Inverter powering air conditioner?

[Ramin]

Do any of you run your air conditioner system with an inverter. The boat I am looking at has ac but no built in generator. I belive it to be a 9,000btu. Its an 87 Hunter 31. I have searched and found that some use the Honda eu2000 and I may go that route, but I am wondering if thier is enough juice to be had in an inverter system to do the job all night and charge durring the day. Any advice would be greatly appreciated!

[brak]

very doubtful. a modest AC would require 8-10 amp of 110v, i.e. something like 1000 watt. Backing out into 12 volt we are talking about 80-90 amps (assuming absolute 0 losses ). Running half the time for 8 hours of the night, you would need 90 amps * 4 hours = 360 amp hours+.

That's about 2 golf-cart sized batteries (drained well below 50%).

Of course to charge back 360 amp hours you would need to run an 80 amp alternator for about 5 hours or so.

[Ramin]

Thanks.

So it looks like it would require too many batteries and too much weight to do the inverter route. When you say golf cart sized, do you mean all six 6 volt or just two of the 6 volts. I drive a golf cart for the church on sundays and do the maintenance on them. There are 6 6v in all to make the 36v total. Are you saying that I would need 2 of them or 2 sets of the 6. My brain hurts.

But I guess 5 hours of charging doesnt make it worth it either way.

Any ideas on any generators other than the Honda 2000?

[mitiempo]

Brak's numbers were a bit off. Golf cart batteries are about 240 AH @ 6 volts. 2 in series is 240 AH @ 12 volts. For 360 AH to only take the bank to 50% SOC you would need a bank of 720 AH - a bank of 6 golf cart batteries in series/parallel.

As far as charging with an 80 amp alternator, running at max you would get 80% charge after about 3 hours. The last 20% would take another 5 to 8 hours as the resistance increases and the batteries accept less and less current.

[Minnewaska]

I can't do all the electrical engineering math for you, but can give you this from practical experience. I have a 400+ amp hour house bank. If the AC is accidentally turned on with the invertor making 110v, it will drop below the auto cutoff in seconds. My invertor is designed not to kill the batts. BTDT

[Ramin]

Originally Posted by Minnewaska

I can't do all the electrical engineering math for you, but can give you this from practical experience. I have a 400+ amp hour house bank. If the AC is accidentally turned on with the invertor making 110v, it will drop below the auto cutoff in seconds. My invertor is designed not to kill the batts. BTDT

My apoligies, but what does "BTDT" stand for?

I'm just wondering if your house bank may not be set up for a high enough discharge rate to run your inverter at max. I am sort of an inventer in my own little shop and have played with inverters alot. I know from experience that you can have alot of amp hours and still not put out the wattage if they arent rated or set up for the right discharge rate. For example a deep cycle sears battery that has 220 amp hours put on a 2000 watt inverter will never reach the 2000 watts alone because its discharge rate can never reach the rate to which the inverter can create the 2000 watts. To do that you would have to have three of the same before mentioned batterie running the inverter at the max 2000 watts. I have a couple of 2000 watt inverters and a 3000 watt inverter that are sitting around to test on. I also have one of the sears batts and two life lines that I may set up to test on. I'll let you guys know how it goes. I am really thinking that I could get enough batteries to do it, but the charge time would be too many hours to make it worth it. Maybe if I upgraded to the alt to a high 225 amp one?

This is all just speculation as I havent even gotten the boat yet, but I have found that although alot of the 30 and 31 ft Hunters have a/c, they only work on shore power. So I will have to get something figured out before I purchase. The wife will NOT tolerate being hot.

[Minnewaska]

Ramin, you might be right. I have no idea. I can run the coffee maker and microwave oven just fine with the invertor. The AC trips it in seconds.

BTDT = been there done that

[deniseO30]

This topic was discussed a couple of months ago. The nature of mechanical refrigeration (ac is actually high temp refrigeration) demands much higher torque and higher horsepower to move the refrigerant through the evaporation and condensing cycle then lower temp refrigeration very small fractional units. Old school refrigeration referred to the loads in horsepower, 9,000 btuh would be about 3/4 HP. 12,000 being 1 hp.
It really isn't practical to run ac on 12volts dc or even 24 volts dc (imho) The battery banks required would nearly double the ballast in most sail boats! The amperage draw through an inverter would also be astronomical.

[mitiempo]

It won't be possible without a generator to power the air conditioner - running all the time. The 225 amp alternator you mention will use about 9 hp at max output. It would require special mounting and belting arrangements as well. And a good 3 stage reg with temp sensors for the alt as well as the batteries. Flooded batteries will only accept about 25% of their capacity in bulk stage but that should not be an issue as you will have to have a huge bank to make it possible. And you can't charge your battery bank past 80 % in a reasonable time. With any alternator/battery combination the last 20% will take many hours. I doubt even after all this, at huge $, the engine in a 30' Hunter could cope.

May I suggest:

[capecodda]

1000 watts AC, even if converted at 100% efficiency (which it isn't) by an inverter, is burning upwards 80 Amps/hr out of a 12 volt bank, and my guess is your 9000 BTU air conditioner is using even more than that. As others have said your potential fixes include too many batteries, too long engine time to recharge, and/or too big an alternator for the engine.

Depending on where you sail, air conditioning off the dock may not be a priority. In New England, and Canada, even on a previous boat with a generator and air conditioning, we we rarely ran the air when not on a dock. Up here at least, the temperatures in the summer at night are reasonable, and its nice to open up the boat (with screens in some places) in Maine and listen to the surf.

On the other hand, when on a dock in a marina, we've found air conditioning to be a very nice option. It allows you to close up the boat, mask noise, and stay cool in marinas where the wind doesn't blow.

Your mileage may vary.