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Post by cottagecamper on Nov 13, 2018 2:23:08 GMT
Hi folks, newbie here (please be kind). I am building a THOW (Tiny House on Wheels). (think of it as an RV) I have one 12v battery (so far) which runs my LED lights. I've been charging it with a converter but I'm ready to install my PV system. I already have 7 Renogy 100watt/12v mono panels for my roof. I need advice on how to wire them. I have a Morningstar TriStar MPPT chg controller which can take 12/24/48v input and 60amps max current (lsc). I want to keep the battery bank at 12v because I run all my lights/DC outlets from it directly.
My roof is nearly flat but only 8 ft wide so I am going to lay the panels end to end in 2 rows down the length of the roof. The THOW is 20 feet long and I want to leave a footprint of space between them to get around if need be. So I have some questions, if you would be so kind to help me.
Can I join one string of 3 in parallel and one string of 4 in parallel and then connect the 2 strings together in series, or do they have to be equal strings, say 3 & 3 panels and not use the 7th to keep it even or does that even matter?
What gauge wire will I need to run between the strings (being they are end to end I will need extentions between panels...is standard 10 AWG ok for that?)
What gauge wire will I need from the array down to the controller 12 feet below?
After we tackle these Q's, I'll be seeking recommendation for how many batteries I should have to utilize all the input and whether I could run my water cooler or fridge from it.
Thanks for your help.
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Post by tattoo on Nov 13, 2018 3:44:26 GMT
That is a really cool looking trailer...
As far as the panel wire size you need, Just buy the wire that renogy sells as it will have the correct ends already attached.. They sell the wire in the length you need....
Can you flip some of the panels around to get the wires closer to each other? That should work if your running them in series or parallel...
What kind of batteries are you wanting to run?? Sealed, flooded?
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Post by swampmonster on Nov 13, 2018 8:15:12 GMT
Well, you have already selected your panels and charge controller, so that means the charge controller is in,,,, ER,,, charge...In charge of how you connect your panels.
The controller you selected is in fact a top quality item. It has plenty of capacity, and can handle many various voltage ranges.....But, if it's input Voc is less that 150 volts, then maybe you can't connect all panels in series, because series add volts to volts x the # of panels.....So two 12V panels in series=24v, where two 12v panels in parallel still = 12v......BUT, with 2 connected in series, and another 2 connected in series, then both pairs connected in parallel still = 24v, but the amps double....Hmmmm, so that means you maybe gotta use max input Voc of the controller as the determining factor as to how they are all interconnected....Total amps will never be a problem, but max Vos certainly might.
No problem yet, but first examine the controller owners manual and discover what the input max Voc is(voltage open current), then look at the data sheet on the back of one of your panels for that panels stated Voc....That will usually be at or close to 22.2 Voc on a 100 watt panel.
Ok, you are half done..Get the required info and do a little simple math considering the laws of basic electricity....Two of those laws state that if we connect in parallel, voltage remains the same, but amps add to amps times the number of items...So 7 12v, 5 amp panels connected in parallel equal 12v (22.2 Voc) @ 35 amps.
But if we instead connect them all in series, then amps remain the same and volts add to volts times the number of items....so 7 12v panels @ 5 amps equal 84 volts at 5 amps...BUT don't forget Panel Voc, where 7 times Voc of about 22.2 equals 155 Voc.
So first examine your controller specs and then using the laws above and your calculator, determine the best connection scheme possible....You may be able to connect all series, or all parallel, but odds are you will have to use series/parallel combination to hit that sweet spot where total volts, Voc, and amps are as high as possible, but not against the wall.
Also keep in mind that series connected panels are very sensitive to shading, even partial shading, where one shaded panel in the series will reduce all panels in that series in their total power output....Parallel connected panels will however react totally different where only the shaded panel is reduced in output.
So...those are the Rules, and that is the good and the bad of it....And with that Friend, I am certain you will make the best decision.
OH, those two laws I cited?....They also apply exactly the same to batteries....So if you already have a 12V battery you are happy with it and just want more storage capacity, simply buy additional batteries exactly like it and connect them all in parallel til you total the amps capacity you seek....Even 100 12V batts in parallel will still be 12V
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Post by swampmonster on Nov 13, 2018 8:55:52 GMT
OOOPS, seeing as how you have 7 panels, and seven is a prime number, then have no choice except to go with 6 panels or 8 panels into a single charge controller if that controller can't deal with all 7 panels in total either series or parallel...You CANNOT split them into two unequal arrays and no matter how they interconnect, it simply will not work on a single charge controller.
Perhaps you can instead send the controller back for refund and buy two lesser controllers that you can parallel into the common bank of batteries, OR you can reduce the panels to 6 or buy another panel.
A single charge controller can handle a prime number of panels as long as long as the total of the panels don't exceed the limits of the controller....But you cannot split them into two unequal arrays into a single controller.
Sorry.
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Post by swampmonster on Nov 13, 2018 10:00:46 GMT
It's NOT because you have an ODD number of panels, you have a PRIME number of panels. If you had 9 panels then you could split them into two arrays with one containing 3 and the other 6, 3 arrays with each 3 panels...Then from there be able to juggle connections within each array to allow them all to meet at the charge controller PV input with equal values the controller can deal with.
But 7 cannot be divided by any number except 7 or 1, so 7 is a prime number, so is five...All odd numbers are not necessarily prime numbers, tho because many can be divided into whole besides 1 and the number in question. numbers, like 9 can be divided by 1, 3 and 9...So 9 is an odd number, and can be divided by a whole number, but it is not a prime number....Where those three 3's can be combined into two units of 3 where six is a multiple of three and there is an equal three left....Or 3 3's can be combined at reduced Voc....
If you had two arrays of five panels, the number 5 is also a prime number, but it is equal to the other 5, so it multiplies to 10 panels, and ten panels can be divided equally into two five panel arrays.
You are dealing with whole panels, so when you divide them, they must be either divided into equal arrays, or arrays that are a multiple of the other. Where each panel remains whole.
Math is fun and it has hard rules just like electricity, because the rules of electricity are based on math, yaknow?
Sorry I missed that fact before I wrote my first reply.
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Post by bupkis on Nov 13, 2018 13:35:39 GMT
Can I join one string of 3 in parallel and one string of 4 in parallel and then connect the 2 strings together in series,
Normally 'strings' are panels in series (or single panels) which are connected in parallel to the charge controller. You can have 2 unequal strings, one of 3 in series and the other of 4 in series, the 'strings' would be connected in parallel. I'd suggest 3 'strings' of 2 panels or 2 strings of 3 panels and ditch the extra! You might care to play with Moringstar's string calculator, it can tell ya which configurations exceed controller limits. string-calculator.morningstarcorp.com/If you happen to settle on 7 'strings' of 1 panel each then 10g wire would not be big enough from the combiner to controller. For controller to battery, make this as short as possible 6g or larger FYI, string calculator results show 5 in series max based on my input of -20C low (and 40C high temperature).
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Post by bupkis on Nov 13, 2018 14:38:57 GMT
But, if it's input Voc is less that 150 volts, then you can't connect all panels in parallel. This is wrong and may be a typo, don't know how you mistype series as parallel 7 'strings' of 1 panel each and Voc = Voc of ONE panel. 1 'string' of 6 (series) Voc could exceed 150v in sub freezing conditions.
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Post by swampmonster on Nov 13, 2018 14:50:06 GMT
Yes, I caught the typo and changed it while you were typing this, LOL....Thanks.
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Post by swampmonster on Nov 13, 2018 15:16:19 GMT
Can I join one string of 3 in parallel and one string of 4 in parallel and then connect the 2 strings together in series,
Normally 'strings' are panels in series (or single panels) which are connected in parallel to the charge controller. You can have 2 unequal strings, one of 3 in series and the other of 4 in series, the 'strings' would be connected in parallel. I'd suggest 3 'strings' of 2 panels or 2 strings of 3 panels and ditch the extra! You might care to play with Moringstar's string calculator, it can tell ya which configurations exceed controller limits. string-calculator.morningstarcorp.com/If you happen to settle on 7 'strings' of 1 panel each then 10g wire would not be big enough from the combiner to controller. For controller to battery, make this as short as possible 6g or larger FYI, string calculator results show 5 in series max based on my input of -20C low (and 40C high temperature). I agree!..If I selected his panels and CC correctly, the Morning Star calculator says his charge controller can handle all 7 in parallel... I also agree he must at each panel's outputs increase AWG to at east 8AWG, then combine them all into 6AWG before they drop into the house....He will need 7 pairs of 10/12 to 8 AWG MC4 conversion connectors, fusing for each panel, a combiner box, and lengths of wire as required.
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Post by bupkis on Nov 13, 2018 15:28:12 GMT
I hope the OP does not do all parallel! if he does then 10g is appropriate for a short run from panel to combiner, but 30-40A combined exceeds 10g current rating, actually it doesn't but NEC limits 10g to 30A and the Voltage drop would be excessive for any length of run.
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Post by swampmonster on Nov 13, 2018 15:39:05 GMT
I hope the OP does not do all parallel! if he does then 10g is appropriate for a short run from panel to combiner, but 30-40A combined exceeds 10g current rating, actually it doesn't but NEC limits 10g to 30A and the Voltage drop would be excessive for any length of run. Yup...That's why I suggested he increase to 8AWG at each panel using 10/12 to 8 MC4 adapter pairs for the runs to the combiner, then in the combiner increase to 6AWG down to the controller.....12V is certainly doable, but can't allow voltage losses in the wire runs. If he can get a stiff 17V to the controller at 40 amps, he can almost weld with it....yaknow, during peak solar hours I'm thinking if has room for 7, he has room for 8, well except if he has a big skylight or other issues on the roof...Either way, 600 watts really is plenty for many folks...His MHOW is no bigger than my motor home, plus he has the advantage to fit it out with more D/C powered stuff than I have to work with....Heck 600 watts connected series/parallel into a 440 amp bank thru a quality MPPT like his will fire the hair off a decent 2000 watt inverter/charger.
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Post by bupkis on Nov 13, 2018 16:27:34 GMT
I hope the OP does not do all parallel! if he does then 10g is appropriate for a short run from panel to combiner, but 30-40A combined exceeds 10g current rating, actually it doesn't but NEC limits 10g to 30A and the Voltage drop would be excessive for any length of run. Yup...That's why I suggested he increase to 8AWG at each panel using 10/12 to 8 MC4 adapter pairs for the runs to the combiner, then in the combiner increase to 6AWG down to the controller.....12V is certainly doable, but can't allow voltage losses in the wire runs. No, you suggested you agreed with me to increase the wire size at the panel, but I totally disagree with that, that would be an expensive waste of money with little gain, 10g can handle 5A easily, I don't believe he is gonna run 100' before combining.
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Post by swampmonster on Nov 13, 2018 17:05:18 GMT
Yup...That's why I suggested he increase to 8AWG at each panel using 10/12 to 8 MC4 adapter pairs for the runs to the combiner, then in the combiner increase to 6AWG down to the controller.....12V is certainly doable, but can't allow voltage losses in the wire runs. No, you suggested you agreed with me to increase the wire size at the panel, but I totally disagree with that, that would be an expensive waste of money with little gain, 10g can handle 5A easily, I don't believe he is gonna run 100' before combining. By the charts and tables you are correct....Kinda sorta....But a buncha tiny losses add up quick, and that too runs into money, yaknow? The guy will be connecting 7, maybe 6 and possibly 8 panels, yaknow?...So that alone is a multiper of loses of 6-8 times the tiny loss at one panel.... The pretty little gal has stowed away an extra 5lbs?....No big deal, but 5X6lbs? WHOAH, girl..You need chop sticks! Hey, after all, he has to buy 10AWG to connect panels to combiner, right?....For not much more money he gets 8AWG, a slight one time increase in cost, but forever payback...Another place I "agreed" with you where you never stated you suggested 6AWG TO the charge controller...Instead you stated FROM the charger...I left your statement as is because I agree as far as FROM the charge controller, BUT I also suggest TO the controller for very same reason as above. I like my gals slim, trim and racy...Lean, mean and quick. But I like my wires FAT.
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Post by bupkis on Nov 13, 2018 17:20:31 GMT
No, you suggested you agreed with me to increase the wire size at the panel, but I totally disagree with that, that would be an expensive waste of money with little gain, 10g can handle 5A easily, I don't believe he is gonna run 100' before combining. But a buncha tiny losses add up quick, and that too runs into money, yaknow? The guy will be connecting 7, maybe 6 and possibly 8 panels, yaknow?...So that alone is a multiper of loses of 6-8 times the tiny loss at one panel.... let me call BS on this also, the losses are independent of each other and do not add up. No, one does not multiple the loss from one parallel connected by the number of panels. A fraction of a volt loss between the panel and combiner for each pair of wires, once combined then ya increase wire size!!! Once again, each string is independent of the others till combined.
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Post by cottagecamper on Nov 14, 2018 2:32:39 GMT
Wow, guys, THANKS! Great detailed responses! And thank you for the compliment on my Tiny House & on my choice of controller.
Irrelevant Point of interest: I do have a total of 8 panels. But 1 is already installed on my 6x10 ft "Cottage Camper" I built 5 years ago. I had purchased 8 to put onto a cabin I built in the mountains, but I sold the cabin before I ever installed the solar. So that's why I have 7 left now for my 20ft THOW.
OK, I do have a basic knowledge of series/parallel math, so I follow what you're saying. I will "ditch one" panel for now and make 2 sets of 3.
The Renogy panels I have are 100watt/12v/5.2amp. The controller max Voc is 125 so no, I can't put them all in series, I agree. Nor all in parallel.
First QUESTIONS: What would be the advantage of wiring 3 pairs in series and then into parallel? It still combines to 24v/15.6a right? Or would you wire one set of 3 in series and then another set of 3 in series and connect the 2 sets in parallel? Wouldn't that math out to 36v/10.4a? Is this where your recommendation for bigger wire gauge comes in?
Supplies: You mentioned that if I went with series into strings and then wire 2 strings into parallel that I'd need to boost the gauge:
"I also agree he must at each panel's outputs increase AWG to at least 8AWG, then combine them all into 6AWG before they drop into the house.... He will need 7 pairs of 10/12 to 8 AWG MC4 conversion connectors, fusing for each panel, a combiner box, and lengths of wire as required."
I'm still thinking to wire the 3 in parallel (12v/15.6a) and then the 2 sets together in series. That brings its math to 24v/15.6a. Wouldn't this allow me to keep using 10g between the panels as well as the 12ft drop into the controller? Would you still recommend bigger wires if I did it my way = 3 in parallel, 3 in parallel and then connected into series? Or is there a reason you'd series first, then parallel?
And once you help me understand my choices at this point, then we can ponder a new question: New QUESTION: My controller manual mentions using 6g/90C or 4g/75C minimum for "carrying the system current" Does that mean out of the charge controller going to the battery? And yes, I will put the charge controller near the battery and also near the inverter.
I have one AGM battery now but will get at least one more. Being that they are sealed, do I still want to put the cc and inverter in a separate compartment? The battery lives inside the storage bench/couch.
Again, gentlemen, I am most grateful for your knowledge and input! Thanks!
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