Electric-assist bicycle uses LiFePO4 batteries

This bicycle add-on uses an electric motor to help you out. This way the motor takes advantage of the gearing normally available to the cyclist. What interests us most about the system is the DIY battery work they’re doing. The cells are using Lithium Iron Phosphate technology. The li-ion cells you’re used to seeing in consumer electronics are actually Lithium Cobalt Oxide. The Iron Phosphate flavor offers longer overall lifespan, better operation between charges over that life, and improved cold-weather performance.  The drawbacks include a 20-cycle break-in period and an affinity for trickle-charging versus faster charging methods.

The 48V cell seen above will provide 30-40 miles of travel between charges. We feel that getting the power plant out of our vehicles is an important step toward energy overhaul but it can only happen if the battery technology makes it possible. Then again, perhaps we’re barking up the wrong tree and should have placed our bets on compressed air.

[Thanks Tom]

Comments

  1. pookey says:

    Holy cow… have you priced those batteries?!!

  2. I believe that one of the other advantage of these batteries was that they aren’t capable of causing a, super hot, self sustaining fire if accidentally punctured (unlike standard laptop batteries).

  3. Lawrence says:

    Good idea, but does not state the weight of the bike, looks heavy to me, if you put this on a mountain bike you would not be able to carry it anymore, like over a fallen tree, electric scooter is the way to go, or as im about to start a project based on the electric scooter, which is electric rollerblades :) and if that works maybe in future those off road skates :D

  4. AS says:

    48V cell? Really? Wow.

  5. mikeymike says:

    look pricey i bet the base model is going to be $3000+

  6. jeditalian says:

    i have a 48v battery on my bike and a hub motor in the front wheel. my uncle built it, and he has it right now because i hit a car and totaled it (the car, not the bike) well not totaled because the car still ran, but it was just beat the fuck up. lol but the bike doesn’t use LiFePO4 because that shit is expensive as fuck, it uses 13650s or something but you can still pick up the bike it’s not that heavy.
    and i haven’t teested it’s full range but it still has plenty of battery after a 20 mile ride. i know it could do 40 miles easy. i’m pretty sure it could do 80 miles on a charge but the question is CAN I do 80 miles lol

  7. jeditalian says:

    18650s*

  8. Hugo says:

    Any details on the electronics? I’m in the middle of designing a BMS for a medium-sized LiFePO4 pack right now and would be interested to see how these guys did it. So far I’m using an LTC1960 charger, and a DS2726 balancer, and the design looks reasonable, I’m just trying to work out if I can reuse the large FET banks for both load control and charging as well as battery protection.

  9. mrgoogfan says:

    18650…

  10. Joshua says:

    I have a brushless hub motor on my front wheel and just upgraded from 3 (13ah) sla batteries to a 12s 10ah pack I built. Its great. 15-20 mile range @ 25-30mph without pedaling and 30-35 with moderate pedaling.

  11. jeditalian says:

    what voltage speed controller? i need to upgrade mine but its mounted on there so nicely.
    thats good u ditched the lead acid.
    i think mine has 36v speed controller, and 48 or maybe 46 volt battery made of a shitload of 18650 cells. i should go to my uncles house and post pictures of all the fucking bikes he has. bikes everywhere, and a badass scooter. everything use to run on car batteries but now its mainly 18650s and some have LiFePO4 but those are expensive and i think he said if you get in a wreck with Li-po’s they can blow up or catch on fire or something

  12. jeditalian says:

    theres the bike a month or two before i hit the suv.
    the batteries are in the bag of course, there is still plenty of room inside, and thats a badass forklift light for safety lol
    and http://hphotos-snc3.fbcdn.net/hs131.snc3/17861_1075525825625_1750605430_149682_3700117_n.jpg is me on it after driving 20 miles to his house.
    i never took any pics of the battery though.
    the speed controller is mounted between the seat and the fork/front wheel
    but the transmission cable was cut because the front right handle was replaced with a throttle, so its always in the same gear.

  13. Carl says:

    I like the compressor idea the best. It is far more efficient, and you don’t have to worry about discharging or battery maintenance.

  14. Thach says:

    What the hell are you guy talking about? Those cell looks to be Headway cell. Those thing can be charge at 5C and discharge at 10C.Where did you dig up the whole trickle charge affinity?

    @colecoman1982 Self sustaining fire? You’re thinking of wrong chemistry my friend. Laptop batteries aren’t LiFeO4. Likewise LiFeO4 do not drive your laptop. They don’t burst into flame like you think.

    LiFeO4 can sustain very high C of discharge and charging without fire. That and if you use BMS( Battery Manangement System) you shouldn’t worry about it.

    @AS No they’re not 48V cell. They’re 3.7V cell arrange in series for the pack.

    For those who think they’re expensive. They slightly more costly than your conventional SLA, but if you think of the weight saving and how long they’ll last, they’re more valuable than others.

    Lastly for those who think this is a novel idea. You can head over to enless-sphere.com/forums to checkout the vast community of electric bike/motorcycle enthusiast.

  15. Thach says:

    @colecoman1982 Sorry misread your post. Ditto on what you’ve said

  16. nwimpney says:

    @thatch: LiFePO4 ;)

    Otherwise it’s all true. The BMS is not so much to prevent fires, as charge imbalances wrecking the pack.

    Still a lot more than SLA, but a lot lighter, and more practical. Add it up over the life of the battery, and they start to look pretty good.

    @jeditalian: 18650 is just a size, and doesn’t tell you anything about the chemistry. I’d assume they’re probably conventional lithium ion cells, so you probably have an extremely good capacity to weight ratio, but they’ll likely have a shorter lifespan, less current capability, and some chance of exploding into a fireball. ;)

  17. jeditalian says:

    yea i didn’t say -ion because i thought all 18650 cells were li-ion, and the same voltage and MaH ratings.. i tried to post links to pics of the bike but that comment was awaiting moderation or something. probably because the URLs were really long because they are the source of the image from my facebook album.
    and No me gusta SLA.

  18. bothersaidpooh says:

    also guys please PLEASE get your lifepo4’s from reputable sources. Guess how many bad cells I found from the certain online supplier. 25% :( :(

    £200+ wasted. The ones that weren’t leaking had lousy self discharge, and internal resistance similar to a cell 1/4 the size.

    due to this i haven’t done any more with them as there’s no way to detect all the bad cells so building a pack would be an exercise in futility.

  19. nwimpney says:

    jeditalian: I figured that was the case. You can get other types of batteries in that size of can. Actually LiFePO4 are commonly available in that size too, so I figured it was worth mentioning to avoid confusion.

    You must have needed a lot of cells, even in Lithium Cobalt Oxide(Common LiIon). 18650 are typically around 2500mAh or so. It would take around 40 to make a decent pack, Right? More than that if they’re mediocre ones. Also, I’m not sure about the discharge rate.. that would scare me a bit if I were using cheap cells in a chemistry that burns aggressively when something goes wrong.

    If cheap cells I’d probably go with 80 or so, and stick to a 25A controller. It would give crazy range I guess.

  20. Tom Moxon says:

    A few comments –
    I wasn’t claiming this was any kind of original idea, many other people have already done it – it’s just a simple “howto” for those folks that might want to try it themselves.

    Yes, the LiFePO4 solution is about 25-30% more expensive than SLA, but LiFePO4 maintains a higher voltage over the discharge, so the performance of the E-Bike, scooter, whatever is better towards the end of the current charge. SLA/Lead Acid drops off in voltage pretty quickly.

    One post mentioned failures in cells/products and they are right, buying from a reputable source is important. One of the reasons to build the battery this way is for the inevitable servicing required as it ages, and being able to swap cells out. The LiPo “prismatic” packaging, or the welded cylindrical cells are not as good for DIY as they are hard solder/weld without right equipmemt. These just take a socket wrench. With the packaged prismatic package batteries, if one cell fails, you are pretty much done – they are hard to fix.

    Another post asked about the BMS, you can find DIY BMS here :

    http://www.batteryspace.com/pcbbmscmbfordiy.aspx

    One of the reasons I started this product was to develop a new BMS circuit, more on that in a few months…

  21. Tom Moxon says:

    @Thach – Yes you are correct, these are Headway 38120S 10AH cells. And you are also correct that they can be charged at 5C and discharged at 10C.
    I think Mike got the Affinity/Trickle charge from the wikipedia article on LiFePO4. It’s partially true, if you treat them gently they will last longer, but you don’t need to coddle them ;-)

  22. Tom Moxon says:

    @Bothersaidpooh – Yes you are right, there are some dodgey battery suppliers out there, best to check the forums are endless-sphere and find out who the bad apples are.

    This is what I use for cell/battery testing :

    http://www.batteryspace.com/computerizedbatteryanalyzerforanybatterypackupto150wor40ampwithsoftware.aspx

    Yes, it’s a really good idea to test everything…

  23. Bob says:

    That design is INCREDIBLY dangerous because the front ring can’t freewheel relative to the motor. If there’s any sort of malfunction in the speed controller, you’re going to get your legs beaten to hell by a several hundred watt motor spinning the crank. Same for clothing getting caught, etc. Start off in too low a gear, hit the throttle thinking you’re in a high gear, and the pedals will drop right out from under your feet and smack the back of your legs, HARD.

    There’s a reason people don’t drive the chain you pedal directly. The safest way to drive the chain is to drive it with an intermediary shaft and freewheeling mechanism. And for god sakes, use a chainguard!

  24. Nick says:

    @Bob: I expect that motor is set up to run very slowly. (As in speed controlled, not torque controlled)

    If not, then you’re totally correct. And yes. I would definitely want a chainguard on any driven chain.

    @Tom: Yes, thanks for the post. Some people just get a little annoyed when they read headlines that present it as if it’s something new. “electric-assist-bicycle-uses-lifepo4-batteries” makes it sound like it’s not a common thing to do. ;)

    It’s cool to see, though, original or not. I’m looking to motorize a bike in the near future, and I like the way you did your pack. I may do one similar, if I can find (or design) a decent BMS that I can afford.

  25. Jay says:

    It’s a cool project. I would have mounted the motor inside the frame. Does having the motor bellow the frame keep it out of the way while peddling?

  26. Tom Moxon says:

    @Bob – Sadly no, you are NOT correct.
    Unlike other systems, this EMtnD does NOT
    have the problems you suggfest, due to an integrated freewheel that is built INTO
    the bottom bracket (and yes, it’s patented).
    “With our fully decoupled drive systems there’s absolutely no motor drag when it’s shut off. When you come to a hill touch the throttle again and sail up without ever shifting or slowing your cadence.” So NO, the pedals do not spin when you are motoring, unless you WANT to pedal with the motor and increase the climbing torque that way.

  27. Tom Moxon says:

    @Jay – Yes, it’s out of the way of the pedals.
    Remember this is an add-on kit for any bike,
    so putting it in the frame would be tough.

    Most electric bikes are crappy as bikes –
    they are heavy and not meant to be pedaled.
    With the EMtnD, you can add it to the really
    nice bike you might already have.
    The motor assembly added about 6-9 lbs to bike,
    but doesn’t adversly effect the pedaling perforance due to the freewheel in the bottom bracket. Depedning on batteries, you add another 6-12 lbs for the batteries.

  28. Tom Moxon says:

    @Bob – yes and I forgot to mention –
    the chainguard is removed in the picture so that you can see the working/construction.
    Yes, a chain guard with a 1kWatt motor is a really good idea -we have a big plastic one that goes on the bike, but take it off for the pictures…

  29. Einomies says:

    @”I like the compressor idea the best. It is far more efficient”

    I can’t figure out why or where people get this idea that compressed air is “more efficient”. It’s basic physics. Air gets hot when compressed and has to be cooled down to fit it in a tank. Heat is lost, that is, energy is lost. In fact, a significant amount of energy is lost. Then when the air is taken out of the tank, it expands and cools down and the pressure drops, making the motor less efficient.

    A compressed air system would use up to ten times more energy than an electric motor with a battery.

    Some special pneumatic motors can remedy this to some extent by having heat exchangers that pull heat from the ambient air, effectively recollecting the lost heat, but the heat exchangers are large and heavy, and not suitable for a motor that has to fit in a car or a bicycle.

  30. Einomies says:

    Oh, and the MDI air cars are a borderline hoax.

    Take an ordinary everyday sedan car. The net output energy requirement is roughly 150 Wh/km, discounting AC/heating and lights etc.

    Gasoline contains 8.76 kWh per litre.

    To get the ordinary car to go 100 km on the energy equivalent of 2 litres of gasoline would require the whole well-to-wheel efficiency chain to be over 85% efficient, which simply can’t be true. The air compressor alone isn’t 85% efficient.

  31. Nick says:

    Einomies: Yes. That one drives me insane. Anytime there’s a discussion about any “alternative” modes of transportation, someone has to bring up that damn “air car”.

    As if pressurized air is free…

  32. v pills says:

    One of the reasons to build the battery this way is for the inevitable servicing required as it ages, and being able to swap cells out. The LiPo “prismatic” packaging, or the welded cylindrical cells are not as good for DIY as they are hard solder/weld without right equipmemt.

  33. fred says:

    It’s cool to see, though, original or not. I’m looking to motorize a bike in the near future, and I like the way you did your pack. I may do one similar, if I can find (or design) a decent BMS that I can afford.

  34. basur says:

    Yes, the LiFePO4 solution is about 25-30% more expensive than SLA, but LiFePO4 maintains a higher voltage over the discharge, so the performance of the E-Bike, scooter, whatever is better towards the end of the current charge. SLA/Lead Acid drops off in voltage pretty quickly.

  35. tütüne son says:

    The LiPo “prismatic” packaging, or the welded cylindrical cells are not as good for DIY as they are hard solder/weld without right equipmemt.

  36. Update:- I’ve had some of mine tested and as expected they are bricked.
    It appears that they may have been faulty returns that were resold as new, as about a quarter of them test 3.1-3.3V which is essentially normal.

    A larger fraction test between 2.0 and 2.4V which I believe may be borderline (2.2 seems to be the lower limit for reliability) and a few read zero or 1.1V

    The guy who tested some of the really bad 2.0V ones said they seemed to intially accept a small charge of about 1/2 an amp but went open circuit after about an hour before the voltage went much above 3V.

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