In order to validate our BMS system at the same time as building our battery, we need to make a board that will give all the same voltages as a 36S battery would. With this, we will be able to connect our AFEs, BMS carrier, and BMS current sense to it and validate the battery system.
We will build a 36S 1P battery system with spare cells in 18650 cell holders. Each of these cells will emulate a module in the actual battery pack.
This test rig should have:
- 36 cells connected in series with voltage taps on each one
- A thermistor on each cell to measure the temperature
- A mount for the current sense resistor and board
- A fuse to protect the batteries
- Switch to easily turn on/off the stack
- Contactor on + and - connections to be consistent with the car implementation
Fuse
Fuse should be rated to around 15-20A, fast blow. Should probably use the same Cooper-Bussman series as we are using for the actual car. Need to find purchase and get the fuses. Ask Joshua Rong for more details on fuses.
Selected the Cooper Bussman XEV10-20-T for its fuse rating of 20A which will protect against short circuits but not interrupt normal operation. Wiring must be sized according to this fuse - must be capable of >20A. Using the Chassis Wiring value from this table:https://www.powerstream.com/Wire_Size.htm, >16AWG wire will work (22A). We will go with 14AWG (32A) for a bit of a safety factor for all of the fuse derating conditions if it is readily available and not too much more expensive. ORANGE wiring for the high voltage will be used, with black and red heatshrink to specify the polarity.
We will need to find a place to purchase this fuse.
Contactors
- Charge Input +
- Output (Motor Controller) +
- Output (Precharge / DC-DC) +
- Common GND Side -
- Secondary contactor to emulate the coil sense contactor, coil wired in parallel with main contactor
For Contactors 1,2,3 I am thinking TE EVC 80 contactors or the solar contactors. Need to check prices and find digikey/mouser links. Apparently these contactors are only available in Europe and only on special order from TE. We should be able to use the contactors that we have in the bay that were used for previous cars. They are on the shelf above the electrical bench right now. We have 4 of them, but only 1 has the contactor sense coil. So we still need the extra contactors. The extra contactors will be these ones (https://www.digikey.com/product-detail/en/ALQ3F12/255-5407-ND/4895301/?itemSeq=316400033). Standard low cost relay from Digikey.
Switch
We should be able to manually turn the battery on or off. Should be rated for at least 20A, probably more for a safety factor. Should also be satisfying to turn on - big switches are nice.
This switch will be inline with positive side of the battery.
Switches such as this seem to be a problem finding - check this video for the importance of choosing a properly rated switch: https://hackaday.com/2018/07/24/a-dramatic-demo-of-ac-versus-dc-switching/
So instead of finding a switch rated for the proper currents, since our relays are rated for the voltages and currents, we will provide a manual way to remove power from the coils. A switch will be wired in series with every relay coil. These switches will be used (https://www.amazon.ca/gp/product/B07M5GGXTV/ref=ppx_yo_dt_b_asin_title_o00_s00?ie=UTF8&psc=1)
The BMS kill switch (connected to the BMS Carrier board) will be this switch: https://www.amazon.ca/gp/product/B07GT4KK7R/ref=ppx_yo_dt_b_asin_title_o00_s00?ie=UTF8&psc=1
Current Sense
Should we have the option of switching in a larger current sense resistor to measure the current more accurately - then we might not have to change current set points when switching code as the reading scales according to the resistor chosen.
We have a couple extra current sense resistors around the bay, so we should use one of these.
We need to figure out the model numbers of the connector and the crimps and wire gauges used for the connection to the current sense housing.
Connectors + Cables
- 12V Input - Molex Ultrafit, 2 pin, +/- consistent with the rest of the boards, 22AWG
- CAN - 2 ports, with BMS carrier in Daisy Chain Config - Molex Duraclik 2 pin, consistent with the rest of the boards, 22AWG
- Charge Input - 2-pin Molex MX150L, 14AWG
- Power Output - 2-pin Molex MX150L, 14AWG