This manual describes the selection and maintenance of large lead-acid batteries used in electric lift trucks. It is intended for service personnel responsible for battery maintenance. Battery repair requires specialized training and equipment, and it is recommended that repairs only be attempted by individuals with the correct tools, equipment, and experience. Most battery repairs are typically handled by specialized repair services.
Function Description:
A lead-acid battery converts chemical energy into electrical energy. This chemical change provides electrical energy. When the chemical reaction has progressed to the point where the battery no longer delivers its rated voltage and current, it is considered discharged. To reuse the battery, a reverse chemical action must occur. The batteries described in this manual can be recharged by an external electric voltage and current, which initiates this reverse chemical action. The lead-acid chemicals store electrical energy until it is needed to operate an electric device.
A lead-acid battery is composed of several individual lead-acid cells. Each cell contains positive and negative plates separated by dielectric spacers, all immersed in an electrolyte solution.
Important Technical Specifications:
- Specific Gravity: The strength of the electrolyte is measured in points of specific gravity. For instance, a solution of sulfuric acid has a specific gravity of 1.835, and water has a specific gravity of 1.000. Electrolyte, typically 27 percent acid and 73 percent water, has a specific gravity of 1.275. In a fully-charged cell, the electrolyte's specific gravity ranges from 1.270 to 1.130. A battery should NEVER be discharged below a specific gravity of 1.130, as this can cause permanent damage.
- Voltage (Potential Difference): A cell generates approximately 2 volts per cell. This potential difference does not vary with the size of the cell. A discharged cell has a potential difference of approximately 1.75 volts.
- Ampere: A measurement of electric current.
- Watt: A measure of electric power. Watts are calculated by multiplying volts by amperes. A kilowatt-hour (kWh) is 1000 watts of electric power used for 1 hour.
- Ohms: A measurement of electrical resistance.
- Polarity: In a battery, electric current flows from the positive terminal to the negative terminal.
- Battery Ratings: Batteries are rated in ampere-hours and kilowatt-hours at a constant discharge rate. A 6-hour discharge rate is standard. Ampere-hours measure battery capacity (amperes × hours). Kilowatt-hours measure total power generated (volts × amperes × hours / 1000). For example, a 48-volt, 600 ampere-hour battery has a rating of 28.8 kWh.
- Battery Voltage Ranges: Lift trucks are available in various voltage ranges. Small "walkie" lift trucks typically use 12 or 24 volts. Larger sit-down rider lift trucks typically use 24, 36, 48, 72, or 80 volts. The number of cells determines the battery voltage (e.g., 24 volts = 12-cell battery, 48 volts = 24-cell battery).
- Maintenance-Free Battery: These batteries use a calcium alloy of lead instead of an antimony alloy, which reduces electrolysis and the need to check electrolyte levels or add water during their lifespan.
- Flooded Cell: A lead-acid battery with free-flowing electrolyte fluid in each cell, consisting of a mixture of sulfuric acid and water.
- Direct Current (DC): Current flow and voltage where the polarity between two terminals is always the same.
- Alternating Current (AC): Voltage where the polarity between two terminals changes between positive and negative at a quick and constant rate.
Usage Features:
- Battery Selection: Battery capacity depends on factors like lift truck size, attachments, and type of work (heavy-duty or normal 8-hour operation). Some work conditions may require multiple batteries. The battery's capacity can be found on the lift truck's nameplate.
- Battery as a Counterweight: For electric lift trucks where the battery acts as part of the counterweight, its weight is crucial for the lift truck's load capacity. The minimum battery weight is specified on the nameplate. If the battery is lighter, the lift truck's capacity is reduced. Blocks and spacers must be used to secure batteries smaller than the compartment.
- Charging Battery:
- Normal Charge: Typically an 8-hour charge for batteries discharged from normal operation. Regular charging intervals depend on usage. Frequent charging of a battery with 2/3 or more charge can reduce battery life.
- Equalizing Charge: A low-rate charge, usually given monthly, to balance the charge across all cells. It's a slow rate for 3 to 6 hours in addition to the regular charging cycle. Do not give an equalizing charge more than once a week. Significant specific gravity differences (more than 0.020) between cells after an equalizing charge may indicate a damaged cell.
- Gradual Charge: Uses a solid-state automatic battery charger. The charging rate starts high (20-25 amps/100 amp-hours) and decreases to less than 5 amps/100 amp-hours when 80% charged.
- Modified Constant Voltage: Uses a generator to maintain a constant voltage, controlled by a resistor. Charging current decreases as voltage across the resistor increases.
- Two-Rate Charge: Uses a high charging rate initially, then reduces it. Two resistors control the rate, with a relay activating the second resistor when cell voltage reaches 2.37 volts.
- Battery Connectors: Heavy-duty connectors link the battery to the lift truck's electrical system. Many have handles for quick disconnection in emergencies. Connectors and handles must be kept in good repair. Disconnect the battery connector during maintenance not requiring electric power.
Maintenance Features:
- Safety Procedures:
- Wear rubber apron, gloves, boots, and goggles/face shield during battery maintenance.
- Batteries generate hydrogen gas during charging; keep open flames, sparks, and smoking materials away. Do not use matches/lighters to check electrolyte levels.
- Lift batteries correctly using a crane or equipment designed for the job, with a spreader bar. Do not use chain or wire rope slings.
- Never place metal materials or tools on a battery.
- Disconnect the battery from the lift truck before maintenance or repairs.
- Disconnect both AC and DC power when working on the battery or charger. Keep positive and negative terminals/cables separate and insulated to prevent short circuits and explosions.
- Keep water readily available to flush spilled electrolyte. Seek medical attention immediately if electrolyte gets into eyes. Special showers and eye wash systems are required in battery maintenance areas.
- Neutralize spilled electrolyte on surfaces with a solution of soda (sodium bicarbonate) and flush with water.
- Only trained personnel should perform battery and charger maintenance, adhering to all government and private safety regulations.
- Maintenance Records: Follow a consistent sequence for recording cell numbers, starting with a positive cell and ending with the negative cable cell. Record the charger's beginning ampere reading for each charge to identify potential problems.
- New Battery Inspection: Inspect for damage. Ensure electrolyte levels are correct. Charge for 6 hours or until specific gravity is correct. Install correctly using a spreader bar and slings. Complete Battery Inspection and Daily Battery Reports.
- Cleaning Battery: Keep the battery compartment clean and dry. Wash the battery with water and a clean cloth, then dry with compressed air. DO NOT use steam, hot water, or high-pressure hoses. Remove any spilled electrolyte from the compartment to prevent corrosion; use a solution of 0.5 kg soda per 4 liters of water, then flush with clean water. Clean the battery and compartment at least every 6 months. If the battery top is wet, check electrolyte level or charger operation.
- Adding Water to Battery: Some batteries have sealed cells and do not require water. For flooded cells, water is lost during charge/discharge cycles. Check electrolyte levels daily. If the level falls below the top of the separators, the cell can be damaged. Always use distilled water. Add water AFTER the charging cycle, never before or during, to prevent overflow.
- Hydrometer Use: For flooded cells, use a hydrometer to measure specific gravity. Ensure sufficient electrolyte in the cells and that the float moves freely without touching the barrel. Electrolyte level affects specific gravity readings.
- Battery Temperature: Electrolyte temperature affects specific gravity readings (e.g., a 6°C/10°F increase decreases specific gravity by 0.003 point). Use a thermometer or special battery thermometer for corrections. NEVER charge a battery above 49°C (120°F) to prevent damage. Ensure adequate ventilation and appropriate charge/discharge rates.
- Troubleshooting Charger: Periodically check charger operation. Monitor battery temperature (should not rise more than 14°C/25°F during an 8-hour charge). Check for continuous charger operation (may indicate low charging rate) or continuous high-rate operation (controls may need repair).
- Knowing When Battery Is Fully Charged:
- Voltage level becomes constant during charging.
- Bubbles appear in the electrolyte when a vent cap is removed.
- Specific gravity reading is constant and within limits for a charged battery.
- Charger meter indications become constant.
- Where to Charge Batteries: Designate a special area for charging to extend service life and reduce maintenance. This area needs a power supply, ventilation for hydrogen gas, drains for cleaning, and appropriate racks (wood or insulated metal).
- Equipment Needed: Lifting device, racks, battery charger, maintenance tools, cleaning area with drain, distilled water, air/water supplies, maintenance records, workbench, spare parts, protective clothing, safety equipment, water source for eye washing, "NO SMOKING" sign, and good ventilation for the charger area.
- Battery Care:
- Keep batteries clean and free of spilled electrolyte.
- DO NOT overcharge or deeply discharge the battery.
- Charge in a well-ventilated area.
- Maintain correct electrolyte levels with distilled water.
- Prevent batteries from freezing.
- Keep batteries charged; discharged batteries in storage shorten life.
- Use the correct charger for the battery; an incorrect ampere-hour rate can cause damage.
- Ensure no short circuits occur when moving batteries.
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