Refrigeration

20140227-211526.jpg We have been dealing with refrigeration issues ever since we started camping and (I think) we finally have a good solution so I thought I’d share my lessons learned.

Note there will be no bird pictures or lyric odes to the wilderness in this post. Strictly one engineer to another :).

This is mostly about refrigeration because that’s something we can’t (actually won’t) do without. We have never used our air conditioner, can heat what little hot water we need on the butane hot plate and snuggle up in sleeping bags on chilly nights but absolutely need cold food storage and properly chilled white wine.

I also don’t talk about gasoline generators. They can provide plenty of 120v AC power but are dirty, smelly, heavy loathsome objects that take a lot of space plus need an accessory can of gasoline. We have a little super-quiet Honda EU2000i and used it once camping. They might be quieter than the noisy kind but the noise just ruined the camping ambience for us. We hated it and never took it camping again.

Our Lil Snoozy came from the factory with a 3.6 cubic foot 120v AC refrigerator much like you would find under a bar top or in a college dorm room. They are cheap, usually under $150 from a big box store, and work fine when plugged in. That’s the rub – they don’t work at all without being plugged in so you lose the cold while driving and you must camp at a site with electricity. The food won’t spoil if your are only driving a few hours and most campgrounds have electricity so the dorm fridge isn’t a bad solution for most campers. In this scenario the only negative thing I can say is that the Magic Chef fridge was kind of noisy. Not too bad but remember it’s running right by your bed.

That wasn’t our scenario though. We knew we would be towing the Snoozy from Michigan to southern Alabama a couple of times per year. This is a 16 hour drive and we usually go about ten hours, get a motel room and than go the rest of the way the next day. That meant the fridge needed to run at least 30 hours without shore power. We hoped to camp at primitive off-the-grid sites once in awhile too. For that we would need the fridge to go at least two, maybe three days.

My solution was to install a 220 ah battery bank and a 600 watt inverter. The fridge required only 80 watts when running and up to 400 w in the first few seconds when the motor starts. This worked fine when brand new. I failed to consider the power the inverter used all the time it was turned on, whether anything was drawing 120 v AC power or not, so this system would have never run the fridge for three days but it did work for two days. In fact the first time we ever used the trailer we were at a National Forest campground without electricity. The inverter ran the fridge just fine from Friday afternoon to Sunday afternoon.

Techie note on running a fridge with an inverter: I have a Samlex 600 watt true sine wave unit. It is 85% efficient and draws 0.6 amps (7 watts) when turned on. The Magic Chef used 80 watts of 120v AC when running. A good guess is that it actually runs 33% of the time. In 24 hours the fridge would consume 80 x 24 x 0.33 = 640 watt-hours. Applying the inverters 85% efficiency means the inverter needs 640/0.85 = 753 watt-hrs plus it’s idle consumption of 0.6amps x 12 volts x 24 hrs = 173 watt-hrs. Total energy drained from the battery 926 watt-hrs. The system efficiency is 640/926 = 69%. Fully one third of the energy is being wasted.

The battery bank holds 2600 watt-hrs of energy so 24 hrs of refrigeration used 35% of the total. Battery life is seriously compromised by full discharge and discharge cycles deeper than 50% should be minimized. Conclusion: the fridge would would work OK for two days but any longer put us deep into the “should be minimized” range.

By the wintertime, when we’ed put a couple of thousand miles on the Snoozy, the fridge would run when the battery was fully charged but would not start when the battery was maybe 40% or 50% run down. When we got back to Michigan last May It wouldn’t start unless the battery was 90% full. It wouldn’t start at all by the time we got back to Alabama in January.

Keep in mind it worked fine when plugged in to shore power. The problem was only when using the battery – the inverter did not produce enough 120v AC power to overcome the starting resistance of the compressor motor. I believe the fridge motor, when new, took a lot less power to start. The manual said specifically not to install the fridge in an RV and I think that is because the motor – compressor unit is not robust enough to take the shocks of the RV hitting bumps.

We needed to have the fridge cool when driving and plan to spend time in April at National Parks in the southwest where campsites with electricity are rare. Our options were to buy another dorm fridge and hope for the best, install a propane system and get a propane refrigerator or get a 12v DC fridge meant for RV or marine use.

I considered a larger inverter but rejected that as a 1000 watt unit is around $500 and is even less efficient as the idle power consumption is greater. There is also a basic electric wiring issue too. For an inverter to supply 1000 watts at 120v AC it would need nearly 100 amps from the battery. This is a huge amount of current and without thick primary cables and high amp connectors the voltage drop between the battery and the inverter will trick the inverter into shutting down as it thinks the battery is almost dead.

Just getting a new dorm fridge was by far the least expensive and easiest to install choice but we were not interested in rolling the dice and most likely dealing with the same problems again. Plus, as I explained above, the inverter wasted a lot of energy, limiting our time running off the grid to two days.

Propane is the standard RV industry solution to this problem. Most RVs have a propane system and a refrigerator that burns the propane to evaporate ammonia and make the fridge cold. Don’t ask me, I don’t know how the heat makes it cold either, but it does. This is old school proven technology that has been around for many decades. The refrigerator in your house uses a different technology. It has an electric motor driving a compressor that condenses freon or some other more environmentally friendly gas to chill the Chardonnay. This is the same way air conditioning works.

You house does not have an ammonia unit, even if you have cheap natural gas to burn, because it is much less energy efficient than the compressor style and you can conveniently get all the electric energy you want from the power company.

Propane is popular in RVs because you can store a lot of energy in a propane tank and can’t conveniently get energy from the electric utility all the time. The 20 pound propane tank on your barbecue grill weighs 40 pounds when full of propane and can provide 120 kilowatt hours of energy when burned. The two golf cart batteries I have in the Snoozy weigh 130 pounds and can provide 2.6 kW-h if drained until dead. Their practical limit is about 2 kW-h. With a lot less weight and 60 times more energy storage I get why propane is so popular, not to mention that it’s the only practical way to get heat or hot water without being plugged in to the grid. Here’s a good link to learn more about propane vs. electricity.

But (you knew that was coming) there are some downsides to propane. First of all it’s not either-or. Even with propane you still need a battery, battery charger and inverter for lights and to charge all the electrical gizmos you can’t live without. Obviously you have to buy the propane and that’s not very convenient, you have to tow the trailer to a station that pumps the propane into your vehicle or unhook the tank and lug it to a refill or exchange store. Then there is concern that a propane leak could cause a fire. Everyone has a propane leak alarm that they use to run their batteries dead when their RV is in storage.

Propane fridges can be had either two way (propane or 120v AC electric to generate the heat) or three way (adding the option of 12v DC power from the trailer battery). Their inherent inefficiency means the 12v option is really only practical when the trailer is being towed and the tow vehicle alternator can supply the 12v power. Propane fridges are expensive, one the size we need runs about $1000.

We don’t have any propane tanks or appliances so getting a propane fridge would be a big deal, finding a place for the tank, installing a regulator, running the propane line, cutting a hole in the side of the trailer to vent the propane combustion gas, etc. No thank you.

That left a 12v DC powered fridge. These are commonly used in boats due to the safety hazards of propane. Like lots of boat equipment they are expensive though, also $1000 and up for a dorm size unit. Searching the interweb produced a company the sold smaller units meant for long haul truckers, apparently with tighter budgets than yachtsmen. Truckfridge’s largest model was 4.2 cu. ft., just a little bigger than our old Magic Chef and cost, freight included, $700.

Since it runs on 12 volts DC no inverter is wasting precious energy and it is made for trucks so is built to take the vibration and bumps. It’s meant to operate off a battery so it is very efficient using only 48 watts when running. Using the same one third on time assumption it sucks up 384 watt-hrs per day. This means it will run for 2.4 days on the same energy it took to the Magic Chef – inverter set up for one day.

We have just finished a two day off-the -grid camping trip and our actual energy consumption supports the 384 watt-hr per day estimate. (Another techie note: we have a Victron BVM 600 energy monitor that measures everything you’d ever want to know about electric usage and the state of the battery.)

With a good bit of fiddling the truckfridge TF 130 unit fit neatly in the Snoozy.

20140227-213601.jpg For a blow by blow description of the installation click here.

Based on our two day test we can camp without electricity or water hook-ups for three days with no concern, four days if we are careful to keep the refrigerator side of the trailer out of the sun and five days if we don’t run the inverter and only charge the phones and computers in the car. The 35 gallon water tank should hold us for five days too with minimal shower use. We used about 13 gallons with one non-minimal shower in our two day test.

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24 thoughts on “Refrigeration

  1. OMG! You ARE an engineer!? I was hoping to find advice for ourAllagash Wilderness Waterway trip this Aug, but even my two glasses of wine could not wade me through all the specs! Guess I will have to go with mainly dehydrated food!….very happy that you have refrigeration though!….and are having a much warmer winter than we are! Safe travels! 🙂

  2. Thank you Denny. You are preaching to the choir, the magic chef never made sense to me. I was lucky enough to find you and your blog. It helps that you use your snoozy as I foresee us using ours. I am forever grateful for your willingness to share your expertise, and experience. I have negotiated many upgrades from the factory because of you. When all is said and done I will give you a full report. But I can assure you the indel is a part of our build and I believe the first they have done. Richard is more than willing to work with folks to create the best product for them.

    I loved lunch in your last post, my sun butter sandwich fell short.

    David

    >

  3. Hi Denny and Sue~ I really enjoyed this post! Taking time to write all that info down is kind of beyond my experience. I appreciate your sharing and am so glad to know you priorities. I can relate. Looking forward to your return. C & M 🙂 🙂

    • Hi Colleen, actually the ‘about the trailer’ page gets lots of views so I thought some of our readers might like to see this level of detail.

  4. Denny,

    Now that you have had the Truckfridge for a while I would really appreciate an update. Has it met your expectations? Thanks for all your great information. Andy

    • The Truckfridge has worked perfectly.

      Having electric refrigeration means we try to park the trailer with the fridge on the north side and if possible get a sunny campsite so the solar panel works better.

  5. Thank you again!! for the incredible share of such valuable information Denny! Your words will live on through this blog & forums you’re in, for EVER!! 🙂 Thankfully, for us all!!

    • Thanks. I actually write the blog for me. I enjoy reading old posts and all the other memories the words trigger.

  6. This is exactly what I was planning for my Lil Snoozy. I am going to add propane but don’t want a propane fridge. I want the 12V/120V fridge, I am thinking Novakool as I have heard good things about them, They do say though they need 30 square inches of ventilation for both intake and out take air. Did you have to add ventilation for your truck fridge? I see some RV’s have external ventilation, but sure if that is mainly for the propane. It makes sense the fridge needs ventilation, just not sure if the Lil Snoozy has enough without any outside vents

    • Hi Shawn.

      1) You mention a 12/120v fridge. If its permanently installed in your trailer there is no need for the 120v option. Your built in battery charger will provide the 12v for the fridge.’

      2) the truckfridge manual calls for at least 10 sq in vent area. The issue with a Snoozy is the curved sides. The back bottom outboard edge of the fridge will hit the fiberglass before anything else. I mounted mine so there is a about an inch gap so air can flow under the unit and up the back where the heat exchanger coils are. (1″ x 20″ wide = 20 sq in) Don’t know if this is the same for a Novakool.

      I imagine a propane fridge would need a lot more venting as there is an actual flame in there. The electric fridges don’t need a vent to the outside, just enough clearance so room air can circulate around it.

      When dry camping we try to park the trailer pointed west so the sun doesn’t shine on the fridge side. Testing with a low but warm winter sun in Florida showed a significant increase in power consumption when the sun heated the fiberglass behind the fridge.

      • Thanks for your quick response. I did some more looking into it and I agree with you that a large enough gap at the bottom, back and top would provide enough ventilation. The Novakool asks for 30 square inches top and bottom. I don’t think it comes with a fan to cool the compressor like the Truck Fridge does, which maybe the reason it needs more ventilation, but the amperage draw is less as well, likely because of the fan. You have a great blog here and really appreciate the info. I want to do virtually only boondocking so having 12V power is critical. With 2x6V deep cycle batteries, efficient equipment and solar I suspect you can go quite awhile without hooking up to anything. I also agree with you on the generators, not ideal from my point of view

      • Further to my recent reply, I might be wrong on the NovaKool not having a fan. They do mention if you don’t have enough ventilation the control panel has ability to accept an auxilary fan, which may mean it does have a standard fan. The lower amp draw is likely because I was looking at the 3.5 cu ft Nova Kool and yours is bigger. The NovaKool draws 2.2 amps when running, and run time obviously depends on ambient temp. etc.

        Curious to know if you use a weight distribution hitch or have sway control? I am looking at getting the new Honda Ridgeline with a tow capacity of 5000 lbs. Not sure if WD and sway are necessary or just over kill

  7. The amp draw might have to do with the size of the compressor too. I don’t know the btu output of either fridge. I did just go turn on my truckfridge 130 to check amp draw. 5 ish for a second or two then stabilized at 3.8 amps.

  8. Oops, forgot the second topic. A WD hitch won’t work with the surge brakes on a Snoozy. I don’t have any sway control either. I do have a heavy tongue weight (390 #) which really helps keep the trailer behind me. We even had a blow out going 65 on the freeway and zero sway.

    I used to tow with a RAV4 V6. It worked just fine, but sagged down on the rear axle a bit. The Jeep has load leveling rear shocks and rides nice and level with the trailer hooked up.

    If the Ridgeline isn’t available with load leveling shocks you might have two people stand on the bumper and see how far down it sags.

    • Thanks for the info. I was thinking of going with the electric brakes. Do you have any opinion on that? I hear surge brakes are a Pain to maintain. I too will end up with a heavy tongue weight as I will have the 2x6V deep cycle batteries and propane up front. I was actually thinking of 2x10lb tanks, with the device (forget the name) that switches from one tank to the other tank when one is empty. That way I will know to fill one without running out of propane. Does this seem crazy in your experience?

      • Two 10 # tanks would be a good idea, easier to handle to refill too. I use 1# tanks for a little Webber grill and have an adapter to hook one of those up if the 20# runs out. Never happened (yet) though.

        I’ve not done any maintenance on my brakes, seem to still work fine. Now that you mention it I should probably check the hydraulic fluid.

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