MSXV - Aux / Supplementary Battery
- Kostubh Agarwal
Regulations - ASC 2024
8.2.C Supplemental Batteries
8.2.C.1 Supplemental, replaceable batteries carried in the solar car may be used to power: Main Power Switch, radios, commercially available electronic panel meters with internal batteries, cell phones, driver ventilation fans (if solely used for driver ventilation), and the horn. All other systems present on the car must be powered off the main battery.
8.2.C.2 Supplemental battery power may be used to momentarily power the battery protection system (BPS) as defined by Reg. 8.3 to verify safe battery parameters before energizing the Main Power Switch.
8.2.C.3 During a battery fault in which the BPS has automatically opened the Main Power Switch, the supplemental battery must be used to power the BPS, BPS Strobe, and BPS Fault Driver Indication. While in such a fault state, the supplemental battery may be used to power any other systems (signal lights, rear view camera, telemetry, etc) that do not provide motive power to the vehicle.
8.3.B.2 Supplemental: All supplemental batteries must have at a minimum Passive Protection for under-voltage where charging occurs remote to the solar vehicle unless they are primary cells. Active Protection is required if charging is within the solar vehicle. No Secondary Lithium battery types shall be used for the Supplemental Battery unless the Supplemental Battery is powering a commercially procured component such as a cell phone or laptop and the Supplemental Battery was intended for this purpose.
8.3.A.6 Passive Protection: System in which measurements are monitored by the driver and where action is driver controlled.
8.3.A.5 Active Protection: System in which measurements are constantly monitored and where actions are taken immediately without operator intervention to open the Main Power Switch should a Battery Protection Fault occur. Any protection faults will latch such that a manual clearing process is required by the driver with the vehicle not in motion and only after faults have been verified clear by the protection system.
8.3.A.7 Battery Protection System (BPS): The system that applies Active Protection to protect battery pack
All registered and sealed battery modules, supplemental batteries, battery protection circuitry per Reg. 8.3, and main fuses per Reg. 8.5 must be fully contained in enclosures that are electrically isolated from the solar car. The enclosures must be constructed from non-conductive, electrolyte-resistant material. No more than two separate such enclosures may be used for the main energy storage. Enclosures must be designed such that they can be removed from the vehicle and placed in impound per Regs. 12.18 and 14.12.
12.18.A.1 All battery enclosures per Reg. 8.4 must be removed from the solar car and kept overnight in an impound box/container that will be secured by the Observer. Teams should recognize that they will need additional power sources if they have to power or troubleshoot vehicle systems while batteries are impounded
14.12.A.2 All charging of solar car batteries shall be monitored by a team member. Unattended charging of the solar car batteries is strictly prohibited.
Battery enclosures may be equipped with a forced ventilation system. Such ventilation systems must pull exhaust to the exterior of the solar car and must be directly connected to the exterior of the vehicle away from any airstream that may reach the driver. The ventilation system shall be powered by the battery system. Provisions should be made to power this fan from the Supplemental battery in the event of a Battery Protection Fault.
14.12.A.2 All charging of solar car batteries shall be monitored by a team member. Unattended charging of the solar car batteries is strictly prohibited.
Vehicle Demands
[MSXV] what are our demands? LV? HV? Infotainment, Driver Fans, Horn?
[MSXIV] used aux battery pack for horn and driver fans, 12V and a current of up to 10A.
[MSXII] The Aux battery was used to power the critical LV systems during the startup and emergency states, also to provide the power required to close the HV battery contactors (current spike 3-4A)
Next Steps
Figure out what the aux will be used for
Research cells and composition
Test
Prototype
Finish
Appendix
[MSXIV] The Aux battery must also be easy to charge, and swappable, and would be nice if it could hold power over a long time as it can be several weeks between turning the car on and off during off-terms.
For simplicity, we would like our Aux battery to be able to power our LV systems directly, without a DC-DC converter between it. Our LV system is 12V, trimmed to 13.5V, so we will need a battery within the same voltage range.
[MMXIV] The Aux Battery needs to be protected, as well as charged by the main battery while the car is operating on the main battery. Aux BMS will be powered by the aux battery itself, and should enter a very low power sleep state while not monitoring the cells.
All protection functions should have the capability to be handled through hardware (with voltage references and comparators) or via software for more advanced monitoring.
This board should also implement a rough State-Of-Charge (SoC) model for the Aux battery using an OCV vs SoC estimation
Resources