Posted by Ziv Magoz
After deciding to go green, I ordered a kit from China to convert my Trek 950 MTB into an eBike. After unboxing, and 30 minutes or so, I had something that runs the eBike at good standards, but not up to Ziv's standards! :-) It had 6 problems: 1. The sensor equipped brake levers are weak. 2. The throttle hurt my wrist on long rides. 3. The battery is too heavy. 4. The charger is too slow. 5. The whole thing is wobbly. 6. The range is only 10 to 15 miles. To solve the wrist pain and weak brakes, I installed a "Pedal-tech"--a sensor that delivers power to the motor according to how fast you pedal. That solved problem # 2, (throttle), and allowed me to put back the original brake levers that which fixes problem # 1, (weak brakes).
In order to fix problem # 5, (wobbly), I moved the controller outside the battery bag pocket and secured it to the luggage rack. I also used two bungee cords to secure the battery case to the rack. Now The major problems left: Problems 6 and 4, (range and weight), can be solved with more advanced battery, i.e. Lithium Ion battery. So I ordered 10 cells from China to test the concept. These batteries give an impressive 42.2V which can take the bike over 30 MPH (I limit the speed electronically to 20 MPH to save battery though). The first test worked well, so I ordered 80 more cells, totaling 90.
Next, the battery enclosure. I decided to go with fiberglass because it’s lightweight and strong. I built the mold for the battery box from cardboard and tape, then covered the mold with two layers of resin and fiberglass cloth. I also made a small mold for the charging port and ignition switch circuitry, then put it inside the box and added more resin and fiberglass cloth. Next I made a little groove at the bottom to fit the bike down pipe and added an aluminum frame to attach it with the fiberglass mat. Then added a layer of Bondo and painted it blue.
In the mean time, the rest of the batteries came from China. Each cell is 3.7V and 3000mAH. When I put 9 cells in parallel to create the basic cell and 10 of those in serial I got 37V battery with 27 AH capacity!.. But like most cheap stuff from China, I knew the cells would not be 3000mAH, but 1500mAH at most, so I'd get about 13 AH of battery, which should hold for 25 to 30 miles. After assembling the basic cell with hot glue, I equalized each cell separately, and then equalized the whole battery over night. There are only 8 cells in each battery cell because some of the cells came dead from China.
I connected the cells to the BMS board, and made sure nothing would explode when chargeing it in less than 3 hours. Bolt it to the bike, and "voila" problem 3 (battery is too heavy), and problem 6 (short range), are solved. Then, in order to increase range and convenience, I added two buttons underneath the handlebar: The button on the right will take the bike 16 - 17 MPH--and with moderate pedaling it will go 19 to 20 MPH; the button on the left is full throttle for those hot days.. :-)
Next was problem # 4 (slow charger). As always, I used an old computer power supply, and removed the power transformer. Added some more copper wires for a quick and dirty solution. But as with every quick and dirty solution it didn’t work well, and at around 40W it would cut off. So I went with the more aggressive approach of reverse engineering the power supply controller. Then I removed the old controller and stripped down all the unnecessary components, and also rewired the power transformer again for a single 42V output. But power supplies need a controller, so I designed a simple controller to tell the power supply to act as a 23 to 42V, 4A smart charger built at zero cost from old parts I had in my electronics box. Connected it to the power supply and loaded it with 30W--checked the voltage: 42V!! Wrapped it up, and tested it with no load: 42.2V--perfect! Then I took it to the garage for real world testing 3.92A! That’s 160W--quite an improvement from the old 27W charger that came with the kit. Put on a grommet and proper cable, then tested it with the battery: It takes 3 hours to charge a complete dead battery!