What inverter for window AC?

[Reducto]

I can't handle not having AC any more so I'm going to install a cheap window box in my van. I'd like to be able to power it for short periods from my batteries but I don't think my 800 watt Cobra inverter will be up to the task. Most people seem to suggest a 2000 watt+ inverter due to the startup power requirements. I can't seem to find any info on whether modified sine wave is fine, though, or recommendations on brands.

Can anyone recommend something not horribly expensive that they've found to work? Or something they tried that did not work?

 

[jimindenver]

I use a Tripp-lite PV1250fc MSW industrial inverter. The last time I ordered one it was $288 including shipping and extended warranty. The are made for starting motors with a heavy transformer to take the surge. They can take double their rated watts for ten minutes and are cleaner than most MSW inverters. Last thing is it can load sense and turn on when your A/C calls for power.

 

[John61CT]

Yes great brand. Besides "will it work?" have to ask "will it last?"

Sometimes used Magnum comes up on eBay, secondhand Xantrex would be good, but don't expect repair service to be available.

Look also at Samlex and Vanner, Victron, MasterVolt, ProMariner.

Some say Bestek can last a while.

The other cheapie Chinese stuff is a cr^pshoot, but if you buy from trusted source with good return policy, try and return if not, only out the shipping.

 

[lenny flank]

That's gonna take an awful lot of solar panels....................

 

[Reducto]

That's gonna take an awful lot of solar panels....................

There are many threads about that already and I never said I was going to rely on solar to keep up. I have other charging sources available.

 

[sushidog]

The highest efficiency window AC is the Frigidaire 5,000 Btu sold at Walmart. It draws 4.0 amps to run, but a brief surge of almost 3 times that at start-up. I'd recommend an inverter that will surge to at least 1,500 watts, as I run a similar unit on a 1,200/1,500 watt genny. Remember, cheap inverters are typically about 80% efficient this means it will draw about 50 amps to run and 150 amps for a few seconds whenever the compressor cycles. If you have 4 typical golf cart batteries (like a Trojan T-105) you will only get about 190 usable AH out of them (at 12v) because of the Peukert effect of your high amp load. This means that if your batteries are fully charged you could get about 3 hrs and 45 minutes out of them at full load (to a 50% charge). If the duty cycle is 50% (meaning that the compressor only runs 1/2 the time) you should get about 40% more run time (as the fan draws some amps too) or about 5 hours and 30 minutes. If this is sufficient then it is doable. But remember you need something to bring them back to full charge, such as a generator, solar or the equiv. If using solar panels, you would need 1,000-1100 watts of solar. Since this won't fit on your roof, you would need to add swing up panels mounted on their side or portables - less if you want to scale back your run time.

See Pandamonium's RV videos to see what I mean by swing up panels.

Chip

 

[Van-Tramp]

Can you batteries and wiring take that sort of load? Unless you have lithium batteries, the lead-acid types simply can not *give* enough power to run an AC unit, even if fully charged. Even if that proves not too be true, you would need to run the AC for more than just a few minutes at a time. It would need to be on for an hour or more just to cool the van at all. Turn it off, and you will be too hot again within minutes. "Only a few minutes at a time" is not a reality.

If you have other means if charging other than solar (what is there other than a power outlet?) why not just use that power source to run the AC?

IMO, you will be wasting your time and money, as well as possibly hurting your AC, batteries, and wiring to attempt this.

 

[jimindenver]

The person that suggested the Tripp-lite to me had his running a side by side residential refrigerator for five years. I feel pretty good about it lasting a while.

The A/C I have is the Frigidaire unit that is rated for 3.9a @120Vac and a clamp meter on the line between the inverter and bank shows it averaging 35a @12v. The newest unit is rated 40w less at 410w and a 6000 BTU unit can be had at 495w while a cheap 5000 BTU unit can pull 515w. The efficient models cost more but are worth it in the long run.

The 750w of solar on my roof produces 660w of usable power during peak sun and that's more than enough to run the A/C and toss the bank a bone. The full 1185w produces over 80a and is enough for the A/C and another similar draw such as the water heater or even the propane fridge on 120Vac and still toss the bank a bone. I could add another 700w or so like on Panda but at this point I don't see the need.

 

[TMG51]

I'm pretty sure most any A/C is at least 1500 watts peak, so yes you would want a 2000 watt inverter. Let us know how it goes.

 

[Boyntonstu]

The highest efficiency window AC is the Frigidaire 5,000 Btu sold at Walmart. It draws 4.0 amps to run, but a brief surge of almost 3 times that at start-up. I'd recommend an inverter that will surge to at least 1,500 watts, as I run a similar unit on a 1,200/1,500 watt genny. Remember, cheap inverters are typically about 80% efficient this means it will draw about 50 amps to run and 150 amps for a few seconds whenever the compressor cycles. If you have 4 typical golf cart batteries (like a Trojan T-105) you will only get about 190 usable AH out of them (at 12v) because of the Peukert effect of your high amp load. This means that if your batteries are fully charged you could get about 3 hrs and 45 minutes out of them at full load (to a 50% charge). If the duty cycle is 50% (meaning that the compressor only runs 1/2 the time) you should get about 40% more run time (as the fan draws some amps too) or about 5 hours and 30 minutes. If this is sufficient then it is doable. But remember you need something to bring them back to full charge, such as a generator, solar or the equiv. If using solar panels, you would need 1,000-1100 watts of solar. Since this won't fit on your roof, you would need to add swing up panels mounted on their side or portables - less if you want to scale back your run time.

See Pandamonium's RV videos to see what I mean by swing up panels.

Chip

How about using a soft start? [video=youtube]

 

[TMG51]

How about using a soft start?

I've had to do that a time or two when several beers in, but always catch up before hitting second gear.

Wait, what?

 

[John61CT]

Genny likely needed, get batteries back to 80-85% in the morning, ideally enough solar to run the A/C with enough left over to finish the long tail.

More genny if lots of A/C needed late afternoon or evening, keep the load off the batteries as much as possible.

 

[jimindenver]

Can you batteries and wiring take that sort of load? Unless you have lithium batteries, the lead-acid types simply can not *give* enough power to run an AC unit, even if fully charged.

VT

If a battery bank can handle a load is really up to the size of the bank. My three Lifeline 8-D's have no problem and actually two would do it just fine. A single 8-D will start the A/C as long as it has the solar to run it afterwards. I used a failing 8-D starting battery to run the original torture test thread here. It ran from 11 AM to 5 PM and I don't think it stressed the 1/0 cables or industrial inverter at all.

I have been told what you can and can't do with solar, etc since I started with it in 2012. Luckily I see it differently in that to me each panel is a micro generator and just like smaller generators can be linked to run a larger load, panels can be put together to do the same thing. So I found out how many amps it took to run the A/C and knowing how much each panel produced knew how many I needed to do the job. It is all just numbers and setting up your systems to do what you want them to do.

 

[lenny flank]

The 750w of solar on my roof 

Holy cow, that must be one hell of a big roof.

 

[lenny flank]

I've had to do that a time or two when several beers in,  but always catch up before hitting second gear.

Wait, what?

I hear they got pills for that now.

 

[jimindenver]

Holy cow, that must be one hell of a big roof.

It would hold more if I were creative but with the 435w tilting panel on the truck there really isn't a need. I could add another 700 watts +/- by hanging panels off the front and rear like on panda but it would require another controller and wiring just to have the ability to run three of the big loads at once.

Hmmmm that would put me over 2kw

 

[Reducto]

Thanks for the brand suggestions. My plan may very well not work but I'm going to give it a shot and will post my results. I have a tiny, windowless, well insulated white van and have a generator but often find myself wanting to take breaks during long drives or to sit in the back and do paperwork. I'd like to see of that can be done without pulling out the genny. I want a bigger inverter anyway.