RVelectricity: Boondocking power requirements – Part 2 of 4

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By Mike Sokol – RVelectricity and the No~Shock~Zone

 

 

Brought to you by CarGenerator.com 

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By Mike Sokol

I believe that as we move forward through the COVID-19 pandemic over the next few years (until an effective vaccine is developed and widely distributed), traditional camping as we know it is going to change radically. Since campgrounds are likely to be overcrowded due to limited vacation options for many of us, many RVers are interested in boondocking (camping without campground power or water services), which give them a lot more options of where to camp.

But boondocking isn’t as simple as just parking your RV in the woods. It’s easy to forget just how much power we use in an RV. And while I don’t have an easy solution for running a rooftop air conditioner from solar panels and batteries (just yet), I have learned a few things about refrigerators in RVs over the last year – which is the topic of Part 2 of this series.


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Choices

Basically you have three choices for refrigeration in a modern RV (four if you count a block of ice in a cooler). Let’s do a quick review of these options along with the pros and cons of each.

3-way/propane refrigerators
This is the old standby that was installed in most RVs for the previous decades. But while refrigeration from propane does work, it has limited cooling power – often taking all day to bring down the temp of new food you just loaded into it. And these refrigerators should be very close to level (within 3 degrees of plumb) or they can tend to overheat and operate inefficiently.

And they’re not cheap at all, costing a lot more than many residential refrigerators like you might find in your house. But they use very little battery power for the control circuitry as long as you have enough propane to run them. So a tank of propane might be able to last most of the week. And a few solar panels could take care of the rest of your electrical power (as long as you don’t try to run your air conditioner).

However, the elephant in the room with any propane-powered refrigerator is the fire hazard if something goes wrong. While modern propane refrigerators should be perfectly safe, if they’re not properly maintained and used very close to level (within 3 degrees) they can become a fire hazard. And the one thing that scares me more than a hot-skin voltage on an RV is a fire inside of an RV. But that’s just my 2 cents…

Residential refrigerators
Just a few years ago we began seeing RV builders stuffing full-size residential refrigerators into RVs. While this certainly looks pretty on the showroom floor, and they work well enough when you’re plugged into shore power, they’re generally not a great option if you’re trying to run off of solar panels and batteries.

Here’s why: A standard 120-volt AC compressor in a residential refrigerator might draw 4 or 5 amperes from the power line when running. That doesn’t sound like a lot, does it? However, that’s at 120-volts AC. If you need to power this from a battery there’s a little 10:1 amperage ratio that creeps into the equation. Because we need to step 12-volts DC to 120-volts AC, you have to multiply the current by a factor of 10x as well. So that 4 or 5 amps at 120-volts AC needed by the refrigerator compressor turns into 40 or 50 amps at 12-volts DC that your house batteries need to supply.

And a standard lead-acid/100 amp-hr battery only has about 50 amp-hrs of capacity to give up before you begin damaging it. Even if the compressor is only running 50% of the time, you might be able to power your residential refrigerator for 2 hours before discharging your battery. If you put in a second lead-acid battery you might extend that to 4 hours of time. And if you put in a pair of Lithium batteries that can be safely discharged down to 0%, you might get 8 or 10 hours of refrigerator time, after which your batteries are completely drained.

Don’t think that simply plugging your RV into the 7-pin brake/power hookup is going to help much. While you might be able to push some amperage from your tow vehicle to the house batteries in your camper, it’s probably gong to only be 4 or 5 amperes of current at 12 volts DC. Remember that your residential refrigerator needs 4 or 5 amps at 120 volts, so it needs 40 or 50 amps at 12 volts, just to keep up with the residential refrigerator power. I have emails from readers saying they drove 8 hours to a campsite only to find that their house batteries were completely drained by the refrigerator when they arrived.

There are DC-DC charger solutions that can provide 40- to 80-amps DC charging power from your truck to your RV, but that requires a special high-amperage wire and connector run from your TV’s alternator back to the trailer hitch, and an appropriate DC-DC charger to control the alternator current so that nothing burns up. And if you go through all the trouble and expense, your residential refrigerator is still going to drain your house batteries in less than 8 hours. I think 120-volt AC residential refrigerators are a poor choice for RVs for those (and a lot of other) reasons.

12-volt DC refrigerators (Danfoss compressors)
I’ve been experimenting with a Vitrifrigo 8 cu. ft. refrigerator for the last several months, and I’ve fallen in love with the 12-volt DC Danfoss compressor that makes it work. The heart of the process is the compressor, and Danfoss is the best in the business. It only draws around 6 or 7 amps at 12-volts DC, instead of the 40 or 50 amps through an inverter that a residential refrigerator needs for power. That means extended battery life in a boondocking situation.

In my lab tests a few months ago, I was able to power it from a single 100 amp-hr Briter Products Lithium battery for over 30 overs before calling it quits with 5% of battery power left. And the fact that the Danfoss compressor is 12-volts DC means you don’t have an inverter wasting your power, to the tune of 10 watts or so. While that doesn’t sound like much, 10 watts over a 20-hour period is 240 watt-hrs of energy. Note that a standard lead-acid battery with 100 amp-hr capacity only has about 600 watt-hrs of power it can provide before it’s down to 50% capacity. So do you want to waste 40% of your battery capacity just to run the inverter? I didn’t think so….

In my opinion, if you want to boondock on solar power, or limited generator recharging power, then the best refrigerator choice has a 12-volt DC Danfoss compressor. I like my demo Vitrifrigo 8 cu. ft. refrigerator/freezer a lot, but Dometic is sending me their own 10 cu. ft. version soon to try out. Plus I still have a my Vitrifrigo portable 12-volt DC refrigerator for road trips.



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CarGenerator™ and HYBRID Inverters like Magnum or Cotek
If you have one of the new super cool HYBRID inverters in your trailer, CarGenerator has big news…. It’s a game changer. A typical air conditioner requires 13 amps AC to run. A hybrid inverter allows you to blend in 10 amps AC easily from your vehicle, and pull the remaining 3-4 amps from your trailer batteries so you really can run your trailer air conditioner for hours by letting your vehicle provide the lion’s share of the power requirement. Stay tuned for more updates on this…

CarGenerator™ Facts and Fiction

  1. No, CarGenerator™ does not use a lot of gasoline. In fact, it uses about the same amount of gasoline per hour as a portable inverter generator. A typical diesel engine idling uses 1/4 to 1/3 gallon of fuel per hour.
  2. Yes, CarGenerator™ is as quiet as any inverter generator. I’ve only done casual testing so far, but it appears that a normal vehicle at idle is quieter than any of my Honda inverter generators. I’ll publish a full study on this later.
  3. No, CarGenerator™ is not a good choice or substitute for a portable dedicated generator if you want to run your RV air conditioner continuously. To do so would require the 2,000-watt version of CarGenerator, a heavy-duty alternator in your car, and a high-idle controller. However, if you have a pair of lithium batteries and a 2,000-watt inverter in your RV, you just might be able to run your air conditioner for a few hours in the evening to cool down your bedroom before going to sleep, and then use CarGenerator to recharge your house batteries in an hour or two of running. Watch for another report on this later.

Read more or purchase a CarGenerator™ HERE.

Brought to you by CarGenerator.com

Read Part 1 of this series HERE.

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.

For information on how to support RVelectricity and No~Shock~Zone articles, seminars and videos, please click the I Like Mike Campaign.

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John
9 days ago

Mike, I think these studies you are doing is of great benefit to us RVERs.
I purchased 2 of the soft start units for my new roof AC’S. Even though I have an 8kw diesel Generator, it turns out that 2 independent AC’s can start at exactly the same time and overload the generator. I was doubtful until you showed the start power curves.
I replaced my propane fridge with a like item 2 years ago because I didn’t want to have to run the generator except when needing the AC’s. I looked hard at Danfoss fridges, but they must be built to EU specs as none come close to fitting in place of American propane fridges. Let us know when the Dometic fridge is available.
Keep up the good work.

Larry H Lee
1 month ago

My Whirlpool full size residential refrigerator uses 125 AHr per day as measured with a Kill A Watt meter over 11 days and that includes the icemaker and defroster.
Larry

Jonathan Schloo
1 month ago
Reply to  Larry H Lee

what does the watt meter typically show for watts used while running?