This blog is the story of taking a 10 year old Twike that has been setting idle in a backyard in Portland, Oregon and restoring it to is former glory and getting it back on the road. It is Twike number 434.
More battery pack construction. Here I am balancing groups of 8 cells. I'm connecting 5 eight group cells in parallel so it results in groups of 8s5p. I'm using the Chargery DB8 balancer and a lab power supply to charge the cells. Only takes a few minutes to achieve a full balance as these cells are brand new. I'll do some full charge/discharge curves on each group of cells before putting them into the pack to identify any cell defects upfront. I'll have more pictures and descriptions as I get further along on the pack construction. I can not tell you how careful you have to be with metal around these very powerful cells. I remove my wedding ring when I work and have a fire extinguisher handy to deal with any meltdowns. Also, note I place the cells into a fire safe container even though it should not be possible to get these cells to burn (safe LiFePO4). Also, I've got 70 8 cell Dewalt DC9280 tool packs to harvest cells from so it will take a while.
I drove the Twike more almost all of my driving in July and August (>800 miles on the odometer now). Unfortunately, very hot temperatures (>104F), some long drives (>15 miles), and some other circumstances resulted in several of the old Ni Cad cells shorting out (death for a Ni Cad). Thus my two 12-13 year old packs were unbalanced and would not charge correctly anymore. With the start of school in September, I parked the Twike while I resumed driving my gas car and plotted the repairs. My first attempt was to charge and discharge all the 20 cell groups to locate the bad boys (which I did) and to attempt to fix them. The easiest way is to charge/discharge candidate groups of cells and measure the capacity of some other packs to locate a candidate group of cells. I was able to do this after a month or two of testing. I replaced one group with the new group but the BMS in this battery failed to come up in the car after I placed it back in the car. Not clear why. In frustration, I swore to give up on trying to use the old Ni Cad cells and move on to my A123 M1 lithium cells. To that end, I finished the design of the pack and over the Christmas holidays, I drew up the design for the new battery packs. I went over to Tap Plastics (right at the start of a big snow storm) and picked up parts needed to build them. Two days of construction and the new packs are done. The picture above is a test fit of the two new battery packs (just the plastic boxes) into the car with the old batteries removed. Fits perfectly with not even a 1/16 inch to spare. I like the very secure fit into the old battery wells. I using ABS plastic. I went with 3/16 rather than 1/4 because I want to maximize cell area. I hope this is strong enough to survive heavy bumps with the cells inside. I'm now into heavy battery pack construction. My goal is an exact replacement for the old packs but with LiFePO4 cells (A123 M1 cells). I'm planning on a 112s5p configuration with the 2.3Ah cells which works out to 4.24KWH pack and a range of 50 to 60 miles (assuming 60WH/mile).