eeasy

Looking for an AC unit that will run on 12V with inverter (4-6 hours run time). Any suggestions? How many batteries would I need?

Wally

Its all about math my friend......first your gonna have to decide how big an AC unit you want........see the power it needs in watts and amps.....from there you will need to find the inverter to be able to cover those needs.......just remember that just because you AC unit use's 800 watts it doesn't mean that you go buy an 800 watt inverter......most people don't understand that when you start up most electrical accessories that they take an initial kick that exceeds what its rated for.....in the case of the AC unit that works at 800 watts it may have a start up kick of close to 1000 watts.......so be sure to compensate accordingly. When you have those first two figured out then you will be able to figure out how many or how big the battery(s) will need to be. Most batteries have a rating that tell you how long they will be able to run with a "Typical" full load on them but not being charged. In the case of most cars that means with the headlights and radio on and heater/AC going....and most are rated for 60-90 min of reserve time. Hope that helps you a bit in your search

eeasy

Thanks for the info. I am looking at a 7-9000 btu AC unit. I have not purchased one yet but I will try to find out the watts needed to run the unit. I am trying to avoid having to put in a generator to just run AC. It is for a 43 Scarab.

Gary Anderson

I think you're going to find the batteries needed will weigh more than a small generator.
Typical AC units use about 50% more amperage at startup. Also consider converter efficiency and actual output curves of the batteries. You're looking at A LOT of battery.

Wally

My buddy has a 38 powerquest......he keeps a small honda gas generator in the engine compartment......when out on the water and wanting AC he starts up the gen and straps it on the swim deck with bungies.....works like a charm and last a good couple hours on a single tank of gas. I think he has the 1000 watt unit and its quiet too

Wobble

I just bought a small generator, the handbook says that you should have 3 times the running watts for items like an AC.

If you need 800watts to run then you should have 2400 to start it.

t500hps

I remember looking into this awhile ago and the 7k BTU A/C I wanted to power took 8 amp to run, but 17 amps at startup. I forgot the conversion, but isn't that around 3000 watts startup? A power inverter might work, but you would need a pair of 8D batteries to supply enough juice.

BadDog

and then how do you charge the batteries? Seems a generator is the only logical solution unless you only stay out one night.

baronbob

I have been through this a lot. Here is the scoop. 8amps times 120volts is 960 watts on the 120volt side now look at the 12 volt side assuming 100% efficiency in the inverter it takes 80 amps times 12 volts to produce 960 watts. an 8-d might give you 200-225 Ampere hours at the very best. 80 into 225 amp hours means that the conditioner will only run less than 4 hours and we have been liberal with the calculations. You will be lucky to see 3 hours. Now lets look at charging the battery back up. One dedicated mondo alternator is lucky to put out 100 amps and it will drop off rapidly as the battery comes up. That is 2-2.5 hr running above 3000RPM to be able to have 3 hours of cool. Doesn't sound good to me. If you have two engines you are no better off as one alternator loafs and the other picks up the load. The Honda is a better choice. By the-way this was a dedicated study which means to say that if you want to run your house battery that is all on top of the above.

eeasy

I am only looking to be able to run the AC for 4-6 hours at a time. We never stay on the boat at night, just would be nice for the HOT summer afternoons in MO. Trying to justify the cost of adding AC without needing a Gen. Weight is not an issue so I just need to figure out how many batteries I need and how big of an inverter.