A/C max watts for off-grid cooling

[Jim.M]

I have just tested 3 5000 BTU window-shaker A?C units.

I am powering all with a harbor freight 1500W (3000W max) inverter. This inverter pulls 2 amps (~48 watts) at idle with no load Off switch really means off, no current draw with the switch in the "off" position. I'll buy a smaller inverter if I need to run low-watt A/C appliances.

First I tried the Frigidaire FRA052XT7. pulls 3200 watts when compressor kicks in. too much for my inverter. $99 at lowes.

next I tried the Keystone KSTAW05A, due to its great reviews. it pulls only 2640 watts when the compressor kicks in. Running with the compressor on, uses 720 watts (6 amps). Unfortunately, it doesn't like the "modified sine wave" AC the harbor fright inverter puts out. Compressor sounds unhappy, and the electronics whine. Plugging into the wall quieted it down. This would be a great unit if one wanted to spring $$$$$ for a pure sine wave inverter, or if you only camp with shore power. $132 at wal-mart.com.

finally i tried the GE AEL05LQ. When the compressor kicks in it pulls about 2500 watts, sometimes only 2200W. Running the compressor on "high" with high fan is around 5 amps (600 watts). Noisy but noise didn't diminish when plugging into the wall. Doesn't seem to care too much about modified sine wave power. $119 at home depot.

I wish I could have kept the keystone, as it is really quiet and smooth, but I'm not going to shell out an additional $300 for a pure sine wave inverter to make it happy. I am keeping the GE.

Since I'm too cheap to buy a generator, I plan to run my car's engine any time I'm running the A/C. I bought 20-foot 2guage jumper cables, chopped out 6 feet of the cable for the battery->inverter cabling, and then re-spliced the jumper cables (now 14' long). The cables cost $48 at oreilly auto; all other sources of 2 gauge wire were prohibitively expensive. Now I have my power leads, and a set of 2-guage jumper cables for $59 ($48 cables, $11 for terminals and butt splicers).

A nice clean way to attach the copper terminals (like these) is to fill up the terminal with electrical solder. Heat the the terminal with a propane torch until the solder melts. Next jam the wire into the terminal. Takes about 10 seconds and no need for a hydraulic crimper!

Hope some of this information is helpful to anyone thinking of buying one of these window shakers.

[bdosborn]

Since I'm too cheap to buy a generator, I plan to run my car's engine any time I'm running the A/C...

Have you checked your alternator rating? It's probably not rated for the 60 amps or so at 12V your inverter will draw and you definitely won't get that kind of output at idle.
Bruce

[Jim.M]

Since I'm too cheap to buy a generator, I plan to run my car's engine any time I'm running the A/C...

Have you checked your alternator rating? It's probably not rated for the 60 amps or so at 12V your inverter will draw and you definitely won't get that kind of output at idle.
Bruce

I've already run the a/c for an hour off a spare battery (just battery connected to inverter). I'll use the jumper cables to charge that battery... my alternator puts out at least 35 amps at idle, so I'm about 15 amps (@ 12V) shy of keeping up at full a/c blast. But this only when the compressor is kicked in. I'm guessing it's not going to take too long to cool down a 4x8 trailer.

[Richard A.]

I am powering all with a harbor freight 1500W (3000W max) inverter. This inverter pulls 2 amps (~48 watts) at idle with no load Off switch really means off, no current draw with the switch in the "off" position.

Yes, but remember that when under load the rule is for every 100 watts AC draw from an inverter you are pulling 10 AMPS dc current.

...next I tried the Keystone KSTAW05A, ... Running with the compressor on, uses 720 watts (6 amps).

That is 72 amps DC

finally i tried the GE AEL05LQ. When the compressor kicks in it pulls about 2500 watts, sometimes only 2200W. Running the compressor on "high" with high fan is around 5 amps (600 watts).

That is 60 amps DC

[lancew]

with all your doing to run your a/c only when car is running. does that mean you are using a remote start for your car. so in middle of a muggy night you can turn your a/c on. how will you shut your car off ? remote switch ? lot of trouble overr a minor "sine wave".

[Jim.M]

Well, all of this is being done to keep the wife cool at Burning Man.

So, I can run the car any time I want (will most likely be unnoticed in the ambient noise). Temps drop to 50 or below at night, so need for late night coolings.

In a real campground, if it was so hot and muggy that I'd need the A/C 24x7, I'd spring for a "full hookups" site and pay the price.

But realistically, living in Las Vegas, getting to a muggy night is many many days' drive away. And if I did need the A/C at night, I can just turn on the inverter, and run the A/C for a few minutes.

The car is only for charging. The battery the A/C runs off has a reserve capacity of 130, so it should run for about an hour or a bit less from full charge.

Still not sure what the 'lot of trouble overr a minor "sine wave"' refers to?

[8ball_99]

Pulling 60 amps will Kill that battery in short time.. I don't mean drain it,, I mean kill it.. Most RVs pulling that kind of load have at least 2 batteries if not 4.. That 120 amp hour battery will not supply 60 amps for an hour. It doesn't work like that.. The rating is based on a set time and set load. IE 2 amps for 48 hours.. Pull less and that battery will put out more the 120amp hours.. Pull more a little less. Pull a lot more and a lot less.. I forget what its called, But a little reading up on deep cycles on the net will explain it better then me..

Also like others said your car will not put out that kind of power at idle. Running a battery down in 30 mins then cranking a car up and letting it idle to recharge the battery for a couple is far from ideal.. For what the inverter, battery and cables cost you could have probably picked up a generator and been much better off. But your right about it not being worth your while to spend 300 bucks on a pure sine wave inverter..

My advice is to make your wife sit in the car while its running when she gets to hot

[MtnDon]

8ball is correct; that battery will have a very short useful life if it is asked to deliver 60 amps.

The amp hour capacity of a battery is usually given at a "20 hour rate". That is discharged at a constant rate over 20 hours. A battery like the Trojan T105 golf cart battery is rated at 225 amp-hours at the 20 hour rate. The same battery has a 5 hour rating of 185 amp-hours while the 100 hour rating is 250 amp-hours.

If that is a regular auto battery it will also fail early from being deeply discharged frequently; they are not built for such use. If it is one of the so called RV/Marine 12 volt batteries it may last longer, but not nearly as long as a battery like a golf cart or industrial battery like the T105.

[bc toys]

Well if your camping around Las Vegas during the summer go up to Mt Charleston in the summer months or go to the Parump side and try wheeler pass road and go in to those camp grounds and in the winter go to Valley of fire or boulder beach or caldwell bay but if your going to stay in the valley in the summer yes you will need a/c Hook up with the las vegas tear jerkers group and have a great time camping

[jeffmutch]

I was reading on another forum a while back about running A/C off of solar. Someone was getting quite frustrated that they'd seen it done, but wasn't sure how. Another guy chimed in to say he was one of the crazy one's doing it, but needed 8 deep cycle batteries to run the A/C for a little over an hour. Then wait a day to recharge the batteries. I don't know about you all, but 8 batteries put's me over the weight limit on my 12 inch tires...

I then purchased a 1300 watt generator off of Craig's for 150 bucks. The noise makes me use it less than intended but It's definitely proven it's worth.

[bdosborn]

I've already run the a/c for an hour off a spare battery (just battery connected to inverter). I'll use the jumper cables to charge that battery... my alternator puts out at least 35 amps at idle, so I'm about 15 amps (@ 12V) shy of keeping up at full a/c blast. But this only when the compressor is kicked in. I'm guessing it's not going to take too long to cool down a 4x8 trailer.

I seems like you have a pretty good handle on the limitations and you've definitely done your homework. I just wonder how the boss is going to like having to turn the A/C off just when it gets everything nice and cool.

Bruce

[Jim.M]

I'll take some pictures of the trailer... I have high hopes but it has been a lot of work!

design goals are:

can stand up in it

can sleep in it

can lounge in it

can eat and cook in it

has a sink

has a shower

has a stove

has a fridge and freezer

has a toilet (porta-potti) (not really required but easy to add)

has a vanity table for the missus

has a full-length mirror

has a/c

has heat

has screened vent windows and large skylight (to see the stars?)

can be towed by my sedan with minimal rear-view blockage (height/width)

has a rear 2" receiver for bike rack and/or cargo basket

and the big one: has to fit in a two-car garage with two cars in the garage as well.

fitting in the garage means it is collapsible/take-apart. for this we have these goals:

each piece can be moved/carried by a single person (me)

trailer can be assembled by a single person (me)

[Ira]

No way you can run an AC off a battery with an inverter.

You need to plug into A/C power, or a generator.

You can even use a cheap and tiny 1500 watt Harbor Freight generator and "box" it to cut down on the noise.

[bdosborn]

Ira? Where have you been?

Bruce

[Ira]

Ira? Where have you been?

Bruce

I've been poor, out of work, but as sexy as ever.

And building a new one in a few weeks!