serial battery block project

[kenkad]

I thought I would share some info on a University senior student project that is being planned for Fall 2017. My interest is specifically serial battery blocks connected in parallel as part of single passenger urban commuting vehicle technology development (fancy trikes/velomobiles).

I have some companies that have been very helpful, especially in helping develop a +/- cell pair connectivity tab specifically for this application. The starting point is tinned flat copper bus strip that was developed specifically to connect solar panels. The strip is 6mm x 0.33mm (comparable to 14 ga copper wire). The first pic shows some preliminary tests to make the connectivity tab. The second pic shows the punch tool made to fabricate the connectivity tabs. Dimples are 6mm dia x 1mm high. Center to center is 19.5mm. The die mold compression springs are in transit from China and should arrive in 2-3 weeks. I will repost a pic of the punch tool with the die springs mounted later. The punched connectivity tab has an M3 copper plated welding stud attached so the cell connectivity junction is accessible to the active charging/balancing BMS controls. The third pic shows a preliminary 3D CAD representation of the top plate of the battery block. There is also a 2x9 configuration plate, which is obviously longer and slightly narrower. In the 2x9 configuration, the top and bottom plate are essentially identical. Not so with the 3x6 configuration.

As i said, this is just a experimental project hopefully for a capable student team. Feel free to copy as you wish. About 75% of the associated electronics has been designed and tested for the system configuration, serial blocks connected in parallel. I am not at liberty to discuss that part any further at this time.

Thanks for looking. Hope this gives others ideas to further such concepts.

 

[kenkad]

View attachment 2Just an update and some comments:
1. punch with die springs and punched contact tabs
2. closeup of contact tabs with dimples
3. acrylic battery block shell with PCB and power connector
4. closeup of power connector
5. initial Al battery shell concept model (actual shells will be machined cast acrylic.

Punch works reasonably well. Tin plated copper bus strip is very soft material so there are very slight burrs on the end rounded edges. Original idea was to punch and dimple. But now punch first and deburr and then dimple in a second process. Note that the dimpling is a double dimple. If you look at the acrylic shells, they have a PCB. The PCB has soldered on special 4-40 nuts for 4-40 flat bottom set screws. The set screw puts pressure on the contact tab making contact with the + and - 18650 battery ends. No silicone bumpers are used in this design (long term compression is bad news). There is a 2 position blade connector (TE type) that is the battery + and -. Cell spacing went from 19mm to 19.5mm with is better for acrylic machining and allows some air movement.

The double dimpling provides a better concept of how pressure is applied by the 4-40 set screw to the contact tab and continuing to maintain a larger area of contact (ring rather than a single point) between the contact tab and the + and - battery ends. This issue may not be obvious initially but is important in the long term.

Anyone is free to duplicate this design to their hearts content. This is just an update for anyone that may have an interest is this type of battery design approach.

 

[spinningmagnets]

Don't be discouraged if very few comment. This is very nicely done, so there's not much for the readers to complain about...

 

[kenkad]

sm,
Hardly discouraged! The entire electrical system needs some new thought. The battery is just one element. My long term interests are projects and technology directed toward single passenger urban commuting technology/vehicles. Unfortunately, not too much thought process or activity in the US academic community or ARPA-E. Battery systems absolutely have to become repairable for this technology to become cost effective. That is my position and I am sticking to it.

I am fortunate, I am retired and have machine tools that allows me to experiment with these kind of projects. More to come later.

 

[kenkad]

another update,
Here is a pic of the connector PCB with the 18650 contact tabs attached. I will mention again that this is 15A max (5C), so, eight battery blocks can give you 120A, assuming that the BMS controller sees that all the battery blocks are within a voltage tolerance. I will post pics of the acrylic final machined blocks next time.

 

[kenkad]

another update,
The acrylic blocks were machined for the cell connection tabs. Here is a pic of where the tabs are in the top and bottom acrylic blocks. The pic includes the top block with the PCB attached (sits on top of the connection tabs and provides the 4-40 set screw hardware so the connection tab can be suitably compressed onto the 18650 cell ends). The power connection PCB (shown previously) with its connection tabs completes the serial battery block +/- connectivity.

 

[kenkad]

View attachment 2Here is the last update I will post.

 

[Pyrotrons]

Excellent work!!!