--- title: "Battery and magneto ignition systems" subject: "Internal Combustion Engines" chapter: 5 key: "semester_6/internal_combustion_engines:battery-coil-magneto-ignition-systems" source: https://www.bctengineer.com/q/semester_6/internal_combustion_engines/battery-coil-magneto-ignition-systems site: BCT Engineering --- # Battery and magneto ignition systems Internal Combustion Engines · Chapter 5: Combustion in SI and CI Engines - Asked in: year not given, 8 marks - Video: [Battery Ignition System of IC Engine](https://www.youtube.com/watch?v=tEpui59xhBI) — Technograph - Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14 - Page: https://www.bctengineer.com/q/semester_6/internal_combustion_engines/battery-coil-magneto-ignition-systems - Whole chapter: https://www.bctengineer.com/md/semester_6/internal_combustion_engines/chapter-5 ## Question Explain with a neat circuit diagram the working of a battery (coil) ignition system. Differentiate between battery ignition and magneto ignition systems. ## Short answer A battery ignition system generates high voltage by collapsing a primary current in the coil via a contact breaker; the induced secondary voltage is distributed to spark plugs. It provides strong spark at cranking but needs a battery. Magneto ignition is self-generating, more reliable at high speed, but gives weak spark during starting. ## Answer #### Battery (coil) ignition system It produces the high-voltage spark (10-25 kV) from a 6 V or 12 V battery. ```text Battery --[Ignition switch]--[Ballast R]--+ | +----------+----------------------+ | Primary | Secondary | | (low) | (high) | +--+--(coil)-----+----------------+ | | [Contact breaker] | [Distributor] --> plug 1,2,3,4 | = Condenser| Earth Earth ``` **Main parts:** battery, ignition switch, ignition coil (primary of 200-300 turns of thick wire, secondary of 20 000-30 000 turns of fine wire on a soft iron core), contact breaker with cam, condenser, distributor and spark plugs. **Working** 1. With the contacts closed the primary current (3-4 A) flows and builds a magnetic field in the core. 2. The cam opens the contacts. The field collapses very quickly, inducing about 250 V in the primary and 10-25 kV in the secondary because of its many turns. 3. The condenser across the contacts absorbs the primary surge, prevents arcing at the points and makes the field collapse faster. 4. The distributor sends the high voltage to the correct plug in firing order; the spark jumps the gap and ignites the mixture. 5. A centrifugal or vacuum advance mechanism changes spark timing with speed and load. #### Comparison | Basis | Battery ignition | Magneto ignition | |---|---|---| | Energy source | Battery | Self-generating (rotating magnet) | | Starting | Good spark even at cranking speed | Weak spark at low speed, hard starting | | Battery needed | Yes | No | | Cost, space | Cheaper, but bulkier (needs a battery) | Costlier, but compact | | Spark at high speed | Weaker, contact bounce | Better | | Reliability | Depends on battery state | More reliable | | Use | Cars, buses | Two-wheelers, racing engines, aircraft (older) | Modern engines use transistorised, capacitor-discharge or fully electronic ignition with coil-on-plug units instead of contact breakers. ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. What produces the high secondary voltage when the contact breaker opens? A. Rapid collapse of the primary's magnetic field inducing high voltage in the many-turn secondary B. The battery directly C. The condenser discharging D. The distributor Answer: A. The fast field collapse induces about 250 V in the primary and 10-25 kV in the secondary because of its many turns. (Key point: High voltage generation) 2. What does the condenser across the contact breaker do? A. Boosts battery voltage B. Absorbs the primary surge, prevents arcing and speeds field collapse C. Distributes the spark D. Advances the timing Answer: B. Without it the points would arc and the field would collapse slowly, giving a weak spark. (Key point: Condenser function) 3. What is the distributor's role? A. Generates high voltage B. Charges the battery C. Sends the high voltage to the correct plug in firing order D. Controls the throttle Answer: C. It routes each spark to the right cylinder. (Key point: Distributor role) 4. Which system gives a good spark at cranking speed? A. Magneto ignition B. Neither C. Both are weak D. Battery ignition Answer: D. Battery ignition does not depend on engine speed; a magneto gives a weak spark at low speed and starts hard. (Key point: Battery vs magneto at starting) ## Related in Internal Combustion Engines - [Differentiate SI and CI engines](https://www.bctengineer.com/question.md?key=semester_6%2Finternal_combustion_engines%3Asi-versus-ci-engine-differences) — Internal Combustion Engines, chapter 2 - [Four-stroke SI engine working and components](https://www.bctengineer.com/question.md?key=semester_6%2Finternal_combustion_engines%3Afour-stroke-si-engine-working-components) — Internal Combustion Engines, chapter 2 - [Engine lubrication systems](https://www.bctengineer.com/question.md?key=semester_6%2Finternal_combustion_engines%3Aengine-lubrication-systems-types) — Internal Combustion Engines, chapter 6 - [Water cooling systems and components](https://www.bctengineer.com/question.md?key=semester_6%2Finternal_combustion_engines%3Awater-cooling-systems-components) — Internal Combustion Engines, chapter 7 ## Related in other subjects - [Battery ignition system and spark timing calculation](https://www.bctengineer.com/question.md?key=semester_5%2Fautomotive_technology%3Abattery-ignition-spark-numerical) — Automotive Technology, chapter 3 - [Battery charger circuit and charging methods](https://www.bctengineer.com/question.md?key=semester_6%2Findustrial_power_distribution_and_illumination%3Abattery-charger-two-methods) — Industrial Power Distribution and Illumination, chapter 9 - [Differentiate wired and wireless systems](https://www.bctengineer.com/question.md?key=semester_2%2Fbasic_electronics_engineering%3Awired-vs-wireless-diff) — Basic Electronics Engineering, chapter 5, asked 2× - [Battery and working principle](https://www.bctengineer.com/question.md?key=semester_7%2Fenergy_environment_and_society%3Abattery-working-principle) — Energy Environment and Society, chapter 5