Running 6k BTU 'Marine Air' conditioner off batteries?

[Gunn]

So last Friday we went and looked at a 1999 240 Sundancer. Needs some work, but a nice boat overall. Anyway, it has a 6,000BTU Marine Air brand air conditioner with reverse cycle heat. Never saw that in any other 240's I've come across, but a *great* bonus for my wife. It worked fine under shore power.

We were wondering if this could operate while away from a dock using batteries and an inverter? I looked at some specs on the Marine Air website and they show that it puts out 6,000 BTU @ 115VAC with Full Load Amps to cool @ 7.0amps and Full load amps to heat @7.7amps.

I've been reading some topcis here today talking about amp-hours, reserve capacities, power, inverters, etc. and it seems that these numbers are reasonable values to run off of batteries for a period of time (though I have not done any calculations, just off the top of my head).

Can it run off batteries? Also, in reading about alternators, they seem to be rated in terms of say '60amp' alternator. Is this output amps @ 12VDC? I assume the higher the alternator output, the quicker time to recharge a battery...or not use the battery at all (running engine while AC is on).

Just looking for options. My wife was quite disappointed when she found out it could not be used while away from the dock, as our plans were to find a quiet spot and drop the hook on summer weekends... (which are hot and humid here on the Chesapeake).

Thanks,

Tom

 

[estebanj]

I haven't checked amp hours either, but if I recall from previous discussions, it is not practical to run A/C on an inverter. You also need to look at amp capacity when the compressor first kicks in.

What I have heard some people do is run a portable Honda generator on the swim platform, although I >personally< also consider this not practical.

Have you looked to see if an after market small generator will fit in your boat?

Esteban

 

[Presentation]

Gunn – first off, I know what you want to hear. You want a way to make it work w/out a generator. After all, they work on our cars without a generator, right? I also looked into this. To sum up – batteries simply do not have enough storage capacity to hold enough power to run air conditioning for an extended amount of time. As you add more and more batteries you are adding more and more weight and cost. The answer is a generator.

OK, so it’s a generator. Now you have two options. Portable or built in.

Built in – the big negative is the cost. I don’t think you can have this done for you for less then $8,000. A 1999 240 you are likely looking in the high 20’s to low 30’s. Adding a built in generator will work but when you go to sell no way are you increasing the value close to $8,000.

Portable – if you go this route go with the quietest, the Honda 2000i. About a $grand. Noisy and you need to store it somewhere. The storage compartments fill up quick.

Really, no good alternative.

Here is my suggestion since you did not buy yet,………I suggest you keep looking until you find the boat you want at the price you want with the options you want.

 

[wkearney99]

If it's hot enough to be a problem sleeping then get a slip. We have a 34' and a genset and there were only about three weekends this summer here on the chesapeake that were too hot to sleep with out AC. Given most slips end up being about $80/night you'd have to spend quite a few nights with a genset to make up for it. And even with the genset we really only end up running it on three occasions; make the coffee in the morning, blend margaritas at night and when getting dressed to go ashore in the dinghy for dinner. The coffee and blender we could handle with an inverter, if we had one. AC down in the cabin when you've come in from a hot afternoon on the hook is a godsend.

Then there's the whole question of safety running a genset at night. Most certainly DO NOT DO THIS without known-working, permanently affixed Carbon Monoxide detectors. Even if you're going the 'redneck' route with a genset on the swim platform, do NOT leave out CO detectors. They're cheap, certainly a lot less than what your family would pay in funeral costs.

But I'd go with Doug's comment, keep shopping until the right combo presents itself.

 

[Dave M.]

You may want to take a look at the bottom post on this link. Skolbe successfully did what you are asking about. The four golf cart batteries give you about 440 amp-hours. Seven amps of AC load would probably draw about 80 amps at 12 volts. If you ran the AC for three hours, you would use 240 amp-hrs from the 440 amp-hr set, so just a bit over half, with 200 amp-hrs remaining. That is not unreasonable, but you would be limited to about the three hours, four if you push it. Then you need to recharge. A 60 amp alternator would indeed put out 60 amps, so if you ran the engine for an hour, you would replace 60 amp-hrs of the 240 used in three hours of AC use. So you would need to run the engine for several hours to get the charge back up to say 80%. You won't get it much over that without many hours of charging, as the last 20% is much slower for the battery to accept.

So, if you run the engine at speed for three hours, you would put back in 3hrs at 60 amps max, or 180 amp-hrs. Add that to the 200 amp-hrs that were left after three hours of AC use, and you have 380 amp-hrs in the battery out of 440 max, or 86%. In reality, before you get to 86% back in the battery, the battery voltage will likely climb, and the alternator will start backing down on the charging current. That is why I said 'max' in the paragraph line above, you won't likely get that much put back just on the alternator. You would top off the battery when you plug in to shore power.

If you run the engine fast enough for the alternator to put out its rated current, assuming that's 60 amps, then the alternator will be supplying somewhat less than 60 of the 80 amps the inverter is drawing. The reason it is 'somewhat less' is that it also has to supply the other DC load the boat happens to be drawing, such as powering the ignition. My guess is that if you ran the AC while on plane, the AC would cycle on and off, and the alternator may well keep up with the AC.

If Skolbe can do it, it is not impossible. You will need very large cables between the battery plant and the inverter, and they need to be within a few feet (maybe not more than six?) of each other. Don't expect a properly designed and installed inverter system to be inexpensive.

 

[wkearney99]

But what good does only three hours operating the AC do you? Just enough time to fall asleep only to wake up from a deep sleep schvitzing like you're in a sauna? But I suppose it wouldn't be a constant draw and might last longer than 3 hours. Then the question is where the heck would you PUT that many batteries?

Use the right gauge wire and you can go pretty much anywhere in the engine compartment.

 

[Arizona240DA]

Gunn, not to tangent, but where was/is the unit located in the boat?

 

[Dave M.]

But what good does only three hours operating the AC do you?

I just put out some numbers that I think reflect what is possible. I make no claim about whether or not it is adequate for Gunn, only he and the family can decide that. I am a left coastie, so don't have a feeling for the weather there at all.

Use the right gauge wire and you can go pretty much anywhere in the engine compartment.

True, but realize that if you have 0.1 ohms of cable resistance between the battery and the inverter, the power loss, I squared * R, is 80*80*0.1, or 640 watts. This is to supply a load that is a bit less than 1000 watts. The cable connections need to be well done.

 

[Four Suns]

Portable – if you go this route go with the quietest, the Honda 2000i. About a $grand. Noisy and you need to store it somewhere. The storage compartments fill up quick.

Ahh yes... the "It's ok to store gasoline tanks and tools that vent gas vapors into the atmosphere in a closed storage area or engine room" debate. I had this argument this last summer with my oldest son who didn't understand why I wouldn't put a 5 gallon jug of gasoline in the transom locker so they could refuel the dinghy when it ran out of gas. Something about those gas fumes venting out.... Boom!

We have a 34' and a genset and there were only about three weekends this summer here on the chesapeake that were too hot to sleep with out AC.

Man... you must boat on a different Chesapeake Bay than me! Hot + Humid + Bugs = No sleep. My boat does not move enough air without the AC to keep the inside reasonable in the summer and if I've had the engines running during the day, it can be 12 hours later and the engine room is still over 100 degrees and radiating into the boat. I will disclose though that my wife likes to crank the AC down to less than 70 degrees at night and put on the big blankets... just need to keep her happy.

 

[wkearney99]

True, but realize that if you have 0.1 ohms of cable resistance between the battery and the inverter, the power loss, I squared * R, is 80*80*0.1, or 640 watts. This is to supply a load that is a bit less than 1000 watts. The cable connections need to be well done.

I agree that connections are very important. Get an appropriate crimper. The hammer type can be bought (or borrowed) from a local battery place. I picked one up for about $30 (instead of $80 at a boat store). Soldering is not your friend in a marine environment due to vibrations. Then make absolutely sure you're using marine-grade wire, NOT automotive or welding wire. And make certain that all connections are sealed. You don't want to let moisture into the connection to cause corrosion. Marine-grade wire is tinned and will better withstand corrosion but not forever if the connections aren't good.

I disagree on your wattage calculation, as you're not mentioning what gauge wire you're considering. Use the wrong gauge and, yeah, you're absolutely going to waste a considerable amount of power through it. But if you're talking about cranking that much power out of the batteries then you'd better be looking at AT LEAST 1 gauge wire or larger. I found a pretty inexpensive supplier for the wire: http://www.skycraftsurplus.com Other than adding a bit of weight and costing a little more it does no harm to use thicker wire. Just make sure the connections are good and that the wire is WELL supported. But you'd want to do this with any wiring, not just heavier gauges.

 

[Presentation]

OK, I am going to back up a bit here.

Per the above replies the inverter + batteries versus generator debate is still alive.

If you are considering this option, the option of inverter + batteries, remember these are not free. You have the expense of the inverter + the batteries. The batteries have a finite life then need to be replaced. The batteries are heavy. By the time you have the above mentioned quantity of batteries you still can not make it thru one night on the hook. Oh, and when you go to sell the boat you increased the value of the boat less then you did if you added a generator.


Some things are easily added for a modest amount of cost. Some of these are DIY type of projects, saving you even more. Unless you are very mechanical, adding a generator or a inverter + batteries is not a do it yourself project for most. Adding a charplotter is much easier.

I’m going to stick to my original suggestion of looking for used boat within your price range that has the major options already included.

If you desire a used small express cruiser with air conditioning away from the dock, find a boat that already has air conditioning and a generator.

 

[MLauman]

I’m going to stick to my original suggestion of looking for used boat within your price range that has the major options already included.

If you desire a used small express cruiser with air conditioning away from the dock, find a boat that already has air conditioning and a generator.

I have to agree with this sentiment. If you already owned the boat and were trying to shoehorn a solution in place with known trade-offs that would be one thing. But here, you are boat shopping and have apparently identified desired components, ie AC & Genset.

Buy the boat you really want.

 

[Dave S]

Even though it's a bit off topic this may be relevant if you are still thinking about adding a genny or an inverter.

I was inquiring about the cost of a generator for my 260DA yesterday at my dealer since I would like to have one. After quoting me a ballpark figure of $9K, he mentioned that the price has gone up about 2 grand because the only generators they can buy anymore are the new ones with catalytic convertors. That's way too much for me so I will continue to do without one. But like everyone mentioned, understand the tradeoffs and what your options are and if posssible try to get a boat with a generator if that's what you want.

 

[Asureyez]

I a 24 foot boat, these complicated electrical systems just do not make economic sense from my view.

If you want to have a cool cabin on a 24, give serious consideration to make a ice chest air cooler as our guys use in Iraq. One simple type is shown here.

http://www.alpharubicon.com/prepinfo/Portableairc.htm

More sophictiated is the use of a water pump and copper tubing where an ice chest full of ice, A copper tube is snaked back and forth accross the bottom (or coiled in a verticle Igloo type) one end plumbed by plastic tube to a small 12V pump (submergable water fountain type) and the output end brought outside the lid by plastic tubing. This tube are connected to a flat coil of copper tube that sets in front of a 12V fan. Water circulates through the air transfer coal and back into the chest by copper tube. The water recycles and melts more ice wnich makes more chilled water and so it goes, and all can run on a few watts and a amp an hour of 12V!

Guys using them claim that a eight pound bag of ice will chill the cabin air all night long.

Could be a very simple garage project to recycle the chilled water from your beer!

 

[Dave S]

I a 24 foot boat, these complicated electrical systems just do not make economic sense from my view.

If you want to have a cool cabin on a 24, give serious consideration to make a ice chest air cooler as our guys use in Iraq. One simple type is shown here.

http://www.alpharubicon.com/prepinfo/Portableairc.htm

More sophictiated is the use of a water pump and copper tubing where an ice chest full of ice, A copper tube is snaked back and forth accross the bottom (or coiled in a verticle Igloo type) one end plumbed by plastic tube to a small 12V pump (submergable water fountain type) and the output end brought outside the lid by plastic tubing. This tube are connected to a flat coil of copper tube that sets in front of a 12V fan. Water circulates through the air transfer coal and back into the chest by copper tube. The water recycles and melts more ice wnich makes more chilled water and so it goes, and all can run on a few watts and a amp an hour of 12V!

Guys using them claim that a eight pound bag of ice will chill the cabin air all night long.

Could be a very simple garage project to recycle the chilled water from your beer!

Excellent point Chad.............sometimes the simplest ideas like this work the best believe it or not. Here's another tip if you go the ice chest route. Take empty plastic quart soda bottles, fill them up with water, and put them in your freezer at home. They will freeze solid and will not crack. Put three or four of them in the cooler and they will last a lot longer than a bag of ice cubes and you will have no moisture comming from melted ice cubes to deal with either. Then simply refreeze the bottles and use them again. We have been doing this for years........I can't even remember the last time we bought bag ice.

 

[Gunn]

Wow, thanks guys for all the replies. I'm really not interested in the big expense of a generator in this boat. And I assume the reason they offer one as an option is that it just didn't make sense to do so. I hate to shoehorn one in there.

I'm not really sure of the specifics of this air conditioning system other than its made by Marine Air. There is an outlet in the cabin on the starboard side with a dial for on/off/fan. Not sure where the blower or condensor is located.

Thanks for the good calculations on the amp-hours. I don't think 3-4 hours of air would work. And as Gary said it gets HOT here. So, either we wait for a coldfront to flow through, or we visit a marina to stay at; not a bad alternative either way for me.

This boat is right in our upper price range, and had the AC as an added benefit. I doubt we could find one with AC + genset in our range, unless we slid back a few years. I'd like to stay in the 1996+ range.

Anyway, thanks again; we'll see how this boat pans out. We're still sitting on it for awhile while we think about it.

Now to go check out this homemade AC...

 

[Turtlesboat]

I have a 280 without a gen and to be honest, I don't miss it. we stayed on the hook about 10 nights this season and the cool air on the water was enough with the hatches open. On the real muggy weekends we stayed in a marina with power and the A/C was nice. Maybe the only thing that we missed was being able to run the microwave on the hook. But I have a electric/alcohol stove and it works even though it takes a bit longer to heat things up using alcohol. I personally think gen's in smaller boats are over emphasized. down south I'm sure it's a must, but up north I don't think it's a big deal.

 

[RiverRat]

Well, this is the whole reason I'm going through an upgrade right now... I had a 240 DA with air and no gen. but wanted to run things out on the water. I also have the 2000i honda gen. which ran things when on the hook. It was a pain, and unsafe. So it just boiled down to an upgrade in boats. We know the type of boating we want to do, it's just a matter of picking the right boat to fit your boating style. For us it meant moving to a 280 DA with a gen.