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Old 16-01-2008, 12:02   #1
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12v or 110v/220v generator - HELP!

Hi All,
Need some input please and hope someone can help.
I want to fit an small aircon unit plus a small freezer to our 46 foot yacht and wonder if anyone else has done anything similar and what way they went?
It's longer term cruising that dictates the freezer need but it does not need to be a big one. It's spouses need thats dicated the aircon for hotter climates - and I'm not arguing!
The big question I'd appreciate practical input on, is deciding twix a 220v or a 12v generator to fill my needs.
I've read the 220v is a more conventional route. But it is heavier, noisier and uses more fuel.
It would allow us to power a 220v freezer plus obviously run the aircon - but would need to be running for the units to work.
A 12v generator is lighter, smaller, and uses less fuel.
But it means we'd probabably best buy a 12v freezer - and add an invertor to run the aircon. Biggest upside is aircon and freezer could run from batteries and the genset kick in only when they get low.
If anyone has experience in doing something simialr and happy to share that, it would be much appreciated.
JOHN
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Old 16-01-2008, 12:23   #2
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AirCon is going to be your largest power munching device. The feezer is not so bad. I have done this. I fitted a domestic freezer inder one of our main saloon berths. It runs off the inverter. It was cheap and easy.
What you need to do, is find out the Ahrs or Watts the two devices will draw over say a 12hr period(yeah I know that's not easy) and then work out how big a battry bank and inverter you need to run these from the batteries. One thing I can say, don't buy and absorbtion fridge. Normally a three way fridge that can run off gas. They are very power hungry devices when run electricaly. A compressor type is the most economical.
A 12V freezer will be the most expensive, a 230V domestic freezer will be the cheaper option.
Just to help further, I took a cheap domestic upright freezer and laid it on it's back. I unscrewed the Compressor unit and gently pulled it out of the bottom(there was plenty of copper tube to do so) and screwed it to the boat framework in the correct way up. It has worked flawlessly for 3yrs now. It cost me NZ$199(normaly $299) on a special and a proper marine unit was going to cost me NZ$1200 and I still had to biuld the freezer box.
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Old 16-01-2008, 12:48   #3
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I have a 12v one lunger 100amp, i fixed it up and tried to use it, but it's so loud you can't even be on the boat when you run it. It is actually louder then my 85hp perkins (keeping in mind we have a well insulated engine room).

Personally I would go with something with a good sound enclosure, 220 kind of gives you the best of both worlds as you can use 120 on one of legs and 220 on stuff llike the a/c at half the amp draw. but that's just my .02 cents (which is actually only worth .005 cents after the stock market yesterday
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Old 16-01-2008, 13:17   #4
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For the loads your describing I'd go wilt a conventional AC gen. You'll have more flexibility in what you can power. The wire needed to carry the amps will be smaller and lighter and less expensive. Most 120/240v gens can be set up to deliver both in single phase applications.
The fuel burn between a 5kw 120v gen and a 200A 12v gen will be about the same @ less than 1 GPH.
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Old 16-01-2008, 15:14   #5
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No way you could run an A/C from batteries alone (though an inverter). The power draw would drain anything except a HUGE battery bank in short order.

If you want A/C, you must go with an AC generator.

I've had both a DC generator and an AC generator aboard my 42' sloop. Lived with the DC generator for 13 years or so, but didn't have air conditioning. It worked reasonably well. And, when I needed 110VAC, I'd simply use the inverter.

After 13 years it was time for replacement. I agonized over another DC unit or an AC unit. I did all the math, repeatedly. Figured all the angles. Bottom line: since I was planning to add air conditioning units, there was simply no contest: it had to be an AC generator.

As was said above, if it's just the frig/freezer you're concerned with, then a DC setup would be fine. But with air conditioning, you really don't have a choice.

One final thought: when you're sizing the generator, don't try to install something which "will just work" or which will just barely handle the load. Be sure there's considerable capacity to account for: (1) heat...generators put out reduced power when hot; (2) loads which are not purely resistive; (3) starting loads (as in motors and compressors); (4) less than optimum fuel; and (5) Murphy. He's always aboard, lurking where you least expect him to be :-)

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Old 16-01-2008, 18:44   #6
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Air Cond for Cruising

A little while ago there was an article in Cruising Helmsman ( an Australian cruising magazine) addressing the issue of power requirements for running an air conditioner, and from memory the conclusion was to power it through a generator.

The recommended unit was a Honda 4 stroke - EU20i I think, the conclusion being that a/c draws very high current each time compressor starts, and the only way to safely and efficiently was to use a generator.

I will try to remember to go through my back issues and find article to provide further and more detailed inormation.

Fair winds

Steve
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Old 16-01-2008, 21:57   #7
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I think you may need to attack the problem from a different angle. What is the total house load in watts if you were to run everything that you might be running simultaneously? Add some fudge factor to that and there is your answer. I can't imagine running air conditioning, which is something that takes anywhere from 1000 to 5000 watts or more being run off of batteries. As someone already said, 220V AC generators produce both 220V and 110V. 220V is produced by combining the two 110 volt legs on the hot side.
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Old 16-01-2008, 22:56   #8
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I used to have an 8KW Northern Lights diesel generator with a noise covor over it. It was pretty darn quiet. You could tell when it was running but the noise was not obnoxious.
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Old 17-01-2008, 02:19   #9
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Being very weight concious I have spent a lot of time researching this. My current thinking is a large alternator and watermaker pump on one of the mains, only 30 HP, and to have a small 2KW honda combined with an invertor that can supplement the surge loads when needed. This setup should enable an aircon rated close to 2kw to survive the startup surges. Run the main when water is needed and charge the batts or run the small gen at other times.
Hope it works

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Old 17-01-2008, 07:01   #10
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The advances in tech relative to variable speed DC compressors and chargers/inverters has been very impressive in recent years. At the Annapolis boat show last October I saw some impressive demonstrations of DC powered A/C units...16K BTU... that were NOT massive power hogs and the start up amps required were much less than older traditional systems. Yes, you would still need a generator but a 5KW DC Genset would more than meet the need for a DC A/C and DC frig/freezers.

The newer DC gensets (like Fischer Panda) have smart controllers and run at various speeds to meet the required charging need. They also auto start are small and very quiet.

If I was buying new and approaching it from an integrated systems standpoint I would definitely go with an all DC system with inverters sized to the AC needs.

Nigel Calder goes into a good bit of detail on the advantages of this approach. One disadvantage though is this approach may cost more up front.


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Old 17-01-2008, 07:28   #11
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Hi,
Yes I read the Nigel Calder book plus looked over a large steel yacht which went this 12v dc + invertor route and that owner was more than satisfied with results. Hence the dilemma.
However, most feedback I've had so far suggests the 110/220v generation is best to cater for AC needs and as I'm easy either way and prefer practical feedback to theory - suspect that's the way we'll look at going.
Fisher Panda appear to get a bit of a bashing on reliabilty etc, and I've heard good things of Mastervolt Whisper gen sets.
Anyone got good or bad experiences with their latest units?
JOHN
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Old 17-01-2008, 07:44   #12
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Quote:
Originally Posted by swagman View Post
Hi,
Fisher Panda appear to get a bit of a bashing on reliabilty etc,
JOHN
Please search this forum. There have been several threads regarding Fischer-Panda.
There was an issue with the engines supplied to FP a few years ago on the 4kw unit. This has long since been resolved. Jeff Till, national sales manager for FP is a member here. He's been directly involved in problem resolution.
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Old 17-01-2008, 07:47   #13
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There are 12v airconditioners

Truckers idling their engines just to run the airconditioner while the truck driver sleeps waste a lot of diesel so companies have started making 12 vdc airconditioners for that market.
Marvin Marine has a 12vdc unit called SeaMach that is avertised to draw 30 amps including the water pump that is rated at 5000 BTU/hr. If one ran a 12v genset in the early evening and then turned it off at bedtime and ran from fully charged batteries the rest of the night a 30 amp draw is livable. (IMHO)
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Old 17-01-2008, 09:08   #14
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YOU GOTTA LOOK CLOSELY!

Yep, at first glance the 12V solution looks do-able. HOWEVER, you've got to look very closely at the specifications.

For example, the lovely little SeaMach (model SMM05ACP) specifications provide the following information:

1. While the "nominal" rating is 5,000BTU, this changes by water temperature. With an inlet water temperature of 75F, the BTU output drops to just over 3,000BTU.

2. While the A/C unit itself draws just under 30 amps, you also need to have a water pump with a minimum flow capacity of 2.1 gallons per minute; this pump will draw additional amps.

Unless you have a very tiny vessel, 3,000 BTU of cooling isn't much. On my 42' sloop, I have two A/C units which total 28,500 BTU. While the larger of the two units (18,500 BTU) is generally enough to keep up with the heat...except on the very hottest days when the temp can rise to near 100F and the humidity is high .... I can't imagine what only 3,000 BTU would do on such a day! At best, it might cool a small cabin.

Additionally, a draw of 30+ amps (including the water pump) over an 8-hour period at night would be something akin to 250AH total draw. This would require a house battery bank of at least 700-800AH (following best practices and taking account of inefficiencies in charging when crusing). Putting 250AH back into your house bank...in addition to the other normal draws (including refrigeration) would take a substantial amount of generator or motoring time.

While we all dream about some miracle technology which would cool us while we sleep without the need to run a generator, IMHO that dream is still elusive.

Bill
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Old 17-01-2008, 09:09   #15
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30 amps for 10 hours is 300 amp hours and 5000 BTU is pretty small. Anyone have a formulae for sizing a system for the tropics and a table to cross reference to watts, my altzhiemers keeps deleting this data from my memory

Mike
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