After installing electrical system from Victron and the 12v air conditioner, RKS Off-Road tested in the desert just north of California City. Their MOTIVE series is about to go through thermal and power testing that will define the final product in production. This is part of a series of tests to reach their launch target: Best in Class Off-Grid Toy Hauler
Why Thermal and Power
Thermal comfort is a major power and fuel consumer, so by building in thermal efficiencies, this will have the largest impact on power efficiency. Sure, they could add more solar (adding more cost and weight, plus a place to mount or store them), but why do that when you can reduce the need for power. The A/C is the #1 consumer of power in warm/hot weather, so let’s address it.
There are so many mobile A/C products out there, all claiming the best. For off-grid they need the best. They started with 120v systems thinking higher voltage means greater efficiency…..not in this case. The 120v A/C’s out there are power hogs and loud. They claim quiet, compact and efficient, but not sure what they are comparing to…maybe the prior version of their A/C. They then looked at the 12v systems and found a couple of products that look good on paper and prices didn’t force a second mortgage. They decided to test Mabru and DC Power Solutions 12,000BTU units.
Mabru – Best on paper, the system they bought is 12v (they also offer 24v) so they did not need a DC-DC converter to step up the voltage. Key attributes that interest us, on ECO mode only consumes 390w and even at MAX they got to 700w with fan of high. Also, the sound is only 33dB, which IS quiet for a rooftop A/C.
DC Power Solutions – Priced similar, this unit shows well on paper but what has us most interested is the performance. The evaporator airflow is high, so they are wondering if this unit will outperform the Mabru overall even though it consumes between 720 and 960w. This unit shows on paper to be quieter than the Mabru, at only 28dB.
There will be three phases of tests conducted, the first two for trailer improvements and the last two for A/C selection.
Test #1: Baseline (current evaluation)
This test is without insulation, only the thermal insulation value of the walls with aluminum connections. This will show the worst case of this trailer and will place an enormous amount of strain on the A/C in hot weather.
Test #2: Insulated (future test)
This test is with same power, A/C and similar thermal attributes, only changes to the trailer design and insulation will be done.
Test #3: A/C
This test is for the selection of system that will be installed on the trailer. Out of respect for the suppliers they will not publish the results of this test to the public. You will know who they thought best because it will be on their production units.
Test #1 - Environment
Test #1 – Set-up
So, this will get some people going ape shit, the entire trip required NO generator, running 400w solar and 400Ah of lithium batteries (Victron). That’s right, ran a 12,000BTU A/C for 9 hours straight with only 400Ah of battery storage and 400w max solar (which reached 320w in the desert at high noon). AND, when the test concluded there was still 20%+ battery capacity. There wasn’t much to do while recording data, but I do enjoy seeing data and conducting analysis. See more about this in the summarize results….crazy cool!
Nothing like a waterfall chart to help understand what used what! Above shows the trailer started with full power, the solar contributed 194Ah and the big consumer was of course the A/C. Why the Waffle Iron? Because I make a delicious waffle, refined from years of cooking for the family. You want the recipe? Ask and ye shall receive! I also wanted to add a ‘heater’ inside the unit to see how well cooling was affected (and it was). Also, it reflects power use for a typical day.
Other Definitions of Categories: ‘Misc Systems’ power use is the overhead power requirements of the inverter plus lights and small accessories like the radio. ‘Main Fan’ is a 4” inline quiet fan I used to keep air fresh inside. ‘Phone Charge’ was higher than usual because not much else to do in that weather plus I was streaming music to the audio system! ‘Fridge’ is a Truma Powered Dual Zone Cooler 96DZ, great cooler. ‘Coffee’ needs no other explanation, it was delicious.
Summary: As a base configuration, the trailer is capable of off-grid power without A/C use. With full or partial sun, the trailer can power indefinitely over the life of the batteries. The solar more than compensates for typical usage without running the A/C for extended periods of time. If planning to run A/C for extended trips off-grid, then need more power generation and/or better insulation of the trailer. The power generation in the case above would require 2x more solar (so 800w should do it), which can be achieved using our deployable rooftop solar or just mounting a few more panels. In the case of RKS, they will be using our deployable solar, so they don’t take up the rooftop patio space on their MOTIVE.
Aluminum: As expected, the Aluminum is terrible at thermal insulation reaching up to 108F inside the MOTIVE. Fortunately for us, there is not much surface area of aluminum. However, they will design in some insulation to address this thermal exposure. The insulation of this on the inside is also critical to avoid condensation inside the trailer.
Walls/Roof/Floor: The wall does have some insulating value acceptable for most weather, with sun on the wall there was a 3-4F difference and without direct sun there was a 6-8F delta. Acceptable for moderate environments, but they are not building for moderate, they build for extreme. So, for extreme heat/cold would also need to be addressed if wanting to minimize power/fuel drain. They will start with insulating the ceiling and covering the underside of the frame. There is also in development an outside accessory which should be tested in the ability to reduce sun impact.
Air Conditioner: The A/C was quite interesting. The fan never turned off, the compressor cycled to protect the system, and the cooling difference between MAX and ECO was not as great as expected for the increase in power consumption. It would be best to insulate the trailer so A/C can remain on ECO to still be comfortable with consistent use, and only use MAX to rapidly cool a hot trailer then change back to ECO to maintain temperature.
Summary: They are very happy with the results for baseline, added no insulation and was able to maintain comfort in the trailer on battery and solar alone. As they improve insulation and other thermal advancements, this will help create power in excess of demand so that trailer power is not a concern. Also, as Their target is to have excess power for EV charging, thermal is a key part of this challenge. More testing to follow soon on thermal and other factors that create more clean power for EV charging!
Important things to know about the ban of small engines:
There are three set-ups we have experience with: 1) power system with generator as back-up 2) power system with generator powering certain items (i.e. A/C or microwave) while the batteries power everything else and 3) fully conversion to battery which we recommend A/C systems that can run off the batteries with minimal power draw (see blog about Mabru air conditioners)
The cost to convert will depend on the set-up. A simple installation where a generator is still used will typically run $8,000 to $12,000. Whereas to go full conversion without generator is typically $20,000 to $30,000 depending on the power requirement and if replacing the A/C with 12v rooftop unit.
So how long would it take to offset that cost of full conversion. If you consider maintenance and fuel consumption we calculate a $20k system would take about 3,000 hours of run time on a generator to off-set the cost. This assumes an average fuel consumption of 1 gallon per hour under a load, and $200 every 100 hours of run time for maintenance. That’s a lot of hours to make up that cost, so who benefits from this:
I don’t believe the ban will have a large effect on the industry. Many vehicles offer diesel and LP generators, and I believe the OEMs will start offering power options without needing a generator. You don’t need to throw away your generator, but if you want to go with a battery power solution then we can help. We are off-grid campers, and we don’t run generators…the best way to enjoy the outdoors.
When we decided to offer Mabru instead of Dometic, there were a few key attributes that led to that decision:
The units are like each other for power consumption ~ 20-55A at 12v, however the Mabru is rated 12,000 BTU while the Dometic is only 6,824 BTU, you get almost 2x the cooling for the same power. So, in essence I can run the Mabru on ECO to achieve the same result as the Dometic on HIGH and consume half the power while also prolonging the life of my air conditioner (less wear at ECO modes). This is also important in our area where going close to 100F temperatures in the desert can happen even in fall and spring, then you need a 12k BTU to cool an RV or trailer.
This is a big deal to us, the ability to have a conversation with indoor voice near the air conditioner. The Dometic is a typical 70dB, while the Mabru is only 33dB. To expand on what that means, the Dometic is like being near a typical washing machine, while the Mabru is like being near a refrigerator. If you like it quieter for talking or sleeping, the Mabru unit wins again at half the noise level.
As costs are going up on most things, affordability is definitely an important factor. The Dometic with install kit is over $3,000, while the Mabru unit is $2,600. We know it’s just $400 less, but that can be used for other things, like buying more solar panels to off grid longer. Or in our case, we can stop dreaming about it and finally buy that Nespresso machine! The Mabru costs less, cools 2x more and is half the noise level (dB). That’s the value people are searching for.
At A Glance: