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Old 02-07-2015, 09:40 PM   #1
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What size portable inverter to run 2.7 DC frdige?

Greetings,

Planning to change out our current AC fridge due to need of raising the cabin floor by an 1 1/2 inch. The current fridge is within a 1/2 of the current floor.
In looking for a replacement in a AC/DC and around 20-24 inches in height the cost seem quite high in terms of a straight DC house hold fridge (Haier 2.7 cu feet) As the Haier is a DC unit the question is how large a inverter would the forum members suggest? The indication from a RV review refers to a 60 Watt light bulb demand.
The thinking from here is the price of a bit ove $115.00 vs 600.00 allows for consideration in using an for the lack of a better description, "Inline" inverter of
(Blank wattage). I would set system up to run on DC at the dock or on the Gen set and switch to the inverter at sea.

Suggestions or thoughts?

Thanks,
Al
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Old 02-07-2015, 10:10 PM   #2
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Do you mean a Haier AC fridge? That's what I run on my boat, it draws about 1.2A at 120V, or about 150W. I run it on a 1000W cheapo inverter. System works fine. I tried a 600W inverter, that did not have enough grunt to get it started.
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Old 02-07-2015, 10:50 PM   #3
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Thanks Ski, Encouraging to say the least. Could you give me a typical run with the unit on at sea? We at one time had a 1000 watt inverter/charger built into the system but took it out when it began to confuse itself and we experienced battery problems. The current fridge is a 12 volt only. Of course when we run it is charged, when we anchor we turn off for the evening. Yes, we have a gen set on board and will turn the fridge back on when it is running. With the DC only the inverter will be activated while running and on the gen set, but we are concerned that being on the inverter on the hook the battery drain will be excessive. That is the area of concern. We have two size 27 12 volt house batteries, Could you give a thought on the period or time lag, for using the inverter? Taking opening and closing the door into consideration, and saying no more than 6 uses of door opening during a meal period. This may not be a useable inquiry formate. I guess any down side to this conversion.
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Old 02-07-2015, 10:53 PM   #4
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O and Ski, how did you wire it to accommodate the transfer from inverter to shore side power source?
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Old 02-08-2015, 12:37 AM   #5
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My panel is set up with transfer switches to go between shore, gen and inv. It actually has two switches to do that, one is the panel breakers with slide locks for shore or gen, and another rotary sw to go between shore and inv. A DC batt switch turns on the inverter.

I only have one grp 31 batt for the house, so that really limits my inverter time with fridge running. This was done intentionally as it is a planing boat and attempts were made to keep it light.

The single grp 31 will run the fridge overnight, but in the morning its charge state is too low to be healthy. So we run the gen for an hour or so at night to top up batts and run fridge and cook and make hot water. Then once fridge is closed for the night, the inverter keeps it cold all night without killing the batt. Opening the door beyond that point makes it run heavy and that kills the batt. Leave door shut and batt is still above 50% in the am. At that point either the main engine or gennie is back up to run the fridge and top up batts.

I've considered adding more house batt, but once I learned how to manage it, it all works just fine.

I rarely stay on the hook for more than a day or so, usually just set the hook to sleep and then motor on in the am. My rig does not like long term on hook, that would require lots of gennie running. Under way, the main engine alt takes care of the fridge on inverter, and topping up batts.
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Old 02-08-2015, 06:08 AM   #6
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The easiest way to switch from shore to inverter power is to have a socket for pole power and another for inverter power , and a 3hirs if you have a noisemaker,

Simply move the plug from one to the other,

Low cost , quick to install, and hard to get confused.
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Old 02-08-2015, 07:55 AM   #7
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I did the same thing to make a ref work on inverter the first one did not last long was to small and burned up I got one much bigger than needed and had it for 5 yrs and still working
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Old 02-08-2015, 08:52 AM   #8
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I'm really confused here. When I read what the OP is saying, he seems to be confusing either and AC vs DC fridge, or is confusing an Inverter for a Charger.

If he has a DC fridge, then he doesn't need an inverter, he needs to be sure he has enough charger capacity to run the fridge and recharge batteries with the gen or shore power.
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Old 02-08-2015, 10:20 AM   #9
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Al

Would not a 12V/110V fridge be easier to use and set up than what you are contemplating with an inverter?
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Old 02-08-2015, 11:12 AM   #10
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Yeah, seems like a DC/AC fridge with it's own built-in power management system would be easier. Our NovaKool fridges (just as an example; there are others) run on DC all the time. If AC is present, the unit automatically converts AC to DC and hums happily along. No separate inverter required. Not dissimilar to AC power supplies for current DC laptops, phone/tablet chargers, etc.

I haven't shopped for cost differences between a ready-made solution and a separate-component solution, though.


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Old 02-08-2015, 11:20 AM   #11
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I've been researching inverters for some time as I would like to be able to run some ac loads while on the hook without running the genset. When determining the battery bank size and inverter size, you need to do a calculation of dc amp requirements.

An AC fridge that takes 1.2 amps at 120v would convert to about 13 amps dc. If the refrigerator runs 50% of the time, that would be a draw of about 6.5 ah or 78 amps over 12 hours. A brand new group 27 deep cycle battery probably has somewhere around a 100 ah capacity. If you ran the inverter for 12 hours while on the hook, the refrigerator alone would use up 78 of the available 200 amp hours. You will have to calculate other dc loads, (lights, pumps, etc) to determine the total dc amp requirement. Most would recommend that you don't exceed 50% of your battery capacity between charges.

This applies whether you use an inverter to power your fridge or use an ac/dc fridge.

Are you considering a modified sine wave or pure sine wave inverter? Running some ac motors on a modified sine wave inverter can cause it to overheat and run less efficiently.
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Old 02-08-2015, 12:32 PM   #12
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Good Morning fellows,

Lot of good information here and a thank you for participating.
Let me qualify that the purchase of a marine refrigerator in the range of $600-800 dollars plus huge freight cost (O-You live in Alaska=Big bucks!) is not beyond my means. However when walking through Wal-Mart and finding a similar size refrigerator in house hold voltage (AC) for $115.00 and no freight I begin to think along the lines of this fits the “Because it is marine it has to cost more” when it may not have to.
How many occasions we read on other forum subjects that home hardware stores or automotive stores, carry items that will transpose over to marine and cost one heck less? That is the mode I used posting the inquiry.
Let us review and respond: FF offered the easiest solution with two sockets however as the fridge is inserted a location accessible on the boat would present a suitable sites, thanks for the suggestion.
Pure Pleasure confirms that a sizable inverter such as the 1000 watt Ski suggested.
Twisted Tree has me confused Disappointed smile The intent is to replace a 12 volt fridge that will be too large after the project with a house hold 110 refrigerator. This will require a converter of 12 volt to 110 which as I understand it, a inverter not a charger. We do have a gen set in the system, however we do not run it continuously while underway. The intent is to employ the inverter while traveling trusting that the alternator will maintain the 12 volt system and allow the fridge to be operated.
Sunchaser- You are correct in the observation and it may well be that we will abandon this 110 option in the end. In the meanwhile having input will confirm our end actions.
Ranger42c: You have hit on the purpose, Not so much cost other than the purchase of one or other mentioned in paragraph one.
BlueYonder: You have provided information regarding pretty much the discussion of what one may expect in the battery life during a 24 hour cycle. I understand somewhat the amp hour stuff enough to know that as Ski indicated, opening the door often while on the 12 volt system will drag the battery down. Knowing this we have always been aware and cognate of the fridge while on 12 volt status.

In the over all, FF’s suggestion will be explored with finding a location that we can re-wire to from the current fridge location were the 110 volt chosen. We have our eye out watching the Seattle Craiglist for a used unit, and if all fails, we will bite the bullet and purchase a 12/110 unit.

Thanks to all

Al-Ketchikan
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Old 02-08-2015, 01:01 PM   #13
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Ok, that clears it up. Proposing a cheapo AC fridge running off an inverter. Exactly what I am running. Can't beat a $120 fridge and a $100 inverter. Yes the cheap stuff may fail, and I in fact had the fridge fail, probably due to coarse AC from the cheap inverter. But it was just a $14 motor starter thingy, easily replaced.

This rig has worked for several years and about 12000mi of travel.

I would recommend using a transfer switch for your whole AC panel, as that allows you to run all sorts of little loads on the inv. Phone chargers, laptop, hair dryer on low...that's my window defogger, coffee pot, rice cooker, toaster oven, etc., all can be run, but you MUST manage the loads. For example, to make coffee, I must turn off the fridge.

If you do power your whole panel, you will need to be diligent about racking off the heavy load breakers and manage the load.

And don't try to run the batt charger on inv!!!!
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Old 02-08-2015, 01:10 PM   #14
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So, what's the deal on those very inexpensive inverters from Harbor Freight? They say not for marine use....why not, especially if used in a fresh water environment and if installed/located with care...
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Old 02-08-2015, 01:13 PM   #15
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I got my for hf the first one didn't last long they traded me for on that was 3000 watt haven't had a problem again
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Old 02-08-2015, 02:48 PM   #16
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It's important to remember that many apartment size fridges require air circulation around the outer surface, sometimes just one side, to allow for cooling of the unit mechanicals. These units are not compatible with flush mounting in an enclosed cabinet without special venting and forced air circulation.

I have an apt size fridge secured to my countertop. I run it from a 1000W inverter. My house bank is 6 GC batteries of 660AH capacity...of which 330 or less is actually available for use. I figure on about 100AH per day during warm weather for that fridge alone, 180 per day for the total boat electrical load. If you buy a $20 Kill-a-watt meter, you can accurately determine your energy budget.

I doubt that 2 group 27 batteries will be able to sustain that fridge for more than a day without becoming depleted.
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Old 02-08-2015, 04:39 PM   #17
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Flywright-
Good observation on charge life of the group 27's. I agree. The thinking is similar as we do with the strictly 12 volt currently in play. As soon as the hook is down and until after cocktail hour when the gen set is running, the fridge is switched off.
What little in and out access to the fridge during dinner preparation seems to have little impact on the fridge contents being effected.
Remember our ambit temperatures on a daily basis during boating season is 50-60 degrees F. We are not dealing with high atmospheric temperatures.
We will normally run the gen set during meal prep and for evening times.
Even then following the meal finish we switch the 12 volt fridge off.
Under those circumstance it would appear that we are not making a large demand on the batteries.
Changing the power structure from 12 volt to 110 an adhering to the same schedule would seem akin to current fridge awarness habits.
Your thoughts on this process?
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Old 02-08-2015, 04:46 PM   #18
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TwistedTree- Whoops! I see you cause for confusion, it is I who inverted AC/DC to phase a pun. Sorry. Better for me to use 12V/110.

I make too many wrong mistakes.
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Old 02-08-2015, 08:07 PM   #19
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I've run a 120V Haier dorm refer on Group 27 Diehards and a 1500W Freedom inverter for a long time.

The back of the fridge cabinet benefits from ventilation. Powered or not.

It'll be fine. Just cast off and go.
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Old 02-09-2015, 08:39 AM   #20
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FOLLOW the Money!

In AK using a house unit and small inverter makes the best use of cash.

On the hook it will take lots of noisemaker time , even at overall $5.00 to $10 per hour to make up the DC cost difference.

For a cruiser that loves to anchor out , and plans on doing it a while the numbers may be very different.

A pure DC unit will require far fewer amps as the units have brains and operate slower and more efficiently when they can.

They will also sense the higher Voltage form engine operation and switch on to operate >free< due to the unlimited source , the alt.

While a house unit works for some it will not be >The Answer< for all.

Mostly it depends on overnight? or over 3 -5 days ?
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