Can a Victron Phoenix Inverter Run a CPAP?

Can a Victron Phoenix inverter run a CPAP? Yes. Even the smallest Phoenix VE.Direct models put out a pure sine wave at 120V and far more power than a CPAP needs. The real questions are how much battery you need for a full night, what the inverter’s own idle draw adds, and whether ECO mode is safe to use while you sleep. Short answer on ECO mode: don’t use it.

Phoenix VE.Direct Models for a CPAP

Phoenix VE.Direct 120V	Continuous at 25°C	Peak	Zero-load draw (12V)	Max efficiency (12V)
12/250	250W	400W for 2s	5W	84%
12/375	375W	600W for 2s	6W	86%
12/500	460W	750W for 3s	7W	86%

Source: Victron Phoenix Inverter VE.Direct 250W–1600W 120V datasheet. 120VAC ±3%, 60Hz, NEMA 5-15R or GFCI outlet.

A CPAP with a heated humidifier and heated hose uses far more power than one running dry. The 12/375 gives comfortable headroom for that.

Can a Victron Phoenix Inverter Run a CPAP All Night? The Math

First, find your machine’s actual consumption. The power supply label shows its maximum rating, not typical draw, so measure it with a plug-in watt meter for a night.

Example (estimate): a CPAP averaging 40W with humidifier, for 8 hours.

CPAP: 40W × 8h = 320Wh
Inverter efficiency at a light load: assume about 80%, so 320 ÷ 0.8 = 400Wh
Inverter idle: 6W × 8h = 48Wh, partly included above
Total: roughly 400–450Wh, about 35Ah at 12V per night

A 100Ah LiFePO4 battery covers two nights with margin. Without the humidifier, the draw often drops by half or more.

These are estimates. Inverters run less efficiently at very light loads, so measure your setup.

Why ECO Mode Is a Bad Idea Here

ECO mode cuts idle draw to about 1W by switching the inverter to standby when the load falls below a set level (minimum 15W). It then switches on briefly every 2.5 seconds to check for a load. A CPAP that drops below the threshold between breaths or when the humidifier cycles could see its power interrupted. For medical equipment, leave ECO mode off and accept 5–7W of idle draw.

Inverter or DC Cable?

Many CPAP makers sell a DC power cord or converter for their machines. Running directly on 12V skips inverter losses entirely and is usually the most efficient option. Use the Phoenix if your machine has no DC option, or if you want one 120V outlet for the CPAP and phone chargers.

Setup Tips

Mount the inverter in a ventilated spot. Its fan helps cooling, but it shouldn’t be in a closed cabinet next to the bed.
Set the low-battery alarm in VictronConnect so you get warned before cut-off.
Add a remote on/off switch by the bed.

Victron’s Phoenix Inverter VE.Direct product page has the full datasheet and manual downloads.

Battery Sizing by CPAP Setup

CPAP setup (example average)	Per 8-hour night, from the battery (estimate)	Nights on 100Ah LiFePO4	Nights on 200Ah LiFePO4
No humidifier, about 15W	About 200Wh (mostly inverter overhead)	About 5	About 10
Humidifier, about 40W	About 420Wh	About 2.5	About 5
Humidifier and heated hose, about 70W	About 750Wh	About 1.5	About 3

Estimates using about 1,100Wh usable per 100Ah at 12.8V, plus about 6W of inverter idle draw. Measure your own machine.

At light loads, the inverter’s own draw is a big share of the total, which is why running a CPAP without a humidifier on an inverter is less efficient than it looks.

Example: Tent or Van Camping for a Weekend

A CPAP with a humidifier at about 40W, a Phoenix 12/375 and a 100Ah lithium battery. Two nights use roughly 840Wh, well within the battery’s capacity. A 100–200W solar panel with a SmartSolar MPPT 75/15 can put most of that back during a sunny day (estimate).

Recharging Between Nights

Charging source	Approx. time to replace 420Wh (estimate)
200W solar on a sunny day	About 3 hours of good sun
Orion XS DC-DC charger while driving	Under an hour
Blue Smart IP65 12/15 on shore power	About 2.5 hours

Estimates.

Monitoring Overnight Use

A SmartShunt on the battery negative shows exactly how many amp-hours the CPAP and inverter used overnight. After a few nights, you’ll know your real consumption and can size the battery and solar with confidence. The Phoenix’s VE.Direct port also lets VictronConnect show the inverter’s output and battery voltage.

Choosing Low-Voltage Settings

In VictronConnect, the Phoenix VE.Direct lets you set the low-battery alarm and shutdown voltages. For a lithium battery, set them to match the battery maker’s figures so the inverter warns you well before the battery’s BMS would disconnect. That gives you time to switch to a backup.

Planning a Backup

For medical equipment, it’s wise to have a second option, such as a spare charged battery, a DC cord for the CPAP, or a portable power station. Check with your CPAP maker for approved power options for travel.

Wiring Checklist

Fuse the positive cable close to the battery, sized to the datasheet.
Keep the battery cables short.
Fit a remote on/off switch within reach of the bed.
Set the alarm and shutdown voltages in VictronConnect.
Run the CPAP for one full night at home before you rely on it away from home.

FAQ

Is a modified sine wave inverter OK for a CPAP?

The Phoenix is pure sine wave, which is what CPAP makers usually recommend. Check your machine’s manual.

Can a Phoenix 12/250 run a CPAP?

Usually, for a machine without heat. Choose the 12/375 if you use a humidifier.

Should I rely on this for medical needs?

Keep a backup power plan, and follow your doctor’s and the CPAP maker’s guidance.

Is there a GFCI version?

Yes. Victron’s 120V Phoenix VE.Direct datasheet lists NEMA 5-15R or GFCI outlet versions.

Can I run the CPAP and charge a phone from the same inverter?

Yes. A phone charger adds only a few watts, well within even the 12/250’s rating.

Sources: Victron Phoenix Inverter VE.Direct 250W–1600W 120V datasheet (victronenergy.com, accessed Oct 2026).