Pure Sine Wave Inverters for CPAP: What You Actually Need
A CPAP needs a pure sine wave inverter, and roughly 300 W of it — but the size question matters far less than the waveform question. What each one means, and why every unit we list already passes.
Top Picks at a Glance
| Rank | Model | Capacity | Output | Weight | Best for | MSRP | |
|---|---|---|---|---|---|---|---|
| #1 | EcoFlow DELTA 3 | 1,024 Wh | 1,800 W | 27.6 lbs | Best Overall for CPAP | $699 | View |
| #2 | EcoFlow RIVER 2 | 256 Wh | 300 W | 7.7 lbs | Best for Travel | $239 | View |
| #3 | BLUETTI AC180 | 1,152 Wh | 1,800 W | 35.3 lbs | Best for Outage Backup | $999 | View |
MSRP shown — street prices are usually 20–40% lower during sales.
#1 EcoFlow DELTA 3
Same capacity as the DELTA 2 for less, with a longer-lived cell and 5 kWh expansion.
- Capacity
- 1,024 Wh
- AC output
- 1,800 W
- Chemistry
- LiFePO4
- Fridge-days
- ≈ 2.3
#2 EcoFlow RIVER 2
Ultralight weekend unit with a 60-minute wall recharge.
- Capacity
- 256 Wh
- AC output
- 300 W
- Chemistry
- LiFePO4
- Fridge-days
- ≈ 0.6
#3 BLUETTI AC180
Big inverter headroom per dollar in the 1 kWh class.
- Capacity
- 1,152 Wh
- AC output
- 1,800 W
- Chemistry
- LiFePO4
- Fridge-days
- ≈ 2.6
There are two inverter questions when you’re powering a CPAP from a battery, and almost everyone asks the wrong one first.
The question that gets asked is “how many watts do I need?” The answer is 300 W, it’s the same answer for every CPAP, and it’s rarely the thing that decides anything.
The question that matters is “what waveform does it produce?” — and that one has a right answer.
The short answer
Use a pure sine wave inverter. Every portable power station in our database has one. Cheap 12 V car inverters frequently don’t, and those are what to avoid for overnight medical equipment.
300 W is enough. A CPAP power supply is rated 65–90 W at maximum. Even the smallest unit here doubles that.
Capacity is your real constraint, not inverter size. A humidified machine needs 500–700 Wh a night, which is a 1 kWh-class battery, and no amount of inverter has any bearing on that.
What does pure sine wave actually mean?
It means the inverter produces a smooth AC waveform matching what comes out of a wall outlet, rather than a stepped approximation of one.
Grid power alternates as a smooth sine curve. An inverter turning battery DC into AC has to reconstruct that shape, and there are two ways to do it:
Pure sine wave reproduces the curve closely. Anything designed for a wall outlet behaves the same on it as it does at home.
Modified sine wave approximates the curve with a stepped square wave. It’s cheaper to build and it runs simple resistive loads — an incandescent bulb, a heating element — perfectly well.
The problem is that a CPAP power brick isn’t a simple resistive load. It’s a switching power supply, and switching supplies interact badly with the sharp transitions in a stepped waveform.
What goes wrong on modified sine wave?
Usually noise and heat; occasionally the machine won’t start at all.
The reported symptoms, in rough order of how often they come up:
- The power supply buzzes audibly — which is a genuine problem for a device whose entire purpose is to run beside your head while you sleep
- The supply runs warm to hot, because it’s dissipating the mismatch
- The machine refuses to start, or starts and then faults
- Over long periods, the supply’s lifespan may be shortened
We haven’t tested any of this, and we’re not going to claim we have — this site is spec-driven research. What we can point at is that CPAP manufacturers generally specify pure sine wave in their documentation, and that the entire question costs nothing to avoid, because every power station we list already provides it.
That last point is the practical one. Pure sine wave used to be a premium feature. In 2026, on any unit from an established brand, it’s standard. You’d have to go out of your way to end up with modified sine wave, and the way you’d do it is by buying a $30 cigarette-lighter inverter for a car.
How big an inverter does a CPAP need?
300 W, which is the smallest inverter any power station ships with.
The sizing rule for an inverter is different from the sizing rule for a battery. A battery is sized on average draw over the night. An inverter is sized on peak draw at any instant.
For a CPAP, peak is the label figure on the power brick — typically 65 W or 90 W. That covers the blower at maximum pressure plus the humidifier element switching on at the same time.
| Machine state | Draw | 300 W inverter? |
|---|---|---|
| Blower only | 10–15 W | Yes, easily |
| Blower + humidifier | 60–90 W | Yes, easily |
| Blower + humidifier + heated tube | 70–110 W | Yes, easily |
| Label rating (worst case) | 65–90 W | Yes, easily |
There is no CPAP configuration that troubles a 300 W inverter. If a manufacturer’s cable or supply is rated higher, size to that rating — but the answer will still be inside what every unit here provides.
Where inverter size does matter is everything else you plug in. If the same battery also has to run a fridge during an outage, that’s a different calculation, and it’s covered in what size power station do I need.
What does the inverter cost you in runtime?
About 15% of the battery’s capacity, which is why the DC option exists.
Conversion is never free. We size at 85% inverter efficiency across this site, matching the sizing calculator:
Unhumidified night on AC: 100 Wh of therapy ÷ 0.85 = 118 Wh from the battery
Humidified night on AC: 600 Wh of therapy ÷ 0.85 = 706 Wh from the battery
Running the machine from a DC cable instead skips the inverter and its 15% entirely. On a humidified night that’s about 90 Wh saved — most of an extra hour of therapy from the same pack.
The catch is significant: most manufacturers do not support the heated humidifier over DC. So the DC route usually means unhumidified therapy, and most of the apparent saving comes from dropping the humidifier rather than from skipping the conversion. That’s a therapy decision to take with your clinician, not a purchasing decision to take from a spec sheet.
Full arithmetic for both paths is in how many watts does a CPAP use.
How do you tell whether an inverter is pure sine wave?
Read the specification, and treat silence as a “no”.
Manufacturers that build pure sine wave inverters advertise it, because it costs more to make. The phrase appears in the spec table as “pure sine wave” or occasionally “true sine wave”.
Where to look, in order of reliability:
- The spec sheet on the manufacturer’s product page. Every power station in our database lists it there.
- The manual. More reliable than the marketing page, and it also gives you the continuous and surge ratings you need.
- The absence of the phrase. A cheap inverter that produces pure sine wave will say so. One that doesn’t mention waveform at all is almost always modified sine wave.
Terms that are not the same thing and shouldn’t reassure you: “clean power”, “safe for electronics”, “smart AC”, or a stated THD figure with no waveform claim attached. “Modified sine wave” is sometimes written as “quasi-sine” or “stepped approximation” — those all mean the same thing.
The practical shortcut: if you’re buying a portable power station from an established brand, it’s pure sine wave and you can stop checking. The risk lives entirely in the cheap 12 V inverter category — the ones sold to plug into a car’s accessory socket — where modified sine wave is still common and the waveform often isn’t stated at all.
Don’t forget the idle draw
An inverter left switched on with nothing plugged into it still consumes a few watts.
Typically 2–8 W depending on the unit. Over 24 hours a 5 W standby is 120 Wh — more than an entire unhumidified night of therapy, burned doing nothing.
During a multi-day outage that’s the difference between three nights of backup and two. Most power stations expose an AC output toggle; use it. The units that handle this best are the ones with UPS pass-through, which stay plugged into the wall and only draw from the battery when the grid drops.
What about solar generator bundles?
The bundles sold as solar generators use exactly the same inverter as the power station inside them — the panels don’t change the AC side at all. So the waveform question is already answered the same way, and the only thing the bundle affects is how you refill between nights.
For CPAP specifically, solar is worth more than it looks: an outage lasting several days is precisely the scenario where you can’t recharge from the wall, and it’s usually accompanied by daylight. Check the unit’s maximum solar input rather than the panel wattage in the bundle, because the charge controller caps at the ceiling regardless of what you connect.
What to check before you buy
- The waveform — pure sine wave. Any established-brand power station qualifies; verify on a car inverter.
- Your machine’s label wattage — on the underside of the unit and on the power brick. Confirms the inverter requirement.
- Your average nightly watt-hours — humidifier on or off changes this six-fold. This is what sizes the battery.
- Whether you need UPS pass-through — for outage backup, this matters more than any inverter spec.
- Whether a DC cable exists for your model, and whether you’re willing to run without humidification.
Where to go next
- How many watts does a CPAP use? — the full sizing arithmetic
- Best power stations for CPAP — the picks and the humidifier problem
- Best Jackery for CPAP — if you’ve settled on the brand
- Best small portable power stations — for travel-sized unhumidified use
This page is spec-driven research, not medical advice. The electrical arithmetic is ours; decisions about your therapy belong with your clinician.
Frequently asked questions
- Do I need a pure sine wave inverter for a CPAP?
- Yes. A modified sine wave inverter approximates AC with a stepped square wave, and switching power supplies — which is what a CPAP's power brick is — can run hotter, buzz audibly, and behave unpredictably on that waveform. Every power station in our database uses a pure sine wave inverter, so if you buy one of these the question is settled. It is cheap 12 V car inverters that are commonly modified sine wave, and those are the ones to avoid.
- What size inverter do I need for a CPAP machine?
- 300 W is enough for any CPAP, including one with a heated humidifier and heated tube. A CPAP power supply is rated 65–90 W at maximum, so even the smallest power station inverter has double the headroom. Inverter wattage is almost never the limiting factor for CPAP use — battery capacity is, because a humidified machine draws 500–700 Wh a night.
- Will a modified sine wave inverter damage my CPAP?
- It may not damage it, but it is not worth the risk or the noise. The common symptoms are an audibly buzzing power supply, a supply that runs noticeably warm, and in some cases a machine that refuses to start. Manufacturers generally specify pure sine wave. Given that every power station we list already provides one at no premium, there is no reason to accept a modified sine wave unit for overnight medical equipment.
- Is it better to run a CPAP on DC or through an inverter?
- On DC, if you can accept no humidification. A DC cable made for your model plugs into the power station's 12 V output and skips the inverter's conversion losses entirely, saving roughly 15% of the energy. The catch is that most manufacturers do not support the heated humidifier over DC, so the DC route generally means unhumidified therapy — which is a therapy decision, not a purchasing one.
- Does the inverter draw power even when the CPAP is off?
- Yes. An idling inverter typically consumes a few watts to stay on, and over a long outage that adds up — a 5 W standby across 24 hours is 120 Wh, more than an entire unhumidified night of therapy. Most power stations let you switch the AC output off independently. Turn it off when nothing is plugged in.