Running a Small A/C Off Lithium, Solar, or a Generator

[nyscilla]

Let me start by saying I have a mental block when it comes to electricity, how it works and all the math involved! Sometimes I think I begin to understand and then it’s gone. So I am sending this out for some input from people who do understand it and I appreciate any assistance.

I have a teardrop I purchased from original DIY builder. It currently has an AGM 100 watt battery which runs the LED lights, Maxxfan, and charging ports (will be used only for phone charging). There is a separate feed for the A/C, microwave and 120 outlets which only runs on shore power (120v shore power with a 30-amp plug).

I live and camp in the desert. This is what I would like to power:
- LED lights
- 12 Volt refrigerator – 40 to 55 watts (all day).
- 5000 btu wall air conditioner – 450 watts (use for two hours to cool trailer before bed)
- Maxx air fan – estimate 20 watts per hour on medium (use for 8 hours each day).

I’d optimistically like to be able to go 5-7 days without having to charge anything (or charging only through a solar panel – the benefit of desert camping). I am told with all the components installing a large lithium battery, inverter, MPPT controller and solar (I could probably fit 200 watts on the roof) would run several thousand dollars (let me know if I am wrong about the cost).

So was thinking maybe I would replace the battery with a large power station. I’d run the 12 volt system into that and could plug the 30 amp directly into it when needed. Is this a feasible solution? Would it be inefficient to run the 12 volt power through the power station? Or is that opposite? If feasible – would 3000 wh be enough, with the knowledge that any time I am camping and using the a/c I would be able to charge the power station with solar (looking at 200 watt movable panels if go this route).

Alternatively, I have thought I could replace the AGM battery with a bigger lithium battery to handle the lights, 12V cooler, fan, and get a generator for the a/c when needed – but that means an additional large item to bring, fuel, and noise. Thoughts on this? Thinking 300 ah lithium with portable solar panels should get me close, and a 2200 watt dual fuel generator to eliminate having to bring extra fuel (other than propane)

Other options I have not considered? Thanks in advance for any help.

 

[nyscilla]

Ok After additional research, I think I can upgrade the AGM battery to 200-300 ah lithium, get the generator, and the generator will also charge the battery when the trailer is plugged in. I am thinking this gets me my 7 days no problem as long as I have propane and is the easiest upgrade to do with my limited electrical knowledge. So one more thing to carry but not too big and not too noisy, and no additional fuel other than the propane I already bring. Am I right or wrong?

 

[Rich796]

Look to see what your lipo or agm battery is rated for, in watt/hours. It's probably something like 1280 W/H. ( for a lipo g24 ). ( you will get more usable power, out of a lipo, than a agm )

1280w/h ÷ 450w/h = 2.84 hrs. In a perfect world you would be able to run the a/c for 2.84hrs. With your current battery Before you needed to recharge it. ( or 2hrs ac & .84 or 380w/h for accessories )

7 days x 2hrs = 14 x 450w = 6300w/h or storage needed. 6300w/h ÷ 1280w/h = 4.92 or 5 batteries needed. With no charging, just to run the a/c. Again in a perfect world.

If you have 200 watts of solar on the roof. And get a reliable 5hrs of charging out of them. You are looking at 200w/h x 5 = 1000w/h. ÷ 450 = 2.22. Or enough recharge capability to run the a/c for 2hrs per day. ( plus a minor amount of battery changing )

So, given your present capabilities it would probably theoretically work. But may be kinda harsh on the battery.

In the desert you'll probably do a little better than 5hrs per day of charging. Even if its not running at full capacity. You'll want to run the panels in series. To take full advantage of the MPPT charger. And adding an additional matching battery, would be wise.

If you used one of the small digital type a/c. Rather than the analog. I believe the digital contoled ones, will turn off the compressor. Once it reaches the set temp. Where the analog controlled ones, run continuously. So that would save you some power usage, mostly likely.

You basically want to balance power used by power generated. And then size your battery/bank for the amount of storage/back up capacity. That makes you comfortable. If you are not able to charge/recharge fully, every day.

A power station is basically just a lipo battery/charger/inverter/ or what ever added capability. All just built in to one unit.

 

[Tom&Shelly]

I think the generator is your best bet.

Since you camp in the desert, you might look into a portable swamp cooler, which takes less energy than true ac. But all I know about those are homemade and experimental.

Tom

 

[Grummy-TNT]

>>>> Where the analog controlled ones, run continuously.

No... the compressor cycles on and off the same. A 5k btu will draw 400w (120v) to start, slightly less running. Of course that means anywhere for 35-40A draw from a 12v battery being inverted to 120v.

 

[Grummy-TNT]

How long you could run a 5000btu A/C unit off your inverter and an 100Ah AGM is... not long. If you were running it off a 200Ah LifePo, a couple of hours is not a problem the way you describe your use. The only way to fully calculate the power use of an A/C unit depends on cycle time... It's the compressor that is the big draw and it turns on and off. However, that on and off is also dictated by how hot it is.

You might actually be better starting your cool down while the sun is up, provided you commit to a few solar panels to the mix. In theory, 4 100 watt panels could contribute 20A to the draw, only drawing 20A from the batteries.

I know you might get more sun than most of us, but if you go 200Ah on lithium, I recommend having 4 100w panels, and 6 panels for 300ah batteries. Cost ? Depends a lot on what battery you buy as the battery(s) is the biggest cost. For example, a 200Ah LiTime will be $320. You will love a lithium over that AGM. A guy named Will Prowse on the Ytube can help you pick out which might be the best deal. Other than that, a Charge Controller (just buy a Victron right away $150), 100w panels are $100 each.
That's $670 and you need some wire. But, if you do it, you wont have to worry about "charging things"... I have a 200Ah setup with 4 panels on a trailer and I love it. I got 200Ah and only 2 panels on my truck camper and wish I had more panel....

But, you didn't mention INVERTER yet... You need an inverter to change your 12v to 120v. If you only need that for A/C, you can buy a smaller 1200-1500w inverter and it will run it fine. If you want to run a Microwave, you'll need larger. I think you can find a 1200-1500 inverter for about $100 these days. I tend to buy the GIANDEL brand on the last few builds. Had some great discussions with them over the phone (same for LiTime batteries).

Regards the generator. I would not want to be without one, but you have to also commit to having fuel available, space for it, and also have the headroom for that additional weight. You do not want it stored inside your rig either. I have used an electric fuel pump setup built in to take fuel right from my fuel tank so I do not have to carry any cans. (It's just "tee'd" into the fuel main line. It has a push button dead mans switch I have to hold, but I also have it on a plug and always unplug it.

If you go generator, understand too that while the 2000w+ units are all the rage, you can save a little weight and dimension by going with 1000w (options might only be Honda, Yamaha and Predator). A 1000w generator can probably give you a reliable 50A battery charge with a 120v battery charger. That can bring your batteries around in a hurry when you need it most.

 

[Rich796]

" You might actually be better starting your cool down while the sun is up, provided you commit to a few solar panels to the mix. In theory, 4 100 watt panels could contribute 20A to the draw, only drawing 20A from the batteries. "

I'm assuming this is just a raw/off the cuff, assumption. Based on generic solar panel data. Or a parallel only set up. Because using a victron mppt solar charge controller. ( Panels in full sun, originated correctly ) I would expect to see closer to 30 amps of output charging current. From, 4 - 100w panels

The only reason I bring this up. Is because, it may not be obvious to people newer to solar power. Is that with a Victron mppt solar charge controller. They are rated by the ;

Maximum allowed input voltage. From the solar panels. ( if you plan on using your equipment, in very cold weather. You need to account for the voltage rise. )

And the maximum allowed, output charging current/amperage. The controller can supply.

If you are making more power/amps. Than the charger is capable of supplying. It will not be going into your battery bank.

So in the above example ( 4- 100w solar panels ) you would be better off. Using a charge controller rated at 30amps output, than 20amps.

This screen shot shows, 2-100w panels, producing nearly 15amps of output charging current.

 

[bdosborn-SMB]

Let me start by saying I have a mental block when it comes to electricity, how it works and all the math involved! Sometimes I think I begin to understand and then it’s gone. So I am sending this out for some input from people who do understand it and I appreciate any assistance.

I have a teardrop I purchased from original DIY builder. It currently has an AGM 100 watt battery which runs the LED lights, Maxxfan, and charging ports (will be used only for phone charging). There is a separate feed for the A/C, microwave and 120 outlets which only runs on shore power (120v shore power with a 30-amp plug).

I live and camp in the desert. This is what I would like to power:
- LED lights
- 12 Volt refrigerator – 40 to 55 watts (all day).
- 5000 btu wall air conditioner – 450 watts (use for two hours to cool trailer before bed)
- Maxx air fan – estimate 20 watts per hour on medium (use for 8 hours each day).

I’d optimistically like to be able to go 5-7 days without having to charge anything (or charging only through a solar panel – the benefit of desert camping). I am told with all the components installing a large lithium battery, inverter, MPPT controller and solar (I could probably fit 200 watts on the roof) would run several thousand dollars (let me know if I am wrong about the cost).

So was thinking maybe I would replace the battery with a large power station. I’d run the 12 volt system into that and could plug the 30 amp directly into it when needed. Is this a feasible solution? Would it be inefficient to run the 12 volt power through the power station? Or is that opposite? If feasible – would 3000 wh be enough, with the knowledge that any time I am camping and using the a/c I would be able to charge the power station with solar (looking at 200 watt movable panels if go this route).

Alternatively, I have thought I could replace the AGM battery with a bigger lithium battery to handle the lights, 12V cooler, fan, and get a generator for the a/c when needed – but that means an additional large item to bring, fuel, and noise. Thoughts on this? Thinking 300 ah lithium with portable solar panels should get me close, and a 2200 watt dual fuel generator to eliminate having to bring extra fuel (other than propane)

Other options I have not considered? Thanks in advance for any help.

I have a 12V Outequip pro a/c I just put on our well insulated van. I have 520w of PV panels and a 400 a-hr of LiFePO4 battery. I could power the loads you've shown if the sun is shining everyday. But there's no way I could go more than a couple of days without charging. The a/c is the big load that will drive your battery size and PV capacity way up. On a hot night we use about 15% of our battery capacity for lights, fan, 12v fridge and a movie. Running the a/c for a couple of hours will easily double of triple that number, depending on how hot it is and how efficient your a/c is. IMHO, a DC powered a/c is a must for offgrid use because it's more efficient than a Big Box window shaker and you don't have any inverter loses.
Bruce

 

[ChainedTraveler]

NYScilla, did you make a decision? I'm looking at a self build too but I'm thinking 24v 2k watt inverter with two 100 ah batteries. Charging would be a small tailgate generator. The system would also double for as a power station for my house to use with a larger generator.