Electric Semi-recumbant Bicycle, W/ Battery Trailer

This slideshow is intended mainly for electric bicycle enthusiasts.
This is an electric bicycle outfitted with a 48-volt, 40amp-hour battery. The battery is so large and heavy, that it required a separate trailer to carry it. The bicycle was not modified much, so the trailer is the focus of the slide-show. The techniques I used to build it are based on my two other (wood--frame) bike trailer instructables. My general technique is to build a relatively sturdy, albeit heavy wood base and then build it up from there with thinner wood, aluminum or other light materials. In this case, the trailer is mostly wood, all around and it's designed to only be large enough to carry the battery, motor controller and a box for the associated wiring, fuses, switches and battery monitoring system (BMS). The batteries (and charger) are Thundersky LiFePO4 (China) sold by Elite Power Solutions: (hard to find just googling) - about $1300:
Note that the batteries are sold for use as scooter batteries.
The BMS is from Batteryspace (about $80)
I took a risk matching this small BMS with these large batteries, but I do so knowing that I am using them for an electric bicycle, not a scooter. That is, I use the throttle in a spread-out duty cycle when I ride and I don't expect to drain the batteries even below 50% in a single discharge cycle, so hopefully the smaller BMS can keep up with the balancing the battery as I use it, as well as when I recharge it. I welcome any advice on the use of these batteries, the BMS or maybe even someone else has used this combo together (though I only saw one instance of this combo on (visforvoltage or another similar site) and he hadn't posted his results yet).
The main improvement in my trailer relative to my past trailers was the inclusion of a ball and socket style hitch, allowing a quiet, strong connection between the bike and trailer. Obtainable for about $14 from:
You can see in the pictures that I combined this with a large hasp (hinge part of locking system for sheds, etc) and various aluminum and steel hardware. The hasp allows up and down shock absorption for when the trailer hits bumps; otherwise I find the shock of all that weight, as it is transmitted to the bike, tends to weaken and eventually shear bolts where the aluminum square-stock of the hitch attaches to the bicycle frame. I use a piece of thick foam to absorb the shock of this vertical motion -with a slightly angles 1/4" bolt providing a upper limit stop for the shock. I piece of 1/8" thick silicone gasket is situated so that the hasp does not rattle when in the relaxed position.
I've ridden it twice, the first time was when I broke the bolts (at end of 60 mile round trip) and the second is just a a test mile or two with the new system as shown in the pictures. So, the hitch still need proving. However, I barely had to pedal in traveling about 30 miles, before recharging at my destination, so I'm happy with the motor/battery performance so far. I had no cutouts due to exceeding any limits of BMS or motor controller. The recharge for each 30-mile trip (1.5 hour ride time) took only 1 to 1.5 hours, which I estimate may have used half the battery capacity). The battery is sold as rated at 40ah for 48v or 2000 watt-hour at a discharge rate of 1C (40a) I believe. My controller max is 40a, so I should see the exact performance in amphours/watthours as the battery is rated, i.e., I expect to be able to run my bike full throttle for one hour straight (assuming the motor or controller don't overheat)
The trip involved many hills, which were no problem. The motor is the "Racer" variety and my wheels are 20", so it is a good balance of torque and top speed.
I get funny looks of course, but the bike alone (before modification) used to get that reaction. The bike is a "Revive" from Giant (sorry, discontinued as of about 2007 I think). http://www.roadbikereview.com/mfr/giant-bicycle-inc/hybrid-bike/PRD_291045_5672crx.aspx

I welcome all comments! Thanks.



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    16 Discussions


    7 years ago on Introduction

    Get things standardized then you can just swap battery packs at the local station. But then you have to have a comfortable seat for sure. Only thing you cant slip through traffic with a trailer, but other than that, its the way I would go with heavy batts.


    8 years ago on Introduction

    I have a Revive bike and have contemplated converting to electric. What is the source of your motor and did you consider front wheel drive? How fast does it go?

    Thank you,

    David Warren


    8 years ago on Introduction

    Thanks mate, good job. I too have the same idea, for an E-bike, E-scooter and E-motorcycle. There is an electric hub motorcycle wheel available now. They are sized for about a 125cc size bike, but they have great performance. I have also considered having a trailer to carry a generator set to allow longer distance travels on full electric vehicles. Mostly I have considered this for an electric car or truck. This would allow the best of both worlds, full electric with plug in charging for local trips, and fuel operation only when needed for long distance trips. Trailer would only be used on long distance trips. For bicycle the same idea could work. Have a small 10AH battery set for local trips, and hook up your larger 40AH battery set trailer for longer trips. And perhaps a small generator for recharging at sites with out electric hookups, like going to the state park or campground. It might take a little bit of time to recharge from a small generator, but it could work while you are enjoying your day at the park and have the batteries at full charge when you are ready to leave.

    1 reply

    I like your trailer concept, I was considering something similar for a scooter I am refurbishing. I wanted to use a trailer for an extra set of batteries to extend the range of the scooter. Looking at the construction of your trailer gives me even more ideas to think about. Thanks for posting your instructable!


    9 years ago on Introduction

    It looks great, but the price you paid for the batteries sounds high enough to buy a whole scooter. I wonder if you could convert a scooter to a single wheel power trailer that could push you. if you made the scooter/trailer so it would sense the chain tension on the bike to determine how hard to push that would be slick.

    2 replies

    I agree. I only recommend buying these parts if you're an ebike nut like me. I certainly think your scooter idea is possible. I've seen websites for trailer pushers (ebike forums, etc). I unfortunately have limited myself to hub motors. I think there is greater flexibility if one knows how to make more specialized motor drive systems using belts or chain drives. I do think I could make a pusher out of a one-wheeled trailer -with the one wheel a hub motor. I have the cheap $100 Nashbar bike trailer but the wheel well was too small for a hub motor. Perhaps I should build a custom wood, one- wheeled trailer. And I admit it would be slick to automate the assist/throttle, but don't know how to do it - I'd probably use a typical twist or thumb throttle and just have a disconnect for the throttle when I wanted to remove the trailer.

    I have fantasized that you could use chain tension (on the top) maybe using the idler setup from a derailleur. You would use the angle between the idlers to mechanically activate the throttle lever. On the other hand it would probably destroy the shifting ability.


    9 years ago on Introduction

    Wow, that's beatutiful! I've been thinking for a while about doing something similar, except I want to put the drive motor in the trailer. Mine will be quite homely compared to yours, though (assuming I ever get it built). Is the hasp there because the spherical bearing in the rod end did not have enough travel? Why didn't you set the trailer up for cargo on top? James

    3 replies

    Thanks! I hope you succeed with your trailer. I admit, it can take a long time The hasp acts in conjuction with the 3 to 4" long bolt (and nut and large washer) as a shock absorber. A thick black foam square is squished by the hasp whenever the trailer hits a bump. Otherwise the constant bumping of the heavy trailer would weaken the entire hitch where it attaches to the bike frame. This is especially true when riding on bike trails (tree roots growing under pavement) rather than roads, which are generally smoother. I originally used smaller (#10) bolts all around the hitch and no shock absorber and it eventually broke two bolts. So I upgraded the size (to 1/4") and number of bolts all around and added a shock absorber - and switched from a U-joint to a ball joint. I don't know if all improvements were necessary, but I think it's bulletproof now. I have two other cargo trailers, so no set up for cargo on top just yet. I can add one later. Just wanted to get this one running for now - for really long trips, not grocery store/cargo trips.

    Forgot to mention - the spherical ball joint seems to have enough travel by itself, though it does only travel up by about 45 degrees (and down 45 degrees too of course). But I doubt I will be riding over abrupt changes in grade that would exceed this 45 degrees. I admit the hasp allows a little more travel, but since I limit the hasp travel as a shock absorber (and the way it is attached) I don't think I'm gaining a whole lot.

    I originally went with a U-joint which had slightly more range of travel, but I don't think U-joints were designed for this use (designed to be a way for a rotating shaft to bend around a corner). I could tell it was going to wear out pretty fast since the slightest inevitable relative forward/backward motion between the bike and trailer (both heavy) were going to cause it to self destruct over a relatively short period of time.

    Another cheap joint I've made in the past is a series of beefy square hinges and thick pins. These were used in my past two cargo trailers. This method is working fine so far, but I don't use these trailers for long distances, so I haven't really tested their longevity. I think the spherical rod end way is the best so far.

    I've sort of obsessed on a way to make a hitch system that didn't stick out to the side like most one-arm hitches. I like the two-arm (one wheel) hitches like what Nashbar makes, but I suspect those have a weak point where the two hitch arms come together at the head of the trailer. I have one and there seems to be excessive play in this joint - which I will probably have to add washers to as the metal wears away.


    9 years ago on Introduction

    wow, that looks really cool, good job. Is your charger inside the trailer? Can you just charge up anywhere?

    1 reply

    I did leave room for the charger, next to the controller, but I think with the inevitable level of vibration in (any) trailer, I'll instead carry it more safely on the bike rack - which has a seatpost shock. Don't want the electronics inside getting unneeded shaking. It plugs into 120v ac, so yes! I recharged at my brother's garage. The whole thing is a bit large for regular bike rack parking, so taking it to work will probably not happen often (though it doesn't need a recharge every commute cycle, which is nice)


    9 years ago on Introduction

    I have two suggestions:
    • Put an image of the final project in the front of the slideshow so you don't have to scroll through 26.7 million pictures to see what you built.
    • With 26.7 million pictures, why not write up a full Instructable?

    Very nice job, though. 5 stars for you!
    1 reply

    You're right. I had trouble in the past shifting pics around with instructables - maybe it will work this time with a slideshow. I would write one up, but the idea was so close to my other two trailer instructables, I didn't have the mustard to write up a third one. I was going to (thus all the pics) but then I saw the slideshow option. I may come back soon and make an instructable. I'd probably include more specs if I did. Thanks!