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Old 06-11-2011, 10:16 AM   #1
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Battery Power Inverter with Roof Mount AC

I have 2 house batteries that are type 8D and provide 450 amp hours total (225 each) I also have another 8D that is for just starting the bus. I can switch all 3 to be connected if I want to as needed. My question is if I buy one of those 5,000 watt continuous 10,000 watt max power inverters, how many minutes or hours will it take before the 2 house batteries go dead by using a roof mount AC? It's a 15k BTU and uses around 14-15 amps and 1,500 watts with the fan and compressor going. I have custom made 8 gauge power cable that is 14 feet long. I have a voltage alarm set to go off at 11.8 volts as well, although the inverter will shut off on it's own if it gets that low.

The campground I am going to does not allow generators or car engines to run between midnight and 6 am. My plan is to turn the bus on at 11:30 pm (because the AC uses 2,200 watts to start up), fire up the AC till it gets cold inside and then kill the engine. A timer on the AC could then shut itself off around 4 am, providing enough cold until 6 am. Then I can turn on the bus or the generator outside with the battery trickle charger and go back to sleep. I put in a brand new 250 amp alternator and have 0 gauge wire between it and all of the batteries. I only need to do this routine for 4 days, as it's an extended weekend trip.

Should I get 2 more type 8D batteries for the house bank or will 2 batteries be enough for 4 hours of AC operation?
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Old 06-11-2011, 02:23 PM   #2
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Re: Battery Power Inverter with Roof Mount AC

I found this caculator: http://www.alternate-energy.net/calculateamp02.html

I was able to come up with 180 minutes or 3 hours with a battery bank worth 450 amp hours drawing 1,500 watts. By adding 2 more type 8D batteries, I should be able to get 900 amp hours and 6 hours or 360 minutes.

Maybe when the sun goes down I can open a few windows and run a few low wattage fans instead.
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Old 06-12-2011, 02:53 PM   #3
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Re: Battery Power Inverter with Roof Mount AC

The beauty of Google and the Internet is amazing!

http://www.dcacpower.com/faq.html#modified
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Old 06-14-2011, 06:23 PM   #4
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Re: Battery Power Inverter with Roof Mount AC

I ended up getting a 6,000 watt inverter made by Royal Power that provides 50 amps. It peaks at 12,000. I plan on using this for the 4 blacklights, refridgerator and TV when I am not using the Onan Emerald 1 Genset (4k watt 33 amps)

I apologize for pretty much answering my own questions here, but I think the information may be helpful for Ascend and other members!
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Old 04-05-2012, 12:41 AM   #5
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Re: Battery Power Inverter with Roof Mount AC

Somehow I don't think that is going to work as you have stated. Here is a link to someone that has done this using a 6k btu window a/c, notice that they have a much larger battery bank. Go down to post 17

http://www.rvnetwork.com/index.php?showtopic=89668
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Old 04-05-2012, 11:45 AM   #6
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Re: Battery Power Inverter with Roof Mount AC

Quote:
Originally Posted by kotflb
Somehow I don't think that is going to work as you have stated. Here is a link to someone that has done this using a 6k btu window a/c, notice that they have a much larger battery bank. Go down to post 17

http://www.rvnetwork.com/index.php?showtopic=89668
Damn that guy has a small power generating plant sitting on his tractor. Pretty cool that he was able to score so many batteries for cheap.
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Old 04-05-2012, 05:52 PM   #7
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Re: Battery Power Inverter with Roof Mount AC

i also have one of those roof top units.. but i also have a 9 amp 1000 watt one...you could get one of those and it would run far longer than the 15 amp ones...
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Old 04-05-2012, 11:33 PM   #8
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Re: Battery Power Inverter with Roof Mount AC

1500watts/12volts=125amp-hours/.9(inverter effeciency)=138amp-hours. That would be about 3 hours to 100% state of discharge. So in the real world you could maybe get an hour and a half of running a 1500watt load from 2 8d's. But I forgot about the Perket effect. Ballpark, one hour, maybe. YMMV.

Running big loads from an inverter gets fun real fast. The voltage drops through the 12 volt wiring gets quite large. Big cables, good connections, and a big battery bank (and big charger.)
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Old 11-26-2013, 12:24 AM   #9
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Re: Battery Power Inverter with Roof Mount AC

Remember that amps AC and amps DC are different,
One amp AC equals ten amps DC.
I hope you have your inverter placed withing just a few feet of your batteries, I also hope you have 2/0 or better gauge wire connecting the batteries to the inverter since you will be pulling.

I have a 6000btu unit that is rated at 4.5 amps AC, it normally only pulls 3.2 amps AC when running, I use a killawatt meter to test its actual wattage/amperage usage.
The 3.2 amps AC that it pulls is actually 32 amps DC coming out of the battery, not including the ~2% cable loss, and the ~8% inverter loss.

I certainly dont know your setup but you might want to consider getting a smaller air conditioner and using a thick curtain to keep the air around your bed at night.
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