# school me on charger/inverters



## RJ2019 (Aug 27, 2019)

I'm slowly replacing and upgrading an outdated system. Actually, my batteries died so I did a big upgrade on those and now I might as well upgrade everything else to match my battery bank. I'm seeing that the charger/inverters combos are a thing now but I have always used a separate charge controller and inverter.

Would one of the combo units work for me? If it matters, I am keeping my system at 12v because the rv is setup to run on 12v. I'm thinking when it's said and done I will be running anywhere between 1000 and 2000w of panels.

What all do I need to know?


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## MichaelK! (Oct 22, 2010)

What you are referring to is what's known as an "All in One" unit, or AiO for short. The typically combine a controller, inverter, a charger and a transfer switch, all in one box. As a general rule of thumb, they are mostly entry-level units designed for economy rather then sturdiness. I wouldn't buy one. They in general have no meaningful "surge capacity", which is typically what you need for starting anything with an electric motor that starts under load. I would recommend a quality tier-1 brand like Magnum, Outback, or Schneider. I like Schneider. I have both a XW+6848 and a Conext SW4024 on my homestead.

I'm assuming the system is for running the RV? I would otherwise recommend you go to a higher system voltage, because 12V is so limiting. The issue is charging amps. With 1000W of panels, charging at 13V, that would be 1000W/13V = 77A. You would need at least a 80A charge controller to handle just 1000W. You would need two controllers of that size to handle 2000W. Midnight, Outback, and Epever all make MPPT charge controllers that can handle amperages that high. I use Midnight 200s for my systems.

Keep in mind that the scale of the solar needs to match the scale of your batteries. You really don't want to be feeding 80A into a 100Ah battery. The maximal charge rate for lead-acid batteries is 1/8C. Maybe 1/4C for Lithium. Let's say you build a 12V Trojan L-16 battery bank for your RV. L-16s have an amphour capacity of around 400Ah. So, 400Ah/8 = 50A.

Keep in mind that you always need to incorporate a fudgefactor into your math because panels never put out their rated output. For panels angled directly at the sun, I use 85%. For panels laying flat on a roof instead of pointed at the sun, then 60%. That means you can't expect a 100W panel to put out more than 60W, even close to noontime, if it's laying flat.

So, here's the math to determine what you need. Feel free to change the parameters to match your equipment. The numbers may change, but the math stays the same.

So, for a 400Ah battery
400Ah/8 = 50A
To get 50A at 13V, you need 13V X 50A = 650W of panels.
If laying flat, to get those 650W, you actually need 650W/60% = 1080W. That could be four 270W panels.

If you wired four 270W panels in series, you'd need a charge controller that can handle 200Voc. The Voc goes up as the temperature goes down. So, a panel that operates normally at room temperature could fry your controller when it goes below freezing. The higher the voltage capacity, the higher the price of the controller. Alternatively, you could wire the four panels as 2S2P. That means two parallel strings of two panels wired in series.


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## RJ2019 (Aug 27, 2019)

Thank you! I did in fact go with L-16s.
I think I want to ground mount the array, I could potentially make it adjustable. And yes, it will be for the RV which is why I want to keep it at 12v.
I don't have any pipe dreams of running any large loads on the system. A small freezer would be nice but not imperative. Mostly for lights (not the stock RV lights, they get hot and use alot of juice), recharging devices, the onboard water pump and a small tv/DVD player for kids in evenings.
I do think it would be easier for me to understand and hook everything up if I buy the components separately. I'm down for that, but I did want to explore the idea of the newer technology


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## MichaelK! (Oct 22, 2010)

I think what you are talking about is sort of like a docking station for your RV. I expect a ground mount will work best for you if you really aren't traveling at all, and your RV is stationary ~100% of the time.

If you want to make a ground mount, feel free to copy my design. It's made out of schedule 40 pipe, and unistruts, that's welded and bolted together. This array could hold up to six grid-tie panels. I split the array into two halves. The bottom T-bar starts with a 3.5" pipe sunk 36" in concrete. A 4' long 4" pipe slips over it with a cap welded onto the end. Horizontal unistruts are welded onto the top of the 4" pipe, along with diagonal support trusses.

The rectangular panel frame gets bolted onto the top of the T-bar via 4 door hinges. That allows the frame to rock up and down for seasonal sun angle adjustment. The 4" pipe can rotate left to right, so it can track the sun from East to West. Rotation is not mechanized. I just go out and rotate the array by hand. It's cheap and it works. I call it hillbilly solar tracking.


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## RJ2019 (Aug 27, 2019)

MichaelK! said:


> I think what you are talking about is sort of like a docking station for your RV. I expect a ground mount will work best for you if you really aren't traveling at all, and your RV is stationary ~100% of the time.
> 
> If you want to make a ground mount, feel free to copy my design. It's made out of schedule 40 pipe, and unistruts, that's welded and bolted together. This array could hold up to six grid-tie panels. I split the array into two halves. The bottom T-bar starts with a 3.5" pipe sunk 36" in concrete. A 4' long 4" pipe slips over it with a cap welded onto the end. Horizontal unistruts are welded onto the top of the 4" pipe, along with diagonal support trusses.
> 
> ...


Ooooohh, I really like that mount! My last one was made from a metal post, a piece of plywood big enough to hold the panel, scrap 2x4 to hold the panel onto the plywood and some baling wire. This is much less hillbilly!😆


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## MichaelK! (Oct 22, 2010)

I am especially proud of the cantelivered trusses on the back of the array frame. Look carefully at the array pic. The two outer trusses on the back are welded to the frame. The two inner trusses however are cantilevered and bolted into place rather then welded. This means the trusses do not interfer with the rocking of the frame to adjust for seasonal angle. The backside trusses keep the frame rigid in the Z-dimension, whereas the diagonals you see keep the frame rigid in the X and Y dimensions. The panels on these frames have survived thunderstorms that topple the Oaks you can see in the background!


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