Home at last

Last night I drove the TWIKE 8 miles from Northwest Portland to my house for the first time. It had to climb over 1000 feet in elevation. This was a real test of the 2nd battery I got working and only the second charge cycle on that battery. I know from experience from the other batteries that it takes several charge cycles to wake up the 10 year old NiCad cells. I expect the range now with two batteries is around 15-20 miles on level ground. I am working on a third pack that should extend that to nearly 30 miles. I have lots of other small things to work on and some larger ones. I need to replace all three tires. I noticed that one has large cracks (not surprising for a 10 year old tire). This must be fixed before I can consider much serious driving. It was amazingly stable at speed and at one point I think I was exceeding the speed limit without realizing it. EV grin here I come!

Legal to drive in Oregon

Today, I found an Insurance agent that would insure my TWIKE and not just for liability, but for collision and comprehensive as well (all at motorcycle rates which is far cheaper than any of my cars). Once I had insurance proof in hand, I stopped by the DMV and applied for a title (including vanity plate). One big smile later, I had a 3 month temporary sticker in hand ready to apply to the back window. Look out, I'm fully street legal with no inspection required.

First 5 miles

Last night I put in the second battery pack I put together with the old Ni Cad cells and one of the 5 tested BMS boards. I was able to set the controller to 2 batteries, download new BMS software from the controller (it did not like seeing 5.24 BMS software when it is 5.1), and do a normal charge to top off the batteries. I put air in the tires, cleaned the outside of dust, and took it for a spin. I gave rides for the better part of 2 hours until I felt I should charge it up again. The odometer read 5.1 miles! I noticed that one pack is stronger than the other as one was supplying more of the current and took more current on the recharge. I'm thrilled that the charging system works as well as it does. I have so much more technical understanding of the entire BMS/BATTERY/CONTROLLER system now that I have debugged all the problems bringing up these old battery packs. I estimate each pack is about 2Ah (2.8 originally) and that puts me at about 16 mile range for the two packs. I should be able to build up the third pack in the next couple of weeks which should get me close to 25 miles of range per charge. This should be enough for my daily commute while I work on getting my lithium battery built (expected range 40+ miles). I'm thrilled! I still have a long list of little things that need attention including the seat belts (retractors are sticking .... may replace seat belts), wood steering handle is split (patch for now), one of the plastic panels under your feet is broken (someone stepped on it while it was out of the car), etc. Also, I need to start the DMV/Insurance stuff now so I can get the vehicle home from Northwest Portland. If all goes well, I will be able to *drive* it home.

First Success!!

On Monday night on March 16th 2009 I put my partially charged reconditioned battery pack in the car with the intent of having the car charge it. Even though with level 2 access I could tell it it only had 1 battery, I could not get it to charge the battery. Then I tried just powering the car. It worked. I was able to put the car in reverse and move the car a few feet! I am working hard on getting the second battery pack reconditioned enough to get about 2Ah out of it which should be good for about 15 miles between the two packs. This is assuming the car will charge them full up. I should know in another week or two if this is possible but it was great to see the car move under its own power. I continue to work on my lithium based design which will eventually replace the Ni-Cad pack.

Latest update on Twike restoration

I have not posted since November, 2008. Sorry about that. Here is a summary of what has happened on this project since then. I purchased the rest of the A123 M1 cells I needed for $5.50/cell. I have 450+ cells now. I have been looking at BMS designs so I can protect these cells (they need to stay between 2.5 and 3.7 volts for best life and safety). Apparently, this is an area that is lacking in good off the shelf solutions. I will either need to pay lots of $$ for a solution (i.e. more than the cells themselves cost) or build my own so I can customize it to my specifics. As part of this effort, I have a demo board of the Linear Technologies LTC6802 chip. It seems to function with my testing so far but I will have to add up the cost of the parts to build a functioning BMS (shunt based design) to see the true cost. In the meantime, I started to do a serious attack on the TWIKE battery BMS setup. At this time, I am not pursuing the software based BMS any further as it became too difficult to see what was going on to try to emulate it correctly without any working real BMS boards. I turned my focus to the hardware itself and will the help of a friend at work, we got 5 working BMS boards to talk to the service program. I also located a disassembler for the BMS software to get a better understanding of how it works. That was fun as I looked at 3800 lines of assembly code! Over the last 30 days, I have been doing charge/discharge cycles on one of the best looking old NiCd packs. I was able to restore about 60% capacity by cycling the old cells. Last night at Synkromotive I carefully soldered back in a working BMS board (14 temp sensors, 7 voltage monitor wires, 14 cell to cell connections, 1 power connection, 1 RS485 4 wire communication connection). As I wired up the last connection, the board red led started blinking! After connecting it to the car and putting the car in charge mode, the car downloaded BMS software to it and began to read out the battery pack voltage! This proves the car charge/controller system is working properly and the other battery pack I was trying to charge has a bad BMS. I also discovered how to get into service mode on the controller (TWIKE Access Level 2). This lets you set all kinds of good stuff on the controller including the number of batteries. I tried setting it to 1 battery (which I did not know was even supported) and it seems to be working happily with 1 battery. When I tried to charge the battery, it complained that the battery was too hot (77 deg C). Clearly, I messed up one of the temp sensor solder joints. I'll have to run the service program to find out which one and fix it before trying to charge it for real. Next steps are to put another working BMS into another candidate battery after I do the battery testing to make sure the cells are good. With two old tired batteries, I should get 10 to 20 miles of range (for testing) while I work on my Lithium solution. I'm thinking 112s4p would be a good starting setup. Even with LION cells and my own BMS for Low Voltage Cutoff and Shunt Based overcharge protection, I may integrate 1 or 2 old BMS boards to make it trivial to keep the onboard controller happy (Both on charge and discharge). A hybrid solution may be the path of least resistance. We'll see. Stay tuned for more.

A123 Lithium Battery Testing (DC9280)

Last night I decided to start testing my lithium batteries in preparation of building a battery pack for the Twike. I have a RC Electronics Watts Up Meter and a West Mountain Radio Computerized Battery Analyzer. I previously found a way to purchase A123 M1 cells (new) in dewalt packs for $6.50/cell so I have 120 cells to build my first pack. I'm going to go with 112 batteries per pack in series (112s1p) to best match the voltage requirements of the Twike, and then parallel multiple packs to get range. The old setup with NiCad batteries was 280 cells in series. That gave a lower voltage cutoff of 280 volts (1.0v/cell) and a upper charge limit of 420 volts (1.5 * 280). In my case, the A123 cells wants a upper charge limit of 3.64 volts so my 112 cells will need to reach 408 volts to fully charge. The low voltage cutoff for a A123 cells is 2.5 volts so this works out to 280 (which happens to match NiCad). So, that is my design target. I took apart my first pack of 8 cells using a T10 security bit (get a long skinny one or drill part of the case). I clipped off the two black wires and one red wire to the internal BMS which I am not going to use. After disconnecting the per cell balancing connectors, I could extract the cells. I had charged them once on the standard Dewalt charger so I knew the cells were all reasonably ok. It will detect and fail to charge a pack if any cell is below 2.5 volts (a possibly harmful condition for a cell if that way for long). A quick check with a meter showed them all pretty close in voltage. I did a 3 amp discharge down to 20 volts (2.5 * 8) to measure cell capacity and see if I had any bad cells. Came out to 2.1 Ah (and 52.8 Wh) which is fine given I did not have it on the charger for several weeks. Both CBA and the Watts UP meter gave the same numbers for Ah and Wh delivered from the pack. I then measured each cells voltage and found them pretty close. No need to do more balancing. I then used a regulated supply to charge the pack back up to 29.12 volts (8 * 3.64) at 3 amps. Took 58.4 Wh (2.156 Ah) to charge it back up. Looks good to me. Now on to pack and BMS design and purchasing more lithium packs. NOTE: I figure the Twike uses about 80Wh/mile so that one pack of 112 cells gives me about 10 mile range (and weights about 17 lbs). I'd like to get to 40 miles range to cover 98 % of my daily trips so I can use it to commute daily to work so I'm looking at building 4 packs (with 448 cells).

Twike BMS emulation in Software

It's been a while since I have posted, but I have not been idle. I have just about given up with trying to get the old BMS boards working (looks like a marginal design when exposed to the elements of the batteries). I'm not sure I have any working boards out of the 5 I have. But, because I must get 2 BMS boards (or something that looks like them) to get the Twike controller firmware happy, I decided to play to my strengths and write a software emulation of the BMS. Documentation of the protocol is non existent from the manufacturer but I found a german open source project doing some of the same things to support running Lithium-Ion battery packs. Armed with a RS485 converter, the knowledge of the fact it runs at 2400 baud and a reference code base to answer some of the hard questions, I coded up a program that allows me to emulate all the operations of the firmware based BMS. I should test it this week now that I am done coding it. If this works, I will be able to try putting a partial charge on one of the battery packs and drive the car around the block. Also, I can verify all the electrical devices and switches and see which need more attention. Also, I have the twike service program (version 3.6) which is a DOS application that does all kinds of magic in talking to the BMS. To debug my program, I installed vmware server and booted DOS 6.22 on a floppy image. I installed the service program to the floppy image and could then run the service program in a window talking to a COM port. Next, I downloaded a trial version of "Virtual Serial Port Driver". This program creates pairs of COM ports connected via a virtual null modem. This lets me connect the Twike DOS service program to my C# BMS emulation program. Very cool. When I was done, the service program was completely happy so I hope the controller in the Twike will be also. Highly recommended technique.