How to setup workstep for ternary lithium battery balance in yesa battery machine
Hello, based on your hybrid vehicle type, Hyundai Kia PHev Module Niro Sportage, with NCM chemistry, Nominal voltage @ 44.4V (12 cell series), max. voltage: 50.4V, min cut off @ 30V and capacity: 30.8Ah to 38.3Ah, our setup is as follows:
Process Sequence:
1. Constant Current Discharge: Discharge at 3A until 3V (out of charge);
2. Rest: 10 minutes;
3. Constant Current Charging: Charge at 2.5A until 4.2V (fully charged);
4. Rest: 10 minutes;
5. Constant Current Discharge: Discharge at 3A until 3V (out of charge);
6. Rest: 10 minutes;
7. Constant Current Charging: Charge at 2.5A until 4V (approximately 80% charged).
Reasons behind:
Step 1: Constant Current Discharge at 3A until 3V (out of charge)
This initial discharge step serves as a controlled depletion of the Battery Pack's stored energy, bringing all cells to a low state of charge (SOC). For NCM (Nickel-Cobalt-Manganese) lithium-ion chemistry, discharging to around 3V per cell (which would equate to approximately 36V for your 12-cell series module, though the exact threshold might be monitored per cell or adjusted for the pack) helps equalize any imbalances in cell voltages that may have developed over time due to uneven usage, self-discharge, or manufacturing variances. The function behind this is to reset the pack to a known baseline SOC, minimizing differences in cell capacities and preventing overvoltage in stronger cells during subsequent charging. The 3A rate is moderate to avoid excessive heat or stress, ensuring safety while fully discharging without hitting the absolute minimum cutoff (your spec's 30V pack minimum, or ~2.5V per cell, which could risk damage if pushed too low).
Step 2: Rest for 10 Minutes
The rest period allows the battery chemistry to stabilize after discharge. During discharge, internal resistances and electrochemical reactions can cause temporary voltage drops or rebounds (known as polarization effects). This short pause lets the cell voltages settle to their true open-circuit values, reducing inaccuracies in the next step. The function is to ensure precise measurements or charging starts from a equilibrated state, which is crucial for balancing as it helps identify any lingering imbalances without interference from transient effects.
Step 3: Constant Current Charging at 2.5A until 4.2 (fully charged)
Here, the pack is charged to its maximum voltage per cell (4.2V, totaling 50.4V for the module), which represents a full charge. This step activates passive or active balancing mechanisms in the battery management system (BMS), if present, by pushing higher-voltage cells to bleed off excess charge through resistors or redistribution. For NCM cells, charging to 4.2V maximizes capacity utilization while staying within safe limits to avoid lithium plating or degradation. The lower 2.5A rate (compared to discharge) is chosen for gentler charging, reducing heat buildup and allowing time for balancing to occur naturally. The overall function is to top-balance the cells, ensuring they all reach full SOC uniformly, which corrects imbalances that could lead to reduced pack performance or safety issues like overcharging weaker cells.
Step 4: Rest for 10 Minutes
Similar to Step 2, this rest allows post-charge stabilization. After charging, cells may exhibit voltage relaxation due to diffusion of lithium ions within the electrodes. This pause ensures the voltages equalize internally, providing a clear picture of the balanced state before the next discharge. The function supports accurate assessment of the charging outcome and prevents proceeding with unstable voltages that could skew the balancing process.
Step 5: Constant Current Discharge at 3A until 3V (out of charge)
This second discharge cycle repeats the depletion process but now from a fully balanced and charged state. It verifies the balancing achieved in the previous steps by discharging uniformly, potentially revealing any residual capacity differences through voltage monitoring. For lithium-ion packs, repeated cycling like this can help recalibrate the BMS's SOC estimation and further equalize cells by exercising them through a full depth-of-discharge (DoD). The 3A rate maintains consistency with Step 1 for comparable conditions. The function is to confirm balance, measure effective capacity (your 30.8Ah–38.3Ah range), and condition the cells for longevity, as NCM chemistry benefits from occasional deep cycles to mitigate SEI (solid electrolyte interphase) layer issues.
Step 6: Rest for 10 Minutes
Again, this rest stabilizes the pack after the second discharge, allowing voltage rebound and chemical equilibrium. It mirrors the earlier rests to maintain procedural consistency, ensuring the final charge starts from a reliable low-SOC baseline. The function is to enhance precision in the concluding step, avoiding errors from post-discharge polarization.
Step 7: Constant Current Charging at 2.5A until 4V (out of (approximately 80% charged)
The final charge to 4V per cell (48V total for the module) brings the pack to a partial SOC, ideal for storage or immediate use without full topping. For NCM cells, storing at ~80% SOC (rather than 100%) minimizes stress, reduces calendar aging, and lowers risks like dendrite formation or electrolyte decomposition. The 2.5A rate keeps it controlled. The function is to leave the pack in a balanced, ready-to-use state post-conditioning, optimizing for long-term health while ensuring the prior balancing cycles have equalized voltages across the 12 cells. This step essentially "sets" the balanced condition for operational use in the Hyundai Kia PHEV module.
Additional Recommendations / Potential Enhancements
- Temperature monitoring/control — NCM is sensitive; aim for 20–30°C during the whole process. If End Temp rises >40°C, slow currents or add forced air cooling.
- ΔV monitoring — Your table has a -ΔV (likely delta voltage) column — track max cell ΔV throughout. Target <20–50mV at rest after full charge for good balance in PHEV modules.
- Safety cutoffs — Ensure over-voltage (e.g., 4.25V/cell), under-voltage, and over-current/temperature protections are active. For a 12s pack, pack max ~50.4–51V.
- Capacity verification — After the second discharge (step 5), compare measured Ah to your module's rated 30.8–38.3Ah. If significantly lower, cells may have aged or need further cycling.
- Optional extra step — If severe imbalance persists, insert a very slow charge (e.g., 0.5–1A) to 4.2V with extended CV hold for aggressive passive balancing.
- Vehicle context — In Hyundai/Kia PHEVs (like Niro/Sportage), the onboard BMS often balances primarily during slow AC charging to 100% (sometimes requiring plugged-in time after reaching 100%). Your external routine is more thorough for a removed module. After reinstallation, a full 100% charge in-vehicle can help the BMS re-learn and fine-tune.
- Cycle repetition — If this is for deep reconditioning, repeat the whole sequence 2–3 times if initial ΔV is high (>100mV).
This setup should yield a well-balanced, capacity-verified module ready for use or storage.
We hope that you can complete the balancing of this group of batteries according to the above instructions and then smoothly install them in the vehicle for use. If you have any questions, please feel free to leave a message below and we will be glad to answer more of your inquiries.