How big of an inverter do I need? (how much, window, Air Conditioner)

[Racelady88]

I have a small window unit A/C that I want to put into my husband's work van. The unit requires 115 volt 60 Hz 15 A. How big of an inverter do I need to push this thing?

This is going to be his birthday present, so any help will be greatly appreciated.

[jdavid93225]

Originally Posted by Racelady88

I have a small window unit A/C that I want to put into my husband's work van. The unit requires 115 volt 60 Hz 15 A. How big of an inverter do I need to push this thing?

This is going to be his birthday present, so any help will be greatly appreciated.

115V x 15A = 1725 Watts
Due to inrush (starting) current, you will want to go at least 25% bigger. I would recommend one even larger than that, probably something around 3000 Watts, though you could probably get by with 2500 Watts. These are for peak load ratings. Sustained load ratings should be around 2000 Watts.

Don't forget that with a window type A/C unit, you will need to mount the shell of the unit outside the van for proper venting of the hot exhaust air. This will most likely need to be out the rear of the vehicle so it doesn't protrude beyond the sides of the vehicle into an adjacent lane.

Also keep in mind that if the inverter is being run off the starting battery that it wouldn't take long for the battery to drain to the point where the vehicle won't start. You will most likely want to be sure that there is a separate battery for the inverter, and that it is isolated from the starting battery so the ability to start the vehicle isn't compromised. You'll also want to be sure that the vehicle's charging system is adequate. Also remember that in order to keep the batteries charged in the vehicle, the engine will need to be run long enough to recharge them.

[cdelena]

I don't know of any automotive electrical system with enough capacity to run a window AC system reliably.

[Racelady88]

Originally Posted by jdavid93225

115V x 15A = 1725 Watts
Due to inrush (starting) current, you will want to go at least 25% bigger. I would recommend one even larger than that, probably something around 3000 Watts, though you could probably get by with 2500 Watts. These are for peak load ratings. Sustained load ratings should be around 2000 Watts.

Don't forget that with a window type A/C unit, you will need to mount the shell of the unit outside the van for proper venting of the hot exhaust air. This will most likely need to be out the rear of the vehicle so it doesn't protrude beyond the sides of the vehicle into an adjacent lane.

Also keep in mind that if the inverter is being run off the starting battery that it wouldn't take long for the battery to drain to the point where the vehicle won't start. You will most likely want to be sure that there is a separate battery for the inverter, and that it is isolated from the starting battery so the ability to start the vehicle isn't compromised. You'll also want to be sure that the vehicle's charging system is adequate. Also remember that in order to keep the batteries charged in the vehicle, the engine will need to be run long enough to recharge them.

Thanks! This is what I needed to know.

I have a brand new deep cycle RV/Marine battery to push the inverter. The unit is going to take the place of one of the rear windows.

He is going to be so excited to have A/C.

[Cosmic]

It is just not the inverter rating. Most cars will not have an alernator / electrical system that can handle that type of load. Something like that will drag a battery down to parade rest in a short period. Maybe a hybrid might be capable of generating that type of power.

You would be better off exploring getting an aux generator that will directly generate 115 VAC. I know it is sort of standard equipment on things like an undertakers hearse. Probably a number of other type vehicles might have something like that. They run off a belt driven pulley about like a car A/C and have a relay / clutch affair to bring it on line when required. The wiring is probably totally separate from the rest of the vehicle wiring.

Might want to research what is available along that line. Plus that also avoids all the inefficiencies of various seried up equipments to give you the final desired result.

[Ultrarunner]

I've set up my Service Van with a 1500 Watt Statpower Inverter back in 1993? and I also have a super quiet Honda 1000 Watt Generator of the same vintage...

The inverter works great... and I even run a small Emglo Piston Air Compressor, Chop Saw, Roto Hammers and a Micro Wave... got have a hot lunch in the Winter...

I also upgraded the Alternator to the largest single pulley Delco I could find... it is rated for Ambulance Duty, added a second RV Battery and upgraded all the wiring to handle the current.

My Starting Battery last 5 to 6 years... my inverter Battery lasts 2 to 3 years.

I also added a continuous duty 12 volt Solenoid with a dash mounted switch to combine both starting and inverter batteries should I need more amperage...

Are you thinking of a RV type A/C unit or one of the $149 Costco 5000 BTU jobs?

[sterlinggirl]

1800 Watts at 12 volts would be 150 Amp draw on the alternator/battery....ouch

Is that right?

I'd look at one of the RV units runner mentioned. They should already be set up to run on 12 volts.

[harry chickpea]

Racelady88, IT WON'T WORK!! I've been there, done that, got the T-shirt.
The laws of physics just don't allow it.

First, as was mentioned, you need a 2KW inverter to get it or a refrigerator to start, due to inrush currents. I used a 2KW Trace inverter/charger that I had and a minimum of two golf cart batteries for power, and a souped up alternator to provide more wattage to charge those house batteries as well as the van battery. At night, the house batteries were cut free of the automobile circuitry, so that I didn't have to worry about the van not starting.

How much power is in a golf cart battery? About the equivalent of less than a cup of gasoline - IF the batteries are new and fully charged. Marine batteries have a different plate design and are not as suited to deep discharge. In either case, unless you want to replace the batteries every few weeks, you can only discharge them about half-way, which depending on the inverter, you might not be able reach anyway. Many inverters now have a setpoint where they cut off if the voltage from the battery drops below a certain level. An AC draws enough current that the voltage level drops to the preset level before the battery is half drained.

Bottom line?
A ROOM AIR CONDITIONER WILL ONLY WORK FOR ABOUT 20 MINUTES OR LESS ON BATTERY POWER FROM TWO BATTERIES.

Once the batteries age, the AC might stay on for as little as five minutes. A single battery might not even provide the amperage to start the AC after the first couple uses.

When I put my setup in my van, my primary purpose was to power a small dorm refrigerator and a microwave and be able to do stealth camping while traveling. When driving from place to place, I was able to keep the refrigerator working for as long as two weeks at a time, by sometimes using my Trace as a charger to put a full charge back on the batteries at a campground. The microwave took longer to cook things when powered by the inverter, but it worked, and overall I was satisfied. I tried the AC on battery power a couple of times, just to see what would happen, and watched the voltage on the batteries rapidly drop. I stopped each time at about 12 minutes and plugged into shore power to run the AC and recharge the batteries before I damaged them.

After the first couple of shakedown trips, I removed the room AC from the van completely, even though I could power it on campground power. Why? Because the automotive AC in a van is similar in cooling power to that of a small house AC. The room AC wasn't enough to keep my conversion van cool unless it was overcast or night, and a 12 volt fan worked as well otherwise. I had better uses for the space, and when I needed AC, I left the van running on fast idle and ran the van AC.

Our camping journeys are less frequent now, and with the price of gas I've removed the batteries, inverter, refrigerator and microwave as dead weight that reduce gas mileage. Instead, I have a big ice chest and a single burner propane camping stove. Stuff won't stay cold or frozen for two weeks, but for overnighters it works fine.

Seriously, an inverter will set you back $250, two batteries will be at least $120, and you won't be able to use the AC for more than 10 to 20 minutes at a time on battery power. You would be better off getting a rooftop RV AC unit for about $500 and having it installed. It'll have more power and be out of the way, but it still won't help if you can't plug it in to shore power.

FWIW, my inverter, FOUR batteries, a 90 watt solar charger, a 5KW generator and less than 15 gallons of gas kept our house powered for over two weeks after hurricane Wilma. Our big refrigerator never was without power, and we had fans and tv, and were even able to do laundry and take hot showers.

[Ultrarunner]

Originally Posted by harry chickpea

Seriously, an inverter will set you back $250.

Boy times have really changed... When I bought my Statpower 1500 I paid almost a $1 a watt all those years ago...

Almost $1500

If you are really serious about finding the most efficient A/C... you need to look at some of the marine units... start at a place like West Marine... I think they have several offerings in the Master Catalog...

[Cosmic]

For that big of an A/C load go direct and generate the power as 115 VAC. Either with a small generator designed to go under the hood and be belt driven off the engine. If you want it with the engine off, just get a small Honda or similar generator and build in a mounting area in the van. Generate the power as 115 VAC. Might be enough left over for other loads depending on its size.

Generator could be designed to mount external over the rear bumper and be easy to remove

Another type of generator is used by big trucks, military vehicles, etc. It is an aux generator with a gasoline or diesel motor designed to run off the vehicle fuel system but not require the main engine to be running. Gives constant power without having to idle the main engine. Saves a ton of fuel. Can be mountd anywhere there is room. Also probably similar lash up's designed for RV's.

You would just get a far better bang for the buck and not have to replace system components every few years.