AC Running on batteries

[trumpetguy]

I have often thought that it would be nice to have a short break in a journey...lunch, nap, etc. and do it with the comfort of Air Conditioning.  I carry a Honda 2000i generator in the truck bed, but the effort of starting it and attaching the cable just seems to be too much effort for a short stop.   Call me lazy.  So I have been researching means by which I can run my AC on batteries for short periods.  I'm not talking hours...just a short time to have that refreshing break.

 

The challenge with AC on battery is something called Locked Rotor Amps.  This is that instantaneous burst of energy required to get your AC compressor turning.  In my case the Atwood Air Command 13.5 has a LRA of 63.5.  You may consult your owners manual for your specific LRA.  The running amps are only 12.5 for mine.  (That's high based on actual experience)  My quandary was that I could run the AC with my Honda 2000i, but when I wired the AC into the 2000 WATT inverter  the compressor would not start.  So began my quest for the holy grail...running my AC on batteries.

 

Solution:

 

Install an "Easy Start" soft start kit by Micro Air which reduces the LRA draw by as much as 75%. https://id144248.webhosting.optonline.net/microair.net/merchantmanager/product_info.php?cPath=4&products_id=4

 

Install a Kisae transfer switch so the inverter knows when there is no shore power.  http://www.donrowe.com/KISAE-TS20A-Automatic-Transfer-Switch-p/ts20a.htm

 

 

 

With some consulting by Steve L (ScubaRX) I finished the project today at 4:00 PM.  With breath held I unplugged from shore power. turned the inverter on, and cranked the AC thermostat down to 80 degrees.  The heat index was about 90 at that time.  To my utter delight the AC cycled on just as it was supposed to.  I was so excited I called Steve to share the good news and we chatted for about thirty minutes while I performed some battery checks.  With solar on the draw was 0.7 Amps...not bad for the comfort of AC.  Steve suggested I turn solar off to see what the actual draw would be.  I was pleased to not that only 4.5 -5.5 amps were being used while the AC was on battery.

 

Now before you get all exercised about ruining my batteries remember that this is a short term thing.  One, maybe two hours while at a rest stop, or to leave our Penny Lane in a cool trailer while we have a meal in a restaurant.

 

The important thing is that it can be done.  Not cheaply at about $400 total...but well worth it for me.

[John E Davies]

Here is a great article on this subject.

 

http://www.technomadia.com/2015/02/the-almost-fantasy-of-solar-powered-rv-air-conditioning/

 

It would be great if Oliver would offer a cutting edge 48 volt dc split air conditioning system, mounted in the wall. But they can't, for a number of reasons. Getting rid of the horribly inefficient roof top location would make a tremendous difference in cooling. The roof is very hot to start with and all those black solar panels just make the heat worse. How could you expect a primitive, inefficient roof A/C to be happy in those oven-like conditions? What is the temperature near the panels on a blistering day? 140 degrees or more?

 

Making the operating voltage 48 volts drops the required amperage to 25% of a 12 volt unit. It can use wiring of very small gauge. That is the major reason bigger aircraft use 28 volt systems, to reduce wire size and weight. It's time rv cooling system design entered the 21st century. The cost would be very high....

 

http://kingtecsolar.com/a-split-ductless-ac-marvel-unveiled-to-the-world/

 

"Kingtec Solar’s unique PV-powered air conditioners are designed with simplicity and economy in mind, and are built to run using free and abundant solar renewable energy. We deliver 100% zero energy consumption for up to 7 1/2 hours on as little as 1000 watts of solar panels for a 16000 BTU AC. These air conditioners feature tri-energy inputs from any combination of solar, grid or batteries and can run in three modes: Energy Saving, Off Grid, or Hybrid."

 

http://kingtecsolar.com

 

Have you tried orienting your Ollie east-west and tilting the panels? What effect did it have on your experiment? Besides increasing their output, it gets their considerable heat away from the top of the roof and the air conditioner.

 

John Davies

 

Spokane WA

[rideandfly]

With breath held I unplugged from shore power. turned the inverter on, and cranked the AC thermostat down to 80 degrees. The heat index was about 90 at that time. To my utter delight the AC cycled on just as it was supposed to. I was so excited I called Steve to share the good news and we chatted for about thirty minutes while I performed some battery checks. With solar on the draw was 0.7 Amps…not bad for the comfort of AC. Steve suggested I turn solar off to see what the actual draw would be. I was pleased to not that only 4.5 -5.5 amps were being used while the AC was on battery. Now before you get all exercised about ruining my batteries remember that this is a short term thing. One, maybe two hours while at a rest stop, or to leave our Penny Lane in a cool trailer while we have a meal in a restaurant. The important thing is that it can be done. Not cheaply at about $400 total…but well worth it for me.

 

Wow, Nice job!

 

Our previous camper was all electric 12V/110V with Coleman 13.5K Polar Mach AC. Purchased a Yamaha EF2400iSHC and never needed to run it more than 30 minutes at a time when away from shore power. The Yamaha would start the 13.5K AC we had.

 

Never thought a 13.5K AC would run just off of RV batteries for short periods. Hats off to everyone involved in the project!!!!!

[trumpetguy]

Bill,

 

I am still pinching myself over the success of the East Start kit.  I ran the AC for three solid hours Saturday when we had a heat index of 95.  I just wanted to see how the batteries would hold up.  The Ollie was in full sun so solar was in full production.  My Blue Sky remote was reporting a net positive of 14 AMPs .  When I switched off the AC and inverter the battery voltage went right back up to normal.  I need to do a test with the solar panels off to see how that affects the batteries.

 

Living in Florida this mod opens up lot's of possibilities for us.  Beach outing with AC for snacks and resting, fishing trips, naps while enroute to a final destination, etc.  We can now stop for lunch at a restaurant and leave our Bichon in thr air conditioned trailer.

 

It will be interesting to see if other makes of AC will work as well as the Atwood Air Command.

[Cobra1169]

TrumpetGuy,

 

Were you able to have the trailer's A/C run off a single Honda EU2000i?  If so, was it able to handle the A/C load along with other appliances running in the trailer?  Did you use a 20 Watt connection to the generator?

 

Thanks --- Cobra1169

[trumpetguy]

Cobra,

 

 

 

I could run the AC with my Honda 2000i even before I installed the Easy Start.  That is a feature of the Atwood unit as opposed to Coleman and Dometic.  The Easy Start allows me to run the AC on batteries without a generator or shore power.

 

 

 

When I do use the generator I have a 20 AMP adapter that plugs in to the trailer shore power cable.

[Cobra1169]

Trumpetguy,

 

Thanks for the insight on the Atwood Air Command 13.5. Now I get how you were able to run it on a single Honda EU2000i. Are you happy with the unit and performance to date? I understand that the fan runs full time on the unit always when the unit is on, not sure it that is such a bad thing. I'd appreciate your feedback and recommendation over the Dometic Penguin II.

 

Thank you

[trumpetguy]

The fan does run all the time but I fixed this by installing a 12v 30A relay controller by  separate AC thermostats.  Google Gresy AC mod on the Casita forum.

 

I love my Atwood.  Can run on the house batteries .

[Geronimo John]

The above thread raises several "red flags" for me that as a Professional Engineer I am required to respond.  Although I believe that several of our OTT owners are quite qualified to mitigate my below concerns.  That said, I also believe that the majority of OTT owners, myself included, likely are not.  As such, I am taking the time to highlight to this second group some concerns with the modification made to the OTT electrical systems as discussed in the above threads.

 

Upon delivery, I asked OTT if I could run the A/C by battery power alone.  The OTT answer was NO.   If I am recalling correctly, the reason given was that the inverter and electrical systems were not designed to provide the continuous power necessary to run the A/C as well as other parasitic and elective loads of the trailer at the same time while on battery power alone.

 

In the case of our trailers, the A/C pulls  1731 watts (Oliver University documentation), add to that normal other loads of an occupied trailer, and the power inverter will be operating near or above its  continuous max load of 2,000 watts.  Should an owner then power up the microwave, water heater (on electric mode) or other electrical loads, several system components will certainly be operating in an overload condition.  Systems running at or above their designed continuous capacity are prone to fail young with the added concern of possible fire or other unforeseen electrical damages.

 

Yes I do believe it is possible to run our A/C off the trailer batteries alone.  But it certainly comes with risks that neither I or the average OTT owner should sign up for.  Granted if solar power is added to the equation, the power available (Battery Power + Solar Power) improves the ability to run the A/C and other loads without generator or shore power.  However you are still facing the brick wall of the capacity of the individual components to do so safely.  To do so safely and to meet UL  requirements, a full re-look, if not redesign of the OTT power systems would be required.

 

For those Owners that are compelled to modify their OTT to run the A/C from batteries (with or without solar), I humbly recommend five safety mitigation efforts:

 

A.  That you instrument your Xantrex Inverter, batteries, and cables to monitor and alarm for temperature and current overloads.

 

B.  As I suspect that your inverter life will be substantially reduced, you may want to consider having a spare inverter in your spare parts box.

 

C.  That you install master battery kill switch(s) accessible outside at the battery compartment to shut down the flow of power from your batteries and solar systems in the event of fire.  This would allow the fire department an ability to more safely fight an electrical fire in your trailer.

 

D.  That you and your family actually practice exiting out the emergency window.

 

E.  The modifications described in the above threads appear to be accomplished without UL approval or testing.  Nor does it appear that they have been designed and documented by a licensed Electrical Engineer.  As such, you may want to know if your insurance will cover the loss of your trailer should an electrical fire consume it.

 

I fully support an owner's right to execute modifications to his/her trailer.  Especially when done by competent individuals, as many of our OTT owners are.  That said, it is my opinion that this modification needs to be cautiously approached by the majority of us.  Thank you.