My first A123 pack design used a large number of aluminium spacer blocks to connect the tabs. Shown below is the first module design in the form of a 4S3P (12v) battery that I’ve been using for a few months now. Initially I had built a pair of 16S3P modules that I used to drive the car to work but found flaws in their functionality.
In general the battery works very well, however it is very fiddly to assemble and requires a lot of custom parts. There are 29 aluminium blocks consisting of 6 different types, the final pack would require 24 of these modules (696 blocks….) I also had some small issues at high current, there was more voltage drop than I was expecting and I had a few loose connections when I disassembled the very first large 48cell test packs. The solution to the voltage drop is reduce the number of aluminium spacer blocks and join the 3 parallel cell tabs directly together and clamp them (tightly!) This reduces the block count in the current path from 5 to 1, that should help with the voltage drop. The solution to the loose connections is a complete redesign of the hard ware used as well as the clamping method for the tabs. Luckily this aligned with the reduction in block count and allowed me to use the required hardware. I’m now using a pair of M5 cap screws with a 4mm allen drive vs an M4 flat head (countersunk) screw with a 2.5mm allen drive. This allows for a much higher tightening torque to be applied to the fasteners, and they are larger and stronger in general. The use of a traditional cap screw means there is a proper surface to use a Nord-lock washer! Jack R of EVTV has been recommending them for years and although I’ve been aware of this for a very long time, they just didn’t fit with my module design. It was time to change the design so that they did work! Below is the revised module design using 13 blocks consisting of 4 types (312 total for the car). The end terminals are different in this test pack but will be the same in the final design, the most positive and negative terminals will be slightly different but there are only two in the entire pack so it’s worthy of extra attention.
The Nord-locks are amazing and do exactly what they say they do! (Thanks Jack R.) I still have some very minor things to revise and tweak with this design, but I will be making the final test blocks today and if all is well I will be making all of the blocks required for the pack. The other part I’ve been struggling with are the holes in the tabs, drilling doesn’t work, a metal punch is better but not perfect, a hole punch (for paper!) actually works very well but is hard to use and align. This led me to find a hole punch that WILL work for me and hopefully I’ve found it! It’s on order so I haven’t tried it yet but it’s a heavy duty paper hole punch with adjustable center to center distance for the holes. This will allow me to set it for the 1.25″ spacing of my blocks and punch each tab in one motion with hopefully consistent spacing and alignment.
Most of the cells have been prepared and tested, leaving lots of punching and assembly work to make the final battery modules, once I have the final details worked out this will be quite fast and easy (I hope!)
The DC/DC converter/charger that I’ve been talking about forever is finally done. The board is designed to hold a raised bracket with a 120mm low profile 12v fan.
I started by milling a copper clad PCB to the desired shape and size to hold the fan. (this is the strongest thinnest material that I had on hand).
Mounted the fan to the PCB with the included fan hardware.
Finally mounted the milled PCB to my DC/DC charging board PCB using suitable stand offs.
I used a low speed (very quiet) low profile computer case fan to keep the height in the desired range. I still need to find a grill or filter to keep fingers and other things out of the fan blades. I have an extra set of 12v terminals on the input side of the PCB, so initially I will be running the fan off of the 12v signal that turns on the board itself.
By day I work for a company that designs and builds control and monitoring systems for service rig and frac equipment. The shop guys do some amazing work making what would otherwise be a rats nest of wires and connectors into beautifully neat and organized works of art. I will be doing my best to duplicate their efforts in my car. I bought a variety of ferrules and fork/ring terminals to eliminate any loose or frayed wiring as well as make things tidy and professional. They also use shrink tube labels and wire wrap labels on every wire at every connection. I’m trying to get a reasonably priced label printer to duplicate those techniques as well, the Kroy K4100 looks like it would work very well for what I want to do, I just need to find a good used one at the right price.
Below is an example of a wire wrap label:
Below is an example of a shrink tube label (from a different brand):
The one thing I’ve learned recently is that if I wasn’t so picky the car would have been done a long time ago! I believe everything will work very well when it’s done though so it’s worth the wait.
I’m living up to my high C personality for those familiar with DiSC profiling/assessment.