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Old 07-31-2016, 07:51 PM   #1
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Help With Solar Wiring?

Hi all, I asked for help in the Arizona Wind and Solar forum, but I know some of y'all know what you're talking about here too.

Copied and pasted from the solar forum:
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 ($50/panel). 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-.../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!
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Old 07-31-2016, 09:55 PM   #2
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Hello,

.How exciting and wow what a deal!
You're gonna love Solar. It's magical.
I'm going to take some time to ponder your questions and see if i have any intelligent answers for you.
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Old 07-31-2016, 10:31 PM   #3
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Good deal on the panels.
with 6 panels at 250 watt you can easily run a small 500 btu window airco.
To make your panels work as efficient a s possible you need a better charge controller. Instead of the PWM controller you are better of with an MPPT controller. Unfortunately more expensive.

If you have a photo of the junction box and sticker of your solar panel then that would be helpful for all the in the know people on this forum. Often solar panels are split in two sections ( 4 wires) It sounds that yous is actually a 21 volt panel.(with no load, that is zero current)
The Current that you mention is probably the short circuit current when both wires per panel are set in parallel.

The solar panel voltage under optimum load is probably 17 or 18 volt. It is listed in the solar panel sticker. The current is then about 13 to 14 Amp.

So for 6 panels you would get 6X13=78 Amps.

The charge controller you have is not able to handle all the panels at the same time. Only two.
The problem with PWM controllers is that they only convert the voltage not the current. As a result the 13 to 14 amps above for one panel or 26 to 28 Amps for two panels will be the same at the input of the controller and the out put of the controller.
The PWM controller regulates down to your battery voltage. Depending on charge level, temperature and some other parameters its output voltage is close to 14.4 Volt. As you can calculate the power charge controller is 14.4X 26 to 28=374 to 403 Watts.
The power from the solar panels is 17 voltsX26 to 28=442 to 476 Watts.

An MPPT controller can help you reduce these losses.
If you are planning on drawing max power fo your airco that power might be useful. If you never draw that power and just want to keep your batteries full then a PWM controller is acceptable.

Your 12 Volt batteries have to be in parallel unless your inverter is made for 24 or 36 volts.

Good luck
later J



So one charge controller for say 100 amp can do or 2 for each 50 amps or 3 for each 30 amps.
With three charge controllers you will gain some efficiency because each charge controller will be hooked up to two panels and so if one set is shaded it will not pull the other panels down.
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Old 07-31-2016, 10:40 PM   #4
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you need at least 24 volts incoming voltage to properly charge a 12 volt system. go with two sets of three panels- 30 volt. you need a fuse or breaker between the panels and charge controller and a fuse or breaker between the controller and batteries. do not mix batteries, 6 volt golf cart batteries are great for beginners. you need a 300 amp fuse between the batteries and the inverter. good luck
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Old 08-01-2016, 09:40 PM   #5
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2KW Solar Panels 8 x 245W Used Made USA Panel Battery Charging 12 24 or 48V | eBay
This is a listing for the same panels from the same place, but I got a better deal. My internet here is too slow to see the pictures but there are stickers explaining something and I think it might show the labels.

The photo has the wires hooked together on each panel in parallel. If I rewired them so that each panel is composed of 2 parts wired in series, wouldn't each panel be 10.55x2=21.1V? Or would it be best to leave them in parallel so that if half the panel were shaded the other half would still work?

It seems that my best bet might be to purchase 2 more 30A controllers and make 3 individual strings of 2 in series. That way if one panel were shaded (and so pulled down the power of the panel wired to it) the other two strings would still work. This would also allow me to use smaller gauge wire between the panels, controllers, and batteries, and would also avoid the need for a combiner box. Can I charge one battery bank (4 batteries) with three controllers?

MPPT would be nice and I know is more efficient, but at this point I am only concerned with cheap. I already have one 30A on hand and would prefer to use it rather than start over. I can always upgrade later.


Before taking on my system I'm going to start with the simpler version of the same thing; my neighbor also bought two of these panels and the same charge controller. I should be able to hook his two panels in series and then to the charge controller and then to the batteries. I have no idea about fuses and such, but I'd imagine what I need is a 30A fuse before and after the controller. Would this suffice, even though the panel is rated at 30.48A? Do I need a 60A fuse? Are there any in between?
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Old 08-01-2016, 09:44 PM   #6
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According to a reply I just got from the seller, the boxes on top (both positive) and the bottom (both negative) are run to the same place and therefore connecting them in series would short out the panel, so I can actually cap off and disregard one of each. He said they are each wired parallel and so do not have diodes.
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Old 08-01-2016, 10:19 PM   #7
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Yes you are right, just checked the e-bay add. So with these low voltage panels you will need two in series. Then hook them up to your pwm charge controller. To reduce losses in the panel wiring inside the panel it would be best if you hook up all the wires. As to optimal share the current evenly by all conductors I would take the same gauge wire as the panel has and run those separately to the charge controller. So you will get two 10 gauge minus wires and two 10 gauge plus wires . The series connection wires between the solar panels go each directly from one panel to the next.

For low pricing you can use square DQO series breakers and boxes from Home depot or Lowes. square D boxes and breakers are UL approved for upto 48 Volt DC.


http://static.schneider-electric.us/...CT9801R108.pdf


So your fuse can be a double pole breaker say 20 Amp. So that allows since they are in parallel 40 amps.
Note that the both of the normally 240 Volt AC bus terminals are now positive and the same voltage. Saves you a bundle because this stuff is available used for cheap.

Later J
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Old 08-02-2016, 07:16 AM   #8
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https://www.altestore.com/store/encl...breaker-p5807/
dc breakers are available too, get a little baby box to put them in.
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Old 08-02-2016, 09:38 AM   #9
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Originally Posted by onenationundergoat View Post
MPPT would be nice and I know is more efficient, but at this point I am only concerned with cheap. I already have one 30A on hand and would prefer to use it rather than start over. I can always upgrade later.
Honestly, you might be better off to get one or two fewer solar panels and put that money towards an MPPT charge controller instead. They provide a great boost in efficiency. Without one you will lose a lot of potential power.

For instance, let's say that you have all the solar panels configured to provide 20 volts. Even when the sun is blazing down perfectly on your panels the PWM charge controller will be limiting the power input because it needs to make ~14.6 volts on average (through pulses). This means that you'll be losing ~26% of the potential power.

An MPPT charge controller, on the other hand, will take that voltage and current and lower the voltage to ~14.6 volts while translating the amps. It can utilize over 90% of your panels potential.

The other big benefit is that you can provide high voltage to an MPPT charge controller. Mine (which is a cheap Tracer 4210rn) can take up to 100 volts DC. Higher voltages don't require thick and expensive wiring like low voltages do.

Something to think about, anyhow.


P.S. ^ That is a very much simplified explanation
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Old 08-02-2016, 06:18 PM   #10
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I got the panels last week so there's not a "buy fewer panels" option now! Haha. I made up a wiring diagram and posted it over on the other forum, but the internet is bad at the moment and I can't upload it here. I had drawn bypass diodes in but then one person made a point that if one of the two panels in the string was bypassed then there wouldn't be enough current to charge anyway. I've been looking up some 50A 12v self resetting automotive fuses and think I'll use those between the panels and controller and between the controller and batteries. So far I'm still thinking two panels in series to one 30A PWM controller, times 3, all hooked to the battery bank.
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Old 08-02-2016, 06:48 PM   #11
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Originally Posted by onenationundergoat View Post
I got the panels last week so there's not a "buy fewer panels" option now! Haha. I made up a wiring diagram and posted it over on the other forum, but the internet is bad at the moment and I can't upload it here. I had drawn bypass diodes in but then one person made a point that if one of the two panels in the string was bypassed then there wouldn't be enough current to charge anyway. I've been looking up some 50A 12v self resetting automotive fuses and think I'll use those between the panels and controller and between the controller and batteries. So far I'm still thinking two panels in series to one 30A PWM controller, times 3, all hooked to the battery bank.

If you don't already have the PWM controllers, it might behoove you to invest in a good MPPT. Most of the solar gurus recommend moving to MPPT when you break that 600W barrier.

Go back and read over HandyBob's writings. He makes a lot of sense...

https://handybobsolar.wordpress.com/
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Old 08-02-2016, 07:25 PM   #12
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Great, you have a plan, go for it. Don't take any safety shortcuts. Be careful with automotive fuses. I am not sure if they are rated for much more then 12 volt. You do not want to get any fires and so on. Better to use some industrial , commercial or marine hardware. Be sure to use fuses that are lower rated then the wiring. Use real solar wire or at least stuff that handles 105 Celsius. It gets pretty hot on a metal roof.

Good luck.
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Old 08-02-2016, 08:05 PM   #13
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BusFiend, it seems that HandyBob specifically and vehemently recommends AGAINST MPPT controllers.

I decided against automotive 12v self resetting breakers because I read up on them and don't want them resetting to the point of failure. I'm now looking at these Blue Sea 50a DC marine breakers. https://www.amazon.com/Blue-Sea-Syst...50a+dc+breaker

The panels come with what looks like 10awg wire on them, but I'll probably need to add more. Now the last thing to figure out; what size wiring to use? As you can imagine each set of two will be farther away from the batteries. The first set will probably be about 10-12ft away, the second set about 20ft, the third set about 28-30 ft. I heard something about gauging down the wire to make it fit into the controller as well. An online calculator that I used said for a 12 ft run I'll need 2awg wire. That can't be right, can it, for them wired in series?
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Old 08-02-2016, 09:24 PM   #14
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Let's start at the beginning. These appear to be older low-voltage/high-current grid-tie panels. Not knowing where these panels currently live in their performance life makes suggestions difficult.

The seller specs them at 10.5 Voc but does not spec a Vmp. "12V nominal" panels are generally rated at 22Voc/18Vmp. Let's say a pair of these panels, in series, is approximately 18Vmp @ 20A or 360W. You send each of three pairs to its own PWM controller. The controller you linked to drops each pair to 14.4V (maximum) at the speced 20A. Already you're down to 288W per pair, under optimum circumstances. Which means you'll lose 216W between the three pairs.

The PWM controller you linked to, while a 3-stage charger, outputs a maximum of 14.4V. Battery manufacturers recommend charging their batteries at 14.7 or 14.8 amps. Once the battery reaches the 14.8V, the controller should maintain 14.8V until the amperage drops off (2-3 hours). 14.4V will have a hard time fully charging a battery bank that has constant loads (refrigerator, etc) under the solar cycle.

Of course, all this depends on the capacity of your final battery bank.

Again, go back and read HandyBobs blog. Directly from his "RV Solar Quick Answer" page (emphasis mine): I personally only recommend MPPT if the system is approaching 600 watts, if the solar panels are those high voltage 44 cell units so that MPPT is needed to use the excess voltage, or if the existing wiring is too small and series wiring the panels can be done to improve voltage drop. (https://handybobsolar.wordpress.com/...-quick-answer/)

Personally, I would run two three-panel-series to a busbar on the roof and feed a single high-current MPPT controller by the battery bank. I would gauge the cabling to maintain a maximum 2-3% voltage drop. Running three two-panel-series to the busbar and feeding a high-current PWM controller is an option. However, approximately 200W charging capacity will be lost with a PWM controller.

Good luck!
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Old 09-08-2016, 12:50 AM   #15
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I haven't got the whole system up and running yet, but so far I've put together two identical systems; one for me and one for my boss. Each uses two panels in series, with 8 awg wire and a 40A breaker between panels and 30A PWM controller, and between controller and battery. My panels are in a spot that gets full sun for about 3 hours a day, and partial shade for another couple hours. Our inverter only allows the battery to discharge halfway, and that little bit of sun is enough to almost fully charge the battery before we ever turn on the generator for A/C in the afternoon.

We can't let the fridge run all night yet until we increase our battery bank and set up the other four panels, but it's an excellent start!

Thanks everybody for all your insight. I'm pleased as peaches that it worked out. Now all that remains is attaching them to the roof before Monday...
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Old 09-10-2016, 06:05 PM   #16
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you need at least 24 volts incoming voltage to properly charge a 12 volt system. go with two sets of three panels- 30 volt. you need a fuse or breaker between the panels and charge controller and a fuse or breaker between the controller and batteries. do not mix batteries, 6 volt golf cart batteries are great for beginners. you need a 300 amp fuse between the batteries and the inverter. good luck

We are just learning about solar too.
Correct me if I'm wrong but isn't it best to use fueses on RV types especially bouncey busses? I heard that breakers will not tolerate vibration or movement.
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Old 09-11-2016, 12:25 AM   #17
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We are just learning about solar too.
Correct me if I'm wrong but isn't it best to use fueses on RV types especially bouncey busses? I heard that breakers will not tolerate vibration or movement.
I don't know, but we're about to find out! Bolting our setup to the roof tomorrow, and heading down the bumpy mountain soon. If the breakers trip from vibration, we'll know about it! And if thy don't, then there's definitely never gonna be an issue because this road is bumpy as all get out.
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