Cycles: calculate in full-cycle equivalents, not in charging events
Count the charge throughput moved, not the plug-in events. An AGV in two-shift operation that tops up 15 % ten times a day moves around 1.5 full-cycle equivalents per day. Over 300 operating days that is about 450 equivalents per year; in hard three-shift operation you reach 500–1,500. A good LiFePO4 cell delivers a wide service-life corridor under this profile and limited DoD, but only if two conditions hold: the cell temperature stays in the window (see below) and the balancing holds the cells together. If one cell in a series string drifts apart, the weakest cell limits the whole pack. Passive balancing in the milliampere range is not enough to compensate for the drift under strong partial cycles; here the balancing capability of the BMS decides the real service life.
Fast charging is a temperature problem, not a current problem
Charging at 1C–2C means: 60 Ah is charged with 60–120 A. The current itself is manageable. What is critical is lithium plating at the anode, which sets in below roughly 10–15 °C cell temperature at high charge rates and irreversibly damages the cell. That is why the BMS has to limit the charge rate as a function of temperature (charge derating) and preheat in the cold. Without this interplay the pack ages during the supposedly harmless top-up. Conversely, charging at 1C–2C generates noticeable loss heat; without a defined heat dissipation the average cell temperature rises over the day, and every degree above the optimum costs calendar life. A cooling and heating concept that keeps the cells in the window of roughly 15–35 °C is not optional with opportunity charging.
Communication: the BMS is a participant on the vehicle bus
Automated guided vehicles (AGV) need SoC, SoH, cell voltages, temperatures and fault flags in real time to control driving strategy and charging request. This is transmitted via CAN bus, usually as a CANopen profile (e.g. based on CiA battery profiles) or as a manufacturer-specific PDO mapping. Define early who specifies the object dictionary: if the battery management system (BMS) is delivered without an agreed mapping, the vehicle controller adapts nothing, and the project fails at the interface, not at the chemistry. Just as important is the fault-case behaviour: what does the BMS report on overcurrent, overtemperature, insulation fault — and does it switch off itself or does it expect the shutdown to come from the vehicle?
Mechanics: vibration and shock are design-relevant
An AGV drives over floor joints, ramps and points. Cell connectors that are only bolted and not designed to be fatigue-proof against loosening and vibration fracture fail in the field. Test against IEC 60068-2-64 (broadband random vibration) and IEC 60068-2-27 (mechanical shock). The consequence for the design: fix the cells with a positive lock, secure connectors against micro-movement, provide strain relief for the wiring. Installation space is no contradiction to robustness here: a pack designed around the chassis uses the battery bay to 90–95 % and at the same time packs the cells fixed and vibration-proof.
From practice
Since 2013 Hellpower Energy has worked with GKS on the power supply of the ROBOT-40 — an autonomous heavy-duty AGV for up to 40 tonnes that is today in service in Japan, Europe and the USA. No off-the-shelf battery fits this vehicle to this day. Hellpower Energy developed two custom LiFePO4 battery packs with a purpose-built enclosure and a battery-swap system: the installation space was predefined, and the vehicle at 40 t payload has no time window for long standstills at the charging point. The swap approach decouples charging time from vehicle availability — a second pack is charged outside the vehicle, the swap takes minutes. For worldwide operation it also counted that the mechanical design survives transport and continuous operation, and that the battery management system (BMS) communication fits the vehicle controller. That is the core: it is not the highest energy density that wins, but the design for the installation space, load profile and interface of the specific vehicle.
A point on responsibility
The traction battery is a component; CE conformity of the complete vehicle is the OEM's (vehicle manufacturer's) responsibility. Hellpower Energy supplies the evidence and interfaces needed for the vehicle risk assessment — shutdown behaviour, fault messages, test reports — so that the vehicle manufacturer can close its CE assessment.
Checklist for the tender
- ✓Load profile quantified in full-cycle equivalents per day, not in charging events
- ✓Target DoD and service-life corridor defined, not the datasheet cycle count adopted
- ✓Charge rate specified with temperature-dependent derating and preheating
- ✓Balancing capability matched to partial-cycle operation, not just passive
- ✓Temperature window and active cooling/heating concept defined
- ✓CAN/CANopen mapping and fault behaviour agreed before build start
- ✓Vibration/shock per IEC 60068-2-64 / -2-27 as a requirement in the specification
- ✓Evidence and interfaces for the OEM's CE assessment clarified
If you are designing an AGV project, it pays to work through the real load profile and the interface together early. Get in touch if you want to discuss the design.