etc)
• regenerative braking
• cruise control
• accessories: car horn and airzounds horn, powerful 12V front/rear lights, phone charging, and more to come...

More specifically, these are the parts I plan to use...

You've obviously thinking hard about your goals and how to reach them. I have a few thoughts for your consideration.

Motor: Nine Continent 2810 (slow 6x10 wind)
... It's a bare hub so I'll have to lace it myself.

9C's are well regarded and you might be OK with that choice. Main consideration is the wattage for 30mph and whether your motor choice can handle it. A 72V battery is OK to push up to 5000 watts, depending on the C-rate of your underlying cells. You'll need at least 2500 watts to achieve 30+mph speeds, per my experience. I'm running a MAC 10T at around 2200 watts to get my close-to 30mph speeds, the goal of my MAC/Trek build, recently completed. The MAC is rated for up 1500 watts but I & many press them upwards of that. I went the Infineon 12fet 4110 controller from EM3ev to do that, with Paul's blessing, as long as I didn't exceed 48V, which is what I'm doing. I hit my goals and am happy and not looking to do more than 30mph on this bike.

Get good spokes - see my MXUS buildfor info on that, and the spokes and sourcing. Spokes are easy to mail, so get them anywhere, including the USA. Genuine Sapim.

Controller: Greentime 15fet 4410 72V 45A to eventually be replaced with 72v Infineon 12 fet 4110 (and CA limited to 20A)...
Eventually I may replace it with an inineon - or not, depends on how I like it.

I've got your target Controller. You should be good on that up to 75V. Passing 60amps is dependent on the balance of other components. Since eBikes are all wire, each component has to handle those amps & its a matter of double checking everything, from wiring, connectors, controller and motor. FYI, motor phase wires are often the weak link and worth a triple check.

Battery: 72V 11.4AH custom pack from LG 18650 2850mah cells and BesTechPower D131 BMS...
... I couldn't find any sources for good 72V lithium packs.

I and many make our own batteries. I'm in a unique class and claim the best eBike battery on the forum (haaha, a challenge). :lol: Same battery on my MAC/Trek 48V as will be on my MXUS 72V build. Genuine A123 AMP20 cells, upwards to 30C-rate, in compression, self-build, fitted to a rear rack pannier style. I and others offer battery construction assistance, kits & parts.

Bike: Haro Vseries V2, aluminum frame, 26" wheels

A good MTB is a great starting point for an eBike build. I'm of the opinion that these LEV's are best as bike, with e-assist and not pressed into moped class vehicles.

Because I don't need huge power, I'll be CA limiting to 20A. 1400 watts will be plenty for 30 mph.

Maybe, maybe not. 20amps - more probably not. You'll need at least 30amps. You would do well to reconsider your math before making a commitment to costs.

 

[mlt34]

Thanks for the feedback and tips, arkmundi!

I really like 9C's for mid range power, and I think I should be staying well within it's limits. Also, the 6x10 wind at higher voltage means I'll be using lower current than most 9C's see.

Regarding watts - I guess I won't know for sure until I sit on the saddle at 30 mph, but right now I'm basing my numbers off a somewhat similar build on my current bike. I've got a 9C 9x7 clone which I can max out at about 25 mph @ 900 watts or so depending on what the wind conditions are. I CA limit to 20A, so a moderate head wind can see me hit the amp limit before I reach top speed. But just flat ground on a clear day, 900 watts is good for 25 mph.

The power required to overcome air resistance increases exponentially and I can't extrapolate it exactly, but I'm hoping that extra 5 mph won't cost me too much more than 500 watts. It could be that I wind up in the 28 mph range or so if I don't want to push past 20A. Or it could be that I bump up my current rating to reach top speed at the expense of a little bit of cell health. I'll have to play that game when the time comes.

Those LG cells were a nice start, but I've got a pile of 26Fs and 29Es that I want to try out. Those will be a bit better quality. We still aren't talking 25R's or A123's, but I don't think my design requirements will call for the type of quality cell that you need. To each his own. Those are some nice cells though, I'm a bit envious I must say :lol:

For spokes I have sapim's that I cut myself. They are 14g. Some say that you have to go up to 12g on big motors, but from my experience the proper tensioning is just as important, if not more important, than how thick your spokes are. 14g is plenty strong when properly tensioned. 12g actually makes it harder to get the proper tension and you're more likely to be riding around on uneven spokes. I've had good experience building my own wheel with 14g sapim spokes and I don't see any reason to stop yet.

That 72V MXUS sounds like it's going to be an awesome bike. I still don't know what I'm going to do with my MXUS yet. I'll be interested to follow yours though.

 

[arkmundi]

The power required to overcome air resistance increases exponentially and I can't extrapolate it exactly, but I'm hoping that extra 5 mph won't cost me too much more than 500 watts. It could be that I wind up in the 28 mph range or so if I don't want to push past 20A. Or it could be that I bump up my current rating to reach top speed at the expense of a little bit of cell health. I'll have to play that game when the time comes.

Well, that's the kicker isn't it? Rolling resistance, the combination of tube to pavement and wind, does increase until you reach physical limits. Hard to theoretically predict, but you should give Grin's Simulator a spin to get at least an approximation. For me, both theoretically and practically, I know I can not achieve 30+mph at lower than about 2000 watts. That's 52V * 40amp. Battery is 48V nominal, 54V actual at full charge, dropping to 52V while riding. Controller, wiring and battery C-rate all delivering 40 amps continuous. FYI, I don't actually achieve 30mph, more like around 28mph and that's with pedalling.

For spokes I have sapim's that I cut myself. They are 14g. Some say that you have to go up to 12g on big motors, but from my experience the proper tensioning is just as important, if not more important, than how thick your spokes are. 14g is plenty strong when properly tensioned. 12g actually makes it harder to get the proper tension and you're more likely to be riding around on uneven spokes. I've had good experience building my own wheel with 14g sapim spokes and I don't see any reason to stop yet.

Yes, right on with that. For my MXUS, I got 13/14 gauge butted Sapim spokes. You should be OK with 14g.

That 72V MXUS sounds like it's going to be an awesome bike. I still don't know what I'm going to do with my MXUS yet. I'll be interested to follow yours though.

Yea. Planning on reusing my Gary Fisher Gitchee - a really good vintage bike that's now in its 30th year of road use, not having replaced anything but wheels. I'm going to get a Rockshox front fork replacement. But everything else will be original gear. May look into a different front gear ratio. Will be try, learn and refine as needed.

It'll be my cargo bike. I have a good steel frame trailer for that bike that can carry a decent load. My MAC/Trek for general purpose daily use. So for motive power I have a MTB pedalling, a front 500watt geared motor on the front wheel, and a MXUS 3000 watt motor on the rear wheel. What I'm curious about is how much poundage I can haul in that trailer. I'll look to press that at upwards to 200 pounds. Will likely quickly upgrade to hydraulic brakes, including brakes for the trailer wheels.

Here for instance is a what-if simulation for http://www.ebikes.ca/tools/simulator.html. You'll want to tweak it