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Old 10-05-2011, 14:36   #1
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Air Conditioning on Batteries Only

Anyone out there run their ac on batteries alone. We want to have system on a 45ish cruising cat that is able to run everything(within reason) without having to use the generator. I recall some threads and or articles regarding this subject but can't seem to find them. Someone was talking about a totally dc system with two powerful inverters and a larger than normal battery bank as well as a generator whose sole job was to charge the house bank. Anyone familiar with a system similar to this?

Thanks Will
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Old 10-05-2011, 14:57   #2
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Re: Air conditioning on batteries only

The only boat I am familiar with that can run the AC's off the battery bank is Steve Dashews, Sundeer something or other. The boat's name is Beowulf, and there was/is a horrendous large battery bank on board. Partially to provide ballast but I believe I remember him stating that the boat could run a week, including AC, just on the battery bank. I know I couldn't afford that many batteries and I already have a crushed disc from trying to change out one 4D battery on my own.

Personally, I'm guessing you are looking at perhaps two 16,000 btu AC's and I'd stick with the genset. Each AC would probably need at least a 3KW inverter, heavy duty selector switches and the power drain would probably not be real good for the batteries.

Not an expert, but just my 2 cents.

Rich
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Old 10-05-2011, 15:10   #3
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Re: Air conditioning on batteries only

Air conditioning on batteries only won’t be practical, for most of us.
In your case:
Assuming an air conditioned space of about 1,800 Cubic Feet, requiring (>14 BTUH/Cubic Ft) about 25,000 BTUH of air-conditioning; you’d consume over 3 KW/Hr of electricity, just to operate A/c. That’s over 250Amps of 12 Volt Power (per running hour).
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Old 10-05-2011, 15:18   #4
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Re: Air conditioning on batteries only

What they said. It's just not practical.
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Old 10-05-2011, 15:55   #5
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Re: Air Conditioning on Batteries Only

As the OP stated the problem, it isn't practical. But running one or maybe two small A/Cs overnight on a big cat may be practical.

A 5,000 BTU unit will cool a state room in the evening. In fact it will probably only have a 50% duty cycle after initial cool down. A 5,000 BTU unit draws about 6 amps AC. That is about 70 amps DC input to the inverter and at a 50% duty cycle it will take about 300 amp hours to run it all night. Not too bad a load for 3-4 pairs of golf cart batteries at 660-880 amphour capacity.

Double those numbers for two staterooms.

But what comes out must go back in. It will probably take at least 3 hours of genset running time to put back those 300 amp hours as the max you should charge flooded cells is 50% of their capacity and the charge rate will drop as they get full. And you need to run the genset at least an hour before bed to cool things down first.

But it is a good way to keep a genset well loaded, running it 4 hours each day to recharge the batteries and cool down the stateroom. Many gensets run all night long at a very light load and end up with glazed cylinder walls.

So, if all you want A/C is for comfortable sleeping at night, this might work. I have read of a few who have tried it.

As far as a packaged solution Mastervolt makes a "hybrid genset" which packages a small diesel generator with an integrated inverter/charger. The genset automatically starts and stops to supplement the inverter and charge up the batteries. So far it is only available in 220/50Hz though.
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Old 10-05-2011, 17:02   #6
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Re: Air Conditioning on Batteries Only

Its basic maths... Most cats max out their battery bank in that size range between 600 and 900 amp hour banks.... that leaves 300 or so max before recharging.... so even if you just ran it overnight without huge solar panels and wind gen. and it "only" used 300 ams hrs from your batteries.... you cant charge the battery bank in the daytime without running the gen. or engines to charge it.....I live in the tropics and the air runs about 80 - 90 % of the time in the day and about 60% of the time at night......there is no way i can run it without the gen running.....my battery bank is 660 amps.......

Also we are all assuming thats all we are running on the boat... probably you have another 30 - 40 amps on refrigeration.. lighting pumps etc.... I have one of those little honda generators... 2000kw or whatever the little red thing is... I plug the air into that... hook up the dingy gas can... sit it on the back swim platform and a 6 gallon tank lasts me a week of running the air in two cabins every night..... thats about 4.oo a night in gas....... and 4.oo a night is very little to pay for cold sleeps in hot weather. The generator has been fail proof for the last year and a half..... and we upgraded to a bigger air con unit When we saw how efficient the little red thing was.
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Old 10-05-2011, 17:16   #7
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Re: Air Conditioning on Batteries Only

Quote:
Originally Posted by djmarchand View Post
As far as a packaged solution Mastervolt makes a "hybrid genset" which packages a small diesel generator with an integrated inverter/charger. The genset automatically starts and stops to supplement the inverter and charge up the batteries. So far it is only available in 220/50Hz though.
My 2006 Mastervolt 6 is set up to auto-start and stop based on battery state-of-charge from the Mastervolt battery monitor.
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Old 10-05-2011, 18:39   #8
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Re: Air Conditioning on Batteries Only

Easy answer, NO!!!!!!
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Old 10-05-2011, 20:48   #9
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Re: Air Conditioning on Batteries Only

Maybe sail in higher latitudes?
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Old 10-05-2011, 20:56   #10
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Re: Air Conditioning on Batteries Only

welcome to the forum.

fans work when you're out on the water. really.

if ventilation is important to you, buy a boat that ventilates really well. then you won't have to air condition it.
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Old 10-05-2011, 21:42   #11
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Re: Air Conditioning on Batteries Only

Quote:
Originally Posted by sailingaway221 View Post
Its basic maths... Most cats max out their battery bank in that size range between 600 and 900 amp hour banks.... that leaves 300 or so max before recharging.... so even if you just ran it overnight without huge solar panels and wind gen. and it "only" used 300 ams hrs from your batteries.... you cant charge the battery bank in the daytime without running the gen. or engines to charge it.....I live in the tropics and the air runs about 80 - 90 % of the time in the day and about 60% of the time at night......there is no way i can run it without the gen running.....my battery bank is 660 amps.......

Also we are all assuming thats all we are running on the boat... probably you have another 30 - 40 amps on refrigeration.. lighting pumps etc.... I have one of those little honda generators... 2000kw or whatever the little red thing is... I plug the air into that... hook up the dingy gas can... sit it on the back swim platform and a 6 gallon tank lasts me a week of running the air in two cabins every night..... thats about 4.oo a night in gas....... and 4.oo a night is very little to pay for cold sleeps in hot weather. The generator has been fail proof for the last year and a half..... and we upgraded to a bigger air con unit When we saw how efficient the little red thing was.
The Honda 2000 will run AC? How many btu's? A 110VAC AC system? How does it handle startup of the compressor(s). I was told this wouldn't work because of startup current draw.
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Old 10-05-2011, 22:48   #12
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Re: Air Conditioning on Batteries Only

Redcobra, I run can run a 5000 BTU AC that has a starting load of over 3000 watts on a Honda 1000 watt generator. After losing power for several days after a huricane I ran a 10,000 BTU wall unit on a Honda 2000. The trick is to install a starting capacitor on the compressor.
This is the company that makes them: http://www.supco.com/images/pdfs/AC%...%20Booklet.pdf
I think many marine ac units are coming with them already installed.
To get an idea of the starting load of your AC, look on the label of the compressor for the "Locked Rotor Amps" or LRA. Your starting load will be close to that.
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Old 11-05-2011, 16:55   #13
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Quote:
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Redcobra, I run can run a 5000 BTU AC that has a starting load of over 3000 watts on a Honda 1000 watt generator. After losing power for several days after a huricane I ran a 10,000 BTU wall unit on a Honda 2000. The trick is to install a starting capacitor on the compressor.
This is the company that makes them: http://www.supco.com/images/pdfs/AC%...%20Booklet.pdf
I think many marine ac units are coming with them already installed.
To get an idea of the starting load of your AC, look on the label of the compressor for the "Locked Rotor Amps" or LRA. Your starting load will be close to that.
Hop car out of curiosity what would you gustimate your fuel efficiency at? How many hours would you say one gallon of fuel provides, or whatever the tank capacity of your generator is?
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Old 12-05-2011, 12:59   #14
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Re: Air Conditioning on Batteries Only

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Originally Posted by redcobra View Post
The Honda 2000 will run AC? How many btu's? A 110VAC AC system? How does it handle startup of the compressor(s). I was told this wouldn't work because of startup current draw.
I plugged a 10000 btu right into it and it went fine ... It did surge during start of the compressor but it does not kick off line. I get about 6 to 7 nights 8 hours approx. per dingy tank of gas with the tank fitting for the generator..... it has 6 gallons in the tank I think so. 56 hours / 6 gallons. 9 hours per gallon or so?
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Old 12-05-2011, 13:53   #15
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Re: Air Conditioning on Batteries Only

Kolya, My Honda 2000 holds a gallon of gas which is not enough to get me through the night. I think I get about eight hours. I just top it off before going to bed and the cabin stays cool long enough that I don't have to go out and restart it in the middle of the night. There is a replacement fuel cap for the Honda generators that allows you to conect them to an external tank. A little 3 gallon outboard tank would let you run all day. Fuel consumption will vary with the air temp and your thermostat setting.

I see Sailingaway runs a 10,000 btu unit on his Honda. I bet his AC came with a starting capacitor. Borrow a generator and try it before you buy a starting capacitor, you might not need one.

Sailingaway, Do you run your generator on the Econo setting?
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