When I planned my travels for the winter of 2014 I did not know what kind of vehicle I would have to travel in. I had first thought of using my Toyota Tacoma pickup truck. I thought I would put a cap on the back of the truck and live in it. I started a design for the interior bed of the truck and went about looking for what cap I would want. I had a list of things I wanted to bring with me and one was a fridge. I had researched and before I had my design for how I was to travel I bought (invested in) a compressor fridge from online reviews. My choice was the high-end Engel compressor fridge for its ability to use so little power.
As it turned out I could not find a cap for my Tacoma that I truly liked due to the sloped sides. I was also running out of time to get a vehicle for January and I was lucky to find a 1994 Class B Coachman in nearby New Hampshire that was to be my first year's vehicle to travel in. My Class B had a 3-way fridge but I knew how much work they involve and how much 12 volt power they use so I ended up using the Class B fridge for dry storage and my Engel fridge for cold storage.
Here is the tag on the side of my Engel Fridge. My model operates on both 12 Volts DC and 120 Volts AC. I bought this with dual power so I can use it at home as well as on the road. The price tag online from Engel was $800 and $60 for shipping to MA. This was an expense purchase and more than what I wanted to pay, but I saw it as an investment.
When not on travel I use my Engel fridge for short and long trips and even for going to the grocery store to put items in that you don't want to spoil or thaw.
It is well known that compressor fridges are great for vehicle dwelling and they use little power. For me this was my goal, but when I came back from my first year of travel I knew I couldn't sustain the cost of fuel for my Class B and travel the way I want. I could not have been more pleased in planning for my second year of travel and switching to a Prius that my small Engel fridge was just the right size to allow me to continue to have a fridge and have room to sleep along side of it. It fits great under the privacy cover too!
From my other blog postings you know that I have done a lot of designing with the Prius including a house battery to power the fridge at night so the Prius doesn't have to run at night. My first year I ran the fridge overnight on 2 12V gel cells at 7 ah each for a total of 14 amp hours. Since you only have use of half the amp hours in a lead acid battery such as these, my Engel fridge got by on 7 amp hours a night!
My house battery had limitations the first year in that when I wanted to hike in the morning I hadn't sufficient time to recharge the gel cells before going out, and I stressed the two batteries. My second year of travels in the Prius I upgraded the gel cells to 3 12V 8 ah batteries for a total of 24 amp hours and half of that was 12, and this provided me a much better buffer for my house battery usage. I am currently planning my third year of travels in the Prius and I am working on a whole new house battery design that I will be posting in this blog about soon.
I like to cook and eat fresh food. To say I like my Engel fridge is an understatement. It just does what it should. It is not a fridge with lots of gages. It has a knob for setting the temp and there is no temp indicator. I fixed this my first year by using a remote outdoor wireless thermometer from Walmart for $10.00 Other than that it just runs and runs and does it efficiently.
How efficient? I didn't know and I decided to perform some tests 3 years after buying it so I could pass the information on to all of you considering a compressor fridge.
The tag on the Engel fridge says 2.5 amps running at 12 volts. The high I measued is 2.65 amps when it first starts and then it drifts down to 2.14 before cycling off.
In standby mode between turning on and off the Engel fridge uses from .184 to .125 amps. This powers the circuits and the LED in the 12 volt plug end so you know there is power to the fridge wire, and another LED on the fridge itself to let you know the fridge has power.
What does all this mean. Well, I did some duty cycle testing.
I put the fridge in the house where it is a constant 70 degrees F
I let the fridge come down to 35 degrees F
The fridge has a 11 minute 45 second total on/off cycle under these conditions.
The fridge runs 2 minutes 10 seconds on during this 11 minute 45 second cycle
So the fridge is off 9 minutes 35 seconds during the cycle.
This is a constant on/off that the fridge goes though.
This results in a duty cycle of 22.7%
If we use the tag on the fridge for amperage draw of 2.5 amps we would have 2.5 amp hours usage if the fridge ran and never shut off. Since the fridge cycles on and off at 22.7% from my measurements the actual usage under these fixed conditions is .57 amp hours.
This explains how my fridge ran overnight my first year on the usable 7 amp hour of gel cell battery power (half of the 14 amp hour rating) If I parked at 6 pm and started charging again at 6 am I would have used all the available 7 amps, thus leaving me nothing if I went to hike.
I solved this problem of needing more power by unplugging the fridge and not running it during my morning hikes. I always kept a 1/2 gallon of my drink of choice in it and this acted as a good mass to withstand the time during the hike, but then I need to spend time charging in the pm and getting the temp in the fridge back to 35 before night so I could run the fridge at night. All this worrying about battery power and the fridge was distracting and why I added a third battery my second year of travels.
This gets me to my new house battery design I am working on to allow more flexibility of power at night. I would like to run other items at night off my house battery such as a USB fan, and with my current design, with only enough power to support the fridge, I can't do this.
Of course I have a Prius with all kinds of power since Ready Mode supplies power from the high voltage drive battery to the 12 Volt Prius system allows me to have the Prius run only when it needs to charge the high voltage battery, but I also like to stealth park and running the Prius even in Ready Mode would cause attention.
I hope this post explains how well my Engel compressor fridge works and how little power it consumes. I need to add that in January, even in the southwest it is cold at night and mild during the day and there are times that the fridge can be unplugged at night. On the other hand, by mid-March it is getting very hot in the southwest and in the car even hotter. Even with my windows cracked for air circulation, it is hot in the car and the fridge is subject to using a lot more power to keep cool and also because it can't dissipate the heat from the condenser. On these hot days with no shade for hours I may leave my Prius in Ready Mode and leave the air conditioning on (set to a higher temp) to help the fridge through that situation. I do put Reflectix around my fridge leaving the fridge vents open to repel the heat and this works well. I don 't have room for foam insulation around the fridge in my Prius design, but you still have the issue of the dissipating the heat from the condenser.