MOTIVE M19 Test Series

Hot Weather Baseline Test

Introduction

At RKS Off-Road testing is a critical part of building a superior product.  Our 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 our 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, we 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.

A/C Selection

There are so many mobile A/C products out there, all claiming the best.  For off-grid we need the best.  We started with 120v systems thinking higher voltage means greater efficiency…..nope.  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.  We 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.  We decided to test Mabru and DC Power Solutions 12,000BTU units.

Mabru – Best on paper, the system we bought is 12v (they also offer 24v) so we 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 we 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 we 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.

Test Process

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 - 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. This blog is talking about this baseline test.
  • Test #2: Insulated - 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 we will not publish the results of this test to the public.  You will know who we thought best because it will be on our production units.
RKS MOTIVE M19HD

 

Test #1 – Environment

We have some great desert for testing, in our case we went close to Mojave.  In the 24 hours of testing not a single vehicle drove by, my kind of place.

Thanks to wunderground.com we were able to pull some good historic charts without charge.  Below is the weather at our desert test site just north of California City, California (not making that city name up).


Sunrise was at 5:46a and sunset 8:03p local time.

Weather Chart for RKS MOTIVE hot weather test

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.  That’s right, we 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 we concluded the test there was still 20%+ battery capacity.  See more about this when we summarize results….crazy cool!


Test #1 – Power Results

RKS MOTIVE Power Results

Nothing like a waterfall chart to help understand what used what!  Above shows that I 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. 

 

Test #1 – Thermal Results

Thermal testing RKS MOTIVE M19

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, we 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 we are not building for moderate, we build for extreme.  So, for extreme heat/cold would also need to be addressed if wanting to minimize power/fuel drain.  We 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:

We 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 we 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 our 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!

 

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