Getting your generator size right is one of the most important decisions in your Sprinter van electrical build. Go too small and your generator will be constantly overloaded, running at full capacity and wearing out prematurely. Go too large and you’re carrying extra weight and burning more fuel than necessary. Here’s how to calculate the sweet spot.
Step 1: List Every Electrical Load
Start by listing every appliance and system that will draw power in your van. For each item, note the running wattage (continuous draw) and the startup wattage (the momentary surge when it kicks on — this is especially important for compressor-based appliances like AC units and refrigerators). Common van build loads include: rooftop AC (1,200-2,500W running, up to 3,500W startup), induction cooktop single burner (1,000-1,800W), residential fridge (100-200W running, 500-800W startup), microwave (800-1,200W), water heater (1,200-1,500W), water pump (60-100W), diesel heater (25-50W), lighting throughout (50-100W total LED), laptop chargers (60-100W each), phone and device charging (20-50W), and a 12V system with inverter losses (add 10-15% overhead).
Step 2: Calculate Your Peak Load
You won’t run everything simultaneously, but you need to account for realistic worst-case scenarios. A typical peak scenario might be: AC running (2,000W) plus refrigerator cycling on (500W surge) plus charging laptops (200W) plus lighting and misc (150W). That’s nearly 3,000W just in that moment. Now add the startup surge of the AC if it cycles off and back on — you could see a 4,000-5,000W spike.
Step 3: Apply the 70-80% Rule
Generators run most efficiently and last longest when operating at 50-80% of their rated capacity. Running a generator at 100% continuously is a recipe for premature wear. Take your peak load calculation and divide by 0.7 to find your ideal generator size. If your peak load is 5,000W, you want a generator rated for at least 7,000-8,000W.
Our Sizing Recommendations
Basic builds (no AC, minimal cooking, mostly 12V systems): A generator in the 3-5kW range can work, though you’ll outgrow it quickly if you upgrade your build over time.
Mid-range builds (rooftop AC, residential fridge, induction cooking, remote work setup): The PowerTech PT-8KSiC at 8kW is the sweet spot for most serious Sprinter builds. It handles AC, cooking, and work simultaneously without breaking a sweat.
Full luxury builds (dual AC, washer/dryer, full residential kitchen, high-draw appliances): Look at the 9kW+ range. The PowerTech PTH-9 provides the headroom you need for builds where comfort is non-negotiable.
Not sure where you land? Send us your build’s electrical load list and we’ll run the numbers for you. Email info@sprintergenerator.com — we do this every day and genuinely enjoy helping builders get it right.