Sunsynk and Deye Lead-Acid and Traction Battery Settings Guide

Key Takeaways

• Motive power forklift traction battery banks, typically constructed from 24 individual 2V flooded cells connected in series to form a 48V bank, provide robust energy storage.
• Standard high-capacity traction banks provide approximately 1000Ah capacity, requiring custom per-cell voltage configuration rather than default sealed battery profiles.
• Absorption charging targets 2.09-2.10 volts per cell (SG 1.260-1.280), while equalization targets 2.15 to 2.17 volts per cell every 60 to 90 days for 10 to 12hrs.
• Critical discharge thresholds must be strictly programmed: 80% DOD rests at 2.03 Volts per cell (SG 1.200), low battery alarm at 1.99 Volts per cell (SG 1.170), and empty floor at 1.96 Volts per cell (SG 1.150).
• Inverter firmware requires a minimum 5% buffer between Shutdown% and Low Batt%, with Restart% set strictly higher than both.

Industrial Traction Batteries in Solar Storage

In South Africa, commercial workshops, agricultural packhouses, and off-grid homesteads frequently repurpose motive power forklift batteries for stationary solar storage. Unlike consumer sealed AGM or lithium packs that communicate via digital CANbus protocols, flooded lead-acid traction cells require manual parameter programming on the inverter touchscreen.

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These energy storage systems are typically made up of 24 individual 2V flooded lead-acid cells connected in series to create a 48V large capacity lead-acid storage battery bank. Because these battery banks are typically around 1000Ah capacity, they can deliver sustained discharge currents throughout extended load-shedding events and can be connected in parallel with additional battery banks to create an even larger capacity storage bank.

Per-Cell Charging Stages & Voltage Targets

Properly charging 24-cell traction banks requires programming precise multi-stage voltage limits. Lead-acid chemistry changes internal resistance and electrolyte density across each stage of charge.

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1. Absorption Charge Stage

Absorption charge is when bulk charging is nearing completion, generally around 80 to 90% charged. At this transition point:

• Inverter voltage regulation should maintain 2.09-2.10 volts per cell across the string.
• Electrolyte specific gravity (SG) should measure around 1.260-1.280.
• Maintaining 2.09-2.10 volts per cell ensures thorough chemical conversion of lead sulphate without overheating the positive plate grids.

2. Float and Trickle Stage

Float charge / trickle charge generally occurs after the absorption charge, when the charge current reduces and the battery state of charge reaches around 98%. Floating at reduced current maintains the bank at full capacity while minimising water consumption and plate corrosion.

3. Equalization Cycle Parameters

Because individual cells in a long series string exhibit slight differences in internal resistance and temperature, cells gradually drift out of balance over time.

• Target Voltage: Program equalization voltage to 2.15 to 2.17 volts per cell.
• Maintenance Cadence: Equalisation charging is recommended every 60 to 90 days to eliminate voltages becoming out of sync.
• Equalization Period: In traction applications, the equalisation charge period would typically be around 10 to 12hrs to allow lagging cells to reach full chemical saturation.

Electrolyte Gassing & Top of Charge Physics

Flooded lead-acid batteries require controlled electrolyte gassing to prevent acid stratification, a condition where concentrated sulphuric acid settles at the bottom of tall 2V cells.

Chemical & Explosive Gas Danger Caveat

Hydrogen Explosion Hazard: During equalization and gassing phases, flooded lead-acid cells emit highly flammable hydrogen gas. Battery enclosures and battery rooms must be equipped with permanent, non-sparking mechanical ventilation or passive cross-ventilation. Never operate open flames, grinders, or unsealed relays near flooded battery banks.

Critical Gassing Voltages

• Gassing Threshold: Gassing voltage is around 2.35 Volts per cell. This is a critical voltage reading to ensure the battery starts the gassing process when the electrolyte starts to mix, scrubbing sulphate crystals from the active plates.
• Top of Charge (TOC): Top of charge voltage would need to be around 2.60 Volts per cell minimum to ensure that the battery has gone completely through the gassing stage/phase and achieved full chemical rejuvenation.

Discharge Thresholds & Depth of Discharge (DOD) Limits

Over-discharging flooded traction cells leads to irreversible plate sulphation and capacity loss. Installers must map the inverter low-battery alarms and cutoff thresholds directly to cell state:

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1. 80% Depth of Discharge: To achieve long service life, traction cells should generally not be discharged beyond 80% DOD. Voltage at 80% DOD would be around 2.03 Volts per cell, with specific gravity readings around 1.200.
2. Low Battery Warning: In the inverter settings, configure the voltage for a low battery condition no lower than 1.99 Volts per cell, with specific gravity readings around 1.170.
3. Empty Cutoff Floor: The absolute lowest operating floor, designated as Battery Empty V, is the voltage at which the battery is considered empty: 1.96 Volts per cell, with specific gravity readings around 1.150. If cell voltage falls below 1.96 Volts per cell, severe degradation occurs.

Specific Gravity Tracking with a Hydrometer

Relying solely on open-circuit voltage can be deceptive, as surface charge and heavy inverter loads temporarily distort terminal voltage.

Maintenance Protocol: Regular specific gravity readings taken using a hydrometer are strongly recommended. Technicians should log specific gravity across all 24 individual cells once a month. Any individual cell exhibiting a specific gravity deficit exceeding 0.030 relative to the string average indicates internal cell imbalance requiring an extended 10 to 12hrs equalization cycle.

Inverter Parameter Configuration on Sunsynk & Deye

On the Sunsynk or Deye touchscreen, navigate to Settings > Battery Settings and configure the lead-acid operating parameters:

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1. Battery Type & Capacity

• Select Lead-Acid (or V mode) instead of Lithium.
• Set Batt Capacity: enter the total battery storage installed (e.g. 1000Ah for a single string).

2. Percentage Threshold Buffer Rules

When configuring discharge percentages:

• Shutdown% Failsafe: The Shutdown% should be considered as a failsafe which will stop the battery from becoming overdischarged and the minimum value should be the remainder from the depth of discharge (DOD) of the batteries being used.
• Low Batt% Buffer: Always configure the Low Batt% higher than the Shutdown% with at least a 5% buffer between them. This 5% buffer allows the inverter to sound an audible alarm or initiate auxiliary generator auto-start before reaching shutdown.
• Restart% Rule: The Restart% setting must be programmed higher than both Shutdown% and Low Batt% to prevent the inverter from rapidly oscillating on and off around the cutoff threshold.

3. Voltage Cutoffs

• Battery Empty V: Program the aggregate terminal voltage corresponding to 1.96 Volts per cell (multiply 1.96 Volts by the number of series cells, e.g. 24 cells). This ensures the inverter will disconnect loads when the battery is completely flat.

4. Recovery via the "Activate" Function

If a lead-acid bank is accidentally over-discharged during severe grid outages and falls below inverter operating thresholds, enable the Activate feature. This built-in function helps recover a battery that is over discharged by slowly charging from the solar array or grid via controlled trickle charging until terminal voltage rises into the normal operational window.

Settings Summary Reference Table

By adhering to these rigorous per-cell voltage thresholds, maintaining a 5% buffer between percentage limits, scheduling regular 10 to 12hrs equalizations, and monitoring specific gravity with a hydrometer, system operators can achieve exceptional reliability and lifespan from heavy-duty traction batteries on Sunsynk and Deye hybrid inverters.