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.
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.