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RVIA Show, New Product Introduction

December 4, 2010 by Larry Cad · 8 Comments  
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One subject that will always create a lot of conversation on the various RV forums is when someone asks about running their air conditioner via an invertor, powered by batteries.  The educated consensus is typically that you can probably do it, but the energy storage capacity of a battery bank will not power the A/C unit for any significant amount of time, thus rendering the system practically useless.  I worked a little math on this and, assuming my math is correct, a typical 13000 BTU coleman A/C unit will consume about 3800 watts per hour and a set of Trojan T-105 6 volt batteries, fully charged, has about 5400 watt hours available, or less than 2 hours of operation until the batteries are fully discharged.  Since we don’t want to discharge our batteries more than about 50%, or about 2700 watt hours, or in terms of a cold RV, about 42 minutes of operation.  In other words, not a very practical arrangement.

Enter the Topleader Group Limited our of Dongguan China who were showing their line of DC operated roof top A/C units.  The photo below shows their DL-1200 unit.

According to their literature, the AC unit operates on 24 volts DC, at 600 watts, and produces from 6200 BTU cooling.  I am going to assume that in the air conditioner has an internal inverter which converts the battery DC voltage to AC in order to run the compressor, either that or it actually operates with a DC motor.  Either of these schemes would be different from the typical US made A/C unit which operates from 120 volts AC.  In addition, the lower power requirement for this unit brings it closer to being useful for the boondocking RVer.

Consider this, a set of 4 Trojan T-105 batteries connected in series to provide 24 volts DC would provide 5400 watt hours at 100 %, or 2700 at 50% discharge.  If the DL-1200 requires 600 watts/hour, this arrangement would provide over 4 hours of operation, or if the A/C is not operated continuously, a fairly good portion of the day.

Unfortunately, the 24 volt series connection for the four batteries is not typical of what we do in the US, and would require a new battery charger, but at least this would be a system that would provide a reasonable solution for boondocking. 

Oh, before we all run off and install this system, and hope that we can recharge the batteries with a solar system mounted on the roof of the RV, a rough estimate is that we would need about 500 square feet of solar panels to accomplish this.  Maybe just use the old Honda generator?

If you are interested in getting more information on the DC air conditioner, here is there website:
http://topleader.en.made-in-china.com/product/dqYQmFOblBkP/China-DC-Auto-Air-Conditioner-AC-2-.html

At this time, I don’t know of anyone in the US who is actively importing this product, so maybe this represents a new business opportunity.

Larry

P.S. if anyone finds errors in my math, please let me know, or leave comments.  It’s been a long time since I did these types of conversions.

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Comments

8 Responses to “RVIA Show, New Product Introduction”

  1. Geoffrey Pruett on December 5th, 2010 5:45 pm

    The 24 volt system may only be leading the market a bit. Many DP’s already have 24 volt sytems for the drive train, down converting to 12 volts for cabin use of legacy systems is not a large step as hardware already exists. 24 & 48 volt buss systems are already used for solar systems, higher voltage means smaller and lighter wiring and less connector headaches with lower currents at juctions. Still, the battery powered air conditioner is still more dream than usefull idea with existing batteries. A pleasant dream how ever!

  2. Bill Mann on December 5th, 2010 7:28 pm

    600 watts equals about 2000 BTU/hr for the input energy. It is impossible to yield 6200 BTU/hr minimum output from 2000 BTU/hr input, regardless of voltage without some other energy being input into the system. Something is wrong with their claims.

  3. Brad Wartman on December 5th, 2010 7:30 pm

    I’m in agreement that it doesn’t make much sense to try & run these A/C units using existing (lead-acid) battery technology. It does, however, present an opportunity to use a more efficient technology.

    A 13000 BTU AC-powered unit requires 3800 watts/hr to run or ~3.5 BTUs/Watt. That in turn requires a 4000 watt generator (which tend to be heavy and expensive) to run the A/C unit when not connected to shore power.

    OTOH the DC-powered unit only requires 600 watts to produce 6200 BTU or ~10.3 BTUs/Watt…nearly 3 times more efficient than the AC-powered unit. Even with 2 of these units you can use a 2000 watt generator and still have plenty of power left over.

    So while it doesn’t make sense to power these A/C units with batteries it does make sense to use them in lieu of AC-powered units where energy efficiency is important.

    BTW, the web site indicates that there are 3 models available with output from 9000-12000 BTUs. I couldn’t find a 6200 BTU model but the 9000 BTU model requires 600 watts of power…maybe that’s the one that’s be referred to in the article? The largest model (12000 BTU) requires 1000 watts…an energy cost of 12 BTUs/watt. That means you could get by with a 1200 watt generator. I’d gladly get rid of my existing A/C unit to replace it with this one and run it from my 2000 watt generator…which would run for 6 hours at a 50% load…instead of a 100-150 pound 4000 watt generator that would 50-100% more fuel to run the same amount of time ;-) .

  4. peholden on December 5th, 2010 7:31 pm

    An interesting idea, but note that this unit produces less than half the cooling of a conventional RV air conditioner. Call me old fashioned (although I do love and use my AC), but a couple of oscillating table fans are surprisingly good cooling options. They’re cheap and use almost no power compared to an air conditioner. In a dry climate especially, I’ll bet the fans would make you feel nearly as cool as the 6,000 Btu AC would.

  5. Jane on December 5th, 2010 7:37 pm

    I definitely like peholden’s comment…have used the old fashioned oscillating fan many times…it also works very good on your outdoor picnic table…..assuming you can plug it into your outdoor lights…lol

  6. Mike on December 6th, 2010 3:46 am

    Would be interesting if you could run them directly off a solar panel when you have enough sun, only dumping excess to the batteries…

    a 205 watt panel is about ~18 square feet (of course “205 watts” is peak watts)

  7. Thomas on January 18th, 2011 12:08 pm

    In and off-grid application, a consumer should buy the highest efficiency A/C possible. Home units are SEER>20. I don’t know the efficiency of this unit. All it says is Energy Efficiency Standard: Level 1 .

    Users could be happy if the A/C took the mean edge off of the heat and brought the cabin down to 85F. A photovoltaic collector could recharge the battery, then the A/C could kick on occasionally. Sit near a fan. Drink ice water.

    How about a swamp cooler? Has that been done in an RV? I would work in the low humidity of the Southwest up to the Oregon desert and probably in the Central Valley of California, too.

  8. new jordan releases on November 28th, 2013 2:35 am

    Tumblr article…

    I saw a writer talking about this on Tumblr and it linked to …

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