Updates appended to bottom of this page
3. Battery Pack
This represents the shape that holds 2040 cells that utilize the various depths around the motor compartment. This design uses the A123 systems 26650 cells.
This 320 pound power pack plus the 200 pound electric motor and 50 pound inverter equals the weight of the gas motor and exhaust system just removed from the BMW.
June 2008 update:
The electronics that monitor and control the battery cells, referred to as the BMS (Battery Management System), is currently under development for the BMW. This BMS design has the ability to be scaled to fit any application. The CRF2eR drive system will use the same BMS circuit boards in fact, integral to each module to eliminate exposed wiring.
In this BMW case, 30 modules slide into the compartments above with various depths, all using the same design form, just different quantity of cell groups in each section.
August 2008 update:
The pack mounting to the chassis begins with inserting the captive stainless nuts inside the chassis. You can see the three holes that were used to install them.
The green lining is VHB acrylic foam tape, used everywhere in the auto industry. I will be leaving the top adhesive cover on since I do not need the high-strength bond to hold the pack_mounting_foot down since the bolts do that already. This will allow it to come off if needed. This makes a resilient pad that the weight of the pack and inverter sits on.
Below (or beside) the holes are the installed nut plates
Stainless nuts welded onto stainless plates are pop-riveted with stainless rivets. This makes a very reliable and robust mounting technique that is easy to work with.
The pack mounting rail on this side includes the mounting of the inverter.
This side takes advantage of 2 studs that were already there to anchor this side rail down.
There will be two "floating" feet on each side rail that will constrain the pack. I am including some compliance to filter high frequency vibrations and to allow for chassis flex.
Next up: cell welding and module packaging
Jan 17 2009 Update:
Here are the 3 module sizes that fit in their respective compartments represented by the model shown below, right.
The very "cubic" Aluminum enclosure will support the 320 pounds of modules that fit into the rigid, multiple compartment structure.
Here is a close up view of how two adjacent modules will couple to form the high current path that makes up the complete ~700 volt series string. Low head-profile bolts with square inner profiles prevents them from rotating while the nuts are tightened.
Left module has a blank BMS slave board plugged in. (right side is shown without bolt and BMS slave boards)
May 2009 Update:
All 30 modules are in place for final Z axis confirmation:
The construction of the ALU enclosure is now underway... The white board is an approximation of the front face shape. The left and right ends of each row will connect externally in a shielded raceway leaving no interconnect wires inside/above the array.
Here, among the array of modules are two with their BMS slave boards plugged in:
The upper is a single board, monitoring/controlling 5 cell groups in this 'short' module form.
The lower is a pair of boards that monitor/control 10 cell groups in the 'long' module form.
On the stacked pair, the upper board contains two rows of LEDs to make the lower board's LEDs visible also. These boards just stack together, sharing a single comm port header.
The black standoffs will be pinned horizontally with each neighbor module to secure them.
July 2009 Update:
Here is basic form of the structure that will hold the modules:
Its a tight fit but has the needed clearances around all 6 surfaces.
Here is the box, face down on the bench with all modules slid into place
The BMS boards will be plugged in last, at the time of power up so the modules are not fragile during handling. For high reliability, all contacts in this system are gold on gold.
Other than the high current conductors, there will be only one cable entering this box, the communication cable, which is optically isolated from the cells.
October 2009 Update:
No longer a cardboard box:
The finished package, with a powder coat finish. I did this primarily for voltage isolation inside the box (prevents runaway plasma events, in this case) but it does make for a fine finish, thanks Tim at Willamette Powder Fab. This inner hood has a complete seal around the perimeter of the box, helping the long term reliability in this rough environment.
The wiring to configure the pack into either 350V or 700V modes is contained within the shielded/insulated outer routing channels.
Here is what I did to the bottom of the pack for thermal control (heating in winter, cooling in summer):
This pack structure has inner ribs that thermally conduct heat from the bases that also makes for a very rigid box. There is no flexing whatsoever with a full load of modules.
Notice the tapered lead-in on the black feet. This helps the pack drop onto its rubber isolated mounting studs when lowering the pack into the motor compartment.
To reduce stress on the input and output fittings, I made a simple support, complete with rubber isolation. Each plane will be "capped" with another layer of Alu.
Jan 1, 2010 Update:
Here is the process of removal/Installation
WIth this custom bar and strap arrangement, I can install/remove this pack with ease by myself, despite the tight clearances.
This custom rolling carrier is built to make access and movement simple.
The cross arms are long for a reason..
To do inside work in the machine shop, I pick up the carrier and pack with my John Deere:
I built this set of forks for my front loader many years ago.. I didn't know then how well it would work for so many jobs later. Another fine powder coating job by Tim at Willamette Powder Fab...
Then, I just place it over the threshold and onto the machine shop floor:
With one hand on the valve control, the other can guide it in easily.
As tight as things are, it fits with clearance, just like it was made for it...
Here is a quick look at how I have connected the modules for initial 350 volt operation:
The 6 rows are connected in pairs here. When I switch over to the HV mode, I will remove the tie bars and wire them into the routing channels as originally planned. I am using 2AWG wire.
April 6 , 2010 Update:
The pack installed:
The modules are all connected except for the column of links just left of center. They will be rotated 180 deg and cinched down to complete the circuit when ready to apply power.
The only thing left is to plug in the BMS boards and connect up the communication.
June 2010 Update:
All links are connected and the BMS slave boards are going in:
Notice that there are no longer exposed conductors. I added FR4 in strategic forms that simply pull out for access to the high current module interconnect jumpers.
I tack in a protector sheet of FR4 while inserting another module so fingers don't bridge across to neighbor modules where there is up to 150VDC between adjacent rows.
To keep the isolation robust, I included another layer of FR4 above the communication wire
The comm ribbon wire exits out in upper left corner of the pack.
You can see the interconnects on this last row
