Home » Public Forums » GMCnet » Feasibility of Running 2 ACs on 4kw Onan
| Feasibility of Running 2 ACs on 4kw Onan [message #298029] |
Fri, 25 March 2016 12:08  |
TR 1
Messages: 348
Registered: August 2015
Location: DFW
Karma: -7
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Senior Member |
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The previous owner of my coach lived in a much cooler climate than I do here in Texas, and I've been chasing down some heat related issues to get my coach ready for use this summer. High on the list is adding a second AC, to keep up with the 100+ degree days that are common here in DFW. If possible, I'd like to do this without upgrading the existing Onan 4kw unit. Looking at some of the newer ACs out there, it appears that I ~may~ be able to get away with replacing the one, original (13.5K btu, I believe) AC unit with 2, 13.5K Atwood Air Commanders. Per this brochure, it states the Atwood 13.5K unit can be run on one, 2000 watt generator:
http://www.askforatwood.com/images/air-conditioners-brochure.pdf
Other than what appears to be a heat-soak/vapor-lock issue with my current Onan in Temps over 95 degrees, (Also on my list to resolve before summer) it runs great. Per the previous owner and the genset's Hobbs meter, it appears to be a lower time unit. We don't do much dry camping, so the genny will only really be used while driving to keep the cabin cool, and the occasional night stopped somewhere while on route to a campsite, which would probably have the ACs set on low for the night anyway. Only other load I would be concerned about would be to run the fridge, which seems to pull around 100 watts. (Though it is about 3-4 times this at startup).
Per the Atwood Brochure, I'm looking at:
1270 Running Watts per AC (X2)
and say another 250 for the fridge and any other ancillaries...
That comes to 2800-3000 watts running, give or take, worst case. The Atwoods are supposed to be easier to start than some other ACs, but am unsure of how much overhead I would need to cover this. I would do my best to stagger starting both units, and try to manage them to prevent both compressors from cycling on at the same time...
Eventually, I do plan to upgrade the generator, but if I can get away with the 4K Onan for now, that's more gas money available to go places. FWIW, our fridge is a 110 volt Avanti home unit... Our rig does have a 2500 watt inverter, and 4, 6 volt Trojan 125s... So I think it would be possible to set up the fridge to only run off the inverter, when using both ACs on the genny if need be, and rely on the alternator to keep the fridge running and batteries up while traveling.
Thoughts?
Mark S. '73 Painted Desert,
Manny 1 Ton Front End,
Howell Injection,
Leigh Harrison 4bag and Rear Brakes,
Fort Worth, TX
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| Re: Feasibility of Running 2 ACs on 4kw Onan [message #298031 is a reply to message #298029] |
Fri, 25 March 2016 13:26  |
Hal StClair
Messages: 971
Registered: March 2013
Location: Rio Rancho NM
Karma: -12
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Senior Member |
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There are load management devices that will keep both compressor's from starting at the same time. The starting loads are probably what will get you in trouble. As the temps rise your Gen Set will loose capacity as will elevation increases(about 3% loss per 1000' ). Depending on the condition of your 4000, you may be trouble when you need it the most.
JMHO, Hal
"I enjoy talking to you. Your mind appeals to me. It resembles my own mind, except you happen to be insane."
1977 Royale 101348,
1977 Royale 101586, Diesel powered,
1974 Eagle Bus 45',w/slideout,
Rio Rancho, NM
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| Re: Feasibility of Running 2 ACs on 4kw Onan [message #298032 is a reply to message #298029] |
Fri, 25 March 2016 13:45 |
lqqkatjon
Messages: 2324
Registered: October 2010
Location: St. Cloud, MN
Karma: 5
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Senior Member |
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Billy Massey may also comment. He lives in Texas. He has a atwood 15.5. Buy the 15.5 unit for the front. Then see if you even need to worry about a second A/C in the rear, and if you do, then put a 13.5 unit in the rear. The additional 250 watts, you will still have plenty of power to run the A/C's and your fridge.
I do not live in Texas. I am in MN, but it does get hot occasionally here. I installed a 15.5 atwood, and I have not yet needed to fire up my rear A/C. Plenty of cooling power coming from the Atwood 15.5, and I do not have good window tint, or insulation. I believe with the one 15.5 atwood, some window tint, or good curtains, you would be able to keep the coach cool with 1 A/C unit in any environment, but that is just my gut feeling, I have not lived in texas, just what I see in 90+day in MN, it cools well.
You also do not have to run the 15.5 full blast. So at a lower setting it will run with less power then a 13.5 at full power?
As for Generator, even though it "will run", you may not "want to run" a set load. I would stick with not going above 75% capacity of the rated generator load. My 15.5 will start and run off a honda 2000, but that generator is wound up, and goes through the gas fast, and with the smaller gas tank, runs itself out of fuel in just a few hours. Running that same A/C a 3000watt honda the A/C does not effect the idle or running of the generator at all, so fuel consumption of that generator is way less then the smaller genset running at max load. the 3000watt is actually quieter then the 2000 watt as well. But the 3000 watt honda is super spendy, and it is bigger and too heavy.
my personal preference these days, is to install get a yamaha 2400ihic. I think that generator will run my 15.5 unit really well, be plenty quiet and not use much fuel. I also think it will fit where the onan is with little modification, and I can set it up to be able to move it away from the coach when parked. But that is just my thoughts, as I have not yet gone that direction. (2017 plan)
https://www.yamahamotorsports.com/generator/models/inverter-ef2400ishc
Jon Roche
75 palm beach
EBL EFI, manny headers, Micro Level, rebuilt most of coach now.
St. Cloud, MN
http://lqqkatjon.blogspot.com/
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| Re: Feasibility of Running 2 ACs on 4kw Onan [message #298060 is a reply to message #298029] |
Fri, 25 March 2016 19:16 |
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Matt Colie
Messages: 8547
Registered: March 2007
Location: S.E. Michigan
Karma: 7
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Senior Member |
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Mark,
As some have eluded, your whole problem will be the starting load(s). I know my BF Onan could pull two of the Mark IVs like I took off. It would grunt when the pump started, but it didn't mind the load. We even did it wrong one time (very early in our experience) and had the water heater cooking (I didn't know it was heating) and I lit the A/C and didn't look down to see Mary punch up the microwave. Old Onan kept running, but the load was a note worthy surprise.
Personally, I think if you have two modern 13.5s and don't start them both at once, the Onan will shrug it off. But it will use fuel doing it.
Matt
Matt & Mary Colie - Chaumière -'73 Glacier 23 - Members GMCMI, GMCGL, GMCES
Electronically Controlled Quiet Engine Cooling Fan with OE Rear Drum Brakes with Applied Control Arms
SE Michigan - Near DTW - Twixt A2 and Detroit
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