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Old 25-03-2017, 16:17   #1
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True 12 volt AC

Hi All,

I'm looking to install true 12 volt AC for the owners cabin on my boat. I have a 1000Ah house battery bank and 480 watts of solar. I would be willing to add a Wind gen if necessary and expand the batteries. Marvair makes a true 12 volt unit with a 12 volt compressor. Anyone have experience or thoughts? Thanks!
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Old 25-03-2017, 16:39   #2
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Re: True 12 volt AC

A little searching on the forum should bring up at least several threads on the subject.
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Old 25-03-2017, 16:53   #3
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Re: True 12 volt AC

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Originally Posted by russellg9385 View Post
............. Anyone have experience or thoughts?
My thoughts are, it takes the same amount of energy to cool a boat no matter where or how you get it and it's going to take a lot of battery power to run an air conditioner very long.

A native 12 volt system might be more efficient than a 120 volt system and inverter but that depends on if the 12 volt system is naturally efficient.

One of the biggest problems with air conditioning a boat is, they are typically not insulated. Whatever heat you remove returns very quickly.

Has the company been around a while? Are there any reviews on their website? Are any being installed in new production boats?

I can't tell you yes or no, just give you a few things to think about.
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Old 25-03-2017, 16:55   #4
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Re: True 12 volt AC

I think you will find that is a 12V DC in system. Marvair may have been taken over.
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Old 25-03-2017, 17:13   #5
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Re: True 12 volt AC

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I think you will find that is a 12V DC in system. Marvair may have been taken over.
I made the same mistake iwhen I looked at the thread Title, in this case AC stands for air con, not alternating current
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Old 25-03-2017, 17:18   #6
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Re: True 12 volt AC

The obvious total lack of understanding of a/c vs. AC and what can be accomplished with DC suggests the OP buy the 12volt Doctors Handbook and start from scratch.
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Old 25-03-2017, 17:20   #7
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Re: True 12 volt AC

The Marvair "nominal 5000BTUh" 12V aircon only gets about 3000 BTUh in practice according to their spec sheet and uses up to 30 Amps.

3000 BTUh may be OK for a small enclosed cabin, but that's about all.
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Old 26-03-2017, 03:12   #8
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Re: True 12 volt AC

Greetings and welcome aboard the CF, Russellg.
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Old 26-03-2017, 08:44   #9
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Re: True 12 volt AC

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The obvious total lack of understanding of a/c vs. AC and what can be accomplished with DC suggests the OP buy the 12volt Doctors Handbook and start from scratch.
Cranky, but fair! I had no idea other than "why the hell would you want 12 volts AC?"
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Old 26-03-2017, 08:57   #10
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Re: True 12 volt AC

I believe that in 'Cruising with the Wynnes' that they mention using soft starters and that they run their air con from their batteries. Might be worth checking out?
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Old 26-03-2017, 09:30   #11
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Re: True 12 volt AC

"Gone with the Wynns" and they have $14,000 worth of lithium batteries.
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Old 26-03-2017, 10:31   #12
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Re: True 12 volt AC

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Originally Posted by StuM View Post
The Marvair "nominal 5000BTUh" 12V aircon only gets about 3000 BTUh in practice according to their spec sheet and uses up to 30 Amps.

3000 BTUh may be OK for a small enclosed cabin, but that's about all.
I looked at their web site, and agree with the above, with the addition of the immediate thought, would I really want to sit in the only seat in the head compartment to get somewhat cool?
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Old 26-03-2017, 11:02   #13
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Re: True 12 volt AC

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I looked at their web site, and agree with the above, with the addition of the immediate thought, would I really want to sit in the only seat in the head compartment to get somewhat cool?
and you'd need one helluva charging system to put that back into your batteries.
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Old 26-03-2017, 11:27   #14
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Re: True 12 volt AC

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and you'd need one helluva charging system to put that back into your batteries.
Agreed
You would need imo at a minimum 1kw of solar and 600ah of battery bank just to support the unit for its nighttime running. Nevermind all of the other power loads on the vessel.
That or a mix of about three hours generator in the am and at least 400 watts solar to complete the charging during the day
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Old 26-03-2017, 17:17   #15
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Re: True 12 volt AC

A small window mount A/C unit pointed down a hatch and a portable generator does the job nicely.
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