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Old 03-06-2011, 14:58   #31
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Check out zrd-dot-com. No real life experience, but having read the web site, having a high output 12vdc generator dedicated to a decent sized battery bank makes sense. The owner says he regularly runs his A/C overnight this way.

Again, no affiliation, no endorsement.
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Old 03-06-2011, 16:01   #32
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Re: Air Conditioning on Batteries Only

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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.
Hey Bash you are right and just think of the small footprint I have a 5000BTU unit installed in my saloon and use it when in the marina for Cyclone season it runs 24/7 as here in Far North Queensland the humidity is over the top and the only way to keep the boat dry is to aircon. Really the only time I use it when cruising is if the no-see-ums ( sand flies ) get really bad I shut the boat and turn on the A/C the Honda 2Kva will last about 8hrs on Eco so I end up with a great nights sleep.
I wonder why people are on boats if they cant live with the beauties of nature and have to have a genset running to spoil the peace Jacko
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Old 03-06-2011, 17:18   #33
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Re: Air Conditioning on Batteries Only

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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
Not a live-aboard here, look forward to it someday, if I can stop practicing on my homestead. Have 11 years off the grid at one time. Cheating, have a gas well with an unlimited tap. Ran my house and homestead off of a Briggs-and-Stratton 12hp riding lawnmower engine. (it was very used when I got it!) Delco externally regulated "lifetime warranty" from Auto Zone driving into forklift batteries. (somewhere else on this forum, someone suggested using a potentiometer!" At 1100lbs each, the seem like a drop in the bucket compared to the lead carried by keel boats. Trace 4024 inverter supplying 115 only to the "house". Go Now, Go Large with your battery bank, you will figure out how to fill them, a XX volt system with direct controlled charge system should qualify as a battery management system and allow you to use the source that best meets the situation.

I did notice that your preference is for a catamaran and this is what is perplexing me, how to do it and still stay light. Gell cell swing keels!!!
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Old 13-06-2011, 15:37   #34
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Re: Air Conditioning on Batteries Only

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My 2006 Mastervolt 6 is set up to auto-start and stop based on battery state-of-charge from the Mastervolt battery monitor.
Hi Folks,
Can anyone help me with info/recomendations for the Mastervolt GPX-5/6's. I am thinking of buying one and havn't been able to locate any reviews other than by vendors.
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Old 15-10-2014, 07:05   #35
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Re: Air Conditioning on Batteries Only

Hello, the last reply on this thread dates back to 2011 and there is a reference to the ZRD website. I was introduced to this ZRD system at the recent Annapolis boat show, ( Oct 2014). This seems like a very well thought out workable system. In the last 3 years has anyone else had ( or spoken to) anyone using this system. It is expensive but there is a price to be paid for quality and reliability claimed. In fact if the ZRD website is to be believed, the true cost over 2-4 years is zero when you take into consideration the fuel savings.

Regards Ian
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Old 15-10-2014, 09:10   #36
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Re: Air Conditioning on Batteries Only

We have many clients (for many years) running high inverter loads like AC from GLi batteries. Li batts support such loads much better than any Pb as there is so much less voltage sag under the loads. So more of the battery capacity can be used without inverters cutting out from low voltage, and the inverters run a bit cooler as well since the higher voltage means a bit less current. We have larger boats with GLi banks running as many as 3x 8kW inverters, powering who knows what AC loads...stoves, water heaters, washer/dryers, air compressors, etc. etc. Not an inexpensive setup...however happy clients.
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Old 15-10-2014, 10:15   #37
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Re: Air Conditioning on Batteries Only

FYI there is another solution but not off-the-shelf (yet, or ever in the USA?). We worked with a company in Japan designing cooling for truck cabin sleepers that would provide overnight cooling when the main engine was off and uses less than 1 amp.

It works this way.

Only when the main engine is running, a small 24 volt refrigeration compressor freezes an eutectic chamber. This is essentially an insulated tank filled with water and glycol to lower the freezing temperature to about 10 degrees F. Running all day the truck engine has minimal electrical load to freeze the holding tank.

At night a small blower drawing about 1 amp blows cabin air through air conditioner like fins in a tube through the holding tank, cooling the air in the cab. Since the normal A/C had already cooled the cab all it had to do was maintain it.
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Old 15-10-2014, 10:42   #38
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Re: Air Conditioning on Batteries Only

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Only when the main engine is running, a small 24 volt refrigeration compressor freezes an eutectic chamber. This is essentially an insulated tank filled with water and glycol to lower the freezing temperature to about 10 degrees F. Running all day the truck engine has minimal electrical load to freeze the holding tank.
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going to take a real big tank to cool the inside of a boat, and most sailboats aren't going to run the engine all day in order to cool it
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Old 15-10-2014, 10:54   #39
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Re: Air Conditioning on Batteries Only

The same concept (freeze a large chiller bank when power is cheap, then use that cold source during the daytime) has been used in skyscrapers for years now. I think the catch for a sailboat would be adequately sizing the chiller bank, and then finding room for it on the boat. How many btu's can you store in how many cubic feet?
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Old 15-10-2014, 10:58   #40
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Re: Air Conditioning on Batteries Only

Well most larger boat AC units are 16,000 BTUs and a refrigeration ton is 12,000 BTU. That's a lot of ice!
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Old 15-10-2014, 11:10   #41
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Re: Air Conditioning on Batteries Only

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The same concept (freeze a large chiller bank when power is cheap, then use that cold source during the daytime) has been used in skyscrapers for years now. I think the catch for a sailboat would be adequately sizing the chiller bank, and then finding room for it on the boat. How many btu's can you store in how many cubic feet?
Another engineering "trick" that can be used in certain climates (where the nighttime temperatures are much lower (60F) than daytime highs (90+F), like in desert areas like Sacramento, and much of northern California east of the coastal hills) is to use evaporative cooling and store the cooler water at night in tanks.

It's great on land and in skyscrapers/office buildings, not so useful on boats. Easier to open the hatch. Also not useful in hot humid areas, and where it doesn't cool off at night.
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Old 15-10-2014, 11:58   #42
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Re: Air Conditioning on Batteries Only

Evaporative cooling doesn't work very well in humid environments, like where boats usually are

No matter what trick you try, it all amounts to how much energy you can make in a given amount of time, however you choose to store it, whether electrical or heat, unless of course you can pump cold seawater from 5000 ft deep or figure out how to make evaporative cooling or similar work.
Your going to have to have a solar farm, a wind farm or a generator or all of them, the energy has to come from somewhere.
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Old 15-10-2014, 15:40   #43
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Re: Air Conditioning on Batteries Only

Thanks for the responses everyone.
Especially Bruce. I went to your site and liked the Firefly batteries. I am not sure of the safety of Lithium batteries yet. Unfounded I know, and the admiral is even more sceptical than me.
If I was installing an electrical system in a new boat I would definitely go the Large battery bank route with inverters and a small diesel DC motor powering a very high output alternator to charge them. However we have large CAT with 2 x 16K BTU aircon units and the Genset is already installed and working. Tough to keep it, because if you do the sums it would probably be cheaper to sell it and the current inverter/charger and install the large battery bank and inverters. Return on investment is 2-4 years depending on usage.
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Old 16-10-2014, 03:19   #44
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Re: Air Conditioning on Batteries Only

In my opinion, A/C on batteries is practical only with lithium batteries. If I were to do this, I would choose an A/C system that runs directly on DC, avoiding the need for a large inverter. I would also keep the capacity of the A/C system to a minimum.
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Old 16-10-2014, 07:49   #45
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Re: Air Conditioning on Batteries Only

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Evaporative cooling doesn't work very well in humid environments, like where boats usually are

No matter what trick you try, it all amounts to how much energy you can make in a given amount of time, however you choose to store it, whether electrical or heat, unless of course you can pump cold seawater from 5000 ft deep or figure out how to make evaporative cooling or similar work.
Your going to have to have a solar farm, a wind farm or a generator or all of them, the energy has to come from somewhere.
That's actually an interesting idea. Most marine units use water that's picked up within 2-3' of the surface. That is also usually the warmest water.

If you had an easily deployed pickup hose that could be deployed even 10-20' down, you might be able to pick up water than is 10-20 degrees cooler, significantly increasing the cooling efficency of the unit resulting in less cycling.

In a northern area (say the great lakes), could you bypass the compressor entirely. It's not unusual in the summer to have 50-60 degree water 5-10ft down in the dead of summer. Simply have a pickup line run that water thru a radiator and run air across it. Now you are simply running a efficent low draw pump and a fan (maybe 5-10 amp total at 12V-DC). Now we are talking about a practical system to run off batteries.

The only thing to ponder is a 60 degree radiator isn't as cold as a typical AC so how much cooling will it generate and is there a way to improve the thermal efficency enough that it is effective.
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