A/C without a Genny

Discussion in 'OnBoard Electronics & Controls' started by Swamplizard, Sep 7, 2016.

  1. Swamplizard
    Joined: Jan 2004
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    Swamplizard Senior Member

    I have an older cruiser with A/C, electric stove top, 12-volt water pump for water pressure etc. Westerbeke died and will probably purchase a smaller diesel unit this winter for the rare occasion that we sleep on the hook.

    Has anyone done the math to see if the following would work when under way?:

    Add secondary alternators to your twin Big Block Chevy gassers
    Have them charging a bank of golf cart house batteries
    Inverter to run A/C while under way.

    when on the hook - use small genny
    when at the dock - connect dock power

  2. Stumble
    Joined: Oct 2008
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    Stumble Senior Member

    It's possible to run the AC from a big alternator, I know a guy running his off of an Atomic4. But wasn't an easy installation. I think it took the better part of a year to build a bracket strong enough to keep the belts from ripping it free.
  3. philSweet
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    philSweet Senior Member

    How big was the genny?
  4. WestVanHan
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    WestVanHan Not a Senior Member

    How many BTU is the aircon?
  5. Swamplizard
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    Swamplizard Senior Member

    6kw genny but designed to run everything including fridge microwave a/c stove top coffee pot water heater etc. not sure on a/c size
  6. philSweet
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    Location: Beaufort, SC and H'ville, NC

    philSweet Senior Member

    So if I understand you, you want to replace a 6kw Westerbeke with something like the following.

    1. A small gas inverter-style generator such as a 3000i. Plus a custom cord to feed into 30 or 50 amp shore power input.

    2. An additional bank of 6 gc-1s

    3. A grid-tie type inverter of about 4000 watts

    4. A marine smart charger of at least 12V x 60 amps

    5. An additional 2 x 125 amp marine alternators

    6. External marine adjustable regulator(s) for each engine

    7. Regulator balancer, such as Balmar Centerfielder II (only works with their stuff)

    8. Plus all the wire, fuses and switches to control this stuff.

    Here's a link to the Balmar centerfielder manual. There is a nice schematic near the end. Not associated in any way with Balmar, I just like the schematic.

    Last edited: Sep 8, 2016
  7. missinginaction
    Joined: Aug 2007
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    missinginaction Senior Member

    Depending on your AC requirements this is certainly doable.

    You can find posts on my electrical system by doing a search but I'll describe it for you. I have a small Silverton Dual Station cruiser that I restored and updated over a number of years. The electrical system is my pride and joy. It's a single Ford gas v-8 with a Yamaha 9.9 high thrust kicker for low speed operation. I run a 5000 BTU window AC unit (no it's not a marine unit, but for an 80 square foot cabin it works very well). This 12.2 SEER unit from Frigidaire consumes a mere 250 watts after start up and runs easily on a Xantrax 1800 watt inverter. I use a small microwave (600 watt), propane for cooking as well, a Whytner 65 quart refrigerator freezer and like you have the usual draws such as ventilation fans, fresh water pumps, radios, stereo, and next year an auto pilot.

    I do need to add that I built my electrical system from scratch. Every accessory installed was looked at in terms of it's energy consumption. All my lights are LED and every appliance, right down to the coffee maker is as efficient as I could find.

    I use a Xantrax True Charge 40 when on shore power and an ACR from Blue Sea Systems to automate battery charging and discharging.

    I'd consider removing the electric stove in favor of propane or butane. Making heat is the #1 consumer of electricity. Be respectful of gas appliances and pay attention to what you are doing and they are quite safe (IMO anyway).

    I installed a 105 amp, low rpm - high output alternator from ARCO Marine. This alternator will charge my batteries all day long at 13.9 Volts with the AC/refrigerator/radios running. Turn the AC off and I'll get14.3 volts. This is at 1500 to 1800 rpm. I may eventually add a 3 stage regulator but for now have had no problems with the stock charging routine.
    I run AGM's for my battery banks and use 2, 105 Amp hour rated 12 volt batteries (20 hour rate) for the house bank and can run my AC all night on the hook, set at 70 degrees. After the ambient air temperature cools down in the evening the AC cycles and does not run continuously. The engine alternator brings the batteries back to full charge from about 50% discharged in a couple of hours.

    Running twins you have more charging capacity, should you choose to spend the money on high output alternators. Install a quality smart charger and some quality batteries of your choice and I see no reason why you couldn't do fine without a generator. You just need to plan your installation and be mindful of your power consumption. And of course get rid of that electric stove.
  8. Swamplizard
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    Swamplizard Senior Member

    Thanks folks great info
  9. mydauphin
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    mydauphin Senior Member

    I noticed on my boat the bilge is a bit cooler than the ceiling/deck in the summer. Was thinking I cool run some pex from the bilge to the ceiling and move some of the heat down, and the cool up. Might be worth 4 or 5 degrees reduction. Just a thought. But I would never pump in outside water. It is mostly contaminated, or full of sea creatures, and thing to sink the boat if it breaks.

  10. PAR
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    PAR Yacht Designer/Builder

    Pumping sea water is pretty routine and very safe. Your engine does it, most production A/C units do it and home made "swamp coolers" do it too, with little harm. Rigging a pipe, set deep, into much colder water is very effective and electrical requirements are very low. The water is pumped through baseboard style of heat exchangers, with small fans blowing over them. A few degrees water temperature difference isn't worth the bother, but once you're over 10 - 12 degrees, then effectiveness jumps up quickly. While in the Caribbean, I pumped 70 degree water up to cool my boat, while surface water temperatures were in the low 90's. Place a "J tube" on the end of the pickup line, so you don't suck up silt and critters.
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