STEP 1: Calculate your current draw
Below is a table containing rough estimates of how much draw common appliances use. You will need to total these up to have a rough idea of how much energy you will be using.
| Appliance | AMPS | Hours Run per Day | Average Daily Consumption (Ah) |
|---|---|---|---|
| Milk Frother | 25A | 2 minutes | 1 |
| GPS | 0.5A | 2 hours | 1 |
| Smartphone Charger | 1-2A | 2 hours | 2-4 |
| Laptop Charger | 1-2A | 2 hours | 2-4 |
| Pedestal Fan | 0.5-1A | 4 hours | 2-4 |
| 750W Toasted Sandwich | 40A | 5 minutes | 4 |
| Toaster | 45A | 5 minutes | 4 |
| LED Lights | 1-2A | 4 hours | 4-8 |
| 12V Water Pump | 6A | 1 hour | 6 |
| Coffee Pod Machine | 90A | 5 minutes | 8 |
| Washing Machine | 7-15A | 15-30 minutes | 8 |
| Microwave | 93A | 5 Minutes | 8 |
| Sound System/Radio | 2-5A | 2 hours | 4-10 |
| Kettle | 147A | 5 minutes | 12 |
| 60L Fridge-Freezer | 4A | 24 | 48 |
| 2000W Induction Cooker | Max 100A | 30 minutes | 50 |
| Rooftop Air Conditioner | 50 – 60A | Up to 3 hours | 55 |
STEP 2: Choose a battery
Battery technology has undergone substantial progress in the last decade, introducing Lithium Iron Phosphate (LiFePO4), commonly known as lithium batteries, as a notable contender alongside the reliable Absorbed Glass Mat (AGM) units and the more economical wet cell lead acid types.
Skipping over hybrid cranking/deep cycle batteries for conciseness, dedicated deep cycle auxiliaries are recommended for most users. While wet cell lead acid batteries are the most budget-friendly, their advantages over newer technologies are limited.
AGM batteries are the cheaper option upfront. Their advantage of lithium batteries is their heat resistance, meaning they can be safely mounted under the bonnet and maintain their longevity. Despite being more affordable upfront than lithium, AGMs are considered outdated and should only be your choice for hot environments.
Lithium batteries stand out as the preferred choice for modern battery systems, surpassing others in various aspects. Compared to AGM, lithium is ~50% lighter, consistently deliver high current, charge quicker, and have twice the lifespan (~3000 vs ~1200 use cycles). However, their higher upfront cost may pose a hurdle.
Simply put, you probably want lithium batteries.
| Feature | 100Ah AGM Battery | 100Ah Lithium Battery |
|---|---|---|
| Weight | Heavier (typically around 60-70 lbs) | Lightweight (around 30-40 lbs) |
| Energy Density | Lower | Higher |
| Cycle Life | Moderate (300-700 cycles) | High (over 2000 cycles) |
| Charging Efficiency | Moderate | High |
| Discharging Efficiency | Moderate | High |
| Depth of Discharge (DOD) | Preferably kept above 50% for longevity | Can be discharged to lower levels without harm |
| Maintenance | Maintenance-free | Maintenance-free |
| Charging Speed | Slower compared to lithium | Faster |
| Cost | Lower upfront cost, but higher cost per cycle | Higher initial cost, but lower cost per cycle |
| Temperature Sensitivity | Sensitive to temperature extremes | Less sensitive to temperature variations |
STEP 3: Power sources
Now’s the time to decide what power source(s) you want to utilise. First we’ll address the two solutions everyone should employ:
From your vehicle’s alternator is a no-brainer. While the vehicle is running, your alternator is already charging your starter battery, so it may as well charge your secondary/auxiliary battery as well.
From your 240V mains charger, also known as “shore power”, is perfect for charging up your batteries at home before or after a journey, or at a powered campsite. Mains battery chargers come in portable devices or can be integrated into your 12v system.
Solar panels
When it comes to recharging auxiliary batteries, relying solely on your vehicle’s alternator is practical only when you’re on the move. No one wants to keep their vehicle idling at a campsite, necessitating an alternative charging method. The commonly adopted solution is harnessing the power of solar panels.
Two primary types of solar panels are at your disposal. Firstly, fixed solar panels, affixed permanently to your vehicle, typically on the roof rack. Secondly, portable solar panels, designed for easy packing when not in use.
Fixed Solar Panels: These panels boast a sturdy design, usually with a glass front and an aluminium frame. Their purpose is a permanent attachment to your vehicle, connected to a regulator or DC-DC charger mounted internally.
The perks of fixed solar panels include avoiding the hassle of setup and teardown at camp. They seamlessly supplement the charge from your vehicle’s alternator during travel, especially if coupled with a solar-prioritizing DC-DC charger.
However, the drawback is their immobility, unable to track the sun’s trajectory, and limiting your ability to park the vehicle in shaded areas. They also occupy roof space that could otherwise be utilized for storage, potentially contributing to increased wind resistance and noise during travel.
Portable Solar Panels: Portable solar panels come in diverse forms, as explored in our comprehensive guide to portable solar for camping. Initially, hard-frame folding panels similar to fixed ones were prevalent, but now, lighter options such as solar blankets and mats dominate campsites.
Opting for a portable solar panel grants you flexibility in choosing your parking spot at camp. Unlike the need to park in the sun for solar energy capture, you can park in the shade and position the panel up to 10 meters from the vehicle.
Connectivity is convenient, whether directly to your battery using alligator clamps or through an available Anderson port on a DC-DC charger or battery box.
Solar Regulator Necessity: Regardless of the solar panel type, a regulator is indispensable. Solar panels produce a voltage too high for the battery to handle directly, making a regulator crucial. Connecting a battery directly to a solar panel risks overcharging, potentially causing irreversible damage.
STEP 4: Charge the battery
Isolators
The battery isolator is a foundational step in the evolution of dual-battery charging systems. It serves as the entry-level choice for most modern setups, offering excellent value. Utilizing a microprocessor, isolators detect when the starting battery is fully charged and then channel current from the alternator to the auxiliary battery for a complete charge. They also safeguard the starting battery from drainage when the vehicle is at rest, ensuring reliable starting. While isolators are a practical addition to any 12V setup, many people simply opt for a standalone DC-DC Charger.
DC-DC Chargers
Advancing to a higher level, the DC-DC charger, when coupled with the right battery, becomes a game-changer. Premium models may feature multi-power point tracking (MPPT) regulators for solar, a voltage booster to support smart alternators, and versatile functionalities. They can even jump-start the vehicle’s starting battery from the secondary unit when combined with a smart isolator.
Battery Management Systems (BMS)
Regarded as the pinnacle in battery charging solutions, a standalone BMS is a technological marvel capable of charging any 12V battery type. It can receive charge from various sources, including 240V and 12V-DC from both smart and conventional alternators, as well as solar. Providing detailed information about the battery’s charge status and remaining time until depletion, BMS units oversee the entire 12V setup, including fuses. Some advanced options, such as Redarc’s Manager 30 and Red Vision systems, can even manage your entire 12V system, controlling aspects like fridge temperature, camp lights, stereo, and other electrical components in your vehicle. This represents a significant leap forward in the world of dual-battery technology, offering users increasingly sophisticated and efficient options for managing their 12V power systems.
STEP 5: Power distribution
Selecting the right batteries and charging methods is crucial, but equally important is figuring out how to distribute power to your 12V accessories from your batteries.
Battery Box: For standard-sized auxiliary batteries like N70, Heavy-Duty Battery Box offers a straightforward solution. Place the battery inside, connect the terminals to the box, and use the various outlets to power your accessories. Battery boxes are typically pre-wired with fuses and circuit breakers for added protection, and have a variety of outlets such as Anderson ports, cigarette ports, and USB-A / USB-C ports.
12V Control Box: An alternative, suitable for multiple batteries or those too large for a battery box, is a 12V control box. Resembling electrical boxes found on houses, these boxes feature ports on the outer face. Customize the box with additional holes for monitoring gauges or custom ports. The battery connects inside the box through waterproof grommets in the side.
STEP 6: Inverters
Need to power 240V accessories on the go? You’ll need a 12V to 240V inverter. They key is to choose aa high-quality inverter with proper electronic protections, meeting Australian and international standards like AS/NZS 4763:2011, UL 458, and IEC/EN 62638-1.
High-power 240v accessories can rapidly deplete batteries. Ensure ample battery capacity and check the maximum discharge current, especially with high-wattage appliances like kettles.
STEP 7: Cabling
Now that you’ve got all pieces, it’s time to stitch it all together.
Example 12V System
Let’s put together an example 12V system that will suit the needs of most people, and should be easy to modify.
Step 1: Let’s use the table to calculate our energy needs in Ah for a smartphone (4) and laptop (4) charger, LED lights (8), microwave (8), kettle (12), and a 100L fridge-freezer (48). These appliances will require roughly 76Ah per day (4+4+8+12+48=76).
Step 2: We won’t be mounting our battery in the hot engine bay, therefore the smart choice is a lithium battery. We’ll go with 120Ah, and we
Step 3: We’ll opt for all 3 charging options. That is, the two I recommend to everyone, alternator and mains, plus solar so that we can camp off-grid for days at a time.
Shopping list
If you would like the exact set-up we’ve described in our example, we’ve put together a simple shopping list of items you’ll need. Note that there is a separate tools section further down.
- 120Ah lithium battery
- Solar panel
- DC-DC charger w/ MPPT controller
- 240V mains charger
Tools
If you are a DIY-oriented, below is a list of basic tools you may need. Note that this list is by no-means comprehensive, and it’s also best to work with a licenced auto-electrician.
- Cable Crimper:
- For creating secure and reliable cable connections.
- Wire Stripper:
- To remove insulation from wires for proper connections.
- Multimeter:
- To measure voltage, current, and resistance, ensuring proper connections and troubleshooting.
- Drill and Bits:
- For creating holes for cable routing and mounting components.
- Screwdrivers and Wrenches:
- Basic hand tools for securing components and making adjustments.
- Cable Ties and Clips:
- For organizing and securing cables.
- Sealant (Silicone or similar):
- To seal any holes or gaps created during installation to prevent water ingress.
- Wire Loom or Conduit:
- Protects wires from damage and enhances the overall appearance.
- Electrical Tape:
- Insulates and secures electrical connections.
- Safety Gear:
- Safety glasses, gloves, and other protective equipment as needed.
Glossary
12V: Standard voltage for most modern Internal Combustion Engine (ICE) vehicles.
240V: Household voltage in Australia.
AGM: Absorbed Glass Mat; a lead-acid battery type.
Amp Hours: Measure of charge flow over time; 1 amp/h represents a current of 1 amp for 1 hour.
Battery Chemistry: Refers to materials and processes in batteries (e.g., lead-acid, lithium-ion).
Battery Isolator: Separates DC flow for multi-battery charging without connecting them in parallel.
Battery Monitor: Measures voltage, current, and tracks remaining charge in a battery.
BMS: Battery Management System; oversees a vehicle’s batteries, preventing issues like overcharging or being too drained.
Capacity: Total energy a battery can store, measured in ampere-hours (Ah) or watt-hours (Wh).
Cold Cranking Amps (CCA): Power for starting; higher CCA means quicker starter motor spin.
Cranking Voltage: Minimum voltage required for a battery to start an engine.
Current: Flow of electricity, measured in amps.
Current Draw: Power consumption of a device or accessory.
Cycling: Discharging and recharging a battery.
DC-DC Charger: Advances from an isolator, ensuring proper charging current for a battery’s profile.
Deep Cycle Battery: Designed for deep discharge, ideal for accessories when the engine is off (AGM or lithium).
Fuses: Safety devices preventing excessive current and circuit damage.
Gel Battery: Lead-acid with gelified electrolyte, offering safety and durability.
Hybrid Battery: Combines deep cycle and starting roles, useful for limited budget scenarios.
Inrush Current: Initial surge when an electrical device starts.
Inverter: Converts 12V to 240V, allowing household item usage during travel.
Lead Acid: Standard wet cell 12V battery, budget-friendly.
Lithium: Modern auxiliary batteries, superior but beware of cheap options.
Ohm’s Law: Describes voltage, current, and resistance relationship in a circuit.
Parallel Connection: Increases current capacity while maintaining voltage.
Power Inverter: Converts battery DC power to AC for appliances.
Resistance: Countering force to electrical current flow.
Shunt: Advanced version of a battery monitor.
Short Circuit: Unintended connection causing excessive current flow.
Smart Alternator: Adjusts output based on a vehicle’s electrical needs.
Solar Regulator/Charge Controller: Manages solar panel charging to prevent overcharging.
State of Charge (SOC): Percentage of a battery’s available capacity.
Top-Up Charging: Periodic maintenance charge compensating for self-discharge.
Volts: Force pushing electrons through circuits.
Wattage: Power measure, calculated by multiplying voltage and current.
