Delving into the intricacies of the Hornet Car’s 12V battery charging system reveals a complexity that surpasses initial expectations, especially when compared to simpler systems like that found in the Pacifica Hybrid. Unlike the Pacifica Hybrid which maintains a consistently high charge state, the Hornet appears to dynamically adjust its charging voltage. Observations indicate an alternating pattern between a robust 14.1V for high charge and a gentler 12.7V-12.9V for trickle charge, seemingly influenced by the 12V battery’s state of charge. This nuanced approach raises questions about the system’s operational logic and long-term battery health.
To investigate potential parasitic current draws, particularly after noticing an unexplained voltage drop of approximately half a volt within a day post-full charge on a recently manufactured Hornet (August 2023), a clamp-on ammeter was employed. Upon opening the hood (while unplugged), the vehicle’s display remained active for 10 to 20 minutes, displaying a “Hood Open Unable to Charge Battery Or Condition Battery/Cabin” message. During this period, a current draw of around 5A was measured at the ground wire, with the battery voltage registering at 12.54V. Approximately 20 minutes after hood opening, the car transitioned into a “sleep” state, with the current reading dropping to a range of 700mA-900mA. Concurrently, the voltage increased to 12.85V-12.90V, suggesting a possible shift to a charging current during this “sleep” mode.
However, several questions remain unanswered regarding the Hornet car’s 12V battery management. The duration of trickle charging during sleep mode (while unplugged) is unclear, as is the precise battery state of health threshold that dictates when charging ceases. Furthermore, it’s uncertain how frequently the charging system activates to assess battery health and initiate trickle charging when the vehicle remains undisturbed with the hood either open or closed. The owner’s manual mentions a 3-week interval, but its accuracy is questionable in real-world scenarios. It’s also noted that actions like opening or closing doors or the hood seem to “wake up” the car. Does this wake-up trigger a full charge of the 12V battery from the high voltage battery, regardless of the initial charge level?
Finally, the conditions that prompt the Hornet car to enter a “high charge” state while in sleep mode are yet to be determined. It’s speculated that a specific voltage level might trigger this high charge state when the car periodically checks battery health. Identifying the exact trigger mechanism and voltage threshold remains a key point of interest for understanding the complete operational picture of the Hornet car’s 12V battery charging system.
