Upgrading to run air conditioner

Generic · February 2012

Hi, I'm new to the forum so hopefully I'm not asking too many questions. I currently live off grid full time in a RV with a 300 watt solar system and a 5000 watt generator. 300 watts is enough for me most of the time and I rarely run the generator.

Since I work nights and sleep during the day I need to run the air conditioner in the summer as where I live it gets near or above 100 all summer long. I want to upgrade my solar to run the air conditioner to save the need to run the generator all day and waste about $20 a day in gasoline.

My plan is 2000-2500 watts of panels, 16 trojan t-105 6v batteries set up for 48v with 550ah, and about a 4000 watt inverter.

Questions:
1. Is this overkill? My air conditioner supposedly uses 1200 watts while cooling. Summers here are clear 90+% of the days. Can I get by with around 1500 watts since the compressor won't be going 100% of the time?

2. Can I get by with less batteries? That amount of batteries should run the a/c compressor about 11 hours before dropping to 50%. If it's hot enough to need the a/c it should be sunny and the batteries wouldn't even be draining if I was collecting more power than using. Maybe just 8 batteries at 48v?

3. Can I leave the 4 batteries I have already connected to the RV for the dc and just plug the shore power cable into the inverter which would be hooked to a separate battery bank? This way I would always have at least dc power. I know there would be loss going from dc to ac and back to dc to charge the rv bank but that shouldn't be a big deal since those batteries wouldn't be drawn down much anyway.

4. Can anyone recommend a large inverter? I would love a Xantrex XW6048 but I'm not sure it's in my price range. A modified sine wave inverter should be fine? 48v inverters seem hard to find. If I dropped down to 24v wouldn't I likely need a second charge controller because of the high amps?

Any questions anyone can answer would be much appreciated. Thanks.

BB. · February 2012

Re: Upgrading to run air conditioner

Welcome to the forum G.

Some comments:

Generic wrote: »

Hi, I'm new to the forum so hopefully I'm not asking too many questions. I currently live off grid full time in a RV with a 300 watt solar system and a 5000 watt generator. 300 watts is enough for me most of the time and I rarely run the generator.

I am a big believer in sizing the genset+AC charger to the size of the battery bank. Otherwise, you can really waste fuel to recharge your system/run occasional heavy loads (power tools, etc.).

Here is a neat thread with lots of details regarding matching a small genset to a battery bank. Probably applies more to your current system (300 watts of panels) than it will apply to your new system.

Question about battery charger selection with EU2000 generator.

Since I work nights and sleep during the day I need to run the air conditioner in the summer as where I live it gets near or above 100 all summer long. I want to upgrade my solar to run the air conditioner to save the need to run the generator all day and waste about $20 a day in gasoline.

My suggestions:

Insulation, double pane windows, awnings, etc. to keep heat off of your home/RV the best you can.
Conservation. Picking appliances and life style to reduce power usage to the minimum needed. I.e., televisions, old refrigerator/freezers, desktop computers both can pull lots of power and dump waste heat into your interior space--And then you have to pay (again) to remove the heat and pump it outside (A/C).
Picking appropriate devices for your needs. The Sanyo (now purchased by Panasonic) mini-split is a very nice unit for off-grid usage. More efficient than normal window A/C units, but also uses an internal "inverter" to soft-start the compressor and run it at the RPM needed for that power setting. Folks have installed the Sanyo's and found that they can be throttled back to low (~3,000 BTU) and not draw much more than 300 watt ever. Very off-grid friendly. Lots of discussions on the forum--Here is one thread.
Next, get a kill-a-watt or similar meter to measure you average power usage (kWatt*Hours per day) for your system and your average loads (watts). Makes system planning much less hit or miss.

Now we can plan out your system.

By the way, with the "right" generator/mini-split AC setup, you could get away with as little as 1-2 gallons per day of fuel (my guess, living in a cool coastal area with no A/C--so what do I know :roll:).

You still may want to use solar anyway--But for pure out of pocket expense--Short term, a genset may not be the worst solution.

By the way, do you have utility power or are you in the middle of no-where? In general, if you have utility power, it is almost aways cheaper to use grid power vs off-grid power.

My plan is 2000-2500 watts of panels, 16 trojan t-105 6v batteries set up for 48v with 550ah, and about a 4000 watt inverter.

Take a look at the new Trojan "RE" series of batteries. Have read some very nice things about them here (seem to last reasonably well, and use much less water than other/older flooded cell batteries).

I don't really want to talk about your equipment just yet... Other than to say I am not a fan of paralleling batteries if it can be avoided. I recommend trying to keep to one string, and never exceed 2-3 parallel strings if you can avoid it (for a whole host of reasons we can go into). And, if you do this right, the 4kW inverter is probably overkill.

Questions:
1. Is this overkill? My air conditioner supposedly uses 1200 watts while cooling. Summers here are clear 90+% of the days. Can I get by with around 1500 watts since the compressor won't be going 100% of the time?

2. Can I get by with less batteries? That amount of batteries should run the a/c compressor about 11 hours before dropping to 50%. If it's hot enough to need the a/c it should be sunny and the batteries wouldn't even be draining if I was collecting more power than using. Maybe just 8 batteries at 48v?

3. Can I leave the 4 batteries I have already connected to the RV for the dc and just plug the shore power cable into the inverter which would be hooked to a separate battery bank? This way I would always have at least dc power. I know there would be loss going from dc to ac and back to dc to charge the rv bank but that shouldn't be a big deal since those batteries wouldn't be drawn down much anyway.

4. Can anyone recommend a large inverter? I would love a Xantrex XW6048 but I'm not sure it's in my price range. A modified sine wave inverter should be fine? 48v inverters seem hard to find. If I dropped down to 24v wouldn't I likely need a second charge controller because of the high amps?

Any questions anyone can answer would be much appreciated. Thanks.

All very good and appropriate questions to ask. My first feeling is you can do it with a much smaller off-grid solar system--especially if the RV is reasonably insulated and shaded (plantings, awnings) from direct sun.

In general, if you do not need 12 VDC to "run your RV"... A 24 volt or 48 volt system will have lots of advantages and should help keep costs down. If you notice for MPPT solar charge controllers, they are rated for maximum output current (i.e., 60 amps) at 12/24/48 volts. Since power=Volts*Current, the same controller charging a 48 volt bank will handle 4x the number of solar panels with the same controller charging a 12 volt battery bank. Also, "higher" voltage battery banks need much less copper to wire up the system (less current, smaller awg wire, smaller fuses/breakers, etc.).

-Bill

icarus · February 2012

Re: Upgrading to run air conditioner

The problem with RV PV systems is that in order to keep the rig cool, you need to park in the shade,, exactly what you don't want to do for PV production. RV roof top a/c units are notoriously inefficient. Going with a PV system is going to be expensive.

Tony

techntrek · February 2012

Re: Upgrading to run air conditioner

icarus wrote: »

RV roof top a/c units are notoriously inefficient.

Some of the modern RV A/Cs are more efficient. My current camper's A/C uses about 1000 watts. Still nowhere as good as a mini-split (I've considered replacing my A/C with a mini-split for 1-2 nights of off-grid use), but better than the older units.

Generic · February 2012

Re: Upgrading to run air conditioner

Thanks for the replies everyone. Unfortunately I don't have any shade to help cool in the summer sun. I have a small 19 foot travel trailer I live in which is newer. I don't know if it's the fact that it is a new a/c or just that the area it needs to cool is small but it seems to be pretty efficient. I will definitely need to see how much power it draws before buying equipment.

Will the kill-a-watt meter work with power from a generator? I would plug it in to the generator, plug the rv into it, and turn on the a/c and refrigerator. My fridge runs off a/c or propane but I would like to run of the inverter too if I could. Would I be able to see the surge power when the a/c cycles on? That is an important number for sizing what inverter I can use.

When I had my rv plugged into a 20 amp GFI outlet on my generator it would trip the breaker every once in a while when the a/c kicked on. Am I correct in guessing that is right about the draw it takes since sometimes it would trip and sometimes not? 2400 watts at 20a 120v. I'm thinking maybe a 2k inverter with 4k surge would work.

Oh and btw grid power isn't an option because the nearest pole is about half a mile away and was estimated $30000 to run lines the rest of the way here.

vtmaps · February 2012

Re: Upgrading to run air conditioner

Generic wrote: »

My fridge runs off a/c or propane but I would like to run of the inverter too if I could.
<snip>
When I had my rv plugged into a 20 amp GFI outlet on my generator it would trip the breaker every once in a while when the a/c kicked on.

When a propane fridge runs on AC, the AC is making heat to substitute for the heat that the propane makes. It is terribly inefficient. An efficient AC fridge has a compressor and would probably work in your situation. The reason your air conditioner tripped the breaker was probably because the fridge was drawing AC power.
--vtMaps

LandKurt · February 2012

Re: Upgrading to run air conditioner

A Kill-A-Watt power monitor only handles standard 15 amp 120V loads. It probably won't work for your 20A trailer connection. It also doesn't measure surge current, just the average power used. But if your A/C units plugs in to a normal 15A outlet you can use the Kill-A-Watt to find out how much power it uses per day and get a handle on your PV and battery needs.

BB. · February 2012

Re: Upgrading to run air conditioner

Generic wrote: »

Thanks for the replies everyone. Unfortunately I don't have any shade to help cool in the summer sun. I have a small 19 foot travel trailer I live in which is newer. I don't know if it's the fact that it is a new a/c or just that the area it needs to cool is small but it seems to be pretty efficient. I will definitely need to see how much power it draws before buying equipment.

Anything to keep direct sun off the windows will be a big help. Depending on insulation, shading (whether free standing "sun cloth", something mounted a few inches off the side/roof of the RV that can be taken down when moving/end of summer, etc.) can help a lot.

Will the kill-a-watt meter work with power from a generator? I would plug it in to the generator, plug the rv into it, and turn on the a/c and refrigerator. My fridge runs off a/c or propane but I would like to run of the inverter too if I could. Would I be able to see the surge power when the a/c cycles on? That is an important number for sizing what inverter I can use.

A Kill-a-Watt meter is "ridiculously" inexpensive compared to the same equipment that I purchased in times past for lab use. Not tremendously accurate--But very easy and quick to use. And even if you happen to blow one up (should not happen on a 15 amp circuit), you are not out much money. About the only two things it does not do real well on--Surge current (only reads about once a second) and MSW (modified square wave) inverter outputs (not that accurate).

However, worth the money for most people.

Realistically, AC motors tend to surge at about 2-5x their rated full load current. Generators (and inverters) all have their own ability to provide surge power (and some equipment may start with a sag--like a fan, but an A/C with electronics may not).

When I had my rv plugged into a 20 amp GFI outlet on my generator it would trip the breaker every once in a while when the a/c kicked on. Am I correct in guessing that is right about the draw it takes since sometimes it would trip and sometimes not? 2400 watts at 20a 120v. I'm thinking maybe a 2k inverter with 4k surge would work.

Yea, a 2,400 watt "typical" A/C unit is very close on a 20 amp circuit (my old RV had 30 amp 120 VAC circuit for main power).

In any case, that is a huge load for solar, and not insignificant for a genset (a 800-1,000 watt A/C unit may run on a Honda eu2000i 1,600 watt inverter generator).

The lack of surge current and the ability to dial back maximum input power to 300 watts make the Sanyo (and others in family) A/C units much nicer for off grid and small genset.

Oh and btw grid power isn't an option because the nearest pole is about half a mile away and was estimated $30000 to run lines the rest of the way here.

If you were building a home and/or planning for long term habitation (plus looking at the property value for a later sale)--That is getting pretty close to "break even" point between being completely off grid with A/C and being on grid with A/C (yes, this is a solar forum--Just a group of practical and cheap folks here--Want you to make your decision with all available options being considered).

-Bill

Les Nagy · February 2012

Re: Upgrading to run air conditioner

Where is your trailer? I have a 3000W+ peak output panel system (16x 205W panels actual) and a XW4548 with 750AH of 48V batteries. My batteries are full just in time for the air conditioner to be needed. The thing is, I live in the most appropriate place for solar in the whole world, the Atacama Desert with the most sun available or so I believe. If you want to use air conditioning you need to account for the sun you have. If you are in the Arizona desert then you probably have close to the same conditions as I, but might need some more panels. If you are somewhere where there is a lower sun then you WILL you need much more.

FYI, I have two notebooks going all day, a refrigerator, a network storage RAID box, a water pump that runs 20 minutes or more a day, a printer sucking parasitic power all day, a satellite and 32" LCD TV during the evening, 2x 60W electric blankets on the bed some nights, a few (3 to 5) fluorescent lights during the night, a microwave a couple of times a day, a coffee maker each day, a toaster for 4 slices each day, and various other power uses each day. Plus, once the batteries are full I turn on the 1400W AC that uses the excess power from my panels once the batteries are charged.

If you are counting on a cheap generator, keep in mind than many of them have such poor quality on the output sine wave that some motors will not be happy.

With 1000W draw from your air conditioner it would be wise to go 48V although it is OK to use 24V. I have been very happy with my all Xantrex system. There are some small issues but overall it has performed very well for the two years I have had it.

niel · February 2012

Re: Upgrading to run air conditioner

sidequestion here for les nagy,
being you are in one of the driest climates on earth, why are you using an air conditioner instead of a swamp cooler? or is it a case of water is as good as gold there?

Les Nagy · February 2012

Re: Upgrading to run air conditioner

Yes, water..... desert..... driest desert in the world.....

Electricity is cheaper than water once you have enough panels. There is also the upkeep of the swap cooler. The water here is full of dissolved minerals and would be a nightmare to clean out every two months. I have considered making a solar still though.

techntrek · February 2012

Re: Upgrading to run air conditioner

Generic wrote: »

My fridge runs off a/c or propane but I would like to run of the inverter too if I could.

The #1 rule for operating off-grid with an RV fridge - run it in propane mode. You can go a month on a 20-pound tank. However, in DC or AC mode it will use about 120 watts which is a huge load to cover with PV.

Generic · February 2012

Re: Upgrading to run air conditioner

Les Nagy wrote: »

Where is your trailer? I have a 3000W+ peak output panel system (16x 205W panels actual) and a XW4548 with 750AH of 48V batteries. My batteries are full just in time for the air conditioner to be needed. The thing is, I live in the most appropriate place for solar in the whole world, the Atacama Desert with the most sun available or so I believe. If you want to use air conditioning you need to account for the sun you have. If you are in the Arizona desert then you probably have close to the same conditions as I, but might need some more panels. If you are somewhere where there is a lower sun then you WILL you need much more.

I live in central Nevada at about the 40 degree longitude. I think I can get by with less than you since I use a lot less power and almost none at night. I have been using about 100ah at 12v a day which mostly goes to the heater furnace blower and water pump.

I plan on building a home here in the future and drilling a well. Once I have a well I will use a swamp cooler instead of A/C but I don't mind getting a larger system now since I will eventually need it.

Am I wrong in thinking if I had 225ah at 48v and more panel power than I use at a single moment I would be fine? If it happened to be a cloudy day(very rare) and I ran the batteries down then the next day I could run the generator to run the a/c while the panels charge the batteries back up. I'm just worried about wasting money on a huge battery bank if I don't need it, the panels just seem more of an investment.

CocoaPah · July 2013

Re: Upgrading to run air conditioner

Les Nagy wrote: »

Where is your trailer? I have a 3000W+ peak output panel system (16x 205W panels actual) and a XW4548 with 750AH of 48V batteries. My batteries are full just in time for the air conditioner to be needed. The thing is, I live in the most appropriate place for solar in the whole world, the Atacama Desert with the most sun available or so I believe. If you want to use air conditioning you need to account for the sun you have. If you are in the Arizona desert then you probably have close to the same conditions as I, but might need some more panels. If you are somewhere where there is a lower sun then you WILL you need much more.

FYI, I have two notebooks going all day, a refrigerator, a network storage RAID box, a water pump that runs 20 minutes or more a day, a printer sucking parasitic power all day, a satellite and 32" LCD TV during the evening, 2x 60W electric blankets on the bed some nights, a few (3 to 5) fluorescent lights during the night, a microwave a couple of times a day, a coffee maker each day, a toaster for 4 slices each day, and various other power uses each day. Plus, once the batteries are full I turn on the 1400W AC that uses the excess power from my panels once the batteries are charged.

If you are counting on a cheap generator, keep in mind than many of them have such poor quality on the output sine wave that some motors will not be happy.

With 1000W draw from your air conditioner it would be wise to go 48V although it is OK to use 24V. I have been very happy with my all Xantrex system. There are some small issues but overall it has performed very well for the two years I have had it.

Wow, that's pretty cool. I will have 900 watts of solar panels, a 6000 watt PowerBright inverter, a 60 amp Tri-Star Morningstar solar charger, and 800 aH of 12 volt batteries. Hopefully this is enough to run my RV air conditioner or space heater? I don't know but there is some room for a couple more solar panels.

BB. · July 2013

Re: Upgrading to run air conditioner

CocoaPah wrote: »

Wow, that's pretty cool. I will have 900 watts of solar panels, a 6000 watt PowerBright inverter, a 60 amp Tri-Star Morningstar solar charger, and 800 aH of 12 volt batteries. Hopefully this is enough to run my RV air conditioner or space heater? I don't know but there is some room for a couple more solar panels.

Slow down here a bit (and welcome to the forum).

We can either review your present setup and see what it can output... Or we can look at your loads, suggest conservation measures/energy star rated equipment, then design/check your design against your needs.

In general, it is difficult to get 6,000 watts from a 12 volt battery bank:

6,000 watts * 1/0.85 inverter eff * 1/10.5 battery cutoff = 672 amps continuous at 12 volt current

It is pretty difficult to get even 200 amps from a 12 volt system--3x that amount--Almost impossible (very heavy copper bars/cables to carry this amount of current with less than ~0.5 to 1.0 volt drop in wiring).

And, if you want to run heavy current from your battery bank for many hours, ideally the average current should be C/8 or less... 800 AH / 8 = 100 Amps maximum:

100 amps * 12 volts * 0.85 inverter eff = ~1,020 watts max continuous power from battery bank
800 AH / 2.5 max surge * 12 volts * 0.85 inverter eff = ~3,264 watts max surge power from battery bank

And, it also depends on your loads... Even a small A/C system can draw between 300 watts and >1,500 watts--That is a very wide range of power requirements.

If you wish, we can move this to your own thread and we can discuss your system and needs.

-Bill

H2SO4_guy · July 2013

Re: Upgrading to run air conditioner

I have the option to use an Exeltech XP-1100 to run the Mitsubishi mini split AC on. It can be done from a 12 volt version or a 48 volt version, they both work. I use an Outback PSX-240 transformer to get the power to 220 VAC. For a time I used a single string of 8D batteries (210 Ah @ the 20 hour rate), which is about the same power as a set of golf cart batteries. This was just a bit too little with all of the other loads, so I got 2 strings of the 8D batteries which were used and worked very well. That setup let me run the AC just about anytime I wanted. It is 9000 BTU and on full-tilt-boogie, uses about 900 watts, but can be dialed back to 210 - 320 watts and pour cool air out slowly which is good after the room is cooled down. I have had the living quarters down to 62 degrees in the daytime! That was when there was extra sun and what the heck, use it or lose it. I am not in direct sun and it is insulated pretty well and the living quarters is only 175 sq ft, so as Vic says, YMMV. Most of my stuff was done on the cheap. Good luck and let us know how it works out. Most that use much power prefer to go to 48 volts DC.

PorkChopsMmm · July 2013

Re: Upgrading to run air conditioner

Generic wrote: »

Am I wrong in thinking if I had 225ah at 48v and more panel power than I use at a single moment I would be fine? If it happened to be a cloudy day(very rare) and I ran the batteries down then the next day I could run the generator to run the a/c while the panels charge the batteries back up. I'm just worried about wasting money on a huge battery bank if I don't need it, the panels just seem more of an investment.

I just (as in yesterday) doubled my solar panels to reach 2.8KW. We live offgrid and my wife and kids use plenty of power. When it is sunny we get more than enough power to run a used A/C unit we picked up -- it consumes ~700 watts. We only run it on sunny days and it has been working well, even when we had less panels. We just wait until the batteries were full to run the A/C. If you only used the A/C when the sun was shining I don't think you would have any problem with a 225 AH battery bank at 48V -- that is the size we have. I am hoping to double it in the next few months, only because we use so much power at night (kids opening the fridge, washing dishes, etc.). Your loads sound a lot less than mine.

ChrisOlson · July 2013

Re: Upgrading to run air conditioner

Generic wrote: »

Since I work nights and sleep during the day I need to run the air conditioner in the summer as where I live it gets near or above 100 all summer long. I want to upgrade my solar to run the air conditioner to save the need to run the generator all day and waste about $20 a day in gasoline.

I don't know if it applies to your situation. But we put in A/C for our house and it has been running 24/7 for the last 13 days in 90-105 degree temps. Our A/C unit is a Trane 2-ton central unit with an air-handler (2,000 sq ft home). Basically, going by nameplate power draw, I grossly underestimated how much power it takes to run an A/C unit.

During the day our solar power runs it fine but it takes a decent inverter to start the compressor in it with other loads going at the same time - the compressor pulls 30 amps @ 240V for starting and 9.8 amps @ 240V continuous for running. However, if something happens where the compressor rotor is locked, like somebody adjusts the thermostat causing the compressor to kick out then try to restart right away, it can stress even our XW6048 inverter because the compressor pulls roughly 50 amps @ 240V for about two seconds before the overload kicks out on it.

So basically, if you size the inverter minimally, figure that your inverter is going to overload and kick out if you ever try to start the A/C with the compressor locked with high-side pressure trapped on the head.

The second thing I learned was that even though we got a pretty decent battery bank there is no way on god's green earth that we can run that A/C unit off battery power during the night. Your ah capacity of your battery bank is usually given at the 20hr rate. The additional load of the A/C unit basically more than doubled our normal daily power consumption, so the higher discharge rate of the bank ended up sacking it out quicker than what my best calculated numbers said it should have - because I didn't take into account the Peukert Effect on the batteries.

In the end our solution was to buy and install a prime power diesel generator to run the A/C and just save the batteries from the torture of powering the thing. When we got adequate solar to carry all our normal loads plus the A/C then we use it. But be aware that also gets your solar controllers and inverter REALLY hot in hot weather. If it starts pulling any power from the batteries at all (solar not keeping up with loads) I went with immediately firing up the diesel and just give the batteries and inverter a rest.
--
Chris

ChrisOlson · July 2013

Re: Upgrading to run air conditioner

I think our A/C unit is probably more efficient than a rooftop camper A/C. Our unit is 20 some SEER and I don't think those camper rooftop units are even 9 SEER - even the newer more efficient ones. The trouble with running A/C is that it's a continuous, relentless draw. We're not exactly frugal at our place, but after we put the A/C in this became our new "normal" daytime average load:

Attachment not found.

My original idea when we put the A/C in was to put in more solar power to run it. It didn't work. Well, it did part time but not like I had planned.

In reality I think you may already have the best option to run A/C on off-grid power - your generator. What you need to do to figure out if solar is even going to be practical is figure out how many kWh your generator is producing in a day to run your A/C and other normal loads now, then apply that to a solar/inverter/battery setup that will produce the same amount of kWh in the same amount of time and determine if it's really going to be cheaper over a period of several years. It might not be.

Your best option at that point would be to buy a more efficient generator instead.
--
Chris

Mangas · July 2013

Re: Upgrading to run air conditioner

To give you an idea what it takes A/C wise, we are running off grid two 2.5 ton central A/C compressors with air handlers 24/7 during the summer. It takes a lot of storage (64 batteries) and four stacked 5500w 48v inverters (two per HVAC zone) to do it dependably while running everything else in the house.

We have don't have any trouble cooling through the night into the morning but, we also enjoy Arizona's full sun summer desert conditions to bring charging/storage back up quickly during the morning. Usually we're there (85%+) by noon. Consecutive overcast rain days will ask the genset to run a few hours a week to keep the batteries charged to meet overnight demand.

Our two Trane XV80s' variable speed central A/C units start (surge) and run at lower amps than some of their other models. The variable speeds are very efficient but they cost more.

If you're going to run central A/C at night, I don't know a cheap way to get there without installing true 48v sine wave inverters (maybe two XW 6048s'), a much larger battery bank and genset able to pick up the slack. The great engineers on this forum can spec the minimums.

ChrisOlson · July 2013

Re: Upgrading to run air conditioner

Mangas wrote: »

If you're going to run central A/C at night, I don't know a cheap way to get there without installing true 48v sine wave inverters (maybe two XW 6048s'), a much larger battery bank and genset able to pick up the slack. The great engineers on this forum can spec the minimums.

We managed to do it with one XW on only 1200 amp-hours. But it took a small diesel generator taking the place the other XW and additional required battery capacity to do it.

For us it's a seasonal load that lasts maybe 6 weeks out of the year. And the rest of the year we don't need the other XW and additional batteries. In places where the A/C is required for longer periods of time we would probably look at doing like you did - just throw more inverters and batteries at the problem.

Either way, like you said, there's no cheap way to get there.
--
Chris

Photowhit · July 2013

Re: Upgrading to run air conditioner

After Chris and Mangas's horror stories, let me say it can be done. First if at all possible you need to plan ahead. Of course you have the RV already, can you park it in the shade? is it a modern RV built for winter use? (Fewer windows, better insulated)

I don't know how big an RV you have, some get pretty silly with multiple 'slide outs', can you get by with just running A/C in a single area/room. A 5th wheel with the bedroom over the hitch would be perfect, a small area to cool.

My experiences; In my cabin 10x16 with a sleeping loft/13 feet tall. built with 6" thick walls. I survived 4 summers on just 4 golf cart batteries, but this was planned out and I slept at night. Once cooled down the duty cycle of the A/C was around 40% during the warmest nights, and I only left the A/C on for 4-5 hours. I did this originally on @1000 watt array (24 volt system). The A/C was a 'window shaker' 5200btu Kenmore from Sears with a EER of 10.7. I added panels so I could run the A/C more during the day and the 5th year finally replaced my batteries with a forklift battery (800Ah @ 24v) This cabin was made for A/C, built with thick well insulated walls, built in the shade.

My new place is a 16x60 - mobile home (well modular for the record, but one look and you'd call it a mobile home!) It is mostly in the sun. I is no better insulated than most of the campers I'm familiar with, and I use to work security for a camping community! the walls are 3" thick or so and there is a single panel window sandwich. a regular single pane window on the outside and a single pane 'storm' window on the inside. It does work better than a single pane window. The mobile is in the sun, and I am currently only running A/C in the back bed room, 13x15. I could run it continuously with the 4Kw array and the same 800ah 24 v battery, The duty cycle is about 70% on very hot days during the day, if I have been running the A/c continuously. It draws @475 watts while on. Fortunately here in central Missouri we have sun with our heat most days. If fact today may have been the first day that the battery did not get topped off. We had over cast skies all day and I had run the A/C all night and it was a warm night low around 78, but it also didn't warm up today. So if I was at home the window fans likely would have kept it reasonable. I had good luck with the pervious Kenmore 5200btu so I purchased the newer version, EER of 11 (from Kmart since they had a 5% off deal going and I could get another 5% cash back by purchasing on line, through www.Fatwallet.com) For 8 hours of A/C in a small area of your camper I suspect you could get by with around a 2Kw array and 225Ah 48 volt system as a minimum, in my neck of the woods. Even if you had to leave the RV in the sun. If you are limiting your self to the existing A/C and want to cool the whole camper. Please give us the specs for your A/C unit!

Mangas · July 2013

Re: Upgrading to run air conditioner

ChrisOlson wrote: »

For us it's a seasonal load that lasts maybe 6 weeks out of the year.
--
Chris

Same here Chris. Since I'm all thumbs engineering wise, I had to throw more money at it to make it dependable. Not very scientific but we stay cool.

You guys really make me look bad.

ChrisOlson · July 2013

Re: Upgrading to run air conditioner

Mangas wrote: »

Same here Chris. Since I'm all thumbs engineering wise, I had to throw more money at it to make it dependable. Not very scientific but we stay cool.

You guys really make me look bad.

Well, I don't know about that - your system looks pretty well laid out and designed to me. But I would not want to own your battery bank. The little diesel generator looked a lot a cheaper to me, long term.
--
Chris

BB. · July 2013

Re: Upgrading to run air conditioner

Just for the heck of it, what are the costs of a battery bank cycling... Look at a 5000 series Rolls battery (the good/expensive ones):

Surrette 2-YS-31PS - 2 Volts, 2430 Amp-hours @~$1,200 per cell. And a 30% cycle life at 4,200 cycles.

2 volts * 2,430 AH * 0.30 cycle = 1,458 Watt*Hours per cycle
1,458 WH per cycle * 4,200 cycles = 6,123,600 WH cycle life = 6,124 kWH cycle life
$1,200 cost / 6,124 kWH cycle life = $0.20 per kWH battery life cost
4,200 cycles / 365.25 days per year = ~11.5 year cycle life

Call the diesel generator ~6 kWH per gallon of fuel @ $4 per gallon (in our area, road tax price):

$4/6kWH = $0.67 per kWH

Color me surprised... The above are just guesses/data sheet numbers, but the cost for battery cycling is actually less than I expected.

There are other costs too (capital costs, maintenance/oil, cost of inverters, shipping of batteries, etc.)--But I was expecting the batteries to be more costly...

However, if you assume the batteries are only cycled (30%) during A/C season (1.5-3 months of the year), and battery life is still in the 10-15 year range, then battery costs easily triple or more as batteries age out rather than cycle out.

So, if you need a much larger battery bank for a relatively few months a year to support AC--Then the genset is probably a much closer match in cost, if not less costly vs a Huge Battery Bank to support those summer time loads.

Another option is to use a smaller battery bank and cycle it more deeply (50% or even deeper). The cycle life is less--but it is only during summer, and the actual $$/kWH cost is less too (deeper cycling appears to be more cost effective). For example using 60% cycling:

2 volts * 2,430 AH * 0.60 cycle = 2,916 Watt*Hours per cycle
2,916 WH per cycle * 2,800 cycles = 8,164,800 WH cycle life = 8,165 kWH cycle life
$1,200 cost / 8,165 kWH cycle life = $0.15 per kWH battery life cost
2,800 cycles / 365.25 days per year = ~7.7 year cycle life

So, deeper cycling a few months a year is still not going to prematurely "kill" this battery bank (according to specs.). And will save you 1/2 of the capital costs on initial installation (30% vs 60% daily cycling during summer AC season).

-Bill

Eric L · July 2013

Re: Upgrading to run air conditioner

s

Another option is to use a smaller battery bank and cycle it more deeply (50% or even deeper). The cycle life is less--but it is only during summer, and the actual $$/kWH cost is less too (deeper cycling appears to be more cost effective).

Interesting comparison there BB. A related minor consideration is that the batteries are likely to be hotter in the summer, giving a little more capacity (at the cost of life cycle).

If you're going to run central A/C at night, I don't know a cheap way to get there without installing true 48v sine wave inverters (maybe two XW 6048s'), a much larger battery bank and genset able to pick up the slack.

Another variable here is the humidity and how much of the cooling comes from dehumidification. I know Mangas is in a drier climate where this doesn't apply as much, but in humid locations like ours (Gulf Coast), small AC units running at a higher duty-cycle (with the compressor on much of the time) really make the house feel better than the big central heat pump unit running intermittently. I remember that people reported something similar in the mini split thread here. The dehumidification effect from the small units makes the house feel much cooler even when the temperature is the same. This makes AC operation easier for us in that it removes the need to deal with the starting surge and running load of a big central unit. In my case, a 4400 watt inverter is sufficient to handle the two small AC units (total cooling of about one ton) that keep the house cool, and still powers the other loads in the house.

Blackcherry04 · July 2013

Re: Upgrading to run air conditioner

I tried a new charging regimen on my Honda EU 2000 with a 5000 btu A/C and Refrigerator . I had ran most of the day on the Battery bank and was down far enough on the battery bank I didn't think I could make it through the night. The AC pulls about 500 Watts when running and the refrigerator about 200 watts , The Honda will idle on the ECO throttle at about 500 watts load. I set the Inverter Charger at 5 AMPS max and Max AC at 6 Amps and let it run all night. The Outback Inverter will do Generator support and would pull the A/C in Bypass and as it cycled on and Gen Support would the start load, it would then charge the batteries during the Off cycle of the A/C so the load stayed constant. I burned less and a gallon of gas in 7 hrs, stayed cool and woke up to a charged set of batteries.

ChrisOlson · July 2013

Re: Upgrading to run air conditioner

BB. wrote: »

Call the diesel generator ~6 kWH per gallon of fuel @ $4 per gallon (in our area, road tax price):
$4/6kWH = $0.67 per kWH

Color me surprised... The above are just guesses/data sheet numbers, but the cost for battery cycling is actually less than I expected.

Our generator is producing 8.5 kWh/gallon at (currently) $3.39/gallon for off-road #2. So our fuel cost/kWh is about 40 cents. It was cheaper than that a couple weeks ago, but they got a new excuse to raise fuel prices - unrest in the Middle East or something. I still got cheaper fuel in my tank right now but I have to figure replacement cost of it when I burn it.

I guess the way I look at it is that the generator only cost me $775 and the monthly outlay for fuel to enjoy A/C isn't all that bad. However, laying out the cash for a big enough battery bank and additional inverter to take the place of the prime generator, all in one lump sump, would hurt. When the generator wears out I bought a rebuildable one so I can rebuild it and run it for another 10,000 hours for less than $1,000. When the batteries wear out it's going to hurt again to replace them.

In addition to the batteries and inverter you have to install the additional required RE generating capacity to actually fill the batteries up. The tiny generator can produce 25 kWh in 10 hours of run time. It would take an additional ~5 kW of installed solar capacity to generate that same amount of power in the same time, day after day. Factor in the cost of that, plus rails and wiring and combiners and controllers - the generator is starting to look simpler and more effective as we go for a load that only last 6 weeks out of the year.

IMHO.
--
Chris

vtmaps · July 2013

Re: Upgrading to run air conditioner

Blackcherry04 wrote: »

The Outback Inverter will do Generator support and would pull the A/C in Bypass and as it cycled on and Gen Support would the start load, it would then charge the batteries during the Off cycle of the A/C so the load stayed constant. I burned less and a gallon of gas in 7 hrs, stayed cool and woke up to a charged set of batteries.

Is that an FX or a GFX inverter? If its an FX, is it really gen support where both the generator and the battery-inverter supply some of the load?

--vtMaps

Blackcherry04 · July 2013

Re: Upgrading to run air conditioner

vtmaps wrote: »

Is that an FX or a GFX inverter? If its an FX, is it really gen support where both the generator and the battery-inverter supply some of the load?

--vtMaps

It's a GFX and Yes it's really Generator Support. All you have to do is set the incoming AC breaker size to what you want the Generator to supply and the batteries will supply the rest. If the Inverter is charging it will cut that back first before using from the batteries.

When I made that post it didn't sound earth shaking, but the Honda's ECO throttle leaves a lot to be desired. While it will work with some loads, a compressor is not one of them, it cannot react fast enough to the load and will drop out. When in ECO throttle it lug's the engine , if you run it full throttle it burns a ton of gas. The way I set it with the idle, it seemed to work better that it ever did before. After blowing one up for the second time, I am getting a little gun shy about how I use them with a load.

Dave Angelini · July 2013

Re: Upgrading to run air conditioner

BB. wrote: »

Just for the heck of it, what are the costs of a battery bank cycling... Look at a 5000 series Rolls battery (the good/expensive ones):

So, deeper cycling a few months a year is still not going to prematurely "kill" this battery bank (according to specs.). And will save you 1/2 of the capital costs on initial installation (30% vs 60% daily cycling during summer AC season).

-Bill

Definitely makes sense but the system needs to be super efficient. What I have done in for some of my customers in the southwest is get rid of the central heat pump and use mini splits. You gain 30% by not cooling/heating ducting and can easily retrofit. Design enough solar to run however many indoor units as you need during the day. Design enough battery to run one of the indoor units at night. The night run can often can keep most of the house cool after the splits run all day. The arrays need to get usable power from dawn to dusk. it works well and can be scaled to house size.

Upgrading to run air conditioner

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