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GlennWest

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Lou's diagram is not showing a combiner box if I reading this correctly. I know I still need to go to larger wire in a box though for down to the controller. Will bringing all the pairs to a central point, combiner box, 10 (positive and negative) wires, keeping wire length equal,  benefit?

2003 Teton Grand Freedom towed with 2006 Freightliner Century 120 across the beautiful USA welding pipe.https://photos.app.goo.gl/O32ZjgzSzgK7LAyt1

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You are correct, Lou's diagram does not show a combiner box.  It is just an example of connecting things in series/parallel configuration.  That diagram is typical of how 6 volt batteries would be connected in series/parallel to make a 12 volt battery bank.

It is always beneficial to keep wire lengths the same, but usually combiner boxes on an RV roof aren't centrally located.  The combiner box location is dictated by where it is easiest to run the wire down from the combiner box to the compartment where the charge controller is.  If you try to keep all the wire lengths the same going from each series pair of panels to the combiner box you would end up with a lot of excess wire laying around on the roof.  Inevitably there will be series pairs close to the combiner box and others a long way from the combiner box.  The the ones that are close would have a lot of extra wire coiled up if you tried to keep the wire lengths the same as the runs from the series pairs installed far away from the combiner box (hopefully that makes sense to you). 

In my case, my combiner box is on the driver side of the trailer near the front cap.  I have a pair of panels at the front of the trailer installed over the top of the combiner box.  This pair has short wires run to the combiner box.  I have another pair of panels in the middle of the trailer with medium length wires run to the combiner box.  My final pair of panels are at the back of the trailer.  These panels have a long length of wires run to the combiner box.  When I wired my series pairs of panels, I cut the wires (pos and neg from each series pair) to length so the wire runs were the most economical and easy to route/secure on the roof.  I didn't worry about keeping them all the same length.  I did leave some excess wire under the panels themselves so I could lift the panels and move them a little (either for future tilting or for possible servicing, etc.).  I also kept the positive and negative wire coming from each series pair the same length so the electrical path for each pair of panels is the same. 

Here is a link to some pictures of my combiner box and the layout of my panels on my roof.  You can see the wiring laying loose on the roof before I connected and secured everything.

Here are some pictures of the final installation with all the wires secured and panels in place.  I ran the wire in split loom cable sheathing and then stuck the split loom to the roof with dabs of Dicor every few feet.  It has all been in place for over a year with no issues.  Some people put Eternabond tape over the wiring to secure it to the roof.  I'm not as much of a fan of that method because it is very difficult to undo once it is all in place that way.

Edited by Chad Heiser

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You want to have equal length wires going to parallel batteries because even a few tenths of a volt difference between the batteries (due to unequal wire losses) will make a HUGE difference in the amount of current going in or out of a battery.  Changing a battery's terminal voltage just a few tenths of a volt can make a tenfold change in the amount of current going in or out of the battery.

The same doesn't hold true for solar panels.  Going from a dead short to the maximum power point on a typical solar panel only changes the current flowing out of the panel by 10% or so.  At the MPP few tenths of a volt plus or minus due to different length wires will only change the panel's output by a few percent.  In other words you don't lose much by having different length wires going to your panels.

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39 minutes ago, GlennWest said:

So I could just wire like the diagram, panel to panel. Then run 2 lines, one positive, one negative to box for penetration. 

Glenn, sure simple straight ladder wiring will "work" and I'm sure many are configured that way and no problems were encountered. Once you make up the five sets of two in series if you tie the resulting + and - together at a combiner/splice box (one wiring method others will work) you can then run two big wires (3500 watts at 77 volts is around 45 amps)  + and - down to your controller. HOWEVER its still electrically "better" (even if not a  "huge" difference) if all the panels were equally loaded which is achievable using the wiring methods described in the Smartgauge diagrams   http://www.smartgauge.co.uk/batt_con.html. AT THE LEAST (if you don't want to go to the trouble and expense to match things perfect) as they explain if you take the final net output off the + of one end of the ladder and the - off the other end hey that's better then nothing and will improve the balance among the ten panels.

SURE you have plenty of power and using a simple ladder wiring procedure works and there may not be that much to gain by doing it to achieve absolute balance. I'm ONLY describing how to achieve the best balance possible even though less then perfect will certainly suffice. Similar the bigger the wire the less the voltage drop but again overkill can become expensive and cumbersome and harder to install and your chosen wiring method (simple ladder or better balanced) doesn't have to be absolute perfect to still function fine n dandy. Its likely using big enough or bigger wire down to the controller will get you more bang for the buck then achieving perfect panel load balance, but I enjoy describing good methods for those who may be extra picky about such things lol..

Hope this helps, I think you have it down now and will have a great system when finished, keep us posted...……...

FUN thread for the sparkies at least lol

Merry CHRISTmas

John T

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You could go from panel to panel with 8 gauge wire, or you could use 10 or even 12 gauge wire from each pair to a rooftop combiner box. 

If you go with the rooftop combiner, using 10 gauge wire from each pair of panels to the box will only cause an extra 0.5% wire loss between a pair of panels 20 ft. away vs. a pair of panels adjacent to the combiner.  That's using 80 volts at 10 amps for each pair of panels.  You'll have to fuse each set of wires in case a short causes the rest of the panels to backfeed into them.

Then use 8 gauge wire to handle the combined 45 amps current from the combiner box to the charge controller.  Assume 25 ft of this so you can put the charge controller adjacent to the batteries and you'll lose 1.77% voltage along these wires, for a combined worst case voltage loss of 2.27%.

Or go with 25 ft. of 6 gauge wire between the combiner and charge controller for a 1.1% voltage loss and an overall worst case loss of 1.6%.

Edited by Lou Schneider
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6 minutes ago, Lou Schneider said:

Or go with 25 ft. of 6 gauge wire between the combiner and charge controller for a 1.1% voltage loss and an overall worst case loss of 1.6%.

Lou I agree and would use AT LEAST 6 gauge. If one figures the absolute max and best conditions with bright sunlight direct overhead  in ideal conditions (yeah right how often does that happen in the real world lol) and lets use for example say 45 amps,  6 Gauge would suffice HOWEVER AND SUBJECT TO if 45 amps just happened to be the "maximum continuous" current (which I doubt meets the definition in this scenario) I never designed to no more then 80% of the wires ampacity IE in the situation IF (likely not here) there were 45 "continuous amps" I would up the wire in that case to No 4. Bigger wire = less voltage drop and bigger is better DUH but practical situation and how much voltage drop one can tolerate enters into the decision...….

 

1 minute ago, GlennWest said:

was planning on #4 welding lead to controller. I have a lot of that on hand.

 GREAT IDEA GLENN welding lead has better flexibility,,,,,,,,,,, better vibration resistance,,,,,,,,,,,,,,good insulation quality and integrity PLUS you will get less voltage drop then using 6 gauge which is still the ABSOLUTE MINIMUM I RECOMMEND REGARDLESS

 Youre gonna have one good system, congratulations, keep us posted

John T

  

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While on subject of welding lead. I plan to use a chevy volt battery complete. I am aware of the golfcart fire. going to build a metal box for mine. It is sealed in a metal box originally. 

2003 Teton Grand Freedom towed with 2006 Freightliner Century 120 across the beautiful USA welding pipe.https://photos.app.goo.gl/O32ZjgzSzgK7LAyt1

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9 hours ago, GlennWest said:

I plan to use a chevy volt battery complete. I am aware of the golfcart fire. going to build a metal box for mine. It is sealed in a metal box originally. 

Glenn, I have attended a few seminars, read and researched (still no expert by any means) the use of a Tesla or Chevy Volt battery in an RV. Sure there can be potential hazards, but if you study what Tom  Morton (Mortons on the Move) did (and several other solar experts) you will gain a lot of insight. To protect and prevent many typical associated hazards he utilized an array of protection devices to shut down in case of overheating, over charging, low charge state and low temperature along with the standard over current and fire protection. While many are satisfied with and "get by" with less hazard protection, FWIW I like your idea of a metal box enclosure. I have seen some stick Lithium batteries in a wooden enclosure say under an interior wood/cloth seat, but that's NOT how I would suggest. I think a metal enclosure with adequate ventilation is a good plan which has to be better than a wooden/cloth enclosure WELL DUH. With proper overcurrent, over or under temperature, and charge monitoring,  the battery in an adequate vented metal enclosure sounds like a good plan to me even though NOT a solar expert......…....    Wood or metal enclosure ????? ITS YOUR RV YOUR RISK AND YOUR CHOICE

PS How many Amp Hours of energy storage will you end up with?????????? 

Hope you have a Happy and Blessed Merry Christmas, good questions good thread you started, I'm glad to participate and look forward to other opinions regarding a metal enclosure.

John T

Edited by oldjohnt
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One huge battery, its gonna take some "serious" copper (adequate ampacity) and over current protection to connect the battery to the Inverters but I'm sure you will handle it Glenn. Gee its fun for the rest of us to spend YOUR money lol

John T  Still in Austin but headed to a warmer Florida after Christmas

Edited by oldjohnt
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Yes it is. I also been kicking around the idea of cooling the volt battery.  Not that I think it's needed. A small container with antifreeze, some tubing and a small pump. 

2003 Teton Grand Freedom towed with 2006 Freightliner Century 120 across the beautiful USA welding pipe.https://photos.app.goo.gl/O32ZjgzSzgK7LAyt1

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11 minutes ago, GlennWest said:

Yes it is. I also been kicking around the idea of cooling the volt battery.  Not that I think it's needed

Glenn, Congratulations, at least you're thinking and concerned about cooling the battery, I've seen some folks just stick 4 or 5 Battle Born Lithiums under a couch (not even in a metal enclosure) and be done with it ????????  Actually cooling isn't real simple, one has to know the watts of heat generated,,,,,,,,,,,the volume and thermal characteristics of the enclosure space and then compute the CFM of air flow etc etc etc . That's a mechanical and thermodynamics question NOT for me an electrical person lol but a sufficient sized metal enclosure with "adequate"  (however much that is???) fan forced ventilation of some sort will surely suffice and has to be better then under a non vented wood/cloth sofa right??.

NOTE in the event you camp in cold climates THEN KEEPING THE BATTERY WARM ENOUGH FROM FREEZING is another important consideration !!!!!!!!!!!

I hope the solar experts and mechanical (heating/cooling) minded and Lithium experts will weigh in, this is getting above my pay grade lol 

John T  (page 16 of the latest Escapees magazine picking an old banjo)

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lAlso checking prices of Multiplus vs quadro units. Quadro goes up to 10k but Multiplus goes up to 5k, 2 5k Multiplus are with $100 of the 10k  Quadro. So may consider suggestion for feeding each leg with separate inverters. 

Edited by GlennWest

2003 Teton Grand Freedom towed with 2006 Freightliner Century 120 across the beautiful USA welding pipe.https://photos.app.goo.gl/O32ZjgzSzgK7LAyt1

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Glenn, back to cooling, if I recall correctly the heat generated is 3.41 BTU per Watt, so at 17,000 watts that would be 58,000 BTU (similar to maybe 1/2 of an x sq ft  house furnace). HOWEVER I just don't envision any full 17KW being used all at once for any sustained time period. That's the maximum CAPACITY yet allllllllllll that much energy use at once is unlikely in my opinion. Sure a person could make all the exact measurements and calculations figuring in the size of the enclosure and its thermal character and figure out how much heat is generated that needs to be extracted BUT IM NO MECHANICAL OR THERMO ENGINEER AND SMART ENOUGH TO DO THAT. Still I strongly agree with your idea of using a metal (versus wood n cloth) enclosure and ventilation and cooling, but sorry, I just have no idea  how much is needed...……..Maybe the mechanical and HVAC minded gents can address your cooling concerns ???????????  

PS as a pure guess if you're running strictly off your battery and say all your big RV loads were running (AC's etc) you could be pulling lets use a guess and say 3000 to 5000 watts (NOT anywhere near 17,000) that would mean 10,200 to 17,050 BTU of heat generated at the battery which needs extracted out of your metal enclosure. (unless you dont care if temp rises inside it how much???)  What it takes to do that may be simply fans and venting, it depends on sooooooooooo many unknown factors like volume and insulation and the ambient temperature etc...Heck no sense in OVERthinking all this, I bet if you use a metal box with an open vent on one end and a couple 12 VDC muffin fans on the other it may (subject to actual loads) suffice BUT NO WARRANTY OF COURSE you gotta do the math to be sure and/or see how Chevy handles it...........……..

 John T

 

Edited by oldjohnt
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Actually my mini splits pulls according to specs 3500ish watts at max heat which is highest. Now it will seldom run at max. We have residential fridge, older unit, came with Teton. Believe folks figure 600 watts for this but it not all the time either. Convection microwave, tv, computers, etc. I can see 8-9k on occasion. That why I considering 2 5k units. And I must confess, the more I read on the programming of the Victron multipass, the more complex this system is. Considering 2 Magnums but loosing some wattage with them. 8800 watts vs 10k watts. 

 

 

2003 Teton Grand Freedom towed with 2006 Freightliner Century 120 across the beautiful USA welding pipe.https://photos.app.goo.gl/O32ZjgzSzgK7LAyt1

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Glenn, while not knowing all the exact loads, I'd ask what are the chances of and how long and how often would the mini splits be running at max while AT THE SAME TIME say the microwave, a coffee maker, a hair dryer, a toaster etc (high current appliances) be running??? As a pure "guess" (no way of knowing sitting here) I suspect there's a darn good chance that 8800 watt Magnum(s) system you spoke of will suffice. Of course, a Killawatt meter and specs and an energy audit could provide an answer, I'm not a fan of running devices at the very top end of their ratings for extended time periods...….Of course you're gonna need proper transfer switching and panel and Neutral configurations.

Again, I'm NOT any Solar expert or mechanical/thermo engineer so take this with a grain of salt, see what the experts have to say.

God Bless and Merry Christmas to you and yours and all here

John T  

Edited by oldjohnt
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Know this is an older post but it about the same thing, so, If I go with 12 panels, will I be good with same wiring? I was measuring while up on top last week and can fit 6 per side with good clearance between them. Slightly different panels. 4400 watts, 56.4 amps, voc 95.2, vmp 78.8. so 2 series and 6 parllel strings? Used victron's sizing tool and they call for the Blue Solar MPPT 150/85 VE.CAN. MidNite Solar sizing chart shows the Classic 150. Close to $300.00 difference. 

 

 

 

Edited by GlennWest

2003 Teton Grand Freedom towed with 2006 Freightliner Century 120 across the beautiful USA welding pipe.https://photos.app.goo.gl/O32ZjgzSzgK7LAyt1

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One other suggestion, I am running two strings with 2 solar controllers. one is series at about 120 volts and the other string in series at about 60 volts. Am using 10 gauge on each string down to controller. Shading on modern panels is not such a big deal anymore. I can have one of the three panels in the string shaded and still get at least 2/3 of the voltage and amps.But with that many panels, you will have to run series parallel or have many controllers and lots of wires. 

Foretravel 40ft tag 500hp Cummins ISM  1455 watts on the roof, 600 a/h's lithium in the basement.

 

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