I never knew cars were once 6 volt?
When car manufacturers settled on 12 volts (transitioning from 6 volts in the 1950s), they had to balance engineering, cost, and practicality:
- Legacy and Standardization
- Early cars used 6V systems, which became insufficient as electrical demand grew (radios, brighter headlights, starter motors).
- 12V was a practical step up without requiring a complete overhaul of component design.
- Once standardized, the entire supply chain (batteries, alternators, wiring, bulbs, relays, accessories) locked into 12V, reinforcing its dominance.
- Component Cost and Availability
- Mass production of 12V parts (bulbs, fuses, relays, sensors, stereos, chargers) made them cheap and universal.
- A 24V car would require unique parts, raising costs.
- Safety Considerations
- 12V is low enough to be considered safe for casual contact and reduces risks during service or accidents.
- At 24V, risks of arcing, sparks, and shock increase, especially in wet environments.
- Wire Sizing vs. Vehicle Size
- For passenger cars, current draw is moderate, so wire gauges needed for 12V systems are acceptable in weight and cost.
- 24V would allow thinner wiring, but the benefit is small in cars compared to trucks or buses.
- Battery Packaging
- A single 12V battery is compact and fits well in most vehicles.
- Two 12V batteries in series (for 24V) add cost, weight, and packaging complexity.
- Consumer Electronics Compatibility
- Most portable devices (phones, GPS, chargers) evolved around 12V car systems.
- Maintaining 12V compatibility matters for the aftermarket ecosystem.
Why Larger Vehicles Use 24-Volt Systems
For trucks, buses, heavy machinery, and military vehicles, the trade-offs shift:
- High Power Demand
- Large diesel engines need powerful starter motors that would draw very high current at 12V.
- Using 24V halves the current for the same power, making starting systems more efficient.
- Reduced Wiring Size and Weight
- Heavy vehicles have long cable runs for lighting, pumps, lifts, etc.
- Higher voltage means lower current, allowing smaller wires, saving significant weight and copper costs.
- Better Reliability
- Lower current also reduces heating, voltage drop, and risk of melted connectors.
- This is crucial in harsh duty cycles of commercial vehicles.
- Battery Flexibility
- Two 12V batteries in series give 24V starting, but they can also be tapped at 12V for accessories.
- This dual-voltage setup is common in trucks.
- Military and Industrial Standardization
- NATO and many industrial standards mandate 24V for interoperability and robustness.
Why Cars Haven’t Moved to 24V (Even Now)
Interestingly, in the late 1990s and early 2000s, there was a push for 42V automotive systems (actually ~36V batteries, charging at 42V) to support growing loads (electric power steering, drive-by-wire, etc.). But manufacturers abandoned it because:
- The cost of redesigning the entire supply chain was enormous.
- Improvements in alternator output, power electronics, and now 48V mild hybrid systems solved the problem without abandoning 12V entirely.
Today, modern cars sometimes use dual systems:
- 12V for legacy systems and consumer electronics.
- 48V for high-power systems (e.g., turbochargers, electric suspension, mild hybrid drives).
✅ In short:
- Cars stayed at 12V because of history, cost, safety, and sufficiency.
- Larger vehicles adopted 24V because of higher power demands, efficiency, and weight savings.
- Future cars are moving toward 48V hybrid systems, but 12V will remain for compatibility.