Inverter sizing
Marine Inverter Calculator
Pick the right inverter size for your boat and see the DC current it will pull from your battery bank. Marine Power Designer computes continuous and peak draw, factoring in inverter efficiency, then cross-checks against your cables and bank.
Why inverter sizing matters at sea
An undersized inverter trips under surge loads; an oversized inverter wastes idle power and forces you to fit massive DC cables and fuses. On 12V systems the difference between 2000W and 3000W can mean 100A of extra cable current — the kind of decision you don't want to make twice.
Formula and assumptions
DC current (A) = AC load (W) / (System V × 0.9)
Marine Power Designer uses 90% inverter efficiency by default — typical for modern pure-sine marine inverters between 20%–80% load. At very low or very high load, real efficiency drops; size for the loads you actually run.
Typical marine inverter loads
- Coffee machine / kettle: 800–1500W
- Microwave: 800–1200W
- Induction hob (single zone): 1500–2000W
- Watermaker: 400–1200W
- Air conditioning (12k BTU): 1000–1800W running, 3000W+ surge
Frequently asked questions
How much DC current does a marine inverter draw?
Roughly: I (A) = AC load (W) / (System V × inverter efficiency). A 2000W load on a 12V inverter at 90% efficiency draws about 185A — which is why 24V / 48V is preferred for large inverters.
What size inverter do I need for a boat?
Add up the AC loads that will run at the same time, add ~25% headroom for surge (fridges, microwaves, induction), and pick the next standard inverter size. Don't oversize blindly — idle losses scale with inverter capacity.
Can I run an induction hob from 12V?
Technically yes with a 3kW+ inverter, but the DC current is brutal: a 2kW hob at 12V is ~185A continuous. 24V or 48V is strongly recommended for any cooking load.
Does my battery bank support my inverter?
LiFePO4 BMS continuous current must exceed the inverter peak DC draw. For lead chemistries, sustained discharge above 0.5C will damage the bank — verify Ah capacity is high enough.
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