--- title: "SLI and station batteries and charging methods" subject: "Industrial Power Distribution and Illumination" chapter: 9 key: "semester_6/industrial_power_distribution_and_illumination:sli-station-battery-charging" source: https://www.bctengineer.com/q/semester_6/industrial_power_distribution_and_illumination/sli-station-battery-charging site: BCT Engineering --- # SLI and station batteries and charging methods Industrial Power Distribution and Illumination · Chapter 9: Emergency and Backup Supply Systems - Asked in: 2071 Magh, 8 marks - Video: [Basics of Battery Charger ||Working Principle of float and boost Mode || Hindi](https://www.youtube.com/watch?v=I-wkfOX_FEI) — Insight Tecs - Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14 - Page: https://www.bctengineer.com/q/semester_6/industrial_power_distribution_and_illumination/sli-station-battery-charging - Whole chapter: https://www.bctengineer.com/md/semester_6/industrial_power_distribution_and_illumination/chapter-9 ## Question What do you mean by starting, lighting and ignition and station battery in an industry? What are the different methods of battery charging system? ## Short answer SLI battery supplies high current for starting, lighting, and ignition in DG sets and vehicles; station battery is a float-charged DC bank for breaker tripping, protection, and emergency lighting. Charging methods include constant current, constant voltage, CC-CV, trickle, float, boost, and equalising. ## Answer #### Starting, lighting and ignition (SLI) battery An **SLI battery** is a lead-acid battery used in vehicles and engine-driven sets to: - **Start** the engine – supply a very high current (hundreds of amperes) for a few seconds to the starter motor; - **Light** – supply head lamps and other lamps when the engine is off; - **Ignition** – supply the ignition system of petrol engines. In an industry, SLI batteries are used in **diesel generator sets, fire-pump engines, forklifts and plant vehicles**. They have thin plates with large surface area for high current; they are kept charged by the engine's alternator or by trickle charging when idle. Usual ratings: 12 V or 24 V, 80–200 Ah. #### Station battery A **station battery** is a large stationary battery bank (usually 24, 48, 110 or 220 V DC) installed in substations, power stations and industrial switchrooms to supply: - Tripping and closing coils of circuit breakers, - Protection relays, control and indication, - Emergency lighting and communication. It must be completely reliable, so it is kept on **float charge** with the charger, battery and DC load in parallel. Thick-plate tubular lead-acid or Ni-Cd cells with long life (15–20 years) are used. #### Methods of battery charging 1. **Constant-current charging** – current held at about C/10 while voltage rises; two-rate variant reduces gassing. 2. **Constant-voltage charging** – fixed 2.3–2.4 V/cell; current falls automatically. 3. **CC–CV (modified constant voltage)** – constant current then constant voltage; used in modern chargers. 4. **Trickle charging** – small continuous current to make up self-discharge of idle batteries (e.g. DG starting batteries). 5. **Float charging** – charger feeds load and battery together at ≈ 2.2 V/cell (station batteries). 6. **Boost charging** – high current briefly after deep discharge. 7. **Equalising charge** – occasional overcharge to equalise all cells. ```text Station battery – float scheme AC ─►[Charger]──┬──────────┬──► DC bus (trip, │ │ control, lights) [Battery bank] │ ``` ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. What does SLI stand for and what is its main duty? A. Standby, lighting, inverter: powering a UPS B. Starting, lighting and ignition: supplying very high current to start an engine, plus lights and ignition C. Station, load, isolation: supplying switchgear tripping D. Slow, low, intermittent: long-duration discharge Answer: B. An SLI battery gives hundreds of amperes for a few seconds to the starter, and also supplies lamps and ignition. (Key point: SLI meaning) 2. Why do SLI batteries have thin plates with large surface area? A. To give very long life of 15-20 years B. To supply high current for starting C. To make them lighter than any other battery D. To allow float charging Answer: B. Large surface area allows the very high discharge current needed for starting. (Key point: SLI construction) 3. What loads does an industrial station battery supply? A. Engine starter motors B. Process motors of the plant C. Circuit breaker trip/close coils, protection relays, control and emergency lighting D. Welding equipment Answer: C. A station battery supplies the DC control and protection system of substations and switchrooms. (Key point: Station battery function) 4. How is a station battery normally kept charged? A. Float charge, with charger, battery and DC load in parallel B. Boost charge continuously C. Constant-current charging at C/10 always D. It is not charged; cells are replaced Answer: A. Float charging keeps the battery full and ready, and the charger carries the DC load. 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