Boat Inverters: What an Inverter Does on a Boat

An inverter on a boat turns the 12 or 24 volt DC stored in your battery bank into mains-style AC, so you can run household appliances away from shore power. What you can run depends on the inverter's continuous rating, the bank's capacity and how the AC side is protected and switched, not just on the number printed on the box.

An inverter turns 12 or 24 volt battery power into mains. The question is never really whether it will run an appliance, it is whether your battery bank and cabling can supply the current for as long as you want to use it.

A three minute kettle boil is a genuinely large withdrawal from a modest bank. Understanding that up front is the difference between a useful installation and a disappointed one.

Continuous load versus surge

Inverters are rated for continuous output and for a short surge. Motors, compressors and power tools draw several times their running current at start up, so the surge rating decides whether things actually start.

Resistive loads, kettles, toasters, hair dryers and heaters, do not surge but they are simply large, and they are large for as long as they are on.

Inverter or inverter charger?

A plain inverter only makes AC from the batteries. An inverter charger also charges the bank when shore power is connected and switches loads over automatically, which simplifies the AC side and removes a separate charger.

Either way, the AC output needs proper earthing, residual current protection and changeover arrangements so shore power and inverter power can never be connected together. That part is safety-critical and should be designed and fitted by a qualified marine electrician.

What the battery side has to deliver

Every mains watt has to come out of the bank at battery voltage, so currents are high. That drives heavy, short cable runs, correct fusing right at the battery and terminations that can handle it.

This is also where lithium changes the answer. Lithium banks can deliver high current without the voltage collapse that makes lead acid struggle with inverter loads.

• Short, heavy DC cable runs, sized for the full load
• Fusing immediately at the battery
• Ventilation for the inverter itself
• A bank that can supply the current, not just the energy

Inverter, combi or shore power

A plain inverter is the simplest option. A combined inverter charger also charges from shore power and can transfer between sources automatically, which suits boats that alternate between marina and anchor.

Anything that connects the inverter output to the boat's fixed mains sockets involves the AC installation, earthing and neutral arrangements, and is qualified work.

Being honest about what suits a boat

Coffee machines, microwaves and induction hobs are all possible with enough bank and enough charging. On a boat with a modest bank and engine only charging, gas or a low draw alternative is usually the better answer, and we will say so.

Frequently asked questions

What does an inverter do on a boat?

It converts battery DC into AC so standard appliances can run without shore power or a generator. It draws heavily on the battery bank, so bank size and charging need to match.

Can you fit a Victron inverter charger?

Yes. Victron equipment sales and installation are part of our work, including the AC changeover and protection around the inverter.

Will an inverter run a kettle?

A large inverter will, but a kettle takes a serious bite out of the bank each time. It is realistic on a decent lithium system with good charging, and marginal on a small lead acid bank.

Can I just plug an inverter into a cigarette socket?

Only for very small loads. Anything meaningful needs its own heavy, fused feed direct from the battery, because that socket and its wiring cannot carry the current.

Does an inverter drain the batteries when nothing is plugged in?

Yes, most draw a small standby current, which adds up over a week on a mooring. Switching it off when unused is worth doing.