RV Electricity – What’s a Danfoss compressor?

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Industry Updates

Could there be a Danfoss compressor in your next RV refrigerator?

Just yesterday I posted my first report on how a Vitrifrigo Danfoss BD compressor refrigerator and a Briter Products 100 amp-hour lithium battery run over 36 hours on a single charge, more than tripling the time that a residential refrigerator could run on the same battery technology. So what exactly is a Danfoss compressor and what makes it a better technology for RV refrigerators?

Glad you asked. Basically these latest generation RV refrigerators use a 12-volt DC Danfoss BD compressor that includes a built-in variable speed controller and load sensor. So instead of the compressor simply being on or off (like the 120-volt compressor in your residential refrigerator) it slowly comes up to speed and provides just enough compression of the coolant to keep your refrigerator at the proper temperature. That means there’s a lot less temperature cycling.

Also, because it’s direct drive from 12-volts DC, you don’t need to add an inverter to step up the 12-volts DC from your battery and convert it up to the 120-volts AC of your residential refrigerator. There’s simply a lot of unavoidable losses in any inverter, so why waste power. If your appliance can use 12-volts DC, then that’s what you should be powering it with.

In my Vitrifrigo experiments over the last month I noticed that most of the time the refrigerator was only drawing around 60 watts from the Lithium Battery, which was 4 to 5 amperes of current at 12-volts DC. Compare this to a traditional compressor residential refrigerator that might draw 3 or 4 amps at 120-volts AC.

As I’ve noted before, your inverter will require 10 times the amount of amperage on the 12-volts DC side compared to the 120-volt AC side. That works out to 30 or 40 amperes of DC current your battery needs to supply to the inverter so it can make the 3 or 4 amperes of 120-volt AC current needed by a residential refrigerator.

I think that simply installing a residential refrigerator in an RV that needs 120-volts AC, even one of the “RV Ready” residential refrigerators that include a built-in inverter, is a poor choice in terms of battery power management. Plus, residential refrigerators were never designed to be able to absorb the shocks and vibration of your RV traveling down the road.

Danfoss has decades of manufacturing experience in the narine industry, and those boats take even more of a pounding than your RV does rolling down the highway. That’s why their DC compressors include internal shock absorbers.

The bottom line is that a refrigerator designed for the marine industry which includes a Danfoss BD series compressor that uses native 12-volt DC power will run from your RV batteries 2 to 3 times longer than a residential refrigerator with a conventional 120-volt AC compressor. And that’s what makes boondocking with an electric refrigerator feasible with reasonable solar and battery power.

Read about my Vitrifrigo/Briter test results in my RV Travel article yesterday HERE.

 

 

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.

Email me at mike (at) noshockzone.org with your questions.

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Will

Great discussion. I run a 130L Isotherm refrigerator/freezer and it uses only 5 amps at 12 volts while running. And the more full, the less the refrigerator runs. I figure it uses about 40 amp hours every 24 hours, which is nothing!

The Isotherm does use a Danfos compressor. Granted the 130L is not a residential sized refer, but if you want to RV off grid and only use solar power, it’s the only way to go. I have 450 watts of panels and 540 amps of AGM batteries and NO generator. With careful management of refrigerated food we can go 10 days without a run to the store.

And the nice thing about a 12V only refer, you don’t have to have your vehicle perfectly on level.

Scooter

Just retrofitted my old dometic absorption fridge with this setup. I have run into several roadblocks but most of them are tied to the old fridge circuitry and making it play nice with the new compressor. I am cautiously optimistic about it.