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  1. #1
    Join Date
    Sep 2009
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    Posts
    105

    Default 12 volt ac units

    has anyone installed one of these 12 volt systems?i see theirs a lot on line.some use and inverter some you need extra batts but theirs one that uses three compressors they shut down one at a time than matains temp with one just wonder if anybodys seen or used them thanks

  2. #2
    Join Date
    Mar 2009
    Location
    Portland, Oregon,
    Posts
    6,583

    Default Re: 12 volt ac units

    The efficiency difference between a 12 vdc motor and a 120 vac motor is great.
    I'd be quite surprised if they worked well, and/or with any efficiency.
    Most people that I am in touch with use either an O/B Marine generator, or one of the Honda EU series generators to power AC units.
    Rick ... aka Ricardo
    Portland, Oregon
    28' SDN F/B w/ twin Volvo Penta 5.7L DP's

  3. #3
    Join Date
    Jun 2008
    Location
    Island Heights, NJ,
    Posts
    1,431

    Default Re: 12 volt ac units

    Not so much an efficiency issue... A typical 5000 BTU 120 VAC window unit requires between 5 and 8+ AMPS. Watts is watts, so.... if a 120 VAC unit needs 600 to 1000 watts to run ( watts = Volts x Amps) that is 120 X 5 = 600 watts to 120 X 8 = 960 watts. IF you assume that the 120 VAC motors and 12 VDC motors are the same efficiency (they aren't). Then the 12 VDC battery will need to furnish 600 to 1000 watts of power which at 12 VDC (approx... ignoring some esoteric EE considerations) is 50 to 80 Amps. To run the AC for 10 hours you will need 500 to 800 AMP hours of usable battery capacity. Now... here is the good part... recharging the battery. At 100% charge (recharge) efficiency, you will need to recharge the battery at 50 to 80 amps for 10 hours to recharge the battery. Recharge efficiency is rarely above 80%, which means 12 hours of recharge for 10 hours of drain.... AND recharging at that rate will surely trash most batteries... then again... if you had a source of 12 VDC to recharge the batteries at that rate why would you need the batteries in the first place?. Last time I was on a A/C'd boat away from a 120 VAC dockside outlet (in the backwater Bahamas) , we ran the 7KW diesel powered genset all night. I'm not a big fan of portable gas powered gensets on boats due to the difficulty in managing safe refueling as well as protection from carbon monoxide poisoning from a "free flow" exhaust.
    Capt Bob
    1969 23ft ChrisCraft Lancer
    Merc 5.7L 260HP/ Volvo 280
    1972 22ft Bristol
    Honda 7.5HP 4 stroke Long shaft

  4. #4
    Join Date
    Mar 2009
    Location
    Portland, Oregon,
    Posts
    6,583

    Default Re: 12 volt ac units

    Take the two-way marine refrigerators, for example.
    The compressor motor is actaully AC and are either 24 vac, 28 vac or sometimes 32 vac.
    When on 12 vdc, an inverter provides the ac voltage..... and when on S/P, a step-down transformer provides the ac voltage.
    The vac motor is apparently used due to greater efficiency, and definitely for a more stable rpm.
    Perhaps this little air conditioner unit does similar. I don't know!

    I agree on the risks of using of the Honda EU units, but will tell you that many people are using them, and doing so safely.
    It's like many things.... ya gots to be smart about it!

    .
    Rick ... aka Ricardo
    Portland, Oregon
    28' SDN F/B w/ twin Volvo Penta 5.7L DP's

  5. #5
    Join Date
    Jun 2008
    Location
    Island Heights, NJ,
    Posts
    1,431

    Default Re: 12 volt ac units

    re: "I agree on the risks of using of the Honda EU units, but will tell you that many people are using them, and doing so safely.
    It's like many things.... ya gots to be smart about it! "

    100% correct but.....Sigh... I've learned over the years to NEVER underestimate the ability of folks to get things totally wrong.
    Capt Bob
    1969 23ft ChrisCraft Lancer
    Merc 5.7L 260HP/ Volvo 280
    1972 22ft Bristol
    Honda 7.5HP 4 stroke Long shaft

  6. #6
    Join Date
    Mar 2009
    Location
    Portland, Oregon,
    Posts
    6,583

    Default Re: 12 volt ac units

    Quote Originally Posted by sandkicker View Post
    ................. I've learned over the years to NEVER underestimate the ability of folks to get things totally wrong.
    Yep! So true! From incorrect wiring to improper fuel lines and connections..... you can dang near name it!

    I participate in another boating forum whereby a few members (over the years) have decided to store their portable generators in gasoline engine bays.
    I recall reading where one guy stored a small chain saw in the engine bay.
    When the risks were brought to their attention, some even argued the point.

    .
    Rick ... aka Ricardo
    Portland, Oregon
    28' SDN F/B w/ twin Volvo Penta 5.7L DP's

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