Help With Wiring Plan

onenationundergoat

Hi, I purchased some old panels. They are 230 watts (were 245 originally, adjusted for age), 10.55V, 30.48 Amps.

I have six of them, one 30A PWM charge controller, and one deep cycle battery (group 27 or 29, can't remember) at the moment. I'll be buying three more batteries. They are regular deep cycle batteries. I also have an 1100w inverter.

I am an intelligent individual who is used to figuring things out on my own but apparently my brain can not comprehend electrical knowledge. From what I understand, I should connect all the batteries together in parallel, and I should connect the panels together by putting two in series and connecting these three sets of two together in parallel. Is that right? Would anybody be able to post a diagram of this for me to be able to visualize it? 

I've read about needing diodes to prevent backflow of power. My panels have square boxes on the back that the positive and negative wires come out of. There are 2 positive and 2 negative on each panel. Are these diodes made into the panel, or will I need to buy diodes and install them in the wiring plan?

We really won't even be using that much power, but the panels were an excellent price because they were used. Typically we run the fridge, the tv/xbox, the fan, the modem/router, and charge our laptops. I'd estimate our power usage to be 500w/hr or less. It would be awesome if we could run our window unit AC off of this system (with a larger inverter of course), but is that even possible?

The controller is this one: https://www.amazon.com/Infinium-AMP-Solar-Charge-Controller/dp/B017TBJWEW
According to the place that we got it from, we should use 12 awg wire to connect it. According to a wire gauge calculator online it says I will need 2awg wire to run the 12 feet or so from the panels (on the roof of the bus) to the controller/batteries. The wire input on the controller definitely does not have a gap big enough for that! 

I was recommended to ask y'all by the folks over at Skoolie.net. A few of them have solar but said asking here would get me better answers!

littleharbor2

Are these your panels?,

http://www.ebay.com/itm/2KW-Solar-Panels-8-x-245W-Used-Made-USA-Panel-Battery-Charging-12-24-or-48V-/201618239416?hash=item2ef1622fb8:g:5H4AAOSwCM5XP0Pv   .

 I have been wondering about them. 216 cells and 4 junction boxes, those are very busy modules. They appear to be 6 volt nominal so yes you would series wire 2 at a time and bring the 3 strings into a fused combiner box. One problem is you should theoretically end up with over 90 amps @ 12 volts. First thing you need to do is get rid of that cheap little charge controller. Charge controllers have backflow prevention so you don't need to worry about that.  Your best bet would be to get a real MPPT controller such as a Morningstar 60 amp version and go at least with a 24 volt system, series wiring all 6 panels .

onenationundergoat

Yeah those are the ones but I got them for $50 so a bit cheaper. I don't have a multimeter so I haven't even gotten to test them yet, but they arrived in good condition, just dirty. 

My school bus conversion is all wired AC, and we use an 1100w inverter from our battery which is currently charged by generator. What is the benefit to going to 24v vs 12v? Wouldn't I have to buy a new inverter? Also, wouldn't I want to avoid wiring in series as much as possible because if one goes out they all go out?  

Also regarding backflow, I'm referring to an event in which one of the panels is shaded or damaged; doesn't there need to be a diode to prevent the other panels from feeding the flow into that non working panel? I don't see how the controller could have any effect on that. 

onenationundergoat

Is the Amp rating of a charge controller to maximum that it can have input? Or is that what it will produce as long as more is input? Is there a limit to how many volts the controller can handle?

onenationundergoat

It might make it easier for me to start simple; My neighbor also purchased two of these same panels and one 30a charge controller. I know I have to hook those two panels in series. Will I need to install fuses/diodes/breakers between them and the controller, or it it a small enough system that I can just go ahead and hook it all together as-is? I do know that you have to hook the battery to the controller before attaching the panels. 

littleharbor2

First off I would be wary of those panels as they are 26 years old and just plain odd. 30+ amps from a single panel is kinda scary.

 The benefits of going higher voltage are many but in your case if you decide to go with 12 volts you will have 90 amps to deal with. There are only a couple charge controllers that can handle that high amperage, the lesser expensive being a Midnite Solar Classic 150. This unit will set you back about $600.00. You could always go with 2 45 or 60 amp MPPT charge controllers which will cost even more.

 You will need a fused combiner box which will cost more of your hard earned dollars. If you series wire them you end up with only one string and no need for a combiner, fuses, extra hardware, etc... not to mention at 24 volts you don't need such an expensive high amperage controller.

 You asked about backflow prevention but you seem to be referring to bypass diodes. I would hope those panels, with 216 cells in them would be loaded with bypass diodes but who knows with these dinosaurs. I was unable to find ANY info on them, probably because they are older than the internet. Not really but close. As to one of them failing on you and taking out the whole string, I would expect that to happen.

 The amp rating of charge controllers refers to how many amps of charging OUTPUT they have.  Most but not all MPPT controllers have an open circuit limit of 150 volts. Some will handle up to 600 volts, some 100 or less.

onenationundergoat

Yeah I couldn't find info on the panels either. I know they're ridiculous and huge, but if I can get them to work, even inefficiently, the price is right. What I'm thinking now is that I could make three strings of 2 in series and connect each string to its own 30A PWM controller. That would avoid a junction box and a high powered controller, and I could still connect the three controllers to my battery bank. But I'd still have to wire in bypass/blocking diodes and fuses, correct? According to the seller the cells in the panel are wired in parallel. There are no diodes. There are two positive connections and two negative on each panel and they are redundant. Connecting those together in series would short the panels. There is also a third box on the side and I'm not sure what that's for. 

I am OK with using inefficient PWM for now until I can afford to upgrade my system.

mike95490

If the panels are already constructed, you will not be able to add "bypass diodes" (they route power around a shaded section of panel)
Charge controllers provide the nighttime Blocking diode function.

onenationundergoat

By bypass diode i mean one that will route power around an entire panel that is shaded in series. I made a diagram, and I'm hoping it'll work out. The controllers to battery part of the drawing looks pretty hairy but you get the gist.

mike95490

You need to use a diode properly in a schematic  ----|>|-----   for us to
tell you if you have the proposed placement correct.

And you need (really really need) to use a high performance diode, with proper heatsinking, because at
30A @ 0,5v you are dissipating 15 watts of heat, which if not gotten rid of, will cook the diode, melt wires, or
damage the PV cell.

BUT, in your case, you do not need to install 30A bypass diodes.  Why?  Because if you loose a panel, and the
diode trys to kick in, 10.5V won't be enough to create any current flow into a battery that needs 14V to be charging,
That's why diodes need to be in the panel, between cells, to be of benefit.

Here's a nifty article about bypass diodes
http://www.digikey.com/en/articles/techzone/2012/dec/active-bypass-diodes-improve-solar-panel-efficiency-and-performance
but at 30A even they will need heatsinking.  And you have to be careful when placing diodes in parallel, you have to have swamping or ballast resistors to prevent one from hogging all the power

onenationundergoat

mike95490 said:

BUT, in your case, you do not need to install 30A bypass diodes.  Why?  Because if you loose a panel, and the
diode trys to kick in, 10.5V won't be enough to create any current flow into a battery that needs 14V to be charging,
That's why diodes need to be in the panel, between cells, to be of benefit.

Ah, that makes total sense! These panels are a headache but at $50 each I'm just gonna deal with it. So I should just scrap the diodes and bypass wires. Other than that, is the diagram correct? Two panels at a time wired in series to one controller with 50A self resetting DC automotive breakers between panels and controller and between controller and batteries?