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Old 08-02-2016, 05:48 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, 06:25 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.
later J
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Old 08-02-2016, 07:05 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, 08:24 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 09-07-2016, 11:50 PM   #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, 05:05 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 09-10-2016, 11:25 PM   #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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