Scalable Battery Pack Switching to Prevent Parallel Cross-Charging
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Solution Overview
Problem
Existing battery pack systems for riding vehicles and high-power applications face issues with cross-charging and uneven state of charge when multiple packs are connected in parallel, leading to reduced cycle life and potential damage, especially when packs are used interchangeably across different devices.
Innovation Solution
A scalable power unit with a battery management system and switching elements that control the charging and discharging of individual battery packs, maintaining balanced state of charge through transistor control and allowing packs to be easily added or removed without tools, with a master-slave configuration for communication and control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If multiple battery packs are connected in parallel to increase capacity, then the energy storage capacity (amp-hours) is improved, but cross-charging occurs when voltage levels are unequal, reducing cycle life and causing potential damage
Solution Approach 1:
The battery management system continuously monitors the voltage and state of charge of each individual battery pack in the parallel configuration. Based on this feedback, the control unit dynamically adjusts the charging current distribution to prevent cross-charging. When one pack reaches full charge before others, the system automatically reduces or stops charging current to that pack while continuing to charge others, thereby preventing overcharging and extending cycle life.
Solution Approach 2:
The system changes the charging parameters (current allocation, voltage thresholds) dynamically based on the real-time state of each battery pack. By monitoring individual pack voltages and adjusting charging currents accordingly, the system maintains safe operating parameters for all packs even when they have different states of charge, preventing cross-charging damage while maximizing overall capacity utilization.
2Adaptability or versatility
If battery packs are made removable and interchangeable for use across different applications, then versatility and adaptability are improved, but maintaining balanced state of charge across all packs becomes more difficult
Solution Approach 1:
Before a removable battery pack is connected to the system, the battery management system performs a preliminary check of its voltage and state of charge. Based on this preliminary assessment, the control unit pre-configures the charging strategy. If the incoming pack has a higher state of charge than others, the system prepares to limit its charging current or exclude it from charging until other packs catch up, thereby maintaining state of charge balance across all packs regardless of their usage history.
Solution Approach 2:
The system continuously monitors the state of charge of all battery packs, including newly connected removable packs. Based on this feedback, the control unit dynamically adjusts charging current distribution to maintain balance. When removable packs are reconnected after being used in other applications, the system detects their charge state and modifies charging parameters accordingly, ensuring that voltage differences do not cause cross-charging or instability.
3Reliability
If a control system is added to manage charging and discharging of individual battery packs, then cross-charging is prevented and reliability is improved, but device complexity increases
Solution Approach 1:
The battery management system is designed to autonomously monitor and control charging without requiring external intervention or complex external control circuitry. Each battery pack's characteristics are automatically detected and stored in memory, and the control unit self-adjusts charging parameters based on real-time conditions. This self-service capability reduces the need for additional sensors, switches, or manual control mechanisms, thereby limiting the increase in overall system complexity while maintaining high reliability.
Solution Approach 2:
The control functions are integrated into a single control unit that manages all battery packs regardless of their configuration or usage history. By merging the control logic and memory functions into one centralized unit, the system avoids duplicating control circuits for each battery pack, thereby reducing overall complexity. The control unit handles voltage monitoring, current regulation, and state-of-charge balancing for all packs through unified control mechanisms.
Data Source
AI summary
A scalable power unit for powering one or more electric motors of a riding vehicle and/or a piece of outdoor power equipment includes a number of interconnected battery packs. The battery pack are received in a battery tray or stacked to form the scalable power unit. Each battery pack is configured to be removed and used separately or added to a combination of battery packs. A control unit selectively opens and closes switching elements to separately control the connections between the battery packs and an electrical load, such as a motor. During charging, the control unit opens and closes switching elements to control the charging rate of the individual battery packs. When the battery packs are connected to an electrical load, the control unit controls the state of the switching elements to selectively discharge the battery packs to power the riding vehicle and/or electric loads.