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Old 10-03-2012, 14:42   #16
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Re: Refrigeration While Cruising

Ed-
"the fridge draws 2.6 amps (5 max on startup) would this be okay for a 1000 w inverter"
5 amps at 120 bolts is 600 watts. If that's the honest number, yes, a 1000W inverter will power it. I would suggest either buying a true sine wave the first time around, or buy a modified sine wave that you can easily return, because most AC motors want a true sine wave and "modified" just doesn't mean much unless you know the exact waveform and the exact motor type, which we won't.
And still make sure it can be returned, because if the startup load actually runs higher for just a short time, and the inverter and fridge disagree...

If you are powering all day and the fridge is drawing 300 watts, maybe half the time, it will be pulling maybe 25 amps from your alternator while it is running. As long as you've got that much to spare, no problem in the daytime, although that will consume some extra hp and fuel as well. (Points for the Engel.)
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Old 12-03-2012, 17:37   #17
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Re: Refrigeration While Cruising

Multipy amps x volts for watts ie 5.6 x 120 Seven Hundred Seventy Two Watts
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Old 12-03-2012, 18:07   #18
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Re: Refrigeration While Cruising

Hey King c. I see a lot of inverters on ebay made by the same name. Any relation? And could anyone recommend one on ebay that I could use?
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Old 12-03-2012, 19:16   #19
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Re: Refrigeration While Cruising

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I debating whether to buy an inverter for my regular size fridge or buy a small dc cooler. Which would be more cost efficient?
I saw an inverter at WM for a hundred bucks that would produce 100 watts, would that be enough for a fridge?
By "small DC cooler" do you mean the ice chest variety or a small refrigerator?

A small inverter is certainly an inexpensive way to go, but not very energy efficient. Keep in mind that inverters are not 100% efficient. You lose energy during the inversion process. This is more pronounced with small cheap inveters -- efficient circuitry costs more to design build. You will probably see at least a 15% energy loss.

Also, don't trust the electrical specification numbers posted on products like household refrigerators. Many of them are WAY off. Spend a little time testing actual numbers with good multimeter before you go to the trouble and expensive of installing in your boat. I had a friend once who bought a small, household grade, ice maker. The numbers on the product label looked reasonable (a little too reasonable for an ice maker). He had a nice custom wooden cabinet built to house it on his nice high-end boat...then he flipped the switch...Holy Amp Hours Batman! Fortunately, that nice wooden cabinet worked out well for storage space. If you consider a small inexpensive consumer grade AC fridge don't make the same mistake -- don't believe any of the numbers you read on the product -- verify them. Cheap comes at a cost in efficiency.

The current designs of direct DC powered refrigeration (like Danfoss) are amazingly efficient. My Danfoss BD-35 based system draws no more than 3 amps at 12VDC (36 watts) after initial cool down. And that of course is only when the compressor is running (about 25-30% of the time). Of course, efficiency comes at a cost, and they are not cheap.
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Old 12-03-2012, 19:42   #20
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Re: Refridgeration while cruising

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One thing to realize is that the DC systems actually have their own inverters. ...
Could you elaborate on what you mean by that?
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Old 12-03-2012, 20:07   #21
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Re: Refrigeration While Cruising

I do have a dc system with these old plugs that have one two slots-one horizontal and one vertical. I'm on a 1986 44 foot Viking. I was told the inverter only works when the genny is on. I only want to run that a couple of times a day.
I"m thinking the easy way to go is just buy a good dc cooler. It's only for 2 months anyways. Then I'll install a cigarette lighter plug in place of the old dc type.
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Old 12-03-2012, 20:30   #22
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Re: Refrigeration While Cruising

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Originally Posted by edbulmer View Post
I do have a dc system with these old plugs that have one two slots-one horizontal and one vertical. I'm on a 1986 44 foot Viking. I was told the inverter only works when the genny is on. I only want to run that a couple of times a day.
I"m thinking the easy way to go is just buy a good dc cooler. It's only for 2 months anyways. Then I'll install a cigarette lighter plug in place of the old dc type.
OK that makes more sense. You probably have a system with an AC-to-DC power supply (would not normally be called an inverter). If it is like the power supply used by WAECO systems then when AC is available the power supply uses it and outputs DC to the fridge. Otherwise the fridge runs directly off DC (more efficient), but whether drawing power from the AC system or the DC system the fridge compressor motor itself is still DC driven.
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Old 12-03-2012, 20:57   #23
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Re: Refrigeration While Cruising

I'd go with a DC unit. No energy lost though an inverter.

That said, the small protable units are not well insulated, and will probably use more energy than a well insulated built in unit.
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Old 13-03-2012, 06:46   #24
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Re: Refrigeration While Cruising

Actually my fridge is a regular full size home fridge. It's definately ac.
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Old 13-03-2012, 17:51   #25
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Re: Refrigeration While Cruising

G'day, mate. How about a few more details:
1. Are you going to be anchoring out alot?
2. Do you have a genset with a battery charger?
3. How big (amp hours) is your house battery bank?

I have run my 110 volt AC, 1/2 hp, refrigeration compressor using a modified sine wave inverter for over a decade now.

"While many larger motor yachts use 110 systems, these tend to be boats that run the generator pretty much around the clock. I can't see where running one off an inverter would be energy efficient."

Here's a different perspective to the quote from earlier in the thread. We are a larger sailing yacht that uses 110 volt refrigeration & watermaker systems which are typically powered by a generator. Depending on the situation (don't need to make water or the batteries don't need charged), there are days that we don't run the generator. We will run the 110 volt holding plate refrigeration using our inverter. Over the last decade or so we averaged around 1.5 hours a day genset time when living on the anchor.

The simple answer is probably yes, with the proper size inverter, you can run your fridge on it. You might want to consider the bigger issue of replacing those amp hours if you aren't going to be doing a lot of motoring. Cheers.
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Old 13-03-2012, 17:57   #26
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Re: Refrigeration While Cruising

The best idea I can think of is to just run my jenny 3 or 4 times per day since I'm only going to be anchoring a few times a week and only going to be on the road for a month or so. Just to keep the fridge cool enough for the basic necessities. I can't see spending so much for inverters and coolers for one month since were are at a dock 90 percent of the time.
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Old 13-03-2012, 18:12   #27
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Re: Refrigeration While Cruising

As others have posted you need to put those amps used back. From the calculation above devide your watts by you volts ie sevenhondred seventy two by 12 uses 64 amps, not very efficent. I would find another way.
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Old 13-03-2012, 18:17   #28
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Re: Refrigeration While Cruising

Remember we are a motor boat not a sailboat. When we are under power the huge battery bank we have is topped up. When we run the genny they are also topped up.
Hopefully this should take care of our fridge which is the only thing we will need to stay active.
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Old 13-03-2012, 19:14   #29
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Re: Refrigeration While Cruising

G'day, mate. O.K., sounds like this is just a once off trip while you are away from the dock. If you can't find a low priced inverter, I would set your fridge to it's coldest setting and then, as you suggested, run the genset 3 or 4 times a day to keep it cycled. If you were going to be at anchor more often, I would look at different alternatives, but your not. All the best, Cheers.
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Old 14-03-2012, 07:38   #30
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Re: Refrigeration While Cruising

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Originally Posted by edbulmer View Post
Actually my fridge is a regular full size home fridge. It's definately ac.
Ah, assumed you were referring to your system when you mentioned DC systems and inverters.
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