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#569470 - 10/23/17 09:06 AM Run refer fron inverter or shore power  
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Boatbottom Offline
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Sacandaga Lake Mayfield, NY
Hi Everybody. Our last boat had a decent size refer on board. The 289 Bayliner I now own has a small one. I had space in the 110v breaker panel, so I I added a mini-fridge in the cockpit. It works great and we keep all of the drinks in the minifridge. Obviously, no shore-power no cooling. As it turns out the Bayliner has an 1800 watt inverter on board, I strung a lead cord to see if it would power the refrigerater and it does. So now I want to string some wire from the inverter to the refer and and wire in a switch of some kind so I can just flick a switch when I leave the dock to change the refer from the shore power circuit to an inverter circuit. Yes! I do realize that if I try to run on inverter all night on the hook it will suck the batteries down to nothing, bu it will certainly be OK while underway. I could just add an outlet, but I like the switch idea. Have any of you already tackeled this? I'm open to ideas and suggestions It draws 0.8 amps (8/10 of an amp). I assume that is running and not start up


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#569474 - 10/23/17 06:51 PM Re: Run refer fron inverter or shore power [Re: Boatbottom]  
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Jack T Offline
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I assume the 0.80 amp draw is 120vac. That makes the refer power 96 W at 120 W AC.
if the inverter were 100 percent, the 12V DC current would be 8 amps. Unfortunately, inverters are not 100 percent efficient (power out- power in). Perhaps the inverter documentation has a table that gives the info.
Or, calculate efficiency and add an amount equivalent to the loss of efficiency.


Have a great day of boating
2012 Monterey 224 FS,
300 HP Volvo Penta with catalytic converters

#569478 - 10/24/17 11:20 AM Re: Run refer fron inverter or shore power [Re: Boatbottom]  
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Sacandaga Lake Mayfield, NY
JackT you are correct. There isn't any documentation for the inverter so I can't answer your questions about efficiency. I can tell you it's more than 10 ft from the battery so there will be plenty of loss.. I'm not that worried about run time for the present. I am interested in figuring out how to wire the refer so I can just flick a switch from shore power to inverter power


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#569489 - 10/24/17 08:44 PM Re: Run refer fron inverter or shore power [Re: Boatbottom]  
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Jack T Offline
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You will need a DPDT (Double Pole Double Throw) switch. This enables switching both the + (hot) and - (Common) wires,. To keep the two sources separate while switching, you will want to have an open center position which would disconnect both before making a connection between both sources..

Also a fuse on both the 12V and 120V side of the inverter (they may already be there in the form of circuit breaker(s) is a good idea.

With a digital meter with the correct ranges, you would be able to measure current on each side (verify that you know how to hook the meter up). Take that current and then go to at least the next amperage rating higher for the fuses (breaker). 0.80 AC amps does not need a heavy current, but it does need thicker insulation than 120 V. Because of higher current on the 12 V side, this wire needs to be heavier. Look up a table to know for sure wire size/current capacity and use at least the next size larger. American Wire Gauge (AWG) sizes are set up for specific current flow. The bigger wires have smaller numbers. And, you are right that longer wires of the same AWG have higher resistance, and may require going to a larger wire. Again, a table will give you this information.

Look up American Wire Gauge on Wikipedia, and the tables are there. #20 wire will carry 7.5 amps at 20* C, with 10.15 ohms/ft. #18 wire will handle 10 amps, with 10.15 ohms/ft. If you know Ohm's Law, you can calculate the "voltage drop" by using the resistance ofy our 10 foot lead wires. "Multiply Amps x Resistance" to determine the voltage drop, subtract that from the supply voltage and you have the remaining voltage.

Now, you already mentioned the starting current of the refrigerator. If you know what that is, then all of your system needs to handle that current.

I am not sure how big this refrigerator is, or if it is a typical freon-based cooling system. I would like to suggest using a 12V electronic solid state cooler/heating box. We have one and they are just great. It plugs directly into the cigarette lighter. Not sure of the current drain, but like you said, if under power, there is plenty of power from the alternator. Or, 120V AC to 12 V DC power supplies are available. We have had one of these for over 17 years and it has yet to skip a beat. The inside of the box, at first, appears small, but that is because the box walls, top and bottom are very thick with insulation. Because there is no need for ice, the box really holds a lot of stuff. I am using a computer with which I am not familiar, so I can not give you a link. But, put in "Coleman 40 Quart PowerChill Thermoelectric Cooler " and you can see many examples. They have them at Walmart and many other stores. Adapters, too. Some can also be switched to be a food warmer.


Have a great day of boating
2012 Monterey 224 FS,
300 HP Volvo Penta with catalytic converters

#569527 - 10/27/17 03:45 PM Re: Run refer fron inverter or shore power [Re: Boatbottom]  
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Boatbottom Offline
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Sacandaga Lake Mayfield, NY
Hi Jack T. It's a small 1.5 Cu/ft "cube" or Mini-Fridge. It uses a danfoss compressor with R600a refrigerant wich is actually butane. I debated purchasing a norcod 12v/110v at defener, but they are way overpriced. I paide about 66 bucks including the tax. Thanks for the heads up on thetype of switch to use.


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#569538 - 10/28/17 07:15 PM Re: Run refer fron inverter or shore power [Re: Boatbottom]  
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Frantically Relaxing Offline
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Best way to run a refer on the water is install 2 more batteries just for the fridge. Best 2 batteries would be a pair of in-series 6-volters.

You'll need an isolator for them so the boat engine and shore power charger will charge them, and a simple disconnect switch.

You'll never have to worry about the fridge stranding you on the water, and bonus- the extra batteries may get you home if the other batteries give out for some reason...

#569546 - 10/30/17 02:28 PM Re: Run refer fron inverter or shore power [Re: Boatbottom]  
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Boatbottom Offline
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Sacandaga Lake Mayfield, NY
Interesting. The inverter was on the boat when I bought it. I was going to have two DC grp 27 batteries in parallel for the "A" side of the battery switch and two DC grp 27 batteries in parallel for the "B" side of the battery switch. I would use the "A" side for starting and the "B" side as the house batteries. That's assuming I can find space for the 4th battery. It's possible I might purchase a new onboard battery charger in the process but the jury is still out on that one.. FR...could you tell me what the advantage of the two 6V batteries are over my planned two 12V? It never occurred to me not to use12V.


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#569562 - 10/31/17 04:01 PM Re: Run refer fron inverter or shore power [Re: Boatbottom]  
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6 volt batteries have a lot of 'minutes capacity', Trojan T105's have a 447 minute capacity@ 25 amps- That means a pair of them will run a 5 amp refrigerator constantly for over 35 hours before being discharged. They're very nice for RVing or overnight boating where you'll have lights on & stuff. However, they're not cheap, and a good, "true" deep cycle 12 volt battery will likely be just fine for your needs, and cost a bit less too.

#569571 - 11/01/17 08:00 AM Re: Run refer fron inverter or shore power [Re: Boatbottom]  
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Boatbottom Offline
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Sacandaga Lake Mayfield, NY
Well FR, you have certainly given me something to think about. If I wire the two batteries in series, I get 12V out, but would I be able to use my existing battery charger which provides 12V in? Or would I need to charge at a 6V rate?


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#569612 - 11/07/17 01:21 AM Re: Run refer fron inverter or shore power [Re: Boatbottom]  
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12 volt charger, ignore the series connection between the batteries and connect to the + and - outputs-

#569620 - 11/07/17 02:16 PM Re: Run refer fron inverter or shore power [Re: Boatbottom]  
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Jack T Offline
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I know that many of you guys know the following, but it doesn't hurt to reinforce the knowledge.

In support of the above discussion, to summarize:

The voltage across two 6 volt batteries connected in series (+ of one connected to the - of the other) is 12 volts. To charge with a 12V charger, connect the charger across the + and - battery terminals that do not connect the batteries.

Here's a YouTube to show some pictures
https://www.google.com/search?q=cha...p;sourceid=chrome&ie=UTF-8#kpvalbx=1

The voltage across two 12 volt batteries connected in parallel (as in switch controlled multi-battery systems) is 12 volts. To charge with a 12V charger, connect the charger on one + and one -. If you want to charge only one battery in this configuration, be sure the battery to be charged is isolated by the switch and connect the charger across just that one battery.

Here's a diagram of connecting two parallel 12V batteries for charging. Click on "9. Two Batteries in Parallel, One Charger"
http://www.batterytender.com/connecting-chargers#parallel-connections




Have a great day of boating
2012 Monterey 224 FS,
300 HP Volvo Penta with catalytic converters

#569674 - 11/16/17 01:05 PM Re: Run refer fron inverter or shore power [Re: Boatbottom]  
Joined: Oct 2014
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Boatbottom Offline
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Boatbottom  Offline
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Joined: Oct 2014
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Sacandaga Lake Mayfield, NY
Jack T, The youtube video was interesting. I understood differece betwee parallel and series, but didn't know that you could charge them at 12V. Hmmmm....Now if I can just find the space.


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