Assembly line covering the 12 V battery and its housing and mounting.
Groups the EarthX battery, the housing and the battery harness. Design Philosophies and Processes: Inherited from the Custom Electronics subsystem design process: 1. Collect the sensor list from every subteam, agree location and type with the designer who needs the data. 2. Split sensors between ECU and dash based on which parameters are engine-critical. 3. Size the charging system and validate it. A custom current measurement board (50 A bidirectional sensing chip, inline on the rectifier-to-PDM wire) measured what the rectifier actually puts back. 4. Build the datalogging parameter list with rates, then check CAN bus load. 5. Validate on a mock endurance: average battery voltage 13.4 V, minimum 12.1 V excluding cranking on CR26I.
From the CR22 electrical write-up, covering the 12 V system rather than the tractive system. 1. Choose the chemistry against what the car has to do on its worst day. CR22 runs LiFePO4. Every car since CR17 has run lithium-ion at competition, but until CR20 the car ran lead acid during the season, and a lead acid battery did not have the capacity for starts: a 12 V Optima had to be wheeled over on a hand truck every time the car needed starting or died on track. 2. Size the charging path with it, not after it. The stator converts engine rotation to 3-phase AC, and all three phases feed the series rectifier/regulator, a ShinDenGen SH847 on CR22, which returns DC to the electrical system so the 12 V battery is not the only source. 3. Validate the pair on the car. The team had not known how much current the stator was actually producing, so a current measurement board was designed specifically to measure what the rectifier/regulator returns and to prove the battery and rectifier/regulator selections.
From the CR22 electrical write-up: - The car has to charge itself over an endurance. That is the requirement the whole 12 V system is judged against, and CR22 initially failed it. - Wire gauge on the charging return is part of that constraint, not an installation detail. CR22's REC+ wire was built in 16 AWG, and the wire heated up over the run until it could no longer carry the current. - Capacity has to cover repeated starts without external help. The lead acid era needed an Optima on a hand truck; that is the failure mode the lithium chemistry exists to avoid. - Rectifier/regulator connectors ran two months or more of lead time on CR22. They did not delay the car only because connectors could be taken off the previous car.
From the CR22 electrical write-up. A current measurement board was built to measure the current the rectifier/regulator returns to the electrical system, because the team had no measurement of stator output at any given moment. It was manufactured in March 2024 and installed on the car in April 2024. It found a real fault. With the REC+ wire at 16 AWG, the car could not charge itself over an endurance: in the Kennesaw endurance, rectifier current dropped significantly towards the end of the event as the wire heated and its current-carrying capacity fell, and battery charge fell with it. The wire was changed to 12 AWG, and the post-Kennesaw mock endurance data showed enough current going back into the system to charge the battery over a full run. That is the validation the board was built for: it proved the battery and rectifier/regulator selections while exposing the wire as the actual limit.
CR22 Issue Log, 2023-12-03, Electrical. Battery voltage dropped quickly during a drive day and all three batteries died. It was initially assumed to be a battery that had not been fully charged. When the car came back to the shop the stator-to-rectifier crimps were found to have failed. Fixed by re-splicing the three phase wire to the connector.
REC+ wire increased from 16 AWG to 12 AWG so the charging system can actually put current back over an endurance, confirmed on a post-Kennesaw mock endurance.
Weighed mass: 1151.7 g (2.539 lb), 1500.0 g (3.307 lb) (recorded as: Battery). Source: Subteam weight books: CR22/Electrical/Design/Full System Analysis/CR22a_Electrical_System_Weight.xlsx
Nothing in CrimsonStorage covers these yet.