Electrical System Calculator
Our electrical system sizing calculator helps you figure out what you actually need for your van build — battery capacity, solar panel wattage, and charging requirements based on your specific devices and usage.What It Does
The calculator takes your list of electrical devices (with wattage and daily usage hours) and tells you:- Daily power consumption in amp-hours (Ah) and watt-hours (Wh)
- Recommended battery bank size based on your desired days of autonomy
- Solar panel wattage needed to replenish daily consumption
- Charging time estimates from solar, alternator, and shore power
How to Use It
1. List Your Devices
Enter each electrical device you plan to run in your van. For each device, you’ll need:- Device name (e.g., “Fridge,” “LED Lights”)
- Wattage (check the device’s label or spec sheet)
- Hours per day (estimate average daily use)
2. Set Your Parameters
- Battery type: Lithium (LiFePO4) or lead-acid — this affects depth of discharge calculations
- Days of autonomy: How many days you want to run without any charging (1–3 is typical)
- Location: Affects solar estimate based on average peak sun hours
3. Review Results
The calculator produces a recommended system spec based on your inputs. This is a starting point — real-world conditions (weather, shade, driving habits) affect actual performance.Common Device Wattages
If you’re not sure what wattage to enter, here are typical values:| Device | Typical Wattage | Notes |
|---|---|---|
| LED lights (all) | 15–25W | Total for all lights on at once |
| Compressor fridge | 40–60W | Cycles on/off; actual draw averages ~50% of rated |
| MaxxAir fan | 5–20W | Depends on speed setting |
| Phone charging | 10–15W | Per device |
| Laptop | 45–65W | While in use; less when sleeping |
| Water pump | 50–70W | Only runs when faucet is open |
| Diesel heater | 10–30W | Electrical draw for fan and glow plug (fuel is separate) |
| Inverter (idle) | 10–20W | Standby draw when inverter is on but nothing is plugged in |
| Induction cooktop | 1000–1800W | High draw; only runs during cooking |
| Coffee maker (12V) | 100–200W | Short duration |
Interpreting Results
Battery Capacity
The calculator recommends a minimum battery bank size. Always round up to the nearest standard battery size (100Ah, 200Ah, 300Ah). It’s better to have slightly more capacity than slightly less.Solar Wattage
Solar recommendations assume average conditions for your location. If you camp in heavy shade or travel to less sunny regions, consider sizing up by 25–50%.The 80/20 Rule
In most builds, 80% of your power consumption comes from just 2–3 devices — usually the fridge, lights, and fan. Focus on getting those numbers accurate. The small stuff (phone charging, occasional appliance use) is rounding error.Limitations
This calculator gives you a solid starting point, but it’s not a substitute for a professional system design. Factors it can’t account for:- Your specific driving patterns (affects alternator charging)
- Exact solar panel positioning and shading on your particular van
- Temperature effects on battery performance
- Simultaneous high-draw devices and inverter efficiency losses
Learn More
- System Sizing Guide — The full manual calculation walkthrough
- Solar Power Guide — Solar panel details
- Battery Bank Design — Battery selection and sizing
- Get a custom electrical design →