- Practice · 8 marks
Battery 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.
Explain with a neat circuit diagram the working of a battery (coil) ignition system. Differentiate between battery ignition and magneto ignition systems.
Battery (coil) ignition system
It produces the high-voltage spark (10-25 kV) from a 6 V or 12 V battery.
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
- With the contacts closed the primary current (3-4 A) flows and builds a magnetic field in the core.
- 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.
- The condenser across the contacts absorbs the primary surge, prevents arcing at the points and makes the field collapse faster.
- The distributor sends the high voltage to the correct plug in firing order; the spark jumps the gap and ignites the mixture.
- 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.
✓ Answer checked by Claude Opus 5.5 (high effort)
Related questions
- Differentiate SI and CI engines · Internal Combustion Engines, chapter 2
- Four-stroke SI engine working and components · Internal Combustion Engines, chapter 2
- Engine lubrication systems · Internal Combustion Engines, chapter 6
- Water cooling systems and components · Internal Combustion Engines, chapter 7
- Battery ignition system and spark timing calculation · Automotive Technology, chapter 3
- Battery charger circuit and charging methods · Industrial Power Distribution and Illumination, chapter 9
- Differentiate wired and wireless systems · Basic Electronics Engineering, chapter 5 · asked 2×
- Battery and working principle · Energy Environment and Society, chapter 5