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Thread: Using AC appliances in boats

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    Default Using AC appliances in boats

    I have a 26 ft boat and have re-worked everything in the cabin. I was looking at adding a little dorm size refrig. To by one for 12VDC cost $600 plus. I read in the West Marine catalog in their advice section you could use a 400 wat DC - AC inverter to run small dorm sized refrigerators. Anyone have any idea if they would draw on the batteries really hard overnight? I'm looking to hardwire the inverter into a fused switch on the dash. Can turn on the fridge/inverter only while the main motor is running or underway to cool things down IF this combo draws too much juice while anchored? Anyone try the AC appliance on an inverter route? Does it work?

  2. #2

    Question

    I have considered a fridge install also, battery draw is my concern. I have a solar charger on my windshield, (tested it the other day), it wouldn't charge a fruitfly, but it keeps up with the bilge pump draw on a sunny day. I have those inverter plug-ins that run a laptop computer and DVD player. My thought is get another battery for it alone, I wouldn't trust it. If it runs less when full of food or runs more when empty, you never know.??? What do the electronically enclined guys think?

  3. #3

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    This doesn't solve your problem but might be food for thought. I bought and keep on the boat a honda eu 2000i generator. Very quiet running machines. The generator has a built in charger that can be hooked up to the batteries to charge if they go dead or also used to power the boat home if my alternators die on the water. The 1000w is smaller but I wanted one for more then just boating. For the same weight as another battery I have a second source of power. Depending on what the fridge draws you might use the generator an hour or two a day to give the battery a charge to keep it going. Also use it to power a microwave to warm up a lunch or dinner.

  4. #4

    Default Tealer, another thing to think of...

    Most refrigerators are designed to operate in a fully upright position; not too sure what the rocking/rolling motion of the boat might do (if anything) to the compressor or if it might "starve" the compressor motor of freon/coolant in rough water??? Most likely a minor issue but something to consider.
    Jim

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    Member Dupont Spinner's Avatar
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    Default

    Quote Originally Posted by Tealer View Post
    I have a 26 ft boat and have re-worked everything in the cabin. I was looking at adding a little dorm size refrig. To by one for 12VDC cost $600 plus. I read in the West Marine catalog in their advice section you could use a 400 wat DC - AC inverter to run small dorm sized refrigerators. Anyone have any idea if they would draw on the batteries really hard overnight? I'm looking to hardwire the inverter into a fused switch on the dash. Can turn on the fridge/inverter only while the main motor is running or underway to cool things down IF this combo draws too much juice while anchored? Anyone try the AC appliance on an inverter route? Does it work?

    You really should run off a second battery for house draws. Most inverters today have an auto shut down for low voltage. So you should be safe there. Also make sure you get one marine approved, they will last longer in the humid enviroments where they are used.

    As far as the dorm sized fridge you are about running close to the upper limit of a 400 watt verter. So consider moving up to at least double and better yet triple the 400. Also the fridge works the harderst getting cold. So use regular household current to cool it down and then switch to inverter use once away from home. Another trick is to turn it to real cold when under power and either turn it off or not as cold when it will see little use(like at night).

    When wiring the inverter run the shortest possible wires you can. Same on the diameter side to....larger is better. I normally use #2 cables for no more then a 6 foot run to power a 1000 watt inverter.

    Here is a link to compare shop some different size inverters.

    http://www.donrowe.com/inverters/inverters.html

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    Default inverter

    I had a 1750 watt inverter I got from my dad, so why not install it in the boat? I like toast with my eggs, and run a blender for fu-fu drinks on them hot days. Works great, and I don't see a reason not to use it for a little fridge. I think I would shut the fridge off at night though, or you will wake up to the inverter's audible alarm at about 4 am. But that's trial and error. Make sure you have a way to charge your batteries if you kill them dead. I have a manual start kicker that will charge mine if I kill them both, but I almost always leave the switch on one battery, saving the other for backup.
    Big wire, short run, on the DC side.

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    Default Fused Switch

    I strongly recommend a DC breaker. If it blows you can reset it. Who wants to hunt for a fuse when it blows only to find one all corroded. When you put the fuse or breaker in put it as close to the battery as you can this will protect the wire if it rubs and shorts out on the run to your inverter. I ended up buying a Waeco fridge for my boat, there was mention of a regular fridge not working at certain angles. I have also heard that the compressors are supported better in the marine fridges and therefore last longer. I agree with you it seems like alot of dough for a little fridge. I want to do the same thing with a small apartment size freezer.

    Chuck

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    Default

    I did the math on how much current a 1000 watt converter would need if you were running a 1000 watt appliance. I = P/E your looking at 80 amp. @ 100% eff. Add another 20 amp or a total of 100 amp/ hr.

    To answer your question, yes you could use a converter to run a small refrigerator, @ 40/50 amp. or use a marine refrigerator @ 3 amps.

    Unless you do things correctly you will have a dead battery @ 3 amps.

    Good luck.

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    A dorm fridge generally runs about 350 or more watts at about 2.5 to 3 amps on 120 volts. The 350 watts is the reason I said that you are better to use at least double your wattage type inverter. You will kill the smaller one in short order. I always try to stay under 80% of the rated capacity, closer to 50% is even better.

    Here is a good explanation of amp hour draw from answers.com

    "A battery’s amp-hour rating indicates the total amount of energy it will deliver at a constant rate of discharge over a period of 20 hours before it reaches a voltage at which it is stone dead for all practical purposes.A 12-volt battery, the most common nominal voltage, is fully discharged at 10 volts. A 100-amp-hour, 12-volt battery will run a 5-amp motor (or a 60 watt light) for 20 hours, and a 200-amp-hour battery will run a constant 10-amp (120 watt) load for 20 hours.That’s the theory. In fact, if a 100-amp-hour battery is discharged at a rate greater than 5 amps, it will not deliver all the advertised amp-hours before it goes dead. On the other hand, if you discharge it at a steady rate of less than 5 amps, you’ll get more amp-hours than the manufacturer’s rating shows—not a whole lot more, but some.That principle applies to most lead-acid batteries found on boats—the faster the discharge rate, the fewer amp-hours delivered. The more slowly energy is taken from a battery, the longer it will last.Sometimes a battery’s work capacity is given in reserve minutes. In the absence of any other definition, this is the number of minutes you can discharge a fully charged battery at a whopping 25 amps before its voltage drops to 10.5."

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    Default

    I do not disagree with your information. A 350 w frig will draw 3 amp @ 115v. If you use a 12v converter @ 80% eff. it would take 445 w to produce 350w.

    445 w @ 12v = 37 amp.

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    Default Can of Worms

    It looks like I opened a can of worms. I ended up with a 1000 watt inverter. It looks like I will use this system while underway and shut down overnight. I've wired it through a switched circuit so I can shut the inverter and frig off at will.
    I set up my boat with two solar panels (12"x24" ea) mounted flat on top of the cabin. The controller is inside. Right below it is a battery isolater switch using heavyguage wire. I run juice to whichever battery is not in active use. System has worked well. I have one battery for house use and one for starting. By managing my solar recharging I can keep both in top shape. If I use the inverter and refrig at a reasonable rate hopefully the battery will last and I won't drain it too quick. I usually only leave my anchoring lights and Chartplotter with the drift alarm on. If the fridge is cold when I get to sleep it should still be decent when I get up in the morning. After the main engine is fired up I can switch everything on and re-charge etc.
    Thanks for all the help.

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    Default Mini-fridge

    Tealer, let us know how this works next year. I've been thinking of tossing out the cheesy ice box in my boat cabin and installing a fridge. I already have plenty of inverter power available. I might need to upgrade my batteries, because I'm sure I'll forget to shut it off on occasion.
    Kingfisher 2525. 225, 20, and 2hp Hondas.

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    Default

    Tealer, as long as you have a low voltage disconnect (which your inverter probably already has) and a automatic battery isolater you should have a bullet proof system.

    I've tinkered around with off-grid power using a generator as my main power source and a 50 watt solar panel to keep the batteries topped up. What your doing is just the same, except its mounted on a boat.

    A couple of things to keep in mind about lead-acid batteries: Flooded lead-acid batteries self-discharge about 4-8% a WEEK or worse as the battery gets older (up to 15% a week), sealed AGM batteries self-discharge about 1-3% a MONTH, dont sulfate up nearly as bad, and they last almost forever if you take care of them.

    Also, routinely draining a battery past 50% discharge, especially one not rated as a "deep cycle" battery is the quickest way to destroy a battery there is - short of taking a hammer to it. Automotive batteries are only designed to be discharged up to 10% depth-of-discharge.

    So you'll need to work out your amp-hour requirement for the fridge for the longest time you'll need it running without external power, then double it to arrive at what you'll need as your battery bank amp-hour size.
    Personally I'm a fan of the Trojan L16 deep cycle batteries, I think they were originally designed as a electric forklift battery.

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    Default Not a good idea

    Tealer, you will need to first find out how much your motor(s) generate AMPs at crusining. If your motor canít generate at least 40 AMPs an hour you will be draining your batteries even if your motors on. Yamaha F150 only generates 35AMPs at maximum RPM. It would be best to use DC refrizerator or freezer. My Norcold DC0051 only draws 3AMPs an hour while compressor is running, and I leave it on all weekend.

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