What Size Inverter for a CPAP, Laptop and Fridge Overnight in a Truck?
Date:2026-10-02 Click:22 Source:Rogerele
Quick answer: Let the fridge decide, not the CPAP. If the cooler is a 12V or 24V compressor on the battery, a REP300 (300W rated, 600W peak) or REP500 (500W, 1000W peak) is usually enough when both nameplates sit under that rating. If an AC fridge must start on the inverter, size for surge: REP1000 (1000W, 2000W peak) covers many compact fridges plus a CPAP and laptop, and REP1500 (1500W, 3000W peak) is safer when startup watts are missing. Match 12V or 24V to the truck, and 120V 60Hz or 220–240V 50Hz to the fridge.
This is for an engine-off night in a sleeper or camper, not a runtime sheet. Appliance watts here are label checks, not Rogerele measurements.
Read the three labels first
Use the CPAP power brick, not a forum average. Without a heated humidifier the load is often under 100W. A humidifier or heated hose is a heater, so read the brick the way you sleep. This is not medical advice, and these pages list no medical-device mark.
The laptop figure is on the charger: commonly 45W, 65W or 90W, and 130W or more on a large brick. Do not plan on the USB port. The 300W and 500W pages list 5V 1A, which is 5W, enough for a phone, not a laptop supply.
Split the fridge. A 12V or 24V compressor cooler belongs on the battery, so the inverter only sees the CPAP and the laptop. An AC dorm fridge, or an RV fridge on its electric element, goes through the inverter. Add that label.
The fridge sets the size, because of surge
Running watts add. A compressor's first second does not. A small AC fridge often runs around 70–150W, then draws several times that to start. If startup is not printed, do not assume REP300 or REP500 will start it.
Peak power on these pages is twice the continuous rating, up to 4000W on the REP2000. Overload shuts the unit down and lights the red LED, which stops the CPAP if the fridge surge is too big.
An absorption fridge on its AC heater is a steady load, often a few hundred watts, not a motor surge. Add it to the CPAP and laptop. If that sum is near or over 1000W, use REP1500 or REP2000. Keep a kettle or microwave off this circuit.
| Overnight case | Inverter must cover | REP model | Rated / peak | 12V no-load, less than |
|---|---|---|---|---|
| CPAP + laptop; fridge is 12V or 24V DC | The two labels only | REP300 or REP500 | 300W / 600W, or 500W / 1000W | 0.3A, or 0.4 |
| Those two plus a small AC compressor fridge | Running watts and a short surge | REP1000 | 1000W / 2000W | 0.4A |
| Startup unknown, or labels near 1000W together | Extra peak margin | REP1500 | 1500W / 3000W | 0.8A |
| Large AC element plus CPAP and laptop | Higher continuous watts | REP2000 | 2000W / 4000W | 0.9A |
No-load is the "unload current less than" line on 12V models. REP500 prints 0.4 on the 12V columns with no unit, and 0.2A on 24V and 48V. Treat 0.4 as amps only as a ceiling.
Which REP pure sine model fits the bunk
REP pure sine inverters run from 300W to 6000W and convert 12V, 24V or 48V DC to AC. A night circuit rarely needs the top of that range. Output is pure sine, with THD under 3 percent on a linear load. That figure is the test condition, not a result at CPAP watts. The product overview calls this output suited to sensitive electronics and names a refrigerator among the examples.
For a US bunk, order 100VAC, 110VAC or 120VAC ±5 percent and 60Hz ±0.5Hz. REP1500-121 is 12V in and 100–120V out. REP1500-241 is that AC on 24V. Models ending in 2, such as REP1500-122, are 220–240V. A CPAP brick is often 100–240V. A fridge usually is not, so match the inverter to the fridge. Order 60Hz where appliances expect it.
Maximum efficiency is not what you get at CPAP watts. The 12V columns list 90 percent maximum. Higher-voltage columns go up to 95 percent (92 percent on 24V for REP500, REP1500 and REP2000). A light night load sits lower.
Net size from the pages: REP500 is 255 × 112 × 60 mm and 1080 g. REP1000 is 275 × 180 × 80 mm and 2500 g. REP1500 is 310 × 180 × 80 mm and 2900 g. REP2000 is 355 × 205 × 95 mm and 3900 g. Cooling is intelligent air cooling, and no noise figure is published, so a fan may be heard in a sleeper. Working temperature is −10° to +50°. Warranty is 2 years.
What it draws while you sleep
No-load current runs all night if the inverter stays on. Eight hours at the 12V "less than" figure is a ceiling, not a test: under about 2.4Ah on REP300 (0.3A), 3.2Ah on REP1000 (0.4A), 6.4Ah on REP1500 (0.8A), and 7.2Ah on REP2000 (0.9A). The REP500 12V cell is printed as 0.4. On 24V the same pages list lower amps, from 0.2A to 0.5A. Switch the inverter off when nothing needs AC.
On 12V models the low-voltage alarm is 10.5V ±0.5V and protection is 10V ±0.5V. Output stays off until recovery, 13V ±0.5V on REP300 and REP500, or 12.3V ±0.5V on REP1000 and REP1500. A starter battery can hit that floor and stop the CPAP. Use a house battery. Runtime is a separate sum from inverter watts.
Match the truck voltage
12V models list 10–15.5V input and over-voltage protection at 15.5V ±0.5V. 24V models list 20–31V and protection at 31V ±0.5V. Do not fit a 12V inverter to a 24V truck, and do not tap one battery of a 24V pair to fake 12V. Order the matching input: REP1500-121 on a 12V pickup, REP1500-241 on a 24V truck, if 1500W is the size you reached. Reverse polarity is listed as fuse burn-out. That does not replace a fuse at the battery.
FAQ
Can I run a CPAP on a 300W inverter?
Often yes, if the brick with your humidifier setting is well under 300W and no AC fridge starts on the same outlets. REP300 is 300W continuous, 600W peak, pure sine, with 12V no-load under 0.3A. If a laptop charger shares the night, use REP500.
Will a 1000W inverter start a truck fridge?
It starts many compact AC compressors: REP1000 allows a 2000W peak. A large compressor, or an AC element already near 1000W before the CPAP and laptop, needs REP1500 (3000W peak) or REP2000 (4000W peak). Keep a 12V compressor fridge on DC.
Does a CPAP need pure sine wave?
Yes. These pages specify pure sine and THD under 3 percent on a linear load. The overview groups a refrigerator with sensitive electronics. Do not run a CPAP or a laptop charger on modified sine.
How much battery does idle use overnight?
Only the no-load line, if nothing else runs. On 12V that ceiling is under 0.3A to 0.9A depending on the model, for as long as the inverter stays on. Eight hours is a few amp-hours. The CPAP and fridge dwarf it. Turn the inverter off when AC is not required.
My truck is 24V. Can I use a 12V inverter?
No. A 12V REP unit protects at 15.5V ±0.5V. Use the 24V column at the same wattage, such as REP1000-241 or REP1500-241 for 100–120V AC, or the 220–240V model if that is what the fridge needs. No-load amps on 24V are lower than on 12V.
