Battery Tab Welding

In the last two days, I have battery tab welded 600 cells into 5 cell groups. The 5 cell groups need to be arranged cell end to end and shrink wrapped. I will do some basic testing to catch any bad cells before going farther. Then, 4 sticks make up one group of cells and I need 14 groups for each pack (560 cells total for the two packs). Once I have that done and two working BMS boards, the Twike will be back on the road. I decided to stop trying to fix the bad BMS boards and just order two new ones from Germany. I'm expecting them shortly. The cells are the "no longer made" SANYO CP-3600CR. I found a place to buy most of their remaining stock for about half of what digikey wants.

Fall Update

I've been busy with other projects but it is time for an update. My twike has set idle for the last 12 months while I sort out battery issues. The old NiCad cells from 1985 are pretty much shot but I have put together (after much testing) two packs with the best cells from the 5 packs I have. Unfortunately, while installing the packs into the car, I shorted out one of the NTC temperature wires on the mid pack fuse resulting in damage to the BMS board. The car will not charge without two (min) working BMS boards, so I'm down until I get that fixed. I finished my testing of A123 cells and found them of high quality and quite reasonable to work with. To make them work with the car will require me to design or purchase a factory BMS solution. To date, this is more $$ than I am willing to spend, so I'm exploring selling all my lithium batteries, buying replacement NiCad cells, and replacing the battery cells myself. The DeWALT LifePO4 packs are now up on ebay.com (selling slowly) and I found a great deal on 3.6Ah SANYO C size NiCad cells (no longer made). I bought enough cells to replace 4 packs with the idea of doing my two packs and 2 packs for a fellow Twike owner in the USA. He agrees with me that the cost of the lithium upgrade when bought from Europe is just too expensive at this time (most of the cost is importing the cells). Next steps are to fix one of the broken BMS boards (or order a replacement from Germany for >$500USD), then begin the process of replacing all my old Panasonic 2.8Ah cells with the new SANYO 3.6Ah cells. I have friend who has a battery tab welder (makes his own A123 packs) who will rent me time and I just need to order some more Nickel tabs (only have 100) and thermistors, some shrink wrap for the cells, and it will be time to perfect the art of pack creation. I hope to have the packs refurbished by the end of the year (given time constrains).

Jan 2010 update, part 2

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.

Jan 2010 update, part 1

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).

600+ miles on my Twike

I'm at 664 miles mostly commuting from work to home and back. Some of the trips have been to downtown Portland in the evening to attend a OEVA meeting which makes for about 36 miles a day (with two charges since my range about 20 miles). Yesterday, I went for a hike in Forest Park with my son Paul. We picked out a nice starting point, drove the Twike there, did a nice 2.5 hr hike and drove the Twike home (10 miles round trip and lots of elevation gain). A true green activity since I charge with 100% renewable electricity from PGE at home. On a more technical note, last weekend I replaced the differential oil with a synthetic brand. This seems to have fixed a lot of the noise problems I was having at 40-50 mph. There is still some noise but much less. I may still need to look at the motor mounts and see that they are lined up and tight. I think next on my list is to fix the canopy from opening so far that it hits the plastic windshield. Over time I think this contributed to is loosing its grip/glue on one half. I still on occasion have problems with the speed sensor going out, mostly when its hot and usually after lots of regen (like on my trips into Portland). Pulling over for 2 minutes and restarting seem to fix it for now. I have email from a friend in England who suggests the speed sensor needs adjusting and gave me details on how to do it, but it is involved and may involve dropping the motor/differential. Not a 5 min job. I have driven every day to work since July 1 except for 3 days when we had 106 or near 106 (really high temps mess with the charging), when I went to Boy Scout Summer Camp (drove my gas car, ugh), and went to Florida on vacation (took a plane!). Every day it gets more and more natural to drive and a gas car feels more and more foreign when do I drive one. My Lexus needs a 90k service and it may be its last ;-)

My Twike meets its first Tesla

Today was the OEVA EV Awareness day in Portland, Oregon. We had vehicles of many types from conversions, to factory production vehicles, to motorized bikes. I was there all day with my Twike since I can now drive from my house to downtown and back and I'm also part of the OEVA group. What made my day though was when a Tesla showed up. The owner is David Stiers who you may remember as the actor who played Charles Winchester on MASH! It turns out his is retired and lives just south of Newport Oregon. He heard indirectly that there was something happening today in Portland around Electric Vehicles and thought it would be great fun to show up. He found our web site and just took it upon himself to drive the 130 miles from Newport to Portland (good to have a Tesla with 240 mile range). Thus this afforded me several things. One, I got to meet him and a fine gentleman and in good humor he was. Secondly, I got to see my first Tesla in person after reading about them for ages. And thirdly, probably not the first but one of the few shots of a Twike and Tesla together. I have a 2kwh pack in the Twike and can go 20 miles, the Tesla has a 50kwh pack and can go 240 miles (and of course top speed is 150 miles per hour). I have him in efficiency but he has me in every other category (except luggage space, I think I win there). Thanks to David for just showing up as he is one of only 3 Telsa vehicles in Oregon (so I hear). In regards to the Twike, it is doing great and it getting regular use as I drive it to/from work everyday.

Today I put on 36 miles (a new 1 day record). I drove the 8 miles to/from work and worked out at Bally's during a late lunch. I zipped home and did a quick top off charge so I could drive all the way to downtown Portland for the monthly OEVA (Oregon Electric Vehicle Association) meeting. Coming home was kind of a challenge in that it is 10 miles, climbs over 1000 feet in elevation and I had it do it with my lights on which suck more power. No problems and I made it with about 30% battery power remaining. With 12 year old NiCad cells, I am not quite sure how much capacity I can rely on. BTW, the picture is of my license plate "Oregon TWIKE". It is a motorcycle plate because in the state of Oregon, a Twike is licensed as a motorcycle.