Recommendations toward my solar plan

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Sportster280T

Member
Joined
Jan 31, 2023
Posts
24
Location
Bancroft, Ont, Canada
My requirements: A/C rarely maybe up to 2hrs at a time (single 3,500btu A/C), Micro wave occasionally but just for warming (not cooking), enough battery to run furnace blower overnight if needed, TV maybe couple hrs & of course lighting which is 12v LEDs.
My plan: approx 800W solar (4x200W panels), 2x100ah Lithium batteries, & appropriate converter & charger, plus a transfer switch to be wired into back of rv fuse panel.
Hard to find many suppliers here in Canada, especially since we live very rural, so I am looking at following solar kit, my plan is to upgrade the charger immediately & add a transfer switch to it, but I do have monetary limits.
Recommendations & opinions gratefully accepted.

 
I'm doubtful that a mere 200 AH of battery bank will run that a/c for two hours, but it depends on how efficient it is (amp draw) and the temperature to be maintained. Are you thinking of the Dometic RTX 1000 or something different? Or just a small window-type a/c unit?

Nobody likes the effort involved, but you need to evaluate your needs based on daily amp-hour consumption and available sunlight for re-charging. You need enough battery amp-hours to get you through a day even if solar charging is limited (weather, shade, etc). Think in terms of running from the battery and re-charging with solar (or maybe a back-up source). At a guess, you need more battery but maybe not as much solar panel (though more is always nice).
 
The A/C is built in unit factory installed on trailer. I know a 2,000W inverter generator runs it.
I went 800 solar thinkin I could add another battery at a later date if needed. I really doubt A/C will be needed much Nov till March or April in Az.
From what I can find.
"Newer models are usually more efficient than older models, requiring closer to 11 amps than 16"
 
I agree with Gary that 200 amp hours isn’t nearly enough if you want to run an AC. And he is also right about running the numbers vs. guessing how much you need. I routinely run through 400-600 amp hours in a 24 hour period, but I do have a big rig, and I like it warm inside so lots of propane furnace use. I have 600 amp hours of LiFePO4 batteries and 900 watts of solar. The solar isn’t enough to completely recharge the batteries on cool winter days (furnace fan + low sun angle). An AC uses a lot more power than a furnace fan.
 
"Newer models are usually more efficient than older models, requiring closer to 11 amps than 16"
Instead of wonder and guess, measure and know. Designing to worst case can work, but only if you don't care how much you spend. If you have the unit close by, do some testing and get the baseline data you need.

Even at the conservative end of your estimate, 11A at 120V is 110A at 12V. Add about 10% for inverter efficiency, so now you're at ~120A. How long will 2 100Ah lithium batteries source 120A? What about other loads, like lights, a TV, water pump, computer. Those are on top of your 120A. For running a microwave for a few minutes I'd say you'd be fine. An A/C for hours, nope.

Lithium batteries hold up well under load better than lead acid but there's still a limit to how much and for how long a given battery will source these kinds of currents. If the manufacturer spec's it then great, otherwise you're either doing the design engineering yourself, or be OK with hooking it up and you get what you get, and optimize as you go.

Consider that even if you had a sufficient bank of batteries to run A/C for some period of time, that energy has to be restored. Then the question becomes when you run a genset or whatever solar array you have can replenish the charge in a reasonable period of time. Ideally you'd have enough solar to run your A/C during the day plus some margin, leaving your batteries to light the lights at night. Otherwise, one A/C run is going to kill the batteries and then you're running a generator anyway. You could save all the battery, solar and A/C frustrations by just using the generator directly instead.

Mark B.
Albuquerque, NM
 
"Instead of wonder and guess, measure and know. "
5th is under 2' of snow with no power??

At any rate let's cancel A/C requirement, in the full summer I've owned this new trailer I've never run the A/C except at home on shore power to check it worked. In 5 yrs of ownership of old trailer, never once run the A/C in it. Not a requirement much up here & don't think it's much requirement in AZ from Nov to March. I do have a 3,000W Inv/Gen if needed.
 
The A/C is built in unit factory installed on trailer. I know a 2,000W inverter generator runs it.
And it's only 3500 btu? Most RV a/c units are 13,500 or 15, 000, but there are a few 8000 btu models for really small trailers. Are you aware that a 2000W inverter draws about 170 amps at full output? That might give an hour of operation.

Sure you can add batteries later (assuming you have allowed for the space & weight), but you stated the design need to run the a/c unit right up front and I took you at your word.
 
Yes 13,500 btu.
I probably mislead in my 1st post, as indicated, I was thinking MAX use, the A/C is not necessary requirement, it might be nice in a very limited instance, if so I could run my 3,500W Generator. It's much like the Micro-wave, while we have never used it when out, I thought if I had enough power to use it for occasional warming purposes, why not!
The reason I'm thinking 800W solar was to have enough to maintain 2 batteries while having an option for a 3rd.
Weight & space for panels or batteries is no issue at all.
Just to indicate our power requirements we've camped for up to 2 months at a time in Utah with nothing more than a single deep cycle battery & a 800 Watt generator. We only ran geny maybe every couple days for an hr or two which we would double up & watch some tv while charging the battery.
 
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