What Size Inverter Do I Need for My Boat?

The right marine inverter depends primarily on what AC equipment you have on your boat, and which of these devices you want to run at the same time.

A boat that uses mainly only phone chargers, laptops, and a television may only need a relatively small inverter. Add a microwave, coffee maker, or other high-draw appliance and a 3,000-watt system may make more sense.

The key is to size the entire system, not just buy the largest inverter available.

Lakes+Bay Supply carries a broad selection of marine inverters and inverter/chargers from Victron, Xantrex, Samlex, and other manufacturers.

Add Up Your Simultaneous AC Loads

Start by checking the wattage ratings of the AC equipment you expect to operate from the inverter.

A 1,200-watt microwave and a 100-watt laptop don't necessarily require a 1,300-watt inverter if they'll never operate simultaneously. But if they might, both loads have to be considered together.

Victron specifically recommends sizing an inverter for the highest realistic combined continuous AC load, rather than simply looking at the largest individual appliance.

For modest electrical needs, something like the Victron Phoenix 1200VA Inverter may be appropriate. Larger loads generally push the system toward 3,000 watts or more.

Account for Startup Surge

Some appliances briefly draw considerably more power when they start.

Motors, compressors, refrigeration equipment, and some power tools can create startup loads well above their operating wattage. An inverter needs enough surge capacity to start those loads without shutting down.

This is one reason not to size an inverter limited by your calculated continuous requirement. Some headroom also allows for unexpected simultaneous loads and future equipment that might be added. At 3,000 watts this Pure Sine Inverter from Samlex should meet most needs. 

Pure Sine Wave Is Usually the Better Choice

For a new marine installation, a pure sine wave inverter is generally the most versatile option.

Pure sine wave output is suitable for sensitive electronics, chargers, appliances, and motor-driven equipment and avoids many of the compatibility problems associated with older modified sine wave designs.

There is no reason to design a substantial new cruising electrical system around modified sine wave, unless a application calls for it specifically.

Standalone Inverter or Inverter/Charger?

A standalone inverter simply converts DC battery power from the house batteries into AC power used for devices, while an inverter/charger adds battery charger functionality. Inverter chargers also typically incorporate AC transfer functionality; this allows the system to use shore or generator power when available, and inverter power when it isn't.

For boats that spend significant time connected to shore power, an inverter/charger can simplify the electrical system and eliminate the need for separate inverter and charger installations.

Lakes+Bay's current electrical inventory includes both standalone models and higher-capacity marine inverter/chargers, including Xantrex Freedom XC PRO units in the 2,000- and 3,000-watt range.

Your Battery Bank Has to Support It

A 3,000-watt inverter does not automatically mean your boat can actually supply 3,000 watts. The inverter pulls that energy from the battery bank, and DC current becomes substantial on a 12-volt system.

Victron specifies increasingly large battery banks, cables, and fuses as inverter capacity rises. For one of its current 12V product families, for example, the manufacturer specifies much heavier DC infrastructure for a 3,000VA inverter than for a 1,600VA model.

The exact requirements vary by manufacturer and model, so always use the installation manual for the inverter you purchase.

Cable and Fuse Sizing Matter

Large inverters can draw hundreds of amps from a 12V battery bank.

Undersized battery cables increase voltage drop and heat, potentially causing the inverter to shut down even when the battery still has usable capacity. The DC circuit also needs appropriately sized overcurrent protection.

Products such as the BEP Pro Installer ANL Fuse Holder are designed for high-current applications including inverters and battery chargers. Fuse type and amperage must still be selected according to the inverter manufacturer's specifications and cable ampacity. Careful planning and research, and potentially professional assistance, is required before any major electrical project is undertaken.  

What Size Inverter Should You Choose?

For light electronics and charging loads, roughly 1,000 watts or less may be adequate. Adding another substantial appliance commonly pushes the requirement toward approximately 2,000 watts. Multiple large AC loads can justify 3,000 watts or more but only if the battery bank, wiring, and protection system are designed for these loads.

The inverter shouldn't be sized in isolation; consider your expected simultaneous loads, startup surge, battery-bank capability, DC system voltage, cable run, circuit protection, and whether you need charging functionality.

The objective is to build a balanced system that reliably supplies the AC loads you actually intend to use, not to install the biggest inverter your boat can physically hold.

You can compare Lakes+Bay Supply's full range of marine inverters, inverter/chargers, wire, fuses and circuit protection when planning the complete system.