All guides · Power and installation
I dimension an inverter based on the appliances that will run simultaneously, and then based on the battery and the installation. The number in the product name is only part of the decision.
List your appliances first
Make a list with power consumption, duration of use, and which appliances you want to use at the same time. A computer and some charging have different requirements than a coffee machine and electric cooking. Also, decide whether two large appliances actually need to run at the same time.
VA and watts are not the same
VA describes apparent power, while watts is the active power. Use the continuous power in watts stated in the datasheet to check your requirements. At the same time, check the temperature at which the output applies.
A concrete example is the Victron Inverter Smart 2000 VA: the manufacturer specifies 1,600 W continuous at 25 °C and 1,450 W at 40 °C. The name does not, therefore, mean 2,000 W continuous power. The figures apply to this product series and cannot be transferred to all inverters.
Starting load must be assessed separately
Equipment with a motor or compressor may require extra power at startup. Check both the appliance's starting demand and the inverter's permitted peak load and duration. A high peak figure without a time specification is not enough to ensure a match.
Calculation example: 1,000 W from a 12 V battery
With an assumed efficiency of 90%, the current becomes approximately 1,000 / (12 × 0.90) = 93 A. If the appliance runs for 10 minutes, this corresponds to approximately 185 Wh from the battery.
90% is a calculation assumption here, not a datasheet figure for a specific model. The actual current changes with battery voltage, load, and the inverter's efficiency.
Battery capacity and current limit are two different things
Ah tells you about capacity. The battery's and BMS's maximum continuous current indicate how large a load they can supply. Both must fit. Furthermore, cables, connections, and fuses must be dimensioned for the installation.
Also consider the no-load power consumption. If an inverter in a hypothetical example uses 8 W without a load, that becomes 192 Wh in a day. An economy function can be useful, but it must work with the small appliances you want to keep turned on.
What should the quote include?
- The exact inverter model and battery voltage.
- Verification of continuous power and starting requirements.
- The battery and BMS current limits.
- Cables, fuses, placement, and ventilation.
- Plan for safe 230 V distribution and potential switching between inverter and shore power.
Permanent connection to the boat's 230 V system must be performed professionally. Never connect the inverter's output to shore power or any other power supply without a solution explicitly intended for that purpose.
Sources and manufacturer documentation
This guide was written by SejlStrøm. Technical information was verified on September 22, 2026. Always use the documentation for the specific model and version.