What size inverter to run a CPAP?
A CPAP using up to 60 W (no heated humidifier) needs only about a 150 W pure sine inverter, drawing about 5.6 A from a 12 V battery. With a heated humidifier (60–120 W), 150 W is at its limit with headroom — a 300 W unit gives more margin.
How to work it out
- Running: 60 W × (1 + 25%) = 75 W → 150 W inverter
- Surge: 60 W running + biggest start-up extra = 60 W
- Battery current: 60 W ÷ 90% ÷ 12 V = 5.6 A (13.9 A at 150 W)
CPAP machines are light loads but sensitive ones, and many people depend on them every night. Champion’s chart lists 30–60 W without heat and 60–120 W with a heated humidifier.
Adjust for your project
More options: Headroom · Inverter eff.
- Running watts, all together
- 60 W
- Continuous rating with headroom
- 75 W
- Surge (peak) rating needed
- 60 W
- Battery current at your load
- 5.6 A
- Battery current at the inverter’s full rating
- 13.9 A
- For motors, compressors, CPAP machines and electronics, choose a pure sine wave inverter.
Battery current at other battery voltages
| Battery voltage | Battery current at your load | Battery current at the inverter’s full rating |
|---|---|---|
| 12 V | 5.6 A | 13.9 A |
| 24 V | 2.8 A | 6.9 A |
| 48 V | 1.4 A | 3.5 A |
What to know about running a CPAP from a battery
- Pure sine only. The machine’s power supply and motor are happiest on clean power; a modified-sine inverter is the wrong saving here.
- Consider skipping the inverter. Some manufacturers sell DC cords or converters for their machines. Running on DC avoids the inverter loss and its all-night idle draw.
- Heat is the big variable. The heated humidifier and heated tube can double the draw. Turning them down or off stretches a battery a long way.
- Have a backup plan. If you rely on the machine, keep a second power source and ask your equipment supplier about approved battery options.
How long a battery lasts is on how long a 100Ah battery runs a CPAP; a small all-night load on a power station is on how long a power station runs an electric blanket.
Different size? Use the full Inverter Size Calculator.
What you’ll need
- Pure sine wave inverter, 1000 WMid-range price
Enough for a CPAP, laptop, TV and small appliances. Pure sine is the safe choice for anything with a motor or sensitive electronics.
See options on Amazon (opens in a new tab) - 12 V 100 Ah LiFePO4 batteryPremium price
About 1.28 kWh rated in a box roughly the size of a group 24–31 lead-acid battery at around half the weight. Check the BMS discharge limit and whether it can charge below freezing.
See options on Amazon (opens in a new tab)
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Frequently asked questions
What size inverter for a CPAP with a heated humidifier?
About 150 W — at 120 W, it draws 11.1 A from 12 V.
How many amps does a CPAP draw through an inverter on 12 V?
About 5.6 A at 60 W through a 90% inverter.
Other common sizes
- What size inverter to run a microwave — 1,500 W pure sine (for a 1,200 W microwave)
- What size inverter for a refrigerator — 600 W or more, with a 1,200 W surge rating
- How many amps a 1000 watt inverter draws — 92.6 A
- How many amps a 2000 watt inverter draws — 185.2 A
Sources
- Champion Power Equipment — Generator Wattage Chart (opens in a new tab) — Typical running and starting watts for household, RV and job-site appliances (a manufacturer’s planning chart — your nameplate wins).
- Virginia Cooperative Extension, BSE-301: Estimating Appliance and Home Electronic Energy Use (2020) (opens in a new tab) — Wattage × hours ÷ 1,000 = kWh per day; watts = amps × volts when only amps are listed; a refrigerator runs at full wattage about a third of the time; typical nameplate wattages.
- Victron Energy — Energy Unlimited (book) (opens in a new tab) — Lead-acid charge efficiency 80–95% (85% suggested as a starting value); battery energy efficiency about 75% for full cycles, about 89% in partial state of charge; inverter efficiencies above 90%.
- Victron Energy — Lithium Battery Smart manual, technical data (opens in a new tab) — LiFePO4 12.8 V: cycle life 2,500 at 80% DoD, 3,000 at 70%, 5,000 at 50% (to 80% of capacity); 92% round-trip efficiency; 12.8 V 100 Ah: recommended continuous discharge ≤100 A (1C), maximum 200 A; capacity about 20% lower at 0 °C; charge only between +5 °C and +50 °C.
- ENERGY STAR — Certified Televisions data set (on-mode power) (opens in a new tab) — Certified models, on-mode watts, retrieved October 2026: 32 in about 27–36 W; 43 in about 45–78 W; 50 in about 61–90 W; 55 in about 64–114 W; 65 in about 85–135 W; 75 in about 120–176 W.