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Old 07-14-2014, 10:13 PM   #1
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Running Air Conditioner on Inverter?

I searched around and there are a lot of older posts that pretty much state one cannot do this. What got me thinking of this was watching this video of a Foretravel (I know, just daydreaming…) 2015 Foretravel ih-45 Luxury RV Review at Motor Home Specialist - YouTube from Motor Home Specialists. In the video they claimed that with their two 2800 watt inverters they can pretty much run everything in the coach, including air conditioners.

My questions are:

How is it that two 2800 watt inverters can handle 3 A/C units? I would think some EMS is at play here but can one 2800 watt inverter handle a single A/C unit?

Is the battery bank needed for this critical? Or could someone with say 4 batteries accomplish the same thing but for a shorter period of time? What if solar was used to keep the smaller battery bank charged? Is that feasible?
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Old 07-14-2014, 10:29 PM   #2
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2800 watts would be 23.3 amps so could easily handle one AC but not two.
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Old 07-14-2014, 10:36 PM   #3
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It may run one AC unit, but the coach batteries will be drained in just a few minutes, so what good is it to have that much power and not have the battery capacity to handle it? This is a sales pitch that once again looks great on the surface but holds no value in the real world. And no solar system that I know of puts out that kind of amperage to handle such a drain on the batteries.
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Old 07-14-2014, 10:45 PM   #4
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As a reference, I have a storm shelter with a 10,000BTU AC & 520watts of solar on the roof. AC is set at 85. Solar system can't keep up with the power draw. And the panels are adjustable for proper angle for time of the year. Three 125AH 12V batteries.
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Old 07-15-2014, 10:46 PM   #5
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Quote:
Originally Posted by bokobird View Post
... In the video they claimed that with their two 2800 watt inverters they can pretty much run everything in the coach, including air conditioners....

Nowhere in this video did they state they could run the AC on the inverters. For all practical purposes, that is impossible. The current draw of only ONE AC unit is far beyond what batteries and solar can sustain. This coach has FOUR AC units! There is no way...

The second inverter is installed because of the residential refrigerator.


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Old 07-15-2014, 11:31 PM   #6
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Quote:
Originally Posted by Rich-n-Linda View Post
Nowhere in this video did they state they could run the AC on the inverters.
You are correct and I apologize for selecting the wrong video from my history when I first posted it. I thought for sure it was the higher-end Foretravel that mentioned this, but it wasn't. It was the King Aire video below, if you fast-forward to 6:30 timeline, you'll see where he states one of the 2800 watt inverters will power the front A/C unit.

2014 Newmar King Aire 4593 Custom Class A Luxury Diesel Motorhome

Now I know an all electric King Aire can be equipped with 16 batteries but my real question is it more than just the inverter that is needed? I realize a small battery bank might only last 5 minutes if that, but, if the battery bank was able to be charged at the same time, would that allow non-generator A/C to be used? The claim is the King Aire will handle it (he even made the claim you could run everything in that coach w/o a problem off the inverters).
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Old 07-16-2014, 03:52 PM   #7
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I have seen it done. HOwever

If running on battery power takes a LOT of batteries,, A single pair of GC-2 Golf car batteries has just over a kilowatt-hour worth of usable power, this is at the 20 hour rate, An air conditioner can eat that in like 45 minutes. So at that rate, perhaps 15-20 minutes tops.. Of course 2 pair the batteies last longer, and the more batteries the longer STILL 20 pair you'd likely make it 19 hours)

Second, if you are doign that while traveling, You need an alternator capable of putting out that much power.. You wil be sucking over 100 amps off the alternator per A/C (135 on my rooftop units).
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Old 07-16-2014, 04:07 PM   #8
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We looked at a Millennium Coach last year, on the drive engine was three 200amp alternators. I lost count of the battery's in the air conditioned almost walk in battery compartment.
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Old 07-16-2014, 11:35 PM   #9
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OK, those answers are giving me what I was interested in - it's a system level design requirement to handle something like that. It's not something easily added to a system not designed for that level of capacity.
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Old 07-17-2014, 12:21 AM   #10
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Roadtrek makes a "green" class B van. A friend has one. It has only one AC unit but a 5000 watt inverter, 8 batteries and I believe a 300 amp alternator added to the main diesel engine (a Sprinter van). It is supposed to run for at least 8 hours.

Those are just reference points for you so yes it can be done...and is being done...but all of the previous comments about sizing the components are right. Yes, correct, it's a total system design.
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Old 07-17-2014, 12:52 PM   #11
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The only practical way to to this is while running with the addition of second alternator or "motor generator" as some call it.

Stationary Inverting off batteries is simply not practical.

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Old 07-17-2014, 01:09 PM   #12
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Country Coach had an option for a second 3000 watt inverter. Now here's the rest of the story: it came with an additional high power alternator. It allowed you to run ONE roof air whilst going down the road without having to run the generator. Though I am unfamiliar with the details of the coaches cited in posts above, I would not be surprised if the set up is similar.
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Old 07-17-2014, 04:49 PM   #13
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Quote:
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The only practical way to to this is while running with the addition of second alternator or "motor generator" as some call it.

Stationary Inverting off batteries is simply not practical.

UD
I'm sure you didn't mean running off batteries with an inverter isn't practical (since that's what all RV inverters are intended for at some point) but mean it's not practical to run an AC off batteries that way. That's usually true with most RV's but actually not true either if its designed to work that way, which the Roadtrek was. It runs around 8 hours using the AC thru the inverter without the engine running. The main engine in this case is actually the only generator and uses the heavy duty ADDED alternator to do that. Roadtrek actually specifies that you run the main engine to charge the batteries. It's an interesting design and you can look it up on their website.

I would agree, as I said, that almost always there's too much current drawn from batteries to run an inverter with a heavy load like an AC. As an example a 13.5k BTU AC would pull around 15 amps at 120 volts AC. That's 1800 watts. If you have to pull that from a 12 volt battery then 1800 watts is 150 amps. That's a lot of current.
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Old 08-02-2014, 06:46 PM   #14
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Quote:
Originally Posted by jwmaustin View Post
I'm sure you didn't mean running off batteries with an inverter isn't practical (since that's what all RV inverters are intended for at some point) but mean it's not practical to run an AC off batteries that way. That's usually true with most RV's but actually not true either if its designed to work that way, which the Roadtrek was. It runs around 8 hours using the AC thru the inverter without the engine running. The main engine in this case is actually the only generator and uses the heavy duty ADDED alternator to do that. Roadtrek actually specifies that you run the main engine to charge the batteries. It's an interesting design and you can look it up on their website.

I would agree, as I said, that almost always there's too much current drawn from batteries to run an inverter with a heavy load like an AC. As an example a 13.5k BTU AC would pull around 15 amps at 120 volts AC. That's 1800 watts. If you have to pull that from a 12 volt battery then 1800 watts is 150 amps. That's a lot of current.
They are now making high-efficiency DC powered solar ACs that produce around 12,000 BTUs, but only draw 500 watts or less when running. They have a variable speed compressor, so rather than simply cycle on and off, they ramp up or down providing not just variable fan speed but variable coolant flow as needed, saving even more power. You still need a lot of battery power to run them for any length of time though. Here's a link: Solar & DC Air Conditioners | 48v DC Solar & Telecom Air Conditioner Heat Pump | Off-Grid Air Conditioning

Here are 3 systems starting around $4k for 5-10hr/day cooling using 4 batteries, going up to around $7k for 24 hour/day solar powered AC system using 16, 6v deep cycle golf cart batteries.

Solar DC Air Conditioning Systems

They also weigh a lot (as lead acid batteries are heavy) with complete 8 battery systems (10-15 hours of AC) averaging around 1,000 lbs. complete with solar panels, batteries, 12,000 BTU 48v mini-split AC, controller, etc. I'm actually thinking about a mid-grade system myself. Of course you could shave about 300lbs off that weight if super expensive, high-tech lithium batteries are used - if money is no object.

Chip
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