RV/Van Life Alternator Charging Calculator
Created by: James Porter
Last updated:
Calculate how long it takes to charge your battery bank while driving. Determine optimal DC-DC charger sizing, estimate charging rates based on your alternator capacity, and plan your travel for maximum battery replenishment.
What is an RV/Van Life Alternator Charging Calculator?
An Alternator Charging Calculator helps RV and van owners understand how their vehicle's alternator can charge auxiliary battery banks while driving. This tool calculates charging times, determines optimal DC-DC charger sizing, and estimates fuel consumption for battery charging during your travels.
Whether you're building a new van conversion or optimizing an existing setup, this calculator takes into account battery capacity, charger amperage, battery chemistry, and alternator capacity to give you realistic expectations for charging while driving.
Understanding Alternator Charging
DC-DC Charger Output: The amperage your charger delivers to batteries
Charge Acceptance Rate: Maximum amps your battery type can accept (lithium accepts more than lead-acid)
Alternator Load: Percentage of alternator capacity used for auxiliary charging
Charging Time: Hours of driving needed to reach target state of charge
Frequently Asked Questions
How does alternator charging work for RV and van batteries?
Alternator charging uses your vehicle's alternator to charge auxiliary batteries while driving. The alternator generates electricity that flows through a battery isolator, DC-DC charger, or split charge relay to your house batteries. DC-DC chargers are most efficient as they regulate voltage and current to match your battery's charging profile, preventing undercharging or overcharging.
What size DC-DC charger do I need for my van?
DC-DC charger size depends on your battery capacity and driving habits. A general rule is 10-20% of your battery capacity in amps. For a 200Ah lithium battery, a 20-40A DC-DC charger works well. Larger chargers (40-60A) are beneficial if you drive frequently and need faster charging. Consider your alternator's capacity and other electrical loads when sizing.
How long does it take to charge batteries while driving?
Charging time depends on battery capacity, state of charge, charger amperage, and battery type. Lithium batteries charge faster than lead-acid due to higher charge acceptance rates. A 200Ah lithium battery at 50% can reach 90% in about 2-3 hours with a 40A DC-DC charger. Lead-acid batteries slow their charge acceptance significantly above 80%.
Can I damage my alternator by charging large battery banks?
Yes, overloading your alternator can cause premature failure. Stock alternators are designed for starting batteries, not continuous high-output charging. Limit your DC-DC charger to 50-60% of your alternator's rated output for continuous use. Consider upgrading to a high-output alternator if you have a large battery bank or need faster charging.
What's the difference between a battery isolator and DC-DC charger?
Battery isolators simply connect batteries when voltage is high enough, providing unregulated charging. DC-DC chargers actively regulate voltage and current, providing proper multi-stage charging profiles. DC-DC chargers are essential for lithium batteries and significantly improve charging efficiency and battery lifespan for all battery types, though they cost more.
How much fuel does idling to charge batteries consume?
Most vehicles consume 0.5-1.0 gallons per hour while idling, depending on engine size and accessories. Idling for battery charging is inefficient - you're better off driving or using solar/shore power. If you must idle, limit sessions to avoid excessive fuel waste and engine wear. Running at slightly above idle (1000-1200 RPM) improves charging efficiency.
Do lithium batteries charge faster from the alternator than lead-acid?
Yes, lithium batteries accept charge at much higher rates than lead-acid. While AGM batteries typically accept 20-30% of capacity, lithium can accept 50-100% of capacity in amps. This means a 200Ah lithium battery can accept 100+ amps, while a 200Ah AGM may only accept 40-60 amps. This results in significantly faster charging times for lithium.
Should I upgrade my alternator for van life?
Consider upgrading if your stock alternator is under 120A and you have a large battery bank (300Ah+) or frequently need fast charging. High-output alternators (180-300A) provide more charging capacity without overloading. However, they're expensive and may require upgraded wiring. Many van lifers find a quality DC-DC charger with their stock alternator sufficient.
Sources and References
- Victron Energy - DC-DC Converter Technical Specifications
- Battle Born Batteries - Alternator Charging Best Practices Guide
- Renogy - DC-DC Charger Installation Manual
- Explorist.life - Van Electrical System Design Resources