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Old 07-18-2018, 01:49 PM   #1
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Question about my setup

Hello and thanks for taking a moment to look.

1st: The list of what I have.

8 100w 12 solar panel (poly)
40a MPPT Charge Controller
6 140Ah Group type 24 Deep Cycle batteries (12v)
3500/7000 Inverter

Thoughts on the configuration of this as a system or should I look at a different kind of battery (ie. a Trojan t105 for example)
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Old 07-18-2018, 04:32 PM   #2
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You have more theoretical panel output than MPPT controller. That's not the end of the world if you assume your panels will not be producing anywhere near their theoretical maximum (which is usually accurate and dependent on mounting (tilt or flat), location/insolation, time of year, shading, etc.).

I assume the "12" in the solar panel bit means 12V? If so, I further assume you wiring in some combination of series/parallel which is why you went with an MPPT charge controller. If any of that is incorrect, there might be something to talk about.

12V batteries (even "deep cycle") are not ideal for RV use but they do work. If you are buying new, you might want to look at 6V GC (golf cart) batteries (for example) - which the T105's are (the cream of the crop).

That is a big inverter for a not particularly large battery bank (6 T105's = 675Ah capacity and 335ah usable). It will certainly work but be sure to have a good battery monitor to keep track of SOC (state of charge) and avoid damaging your battery bank. I haven't done the math but would guess it'll exceed the discharge C-rate of your batteries if you run it at maximum.
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Old 07-18-2018, 11:23 PM   #3
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Thanks for responding. Yes the 12 is 12v in the panels. So for battery. I currently have 6-140ah batteries. Total 840ah. I was gifted them. So I’m not going to complain much. Also you said that the 40w charge controller is not sufficient enough. Is that at 12v or 24v?

And can I wire the panels for 24v and have them charge 12v batteries? My understanding was the charge controller would handle the conversion.

Again thanks for all the info.
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Old 07-19-2018, 05:47 AM   #4
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Well... I didn't mean to say that the CC (charge controller) was insufficient - only that it would not pass thru the full (theoretical) output of the panels. Regardless, you are right on the money with the battery bank voltage. If your CC will work with a 24V battery bank, then it can handle all that those panels can produce (40 amps x 24 volts = 960 watts). Sorry about that... it seems that so few people consider anything but a 12V battery bank that I've started assuming incorrectly...

Yes, MPPT CC's are designed to take a high voltage input and convert it to the voltage required by the battery bank. There are limits of course.

With your 6, 12V batteries connected in series/parallel to form a 24V battery bank, your inverter must accept a 24VDC input. Same for other DC components OR you will need a 24V-to-12V step down converter to power them (I have one 30 amp step down converter than powers all of my 12VDC components but many of them are 24VDC (such as water pump, many lights, etc.)).

Using an even number of panels, you can wire them in a variety of series/parallel forms. What is the input requirements of your MPPT CC? It *may* have a minimum input voltage requirement that will dictate how the array is wired.
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Old 07-23-2018, 10:43 AM   #5
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So to update:

I changed the 40A charge controller to an 80A charge controller after doing a little research on what JDOnTheGo suggested and he was completly correct.

the Math: 800w of solar divided by the 12v supply is 66.6A to the batteries.. so a 40A charge controller would no be strong enough for the PV that I have. So to his point, I upgraded.

Now to mount it all on the roof and get wiring.
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Old 08-03-2018, 02:57 PM   #6
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Quote:
Originally Posted by trinitysj View Post
So to update:

I changed the 40A charge controller to an 80A charge controller after doing a little research on what JDOnTheGo suggested and he was completly correct.

the Math: 800w of solar divided by the 12v supply is 66.6A to the batteries.. so a 40A charge controller would no be strong enough for the PV that I have. So to his point, I upgraded.

Now to mount it all on the roof and get wiring.
Keep seeing mount on the roof in all this solar jargon. Also x # of panels but no size specs. How much area is covered to get how many watts? And where can I get the algae eaters to put in the terrarium to keep them clean? LoL! I'm thinking I want solar but don't know what will fit and be best for my application is there a database with the specs?
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