Welcome to my J.A.M. (Just Ask Mike) Session, a weekly column where I answer your basic electrical questions. If you’re a newbie who’s never plugged in a shore power cord (or ask – what’s a shore power cord?), or wonder why your daughter’s hair dryer keeps tripping the circuit breaker, this column is for you. Send your questions to Mike Sokol at mike (at) noshockzone.org with the subject line – JAM. Today I discuss CPAP (continuous positive airway pressure) machines.
My wife and I enjoyed your lectures at the F.R.O.G. rally in Goshen, IN.
I have a 2017 Georgetown 335DS with a Xantrex PROwatt SW 2000 inverter to power our LG residential refrigerator. It works great. If I read the label correctly on the fridge, it uses 115v at 5.2 amps. My wife and I each need to use a CPAP [continuous positive airway pressure] machine when we sleep. Again, if I’m reading correctly, each CPAP draws 1.5 amps. The fridge is plugged into one of two outlets on the inverter. Next to the unused plug, it is labeled “120Vac 16.6 A Max.”
Could I connect a plug to outlet number two on the inverter and run a power line from it to a newly installed double outlet in the bedroom to power the two CPAP units and still power the fridge while boondocking? If this idea of mine is technically/electrically doable, do you think it would void a warranty? Thanks. —Tom L.
Yes, this should easily work. And no, it should not void any warranties. Let’s go through the math, since you sent along a bunch of pictures. (Thanks very much.)
Inverter power available
Here’s a close-up picture of the outlet on your inverter. Everyone, please note that it says 16.6 amps max. We can double-check this by multiplying 120 volts times 16.6 amps and see that it equals 1,992 watts. That’s close enough to 2,000 watts, I think.
That shows that we indeed have 16.6 amperes of current available to power everything connected to the inverter. So, as long as we don’t get near 16 amps at 120 volts, it should work.
Refrigerator power needed
Now let’s take a look at the power needed by your refrigerator. As noted on the nameplate, it does require 5.2 amperes of current at 120 volts while the compressor is running. That’s normal for a residential-style refrigerator with a 120-volt compressor.
If you’re counting watts, then 5.2 times 120 volts equals 624 watts. While in defrost mode it should lock out the compressor and draw 350 watts, which we can reverse calculate as 2.9 amps at 120 volts. Everyone with me so far?
Watt about those CPAP machines?
According to the nameplate on the CPAP machines, each one uses a 90-watt adapter which is rated for a maximum 1.5 amps at 120 volts. That would be 180 watts at full power even though there’s a 90-watt rating.
But, generally, power supply adapters can supply more amperage than is needed by the appliance. However, to be on the safe side, we’ll use the 1.5 amperes at 120-volts rating for our calculations.
Let’s add it all up
- 5.2 amps for the refrigerator
- 1.5 amps for CPAP 1
- 1.5 amps for CPAP 2
- 8.2 amps Total Current Needed
- 16.6 amps Available Inverter Current
You should be able to simply run a high-quality power strip from the output of the inverter to your CPAP machine power supplies. Your total load should require less than 9 amperes of current, and your inverter is rated to be able to supply more than 16 amperes. So, all is well. Yes, there will be a bit of a compressor starting surge, but I’m pretty certain your 2,000-watt inverter should be able to handle the additional compressor starting surge.
Note that I typically don’t recommend power strips for any high-amperage loads such as a space heater. But at 1.5 amperes per outlet (3 amps total) any decent power strip should be able to power the two CPAP machines properly.
That’s a wrap…
OK, everyone. Remember that electricity is a useful and powerful force, so we all need to pay attention to safety precautions while using it.
Let’s play safe out there….
Mike Sokol is an electrical and professional sound expert with 50+ years in the industry. His excellent book RV Electrical Safety is available at Amazon.com. For more info on Mike’s qualifications as an electrical expert, click here.
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