Replaceable batteries required to power some components of the car. (Need to update this more)
Supplemental Battery Constraints:
The battery shall be able to energize protected LV systems until the main battery is energized
The battery shall be able to power protected and emergency systems in the case of a fault condition
The battery shall be mounted to the LV cutoff board and be easily swappable
The battery shall be able to power the average load until the end of the race day (8 hrs)
The battery cannot overheat
Voltage:
Nominally 12V, however voltage levels should not be altogether too significant as voltage is further downregulated to logic levels on each individual board.
Energy Capacity:
Load | Description | Energy Demand |
|---|---|---|
Horn | Horn must be able to be run for 5 minutes in an emergency | 10 Wh |
Emergency Telemetry | Assume 2.5W for a raspberry pi, 8 hr race day (super over-the-top) | 20 Wh |
Driver Fans | 1 Noctua NF-F12 iPPC 3000, 3.6W max (Reused from MSXIV), 8 hrs (Asked Nita) | 28.8 Wh |
Total | 58.8 Wh |
Required Capacity: 4.9 Ah
Current Demand:
Load | Description | Current Demand |
|---|---|---|
Horn | Direct driven 12V horn | 10A |
Telemetry | Raspberry Pi (Assuming switching regulator at 90% efficiency to downregulate 12V to 5V power) | 0.56 A |
Fans | 1 Noctua NF-F12 iPPC 3000, 3.6W max (Reused from MSXIV), typ. current of 0.26 A, max of 0.3A | 0.3A |
Contactors | 3-5A | 5A |
Constant Discharge Rate | 0.86A | |
Maximum Discharge Rate (Startup) | Maximum discharge rate to energize contactors | 5A |
Maximum Discharge Rate (Horn) | Maximum discharge rate from all emergency systems + horn | 10.86 |
Battery Choices
Batteries investigated over multiple areas are found in the attached file.
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Final Battery Choice
The final battery chosen is the Maha Powerex Precharged 10000mAh D cell battery in a string of 10 cells, as it has already been purchased. It has a capacity of 120Wh, and can deliver an approximate maximum constant discharge rate of 27A, assuming a nominal capacity of 9000mAh and discharge characteristics typical of NiMH batteries (3C).
Thermal Constraints
As the D cell battery has an internal resistance of 18mOhm at full discharge, the maximum heat generation will be 2.0072448W for 5 minutes, assuming the horn is running.
Using a temperature rise calculator, it was determined that if a 10cmx10cmx10cm cube-shaped enclosure with 1cm thick PET walls, with a heat generation of 4W and the ambient temperature is 30 degrees, the temperature would rise by only 2.67 degrees
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(module design coming later)
Must be easily swappable
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