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Old 02-06-2015, 09:03 PM   #1
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Inverter Question

I would like to install an inverter to power my 10cf refer while motoring. I wouldn't only use it this way. My question is would the alternators charge the batteries sufficiently to power he inverter. I was thinking about a 1500 watt inverter that would be dedicated to the refer and plugged into the inverter while under way.
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Old 02-06-2015, 09:25 PM   #2
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Maybe, but you need to supply more information. What are the running watts of your fridge? What is the configuration and amp output of your alternators? What sort of battery bank do you have? An inverter can run down (and destroy) an engine start battery quickly.

Now some things to think about. Your fridge may only draw 150-250 watts, but it will take hours of constant running just to cool down. The very best inverters are only about 90% efficient, plus you need SOME power from your alternators to charge the batteries and run your normal loads (Lights, radio, plotter, etc). Running a main engine to power house loads gets expensive both in terms of fuel and wear and tear of your most valuable machinery.

If you're only going to power the fridge when you're underway anyway, then it may work out if you have a reasonable house bank and alternator setup.

Ken
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Old 02-07-2015, 07:32 AM   #3
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The problem is batts can only accept a charge at a slow rate , or they boil.

Its not like filling a pool with a fire truck , big source quick fill.

No problem finding an alt that can run a house reefer with an inverter , and charge the batts (to their limits) at the same time.

The problem is engine run time , replacing 200AH may take all day.

One solution is cold plates , eutetic refrigeration , with a 10 Hp engine driven compressor.

The other is a propane reefer , so no electric required.

The most common compromise is a large heavy batt bank , a larger alt to fill it , an SOC meter to work as gas gauge for the house batts , and a noisemaker to run long hours to fill the batt .

In some areas a solar panel or 2 is a great help in bringing the batts above 85% full.
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Old 02-07-2015, 08:29 AM   #4
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Quote:
Originally Posted by GreenSailor View Post
I would like to install an inverter to power my 10cf refer while motoring. I wouldn't only use it this way. My question is would the alternators charge the batteries sufficiently to power he inverter. I was thinking about a 1500 watt inverter that would be dedicated to the refer and plugged into the inverter while under way.
I'm reading your question differently than the other guys. If you have a refer that is tied to shore power when docked, and just wank to be able to power the refer when day cruising, the answer is yes. A friend of mine has a a beer and sandwich fridge as he refers to it on his boat. It's tied to shore power at the dock and runs off an inverter when cruising. If he anchors for an hour or so, he just turns the inverter off and mass (contents) within the fridge keeps everything reasonably cold until he starts the engine and turns the inverter back on.

As already mentioned, check the amp draw of the fridge (usually on tag inside door) and alternator amp tag. Inverter needs to be somewhat oversized to handle start up surge. Don't skimp on battery wire size. Locate inverter as close to battery as possible.

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Old 02-07-2015, 09:10 AM   #5
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GreenSailor:

To support the OP's opinion with some facts:

Your fridge is going to draw about 300 amps when running. My home fridge draws that much as measured. That will take about 30 amps DC to power an inverter to run it. If it is already cooled down, then depending on how much you open the door, the average could be half or less.

Your engine's alternator will easily put out that much current, but the inverter will probably have to draw down the batteries a bit before the alternator puts out that much. Depending on the size of the battery bank this could take an hour or so. But then the alternator will keep up. At the end of your motoring you probably will have about 75% charged batteries.

No problem, when you hook up to shore power the charger will top that up in a few hours.

You don't need a huge battery bank to do this, even 100 amp hours will work, but I would prefer 200.

And you don't need a 1,500 watt inverter just for the fridge. Look at the label on your fridge and size about 50% more for best efficiency.

David

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Old 02-07-2015, 10:03 AM   #6
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I took the liberty of reading your other two posts, about planning to buy a trawler to take from the Great Lakes down to FLA and the ICW.

An inverter (1500-2000 Watts) is a great idea. Some would say a must-have.

Assuming you don't have a proper 12VDC marine fridge, you can easily run a household (120VAC) fridge off an inverter like that. A lot of people nowadays seem to be using small (and inexpensive) household fridges in their boats, instead of expensive marine units. Not as efficient, but the cost savings is a consideration.

With an inverter, you can also run chargers for laptops, tablets and cell phones, maybe some lights if you have 120VAC fixtures, at the same time. We use the microwave (small 900W model) and a small vacuum cleaner frequently. You can plug in Christmas lights if you want to join a boat parade. You'll find lots of uses for an inverter.

Here's the important part: Whether your fridge is 12VDC or 120VAC, whether you have an inverter or not, you need to have some way to supply power when you're not underway or attached to shore power. That would be your "house" battery. Typically, this is a bank of two or more deep-cycle 6V or 12V batteries.

The house bank is rated for a given number of Amp-Hours. So if you use 100 AHs in an average 24-hour period, you need (1) a house bank of at least 200AH (since you should avoid draining it more than half-way) and (2) some way to put 100 AHs back into it at least once or twice a day.

If you have an 80A alternator on your engine, you might assume 50A available to charge the batteries at cruising speed. Thus, a minimum of two hours underway will theoretically recharge. But of course, the batteries won't accept the full 50A as they get closer to fully charged. On the other hand, it's OK to get them to 80% or 90%.

Or, if you have one, run your generator for an hour or so, twice a day, to charge batteries, heat water, cook meals, wash dishes, etc. Typical inverters used in trawlers are also battery chargers. So the batteries will be topped off during these times.

Unfortunately, you'll need to do some math to figure out your maximum AC and DC loads, your average AH usage, and what size house bank, alternator, inverter, charger, solar panels, and/or generator you'll want.

And, of course, you'll need to estimate how long you plan to be away from shore power and how long you'll be running the main engine(s) each day, on average.

There are as many different solutions to these equations as there are boaters. I'd say the numbers I used as examples above are not out of the ballpark for a lot of modest-sized cruisers, but there are many members here who find totally different values work for them.
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Old 02-08-2015, 04:22 PM   #7
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By Golly much of what is said confirms my thread also within this specific forum. I am becoming more convinced with installing a house hold 110 fridge with this input.
There may be other forums than Trawler Forum that give information, however in my opinion the sharing on Trawler forum is way above and appreciated.

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Old 02-08-2015, 07:51 PM   #8
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This is how I've run my fridge underway for the last 15 years. One of those years was a summer's long cruise.

No problems.
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Old 02-08-2015, 07:56 PM   #9
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I agree I have run a house hold refrig on a inverter for 15 years and it is even the same 1000 watt inverter with no problems.
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Old 02-08-2015, 08:13 PM   #10
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Al and Funangler, Thanks, even more encouragement. Could I prevail on you fellows o give me your wiring process? I have a 110 outlet behind the current fridge location. When on shore power that box is excited. Now, the inverter will need to be connected to the batteries. The inverter has the female 110 outlet. the missing piece in my mind is how to place a switch between the 110 /inverter connection.

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Old 02-08-2015, 08:44 PM   #11
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With out looking at it I'm afraid to give much advice in detail. It is fairly simple use the largest battery cable you can stomach to buy and keep it as short as you can. Keep the inverter out of the engine compartment. The simply method is to wire one outlet out of the inverter and plug the refrig when you want it powered.
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Old 02-08-2015, 09:10 PM   #12
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With out looking at it I'm afraid to give much advice in detail. It is fairly simple use the largest battery cable you can stomach to buy and keep it as short as you can. Keep the inverter out of the engine compartment. The simply method is to wire one outlet out of the inverter and plug the refrig when you want it powered.
I agree. I don't power my entire 110V AC system with my inverter. The inverter output passes via an extension cord to a power strip which allows me to plug in my few AC items on one countertop. My inverter has a remote on/off switch with an indicator light which is mounted on the side of the cabinet in which the inverter is mounted. It's a simple matter to switch the inverter on or off. The fridge power plug gets repositioned to the inverter power strip as needed.

All outlets are GFI protected, including the inverter outlet.
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