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Introduction
Zark (VIN 29) has been sitting battery-less for a few years.
After long deliberation weighing the pros and cons of getting new Optimas versus installing a Li-Ion pack, I decided to go for the latter.
- Reasons for Li-ion
- Optimas are now known to be inconsistent, and I don't want to deal with a battery dealer exchanging them until I get a set of 13 good batteries
- A Li-Ion pack with an Elithion BMS will offer a proving platform for the BMS and display the technology
- Reasons against Li-Ion
- Mechanical installation of the cells, rewiring power cables
Plan
Traction pack
Cells
- Prismatic Li-Ion cells
- For a one-off project, Prismatic cells are harder to fit in a given space, but are easier to inter-connect (as opposed to small cylindrical, that are easier to fit but harder to interconnect)
- Thundersky 40 AH Prismatic Li-Ion cells
- They are available, and I have a good source of them
- The 40 Ah cell is the only one that will fit, upright, under the seat
Cell arrangement
We can only fit 104 cells:
104 cells, in a 52S2P arrangement, physically divided into 14 batteries, electrically divided into 6 banks
Batt Bank Cells Arrang Loca Placement
6 1 50 25S2P SEAT
8 3 54 27S2P HOOD
__ _ __ ______
14 4 104 52S2P TOTAL
We could also fit 4 pairs in the storage area, but that hardly seems worth it
- Energy and max cell voltage vs number of cells in series:
- E [wKh] MIN NOM FULL - - - - - MAX
CELLS 2.5 3.2 3.6 3.7 3.8 3.9 4 4.1 4.2 Cell voltage
48 12.3 120 154 173 178 182 187 192 197 202
49 12.5 123 157 176 181 186 191 196 201 206
50 12.8 125 160 180 185 190 195 200 205
51 13.1 128 163 184 189 194 199 204
52 13.3 130 166 187 192 198 203 <---------------------------------
53 13.6 133 170 191 196 201
54 13.8 135 173 194 200 205
So, with 52 cells in series, the pack voltage will range from 130 to 203 V, the cell voltage from 2.5 to 3.9 V, and the energy will be 13.1 kWh,
Banks
* A - Blue cable, green code - Under seat
* B - Blue cable, yellow code - not used
* C - Red cable, green code - not used
* D - Red cable, yellow code - Under hood, top set
* E - Green cable, green code - Under hood, front set
* F - Green cable, yellow code - Under hood, bottom set
* G - No cable, green code - not used
* H - No cable, yellow code - not used
Power connections
- Between face-to-face cells, we use stock straps from Thundersky
- Between adjacent cells in a battery that are not face-to-face, we make our own straps, similar to the Thundersky ones, just longer
- 2 pieces of 20 mills copper, 0.75" wide strips, hump in the middle, held together by 0.75" heat shrink tubing
- Between batteries, we use 4 AWG wire, terminated with insulated ring terminals, 4 AWG / 1/4" stud
BMS
- Elithion Lithiumate Lite BMS
- Cell boards mounted on cells (one cell board per buddy pair)
- Just a few cables between cell boards and a BMS controller
- Monitors and reports the state of the pack
- Stops the charger when battery is full
- Stops the motor controller when battery is empty
Charger
- The Elithion charger won't work. We'll need a lower voltage charger.
- The Zivan charger won't work either (in any case, I have a 220 Vac charger and I want a 110 Vac charger)
- In the end, decided to use solar panels instead of a charger
12 V source
- 12 V battery
- Better able to source the peak power required by the 12 V system, than the Vicor DC DC converter
- Allows starting the vehicle without having a constant drain on the traction pack
- DC-DC charger
- Charges the 12 V battery from the traction pack
- Relay on its input is on only when vehicle is on or plugged in: saves the Li-Ion battery if parked a long time
- Small: only needs to replenish the average load
- Designed to handle more than 200 V in: higher than the Vicor DC-DC
Wiring
- Redouble ground wiring
- Redouble 12V wiring to fuse block
History
- 7/2/09 Start of project
- 7/7/09 Fit mock-up cells into Sparrow
- 8/7/09 Received the cells
- 10/14/09 Installed cells under seat for fitting
- 10/18/09 Mocked cells under hood
- 10/24/09 Completed hood batteries
- 11/19/09 Completed all batteries, tested the BMS, carved the lower tub under the hood, most batteries in vehicle
- 03/13/10 Spring time: starting again after 4 months
- 05/25/10 Restarted project, now that weather is nice
- 05/26/10 All batteries in place, BMS talking to all cells, all cells OK
- 06/08/10 Drove around a bit, for the first time
- Nov 2011 Installed the Lithiumate Lite BMS
- 11/30/11 Drove 50 miles
- 12/15/11 Drove an additional 22 miles, for a total of 72 miles (winter driving)
- 12/16/11 Started recharging
- 3/4/12 Done recharging: 79 days
