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Old 30-07-2007, 13:27   #1
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Small AC

I was thinking about getting a tiny 110V AC for the boat for the unbearable nights.

The idea is as follows. We have a lift off panel in the aft cabin where we sleep (not a stand up cabin) which open to the port lazerette. I would make a new panel to fit with the same hardware with the small AC installed and open up the cockpit access to the lazarette to furnish fresh air.

The little unit is 5.2 amps puts out 5000BTUs and is 15.5x11x12... small enough to stow in the lazerette. I computed the 5.2 amp draw and it is 625 watts and we have a 1000 watt inverter. It cost about $150 so the price it right.

Would this kill the batts running for a few hours an evening? My batts have 500 AH capacity I think it is way oversized for the sleeping area, so I imagine we would shut it down and maybe turn it back on if things warmed up. Do they surge on start up and would that trip the inverter breaker?

Alternatively, I could make something to fit into the companionway or the main hatch if it can cool the whole boat.

Has anyone attempted such a project?

jef
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Old 30-07-2007, 13:41   #2
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Jef,

Nice try, but no cigar :-)

5.2 amps or 625 watts RUNNING, but 2-3 times that on startup. Your inverter is unlikely to be able to handle the startup current.

Further, 625 watt = about 50 amps @ 12.6 volts, so you'd be putting a 50-amp draw, plus the inefficiencies of an inverter...say 15% or so.... on your 500 AH battery bank. Since only about half that is really available, or 250 AH, you'd be lucky to get much more than 4 hours from the A/C run off the house batteries/inverter, even if the 1000 watt inverter could handle the startup load, which I doubt.

A larger capacity inverter and larger battery bank might buy you some cool air for a few hours without major difficulties. And, you could always run the engine/alternator while you cool down the cabin before you sleep :-)

By the way, if you DO get up to Maine you won't need the A/C. I've actually used my Espar heater already this summer!

Bill
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Old 30-07-2007, 13:52   #3
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Bill,

I knew you would suss that out. We could run the engine to cool down.

It's very rare that the air is too hot in the evening and too humid to sleep. I have a Hella fan which blows right on our heads and it is usually too cold in the am. But there are those rare windless super hot humid days in the summer here in LIS which wifey can't tolerate so I thought... a tiny window AC.

She loves the Espar and it gets plenty of use even over July 4th in Newport in the evening.

One thing about the drain.

The unit is rated for 5.2 amps at 110v. I used a spread sheet which returned 612 watts. I understood this to mean that it was like lighting 6 - 100 watt bulbs. Can't my 1000 watt inverter run 10 -100 watt bulbs? Would the 625 watts draw 50 amps in 1 hr?

I seriously doubt that it would have to run more than 1/2 hr to cool the small aft cabin sleeping area... no? If I put it on every few hours for 15 - 30 min... it might work... no?

Jef
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Old 30-07-2007, 14:25   #4
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Jef,

When is a load a load?

There are different types of loads. The hardest for inverters and generators to handle are pure resistive loads (like light bulbs or heaters/toasters/hair dryers, etc.). A/Cs are pretty close.

But it's not just the load when running; the important parameter is the STARTING load. A motor or A/C compressor draws a lot more current when it starts up than it does when running. Usually, you want to spec a power source at 3 to 4 times the run load. I doubt seriously if your 1KW inverter will handle the startup load of even a small A/C. As I noted, a larger one might well handle the load.

Yes, the 625 watts would draw more than 50AH in one hour (625/12.6 = 49.6 x 1.15 = 57AH).

I think you might be able to squeek by with a couple hours A/C on batteries only IF you had a large enough inverter, but it would be tough on the batteries for sure. Running the engine for awhile would help keep the total load manageable.

Worth a try, anyway! Good luck.

I'm off to Maine in the AM, so won't likely be on the Board for awhile.

Bill
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Old 30-07-2007, 14:34   #5
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Bill,

Have a great cruise. I am going to try to sail up there in mid or late august. Where are you sailing?

I believe the 1000 watt inverter does have the abilty to hand surges of higher loads but it would take a try I suppose.

I won't get a larger inverter... so I don't know that I will give it a try.

jef
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Old 30-07-2007, 14:39   #6
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Watts = I * E. Current times Voltage. So, Current is 5.2 amps times 110v = 572 Watts ... Watts divided by 12 V(DC) = 47.6666 amps. And Bill is absolutely correct on both other accounts: the inefficiencies of the little 1000W inverter is at least 15% would put you at about 58 amps (12 volts) and, The start up current is very often double (if not triple the normal current). So, just going DOUBLE current; would be 116 amps at 12 VDC = 1392 Watts. It will never get started.
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Old 30-07-2007, 15:40   #7
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Jef,
I've just added a small 5000 BTU Sunbeam to my boat to replace the CruiseAir Carry On that came with the boat. Based on the documentation that came with the unit I am calculating that the start up will be 1650 watts which means a 2kw generator at the least.

Down here on the gulf coast I can dry out the boat with under 2 hours run time although I tend to keep it running longer since I'm tied to shore power.

I made a simple canvas cover that fits the hatch tightly (unlike the Cruise Air) and a harness to carry and secure the unit. A 1x4 supports the front of the unit in the hatch and is groved to channel water away. A fan keeps the cool air moving. The whole deal is under $100 and about 4 hours build time.

I'm amazed that Cruise Air has not caught up with technology and made a smaller hatch mount unit. bench pressing a 80 lb unit through a hatch is bad enough but having to carry it the length of the boat and drop it down the companionway like you have to do on a C&C sure makes a window unit that is half the weight and one third the size look mighty good, especially when it is one tenth of the price.

pv - still sweating at anchor

BTW the Cruise Air is for sale $250
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Old 30-07-2007, 15:53   #8
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The Xantrex 1000 is rated for a surge to 2000 watts so it may be able to hand the start up surge.

We're not at dockside so if this won't work at the mooring it's a non starter. I am not getting a genset either as I can't stand the noise and the nussance.

I suppose I could look for even smaller AC units...

jef
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Old 30-07-2007, 16:07   #9
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I don't have A/C on board and this thread is of interest. Does anyone know how many BTU's get cranked out of an engine driven compressor / refrigeration system for a holding plate system?

Hmmm.....
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Old 30-07-2007, 16:21   #10
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If you had a hold over plate that you blew air over it might work, but havuing the engine running is a non starter.

It appears that the smallest window ac is 5000 btu and rated at 4.7 amps... designed for rooms of 100-150 sq ft.. that would cool my entire boat!

jef
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Old 30-07-2007, 16:36   #11
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It goes by cubic feet. Say 125 sq feet x 8 feet tall, so 1000 cubic feet is what it's designed for in a well insulated room in a house. Boat's aren't as well insulated, as least mine's not, so that will have to be factored into cooling requirements. I'd say derate it by 1/2, right?
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Old 30-07-2007, 16:59   #12
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Depends... my hull is cored and seems to be well insulated. I am sure a 5000 btu would cool it, but finding the amps is the issue.

jef
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Old 30-07-2007, 22:31   #13
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Just get a small 2000W gen to run it. Just watch the exaust fumes.
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Old 31-07-2007, 03:09   #14
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The Adler Barbour “Cold Machine” (utilizing a Danfoss BD50F compressor) is rated at 650 BTU/hr. maximum @ +25F evaporator.

Glacier Bay used to offer an 6000/BTU/h Air-Conditioning accessory (“Arctic Air” ?), for their holding-plate style refer units.

A rough rule of thumb, is to size air-conditioning at about 15 BTTU/h of cooling per cubic foot of cabin volume.
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Old 31-07-2007, 13:01   #15
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Hi,
Just for fun, Google "portable air conditioners". You will find pages of small, free-standing floor units about the size of a dehumidifier (which they also are). They vent to the outside with a 5" hose and can be had as large as 15000 btu, still running off 115VAC. I am seriously tempted to put one of these in our shower stall. They only cost around $400 or less. The better one are a heater, A/C, dehumidifer and a fan. Because they don't use a water pump, the starting loads should be quite a bit less, perhaps allowing the inverter to work??
Richard
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