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:
http://elitepowersolutions.com/products/product_info.php?cPath=1_24&products_id=86
Note that the batteries are sold for use as scooter batteries.
The BMS is from Batteryspace (about $80)
http://www.batteryspace.com/index.asp?PageAction=VIEWPROD&ProdID=5046
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:
http://www.drillspot.com/products/153530/Ccvi_Bearing_Company_EF8TYS-W_Studded_Spherical_Female_Rod_End
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.