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About Loki

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    Hilton head, SC

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  1. In a previous post, I described my 1750 Watt solar installation on the roof of my 29 ft. Arctic Fox 5th wheel trailer. Today, I am going to share the rest of my project: becoming independent of generators and shore power. Tu make optimal use of the solar power supply, I chose to install two Tesla Lithium battery modules instead of using a large lead acid battery bank. Each module weighs 55 lbs, has a storage capacity of 5.2 KW and runs with 24 V. A lead acid battery bank with a comparable capacity would weigh hundreds of pounds (400 lbs my best guess), but what is even more advantageous with lithium batteries is that they can routinely discharged down to 15% of their capacity without compromising longevity. With the discharging limit for lead acid batteries being around 50-60%, you would need even more batteries to match the usable power reserve of these two lithium batteries. I decided to keep the 24 V system completely separated from the 12 V house system, in order to keep things simple and straightforward. The solar panels feed into a Magnum PT 100 MTTP charge controller, which powers a 24 V bus that is connected to the batteries and a Magnum MSH 4024 RE inverter. I chose this 4 KW inverter because it is able to work in Hybrid mode: When connected to shore power and the AC load gets close to the maximum amps available, the Magnum supports the AC load by inverting and prevents tripping of the shore breaker. I left the built-in 12 V system untouched, meaning I kept both the two 12 V batteries that came with the unit as well as their converter-charger. When disconnected from shore, the 12 V batteries are being charged with the built-in charger using the solar/inverter power. I installed, however, a switch that enables directing solar power from the PT 100 to the 12 V batteries, just in case the 24 V system fails to work, from whatever reason. The only real downside with lithium batteries (besides the price) is their sensitivity to low and high temperatures as well as to overcharging and over-discharging, so I had to design and build some protection circuitry. The electricity to and from the batteries goes through two Victron Battery Protect units (basically unidirectional solid state relays) rated at 60 A and 200 A, respectively. They shut off at 20 V on discharging and 24.6 V on charging, and are connected to two temperature sensors that disconnect from charging below 35 and above 120 degrees, respectively. I also installed a heating blanket around the batteries that starts heating around 35 degrees, and a radial fan blowing air into the compartment from the outside if above 100 degrees in the compartment. The first pic shows the installed units without the batteries. On the upper right side, the solar charge controller, and on the compartment floor the Magnum inverter. It also shows the control panel with the protection circuitry that I built. Upper left corner, two circuit breakers in line with the two blue Victron Battery Protect relais guarding the charging and the discharging flow. Also shown is the switch that directs the solar current to the 12 V or the 24 V system, 4 temperature control modules, and in the lower right corner the Magnum battery monitor unit. The second pic shows the compartment with the two Tesla battery modules in place. The blue unit above the control panel is a 600 W Samlex inverter that is powered by the 12 V batteries and is used as backup if the 24 V system fails. The entire installation is super-compact and uses less than half of the front compartment, just about 8 square feet. My maiden voyage with this installation took me across part of the Southeast and included a week of boondocking. I planned a longer boondocking experience, but a week of rainy weather put an end to that - no sun, no solar! Bottom line is, on a sunny and warm day it is no problem to run the air conditioning and the fridge with the battery and the solar. And this was October, with the sun already pretty angled and the peak temperature still 88 degrees. Especially on long, hot travel days it's so nice to have the RV air-conditioned when you stop or arrive at your destination.
  2. Part of the design process for my solar installation was weighing the pros and cons of parallel vs. serial wiring. With 5 panels, each of which delivering up to 37 V, some parallel wiring was inevitable, so a combiner box could not be avoided. In the end, I found the advantage of harvesting the sun light more efficiently under partly shaded conditions outweighed the additional cost of less than $50 for the thicker wire, so all panels are wired parallel.
  3. I love boondocking,and I hate generators. Recently, I sold my 37 ft 5th wheel and bought a 29 ft Arctic Fox 27-5L, because I was fed up with being stuck in tight National Park and State Park campgrounds. When I climbed on the roof for the first time and saw how cluttered the roof was with exhaust pipes, hoods, AC unit etc, and considering a usable roof length of less than 25 ft, I all but gave up on the dream of installing a meaningful solar power plant on this roof. But after taking exact measurements of the roof and the obstacles, and realizing how far the solar panel industry has come in terms of power output per square unit, I started some serious research. And came up with the solution of installing 5 of 350W monocrystalline JA Solar panels. They are about 38"x79" big and cost me less than $200 per piece (plus freight), which is a steal deal compared with what other dealers charge.Because several roof obstacles are about 40" away from the roof edge, I was able to squeeze 5 of these panels on the roof (see attached pic). Of course, mounting them so close to the edge and to hoods etc. was pretty challenging,and I had to use slightly different methods to fix the panels to the roof, depending on their location. Since no solar mounting hardware available on the market could be used because of the tightness, I devised my own, relatively simple method by using pairs of slotted aluminum angles in each of the four corners of a panel. Each angle was about 10" long; one was screwed to the panel, the other one on the roof in a way that aligned the slotted sides of the angles so that they could be bolted together (see pic). One of the panels had to be raised about 7" above the refrigerator exhaust hood, but that was the only more complicated construction (see pic). The 10 wires from the panels are connected in a combiner box that sits atop the hole that I had to drill right above a wall that is already used as a wire raceway. I chose AWG 1 wire from the combiner box to the solar controller (that sits in the front compartment), which probably is an overkill, but the cost difference is negligible compared to the overall cost of the project. In a subsequent post, I will talk about the installation of the solar controller, a 4000W inverter, 2 Tesla battery modules, and the necessary control and protection circuitry. And, of course, about the practical experience with running the entire coach off grid, with water heater, AC, microwave, toaster, hair dryer and all the other power hungry gadgets.
  4. Loki

    Tesla battery for RVing

    Considering the fact that lead acid batteries can be only discharged down to about 65% of their capacity on a regular basis without compromising their life expectancy, whereas a lithium battery can be used down to 15% for their entire life span (which per se is much longer than that of a lead acid battery), you would need about 8-10 conventional 110 Ah batteries to yield the same usable energy before recharging. That's more than 10 times the space and weight. Of course, nobody is doing that - more than 440 Ah is not practical. But that's about half the usable energy and 5 times the weight of a Tesla battery module.
  5. I think, everyone who wants to get serious about living off-the-grid (and saving thousands of dollars annually) wants to watch how these RVers enhanced their boondocking capability by replacing lead-acid batteries with a Tesla battery module:
  6. I own a 2012 Montana 313RE I have travelled with over 40,000 miles. While it is a great 5th wheel with only minor flaws, it's not really suitable for longer stays in winter weather. I have added a few things that made 2 or 3 weeks managable under freezing conditions, but it wasn't too comfy, so I'm thinking about getting a new one with 4 season suitability, like with the quality level of a Mobile Suites or one of its siblings. Also, we weren't too happy with the length of the trailer; with its 36' it proved to be too long for quite a number of national or state park campgrounds, where we prefer to stay in. So we started looking for a 5th wheel with a length of 32' or preferably shorter, but with all the whistles and bells that make an RV 4 season capable. And I couldn't find any! Closest I found were the Mobile Suites 32 RS3 or the Tradition 340 RES, but they are 33'8" or 34' long, respectively. I understand that most people who need 5th wheels with fulltiming capability would also want something that is more spacious, so most of them are in the 36' to 43' range. But nothing smaller than 32'? Or does anyone know something I couldn't find?