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Old 12-03-2019, 20:11   #1
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How to run an 18000BTU A/C at Anchor

Hi Everyone :
I have a 38īsailboat that we purchased 10 months ago. We live in S. FL. and the summer months get brutally hot. There is an 18000 BTU A/C on board, but no Genset. There is no room to put one in, as space is limited and extremely expensive. I have (2) 4D AGM parallel Batteries as house bank and (1) 4D AGM for the Magnum 3300 KW inverter. (4) Solar Panels at 80 Watts each. It had an Eclectic wind generator which was not on the boat when I bought it. All that would be needed would be the wind generation system everything else is in place.

What would be the best and most economical way to be able to run the A/C while at anchor? Would it be with a soft start and a 2200 KW generator? Thru the 120V system or would the inverter be the best way and charge the batteries with the generator? or is there any other way you can suggest?

Thank you in advance for any help that you can give.

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Old 12-03-2019, 20:51   #2
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Re: How to run an 18000BTU A/C at Anchor

18000 btu roughly translates to 4000-4500 watt so a 2200 watt generator wont be able to run it as you are 2000 watt short and neither will your 3000 watt inverter as its 1000 watt short

4000watt divided by 13.8 volt is 289ampere , so you would be able to provide almost 300Ah from your battery bank to run your A/C ? (A 600Ah lead , agm or gel batt bank will run your A/C for one hour before getting close to empty)
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Old 12-03-2019, 21:18   #3
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Re: How to run an 18000BTU A/C at Anchor

No way without a 5 kw generator.

Open the hatches, add a windscoop or two and enjoy the silence.
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Old 12-03-2019, 22:24   #4
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Re: How to run an 18000BTU A/C at Anchor

I'd ditch the ac unit. Save yourself the cost of not just getting a system to be able to handle it, but the cost to run it. Itd open up space for more storage.

Wind scoops, 12v fans properly placed can help create a good draft at lower power consumption. Not economical to run AC unless you are on shore power
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Old 12-03-2019, 22:41   #5
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Re: How to run an 18000BTU A/C at Anchor

What rules the following video out is you said "economical" but if you throw economics out the window, yes it is possible:

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Old 12-03-2019, 22:51   #6
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Re: How to run an 18000BTU A/C at Anchor

impractical, not just too expensive
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Old 12-03-2019, 22:56   #7
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Re: How to run an 18000BTU A/C at Anchor

Sail to Maine?
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Old 13-03-2019, 01:58   #8
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Re: How to run an 18000BTU A/C at Anchor

Thanks for the video RSN48. What I meant about economical was not installing a $9k dollar generator on the boat. Do you think that it would be able to run with the soft start and a small 2200 generator? I think that the cost would be around $1000.00 to install.
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Old 13-03-2019, 03:18   #9
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Re: How to run an 18000BTU A/C at Anchor

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Originally Posted by ReneJK View Post
18000 btu roughly translates to 4000-4500 watt so a 2200 watt generator wont be able to run it as you are 2000 watt short and neither will your 3000 watt inverter as its 1000 watt short
While 1 watt is roughly equal to 3 btu-hr, you aren't directly converting electricity into coldness, so you can't do a literal conversion of the air/con rating into watts.

What you are doing is extracting EXISTING heat BTU from the inside air and transferring it to the water the boat is sitting in. Imagine picking up a chunk of ice from outside and bringing it inside to cool down your drink, the energy you expend picking up the ice and carrying it inside is not equal to the BTU value the ice has for cooling of the drink.

Now back to the question. We used to have a 12k btu that I measured at around 12amp @ 120v when running (or about 1450w). 18k btu is about 50% more so probably a bit north of 18 amps (just shy of 2200w) though it might not be exactly a linear relationship so this is a rough estimate.

Running it off solar or wind...not for any practical length of time. 320w of solar will generate around 1300w-hr per day. If you use nothing else, you have a little over 1/2hr of run time generated (1300w-hr/2200w). Wind will do a little better if it's a windy day but if it's calm hot and sticky, it adds nothing. (plus if you aren't using it as it's generated, you need a big battery bank to store the necessary power)

Now to the portable generator, this is a viable option but likely not a tiny 2200w unit. Most manufactures advertise "PEAK" output. Continuous output is likely 1600-1800w, so likely not enough to keep up with 2200w continuous.

You are probably looking at something around 3500w with the soft start capacitor to run 18k btu.

PS: make sure to take safety precautions using a portable generator. It can be done with reasonable safety but it's also easy to be unsafe. In particular the CO from the exhaust if you don't have a good place to direct the exhaust. Then there is the heat from the exhaust and safe gasoline handling (similar to dingy motor gasoline handling).
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Old 13-03-2019, 04:08   #10
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Re: How to run an 18000BTU A/C at Anchor

You can not do what you want with existing batteries and equipment. Period.
Here is a link to battery powered A/C set up.

https://www.coastalclimatecontrol.co...tallation.html
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Old 13-03-2019, 05:41   #11
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Re: How to run an 18000BTU A/C at Anchor

The soft start alone is going to be over $300.

https://www.microair.net/products/ea...nt=30176048267

I would prepare for the final install to be closer to $1500 minimum, after you've done all cabling and such, and have a very low end generator.

You'll also be making a lot of fuel runs. Factor that cost in as well.
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Old 13-03-2019, 05:49   #12
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Re: How to run an 18000BTU A/C at Anchor

Triple that or more
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Old 13-03-2019, 06:52   #13
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Re: How to run an 18000BTU A/C at Anchor

The reality is that the hot days here in S. Florida for the 4 months will make it worthwhile, meaning the $1000.00 cost for the a/c, this would be what I would be probably spending if I buy the soft start and buying a 2500kw genset (not Honda) at $550 +/-..

I was thinking that the genset would be recharging the batteries and not running the a/c direct, can this be possible?

Thank you all of your input much appreciated.
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Old 13-03-2019, 06:56   #14
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Re: How to run an 18000BTU A/C at Anchor

Quote:
Originally Posted by ReneJK View Post
18000 btu roughly translates to 4000-4500 watt so a 2200 watt generator wont be able to run it as you are 2000 watt short and neither will your 3000 watt inverter as its 1000 watt short

4000watt divided by 13.8 volt is 289ampere , so you would be able to provide almost 300Ah from your battery bank to run your A/C ? (A 600Ah lead , agm or gel batt bank will run your A/C for one hour before getting close to empty)

Is the air con a 120volt unit or 12volt unit. I thought the OP sad he would be powering it off the inverter. Lots of vids on the Easy Start unit and there is one where they are powering a 16000 BTU unit with the Honda 2200.


I think the 3000 watt genny would do it. The Op could try it with one 2000 and if it didn't kick then could get a second Honda unit and tether them. I wonder if you could simply turn one of the gennys off once the compressor is running.
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Old 13-03-2019, 07:16   #15
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Re: How to run an 18000BTU A/C at Anchor

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I was thinking that the genset would be recharging the batteries and not running the a/c direct, can this be possible?
It's possible in the general sense but not with the specifics you gave.

As indicated, the air/con is likely going to want around 2200w continuously and the 2200w generator is likely rated for around 70-80% of the 2200w peak rating when used continuously.

Also you are going to need a monster battery charger...probably north of 250amp @ 12v as they aren't 100% efficient.

Then you have to look at the ratings of the inverter. Is that peak or continuous rating. Also, some inverters get funky with starting loads and will cut out.

It really is more cost and complication than getting a bigger generator (or a pair of 2200w that can be paralleled)
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