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Old 18-02-2015, 13:04   #16
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Re: My quest for a quiet night - Inverter transiton for a power boat money question

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Originally Posted by darylat8750 View Post
No reasonable battery bank would run our air conditioning all night............
Or anyone else's. Get that thought out of your mind. Figure out how to minimize your electrical usage and learn to live with that. Small fans use much less power than air conditioners. LED Lighting uses about 10% the power as incandescent.

I'm not suggesting not upgrading your batteries and inverter, but remember, once you leave the dock you must be self contained until you get to the next dock.

Remember, batteries are not permanent. You will get three to seven years of service (yea, someone will pop up and say his lasted longer) out of them and then have to replace them.

If it gets unbearably hot, take a slip in a marina and run the AC. You can spend a lot of nights at marinas for what it would cost to try to run that AC
from batteries.
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Old 18-02-2015, 13:12   #17
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Re: My quest for a quiet night - Inverter transiton for a power boat money question

I have an aft cabin berth, 460AH of batteries, and 280W of solar. I don't see why you need to run your generator at night?
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Old 18-02-2015, 13:16   #18
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Re: My quest for a quiet night - Inverter transiton for a power boat money question

Guys, right now I don't have an inverter which is why I have to run the generator.

I didn't think about the load from the A/C's so I need to take that out of the thought process.
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Old 18-02-2015, 20:11   #19
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Re: My quest for a quiet night - Inverter transiton for a power boat money question

Well if you run the A/C, it will make noise and still won't be quiet.
I suggest you need better insulation, so you can cool down the sleep area with gen running, and then turn it and the A/C off for the night and stay cool and quiet.

Having a big battery bank and inverter isn't bad idea in any case, just not sure it really solves your problem.
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Old 19-02-2015, 05:03   #20
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Re: My quest for a quiet night - Inverter transiton for a power boat money question

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Well if you run the A/C, it will make noise and still won't be quiet.


Good point. When we have both ACs on, we can hear those almost more than we can hear our generator. One component is fan noise, another is the seawater pump, depending on where we are in the boat.

Recapping: K9 hopes to run ACs (and other stuff) overnight at anchor without genset noise, and postulates an inverter/battery bank might solve that. Note that K9 is in FL, with hot humid summers. I think no mention yet about whether the genset is diesel or gas. If former, overnight running could be acceptable, except for noise. If latter, maybe not so much.

If the inverter won't run ACs... as several have suggested... perhaps another course of action is to simply beef up battery banks (as proposed), reduce consumption (LEDs and so forth), run the ACs when the genset is operating anyway, and go the fan route. (Or enjoy marinas during the most unbearable part of the season. ) For that, inverter(s) may or may not be necessary at all; depends on the "other stuff."

??

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Old 19-02-2015, 13:45   #21
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Re: My quest for a quiet night - Inverter transiton for a power boat money question

Great recap!

The genny is diesel and you are correct that hot humid Florida nights are what I get to experience. With three A/Cs running it barely breaks 78 degrees in the cabin during the day and maybe hits 72 at night.

Oddly enough we are forecasted to get down to 19 degrees tonight!

When we are in a marina and hooked up to power you can barely hear our A/C's running so I'm not sure what I would hear, if anything, with them on an inverter.

Known power draw would be the fridge and freezer which is 115v at 3amps per appliance. Up to three A/C's at 115V at 11amps. The occasional LCD TV on for 3-4 hours a day to watch movies, the coffee maker in the morning and the microwave on for 3.5 minutes to cook popcorn.

Doing the math that comes out to 3795 watts for the A/Cs, 690 watts for the freezer and the fridge and add another 400 watts for good measure to the TV, microwave and coffee maker.

If the A/Cs cycle for 8 hours a day that's 1/3 which is 1265 watts in a 24 hours period right?

The fridge and freezer would cycle at 1/3rd as well which puts it at 230 watts.

For anything like using the cooktop or water heater I would run the genny which would recharge the batteries too.

Am I looking at this correctly?
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Old 19-02-2015, 13:58   #22
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Re: My quest for a quiet night - Inverter transiton for a power boat money question

Take your AC amp draw and multiply it by ten. That's roughly the current you will be drawing from the batteries at 12 volts DC. Don't worry about watts. Your 11 amp airconditioner will draw roughly 110 amps from your battery bank. That's each airconditioner. Running one for eight hours would consume roughly 880 amp hours. Can your battery bank handle that?

If it was actually practical to power a boat's AC with batteries, people would be doing it. Boats would come from the factory with battery powered airconditioners. They do not.
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Old 19-02-2015, 14:07   #23
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Re: My quest for a quiet night - Inverter transiton for a power boat money question

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Take your AC amp draw and multiply it by ten. That's roughly the current you will be drawing from the batteries at 12 volts DC. Don't worry about watts. Your 11 amp airconditioner will draw roughly 110 amps from your battery bank. That's each airconditioner. Running one for eight hours would consume roughly 880 amp hours. Can your battery bank handle that?

If it was actually practical to power a boat's AC with batteries, people would be doing it. Boats would come from the factory with battery powered airconditioners. They do not.
About to post the exact same but you were faster on the draw.

Yes, a simple rule of thumb is ten times the amps when going from 120V AC to 12V DC. If you want to get picky when you allow for inefficiencies, power factors, etc it will be even worse.

In specific, technical terms, it would take a ton of batteries to run a single air con overnight. And to charge them in a reasonable amount of time would take a MONSTER battery charger.
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Old 19-02-2015, 14:08   #24
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Re: My quest for a quiet night - Inverter transiton for a power boat money question

Wonder what your 'goodies' are that you run all night? Could we get a list?

Very light consumption:
- TV, fans, LED lighting, LED anchor light, occasional microwave oven, occasional power tools (drill, palm sander, vacuum, and kitchen appliance

Manageable (if your are willing to run generator/ or main engine for 30-1hr sometime in late morning):
- Small refrig, 3-5 minutes of toaster, hairdryer, single-serve coffee/ then turn off after each use, carafe drip coffee/ turn off after made/ use microwave to heat up for late risers. Small water heater/ 15 minutes/ turn off

What you can't do with inverter/ battery system you described:
- Run air conditioning all night, run hot water heater all night,
run electric heater or anything that makes heat on all night (coffee pot, ...).

Things that 'heat' usually pull 10 -15 amps/ 1000w -1500 watts at 120v. When run from 12v via an inverter the very rough rule of thumb is take the 120v amperage (in this case- 15A and multiply by 10. 15A x 10 = 150A at 12V (via Interner). Even your spec'ed battery system would soon be dead at that constant load.

But without these big loads, my typical evening battery load, with TVs on, 4 cabin fans, smallish frig, cabin LED lighting lit up like an operating room, all iPhones/Pads charging, (what else is there??) is about 10 amp average discharge rate for approx 3 hours while everyone is up at night and average of 2 amps while sleeping (TVs & lights off)... I typically used abt 50 amp-hours... less than 1/4 your battery capacity. 50 amp-hour drain is a good target because it allows you to fully recharge the batteries the next day with about an hour of generator run time or 20a of solar for 5 hours. Or you moving your location using your main engine for an hour or so. Or, at 50 amp-hour usage and a little or no solar charging you can stay put in totally silent mode for two days.

What you can't






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Old 19-02-2015, 15:34   #25
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Re: My quest for a quiet night - Inverter transiton for a power boat money question

Well shoot... I was really hoping to be able to run an A/C but understand now why I cannot. I'll just have to tick off the neighbors in the anchorage if its too hot.

The goodies are simply that, things like the TV or the coffee maker and the microwave. Things that I don't considered very high value but would like to be able to run. The mandatory is the fridge and the freezer though.
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Old 19-02-2015, 15:40   #26
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Re: My quest for a quiet night - Inverter transiton for a power boat money question

Fans are really effective, particularly in humid climates like FL and particularly for sleeping as you can direct them exactly where you need them.

12 volt DC fans are expensive, especially those for the "marine" market, but AC fans, run off the inverter, can be dirt cheap and you can have a small one for each bunk.

With a fan and the hatches open you can hear what it going on outside better than with A/C which can actually lead to more restful sleep!
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Old 19-02-2015, 15:53   #27
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Re: My quest for a quiet night - Inverter transiton for a power boat money question

If you are worried about noise then get an exhaust separator for the generator and you can also use them for the air conditioners. The water exits the boat below the water line so you don't get the splashing noise which can be a great irritant. Also, as has been previously mentioned ensure your generator is in a good sound enclosure and maybe even add sound insulation to the inside of space that the generator is in.
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Old 19-02-2015, 16:10   #28
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Re: My quest for a quiet night - Inverter transiton for a power boat money question

Reducing your consumption will mean you can run the gennie less. We only run our gennie to heat hot water or top up the batteries if the solar cant keep up. Start with changing your usage. We don't go without. We just don't use inefficient power hogging appliances.

We don't use our 2000W inverter much now We've moved nearly everything to 12V. The laptops and tv can run from 300W plugin inverters. We only turn the inverter run when running the microwave or barmix.

We have 675 Ahr house battery, 280W solar and wind.

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Old 20-02-2015, 05:17   #29
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Re: My quest for a quiet night - Inverter transiton for a power boat money question

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Well shoot... I was really hoping to be able to run an A/C but understand now why I cannot. I'll just have to tick off the neighbors in the anchorage if its too hot.

The goodies are simply that, things like the TV or the coffee maker and the microwave. Things that I don't considered very high value but would like to be able to run. The mandatory is the fridge and the freezer though.


The inverter idea may still be a good one, even if it doesn't solve the ACs. Or maybe multiple smaller point-solution inverters... And in any case, more battery is almost always better. Multiple fans could do quite a lot for you...

Consider what other boats in the anchorage are doing. If they don't have their gensets running, how might they be dealing with the heat and humidity? Or if they do have their gensets on, yours won't be much of a problem.

FWIW, if you have DC/AC fridges/freezers (or other DC/AC goodies), running them via AC-inverted-to-DC is less efficient than simply running them straight from DC. There's some energy loss involved in the inversion process...

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Old 24-02-2015, 10:38   #30
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Re: My quest for a quiet night - Inverter transiton for a power boat money question

Consider buying a whisper quiet Honda 1000 or 2000 watt generator to charge the batteries more slowly. You won't know it is running.
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