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Solar question


Daveh

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I am talking with a fifth wheel manufacturer who told me they had a 10 gauge wire run from the roof to the battery. (I had asked prior to the sale and they assured me in writing the system was sufficient for a large system.) When I objected that a long run run of 10 guage could not even meet the 3% volatge drop standard for a very small system, much less categorize a trailer as Solar Ready they essentailly told me I could take it or leave it and offered to rescind the contract. I am trying to decide whether to take them up on that offer. Later the comapny wrote to say their system runs 8 gauge, not 10, to the controller and then 10 gauge to the batteries. Am I missing something? That seems like a criminally poorly designed system. Why would anyone decrease wire size into the batteries? Is there any RV manufacturer, much less dealer, that knows what they are talking about? I have about $65,000.00 on the line and they are willing to let the deal go over a few hundred in wiring. I keep looking back to see if I am missing something but I don't think I am. Am I? I am being treated like I am an unreasonable ass and I honestly only want an honest and logical explanation. I figure I need 4 gauge wire to the batteries. When is the RV industry going to actually involve electrical engineers and stop false advertising?

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everything is relative. A 100 watt system is large to a 10 watt system. If your looking at a larger system with #8, I would use a higher voltage (maybe 36-42 volt set of panels and a MPPT controller.

 

It is something to work with, if everything else is good, go for it. 90% of the manufactures are clueless on solar.

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I understand 8 is better thab 10 (but not why they would selfdefeatingly run 10 after 8) but from what I am reading both cause voltage loss far in excess of the allowed 3% voltage. Handy Bob https://handybobsolar.wordpress.com/the-rv-battery-charging-puzzle-2/ and our own Jack Mayer are exceptionally clear on these point. Jack says "

  • The system is under-wired. The wire run from the solar panels to the controller, and then on to the battery bank, is sized too small. It should never be less than #6 cable, and I use #4 routinely on 12-volt nominal systems. Manufacturers commonly use #10. That is way too small for all but the smallest system. The only exceptions to this are with higher-voltage systems (more on that later). USE the wiring tables or online calculators to determine the correct size wire, and then go a little heavier. The wire size is not an "opinion" - it is simple physics. Use the calculators.

I cannot get beyond Jack's statement that is simple physics. I used the calculators and got clear results. This has been like debating whether the earth is round. What do you base your opinion on Yarome? They are also saying it is okay. The charts and calculators say I could maybe run a single 50 watt panel. But thats it without a full rewire.

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yea Bill I am running the numbers with high voltage with MPPT. MPPT not an option through the dealer. It gets down to about a 5.5% loss before added in any mppt recovery. Maybe acceptable. Not ideal and frustrating, considering the thing is not built yet and we are talking about changing a single run of wires from 8 to 4. I would think the material costs diff is less than 200.00.

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The issue is simple, yet complex. It totally depends on if you are using a high voltage system. Run the numbers with the actual Vmp/Isc of the panels and the distance. There ARE cases where #8 is adequate on high voltage systems. On nominal 12 volt systems (around 18 volts) #8 is not adequate, but it can be on a high voltage system.....

 

It IS simple physics. Just run the numbers and see if it will work. The wire size may require that you run a very high voltage set of panels ....eg. panels wired for in excess of 60 volts.... This will require series or series/parallel wiring of the panels.

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Okay, the size of the conductors FROM the Solar Panels TO the Solar Charge Controller IS NOT ANY SET OR MAGIC NUMBER YOU READ SOMEWHERE (like 6 or 8 or 10 gauge should be used), it depends on several factors, some of which I will list below in an orderly systematic engineers approach to compute what size wire is required from panels down to your charge controller. NOTE yes, bigger wire is better as it reduces voltage drop WELL DUH but lets look at in a reasonable engineering and cost efficient PRACTICAL manner: If you are passing 20 amps over 20 feet but want to use No 4 Wire (or some number gauge some other dude uses or you read somewhere), fine its your choice not mine, I'm ONLY describing the tools and method to compute what can work.

 

 

1) At what net Voltage are you operating??????????? Nominal 12, 24, 36, 48 etc depending on your series or parallel or series/parallel combination. NOTE the Open Circuit Voltage of any panel is higher then that which they produce once connected to a load (your batteries). However, since when loaded their output is a bit higher then nominal fully charged battery voltage of 12.6 (perhaps 13.2 to maybe 14.8 depending on controller and panels and batteries) I listed the nominal voltages above of 12 or 24 or 36 or 48 etc so you might understand where I'm coming from. NOTE I'd prefer to operate at higher total solar panel voltage configurations (as in series) as higher voltage reduces the current and also reduces voltage drop!!!! If you can operate multiple panels at say 24 or 48 volts etc by using series connections, I would choose that over several 12/s connected in parallel.

 

2) What is the total max Watts of all your panels combined, IE do you have say 100 or 200 or 400 or more total combined watts???????

 

3) Once you have your total voltage and total watts, you can compute the approximate current that flows from your panels down to your charge controller using derivations of Ohms Law. Power in Watts = Volts x Amps, and Current I = V/R. If you were operating at say 24 volts nominal and you had a total of 400 panel watts, 400 = 24 x I, I, so I = 400/24 = 16.7 amps. (that would require just a tad over what 12 AWG (20 amp) wire is rated for, meaning you should use 10 Gauge SUBJECT TO DISTANCE AND VOLTAGE DROP!!!!!!

 

4) Once you have computed your max continuous current, you size the conductors to have a minimum ampacity of 125% of the max continuous current. IE if you used 12 gauge 20 amp wire, I wouldn't allow more then 16 amps of current. if you use 10 gauge 30 amp wire, Id pass no more then 24 amps.

 

5) Once you have computed the current and necessary conductors, YOU CAN CALCULATE THE VOLTAGE DROP knowing the distance of the run. If the voltage drop is more then desired, you increase the wire size to make it acceptable.

 

SOOOOOOOOOOOOOOOO that is the only and engineering sound way you can calculate the size of the conductors required from you panels to you charge controller NOT by some magic number you read somewhere like 10 Gauge or 8 Gauge or 6 Gauge. Its depends on Voltage,,,,,,,,Current,,,,,,,,,,,,Wattage,,,,,,,,,,,Distance,,,,,,,,,,Voltage Drop.

 

If I had your total solar panel watts and voltage configuration and distance of the wire run I could compute the voltage drop

 

SUMMARY 10 Gauge wire may be just fine or it may NOT HOWEVER you cant just accurately randomly say it is or it isn't based on what someone else used or recommended AS IT DEPENDS ON VOLTS AND WATTS AND CURRENT AND DISTANCE OF THE RUN!!!!!!!!!!!!!!!!

 

YES, bigger wire is better as it reduces voltage drop and if 10 Gauge is required using engineering calculations, I'm just the type of guy who may go ahead and upgrade to 8, I'M A CONSERVATIVE LOL However I likely wouldn't use 4 Gauge, get the picture??????????

 

FINAL NOTE CONSULT WITH THE PANEL AND CHARGE CONTROLLER FOR RECOMMENDATIONS!! In the event Voltage Drop is more critical then normal (may well be the case where a charge controller and panels are concerned) THEN DO AS THEY SUGGEST NOTTTTTTTTTTTTTTTTT THE ABOVE AND NOT WHAT YOU READ OR SOMEONE ELSE SUGGESTED!!!!!!!!!!!!

 

John T Too darn long retired electrical engineer and rusty as an old nail SO NO WARRANTY do what the manufacturer says, not us

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PS Yesterday I spoke with tech support regarding my MPPT Solar Charge Controller and its operation. To fully utilize the MPPT operation instead of it reverting to PWM control, he suggested I run at the higher voltages, perhaps at least 24 or even 48 instead of only 12 volts (like if you had two twelves in parallel) since that may not allow the full MPPT capability. So again, depending on how many panels you have and what series/parallel combination you choose and distance of your run, the 10 Gauge might "suffice" but I agree its a bit chincy regardless and if had been the RV electrical design engineer I would have specified at least 8 Gauge not knowing the users panel configuration or even 6 Gauge. If you stay with the 10 gauge Id run at 24 or 48 volts and again ONLY by performing the calculations I listed above can you arrive at what's really required. If you ran at 48 volts and had 400 watts of panel total, I would = 400/48 = 8.33 amps, in which case 10 Gauge 30 amp rated wire may well suffice, subject to voltage drop and distance. NOTE yes everyone I realize the voltage once connected to the battery load will be less then a panels open circuit voltage but at higher voltage the current is even less and my use of 12 or 24 or 48 is intentional!!!

 

SINCE YOURE STUCK WITH 10 GAUGE WIRE HIGHER VOLTAGE UP TOP WILL IMPROVE YOUR OPERATION !!!!!! Im NOT saying its best or perfect ONLY it may "suffice" subject to distance and voltage drop and manufacturers recommendations.

 

John T

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+1 to what oldjohnt and Jack Mayer said. In the old days, when everyone just hooked up solar panels in a parallel array, thick wires (e.g.: lower gage number) were encouraged.

 

Since the advent of MPPT solar charge controllers most of us have some series component in our solar array and run at least 24volts. I know guys who run series-only and total maximum voltage of 140vdc! I think he's using speaker cord wire down to his controller... (just kidding!).

 

From the solar charge controller to the batteries it's a far different deal. Most of us site our charge controller as close to the battery bank as possible and use the largest cables possible because that circuit has to operate at the voltage of your battery bank (which, for many - if not most - of us will be 12vdc (nominal) but there's at least one guy on this forum who runs a battery bank (LiPo) at 48vdc).

 

So if changing wires is a PITA just design your solar array to conform to the size of wires you have.

 

WDR

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Thanks everyone. I appreciate your time and thought. So earlier this morning I got an email saying there is no 8 gauge only 10 gauge. Good grief. John, I did run all the calculations and sent them excel spreadsheets. I never got a response except this is what we sell and it will work. They were telling me that a 450 watt system with 17 voltage, 27 total amp with 3 panels, pwm controller AND 10 gauge wire would work. They do not even offer higher voltage panels as options and no m ppt controller as an option. I know I can make a system that works but they insist this design works which makes me doubt the whole company and product. I want at least 600 watts. I will need to go with higher voltage panels and mppt butt hate the idea of series because of shading problems. Dave

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The #10 wire would concern me. Yes it will work but there is loss and the output will be reduced some amount depending on the voltage and length. I also use lower voltages more inline with what a system will provide a discharged battery. If the distance from the controller to the battery is very long this can not be overcome with high voltage. Instead of prewired could they provide some conduit for the wire? Then you could easily install what you want.

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It is almost unheard of for any RV manufacturer to install adequate solar prep or factory solar systems. There are exceptions of course. My advice would be to purchase the rig you want without regard to any factory solar equipment. Then either install the system you want yourself or have it done by a reputable installer. After market installs are really not all that difficult and usually result in a much more satisfactory system.

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Yea Rif. Guess I thought I would be the guy to force them to reality. But this is making a rocky start to retirement. The dealership service guy is good. He said has had no luck pulling larger wire through existing conduit. I may just have him drop larger wire to planned controller location since he has done it before and then slowly plug away at the rest. I am hearing people say to cool my jets and I think I will just go ahead.

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There can be shading issues with series-connected solar arrays. But that only becomes an issue if there is shade on a panel. If there is little chance of shading - or if shading is only possible at very low angles of incidence (e.g.: late in the evening or very early in the morning) because of air conditioners or vents, then shading becomes pretty much a non-issue. We have gone to a series-parallel system and it seems to be working fine for us. And we do not use a crank-up TV antenna (we replaced that with the Jack).

 

The panels are mounted on the rooftop, after all, and t he only times we are parked in shade is when we're in an RV park with power.

 

I would not consider any panel array with less than 24vdc (nominal) to the solar charge controller. And I would not consider any installation without an MPPT solar charge controller.

 

If those three solar panels they say they'll put up on top of your RV's roof can be wired in series you'll have a 36vdc (nominal) system and #10 wire will almost certainly suffice (except, perhaps, on very cold mornings in full sunlight - you should do the numbers based on the panels specs).

 

Swapping out their PWM charge controller for an MPPT model should be a pretty easy job.

 

You might ask them what the cables are leading FROM the charge controller to the battery banks are.

 

How much extra is their installation over-and-above the base price of the RV?

 

Most of us run the cables down the refrigerator vent, anyway. I run mine into the fridge vent and then immediately into a closet with a Midnite Solar circuit breaker panel mounted against the outer wall and then straight down six feet and forward 2 feet to the controller. It would surprise me if you couldn't do this yourself for half their price and with much better components.

 

WDR

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What they are proposing for a solar system at 17 volts will not work well. Period. It WILL work...just not well.

 

As I always say - run the numbers based on your design parameters and see if their little #10 will work. Or design to it. Or pull new wire. I'm sorry to sound harsh, but you are dealing with idiots (in this area). You will get nowhere, typically.

 

On the topic of voltage and charge controllers, and MPPT. Each charge controller and the software algorithms they use has a "sweet spot" range for incoming voltage where they operate most efficiently. Many manufacturers publish that. Morningstar, for one, does. So does Outback. Most of the efficiency curves for a 12 volt nominal system (battery bank at 12 volts) operate most efficiently in the 30-40 volt (incoming) area. It drops off before and after that. Not a LOT, but some.

 

PS. Sorry I have not been responding fast to this thread. The Solar Rally is in full swing, and we are busy actually doing systems....so I'm not monitoring the forums as much.

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Not a problem Jack.I wish I could be there I have a couple more months to work. I have been looking at the Solar approx 30 volt 280 watts. I would then get Morningstar m ppt. Thanks for your thoughts also WDR. They run 10 from controller to battery but l new I would never use that since I am relocating battery.

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What they are proposing for a solar system at 17 volts will not work well. Period. It WILL work...just not well.

 

As I always say - run the numbers based on your design parameters and see if their little #10 will work. Or design to it. Or pull new wire. I'm sorry to sound harsh, but you are dealing with idiots (in this area). You will get nowhere, typically.

 

Jack's observation is spot-on. Most RV manufacturer's ideas about solar are marketing-based and depend on ideas that were in vogue 5 years ago (or more) when they could sell an RV with "solar included" that had one 100-watt panel and a PWM charge controller. After all, practically no buyers know different. Heck, one of my clients - a registered Professional Engineer (civil) and Surveyor - has a TT with that installation and proudly showed it to me (knowing that I am an active advocate of solar power). It probably does keep his battery bank up when it's sitting next to his house with no power, though.

 

The ideas on this forum (and a few others) are far, far ahead of that curve and the manufacturers really have no way of dealing with that. Or interest, for that matter.

 

When motor homes selling for $750,000 proudly show photos of four 12-vold solar panels on their rooftops you know there is a disconnect somewhere.

 

WDR

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The ideas on this forum (and a few others) are far, far ahead of that curve and the manufacturers really have no way of dealing with that. Or interest, for that matter.

 

When motor homes selling for $750,000 proudly show photos of four 12-vold solar panels on their rooftops you know there is a disconnect somewhere.

 

WDR

Not totally true. New Horizons puts on well designed contemporary systems. Properly wired, with state of the art components. I do the design for their systems and have spent time training their factory people - where required. They have a very good electrical crew who WANT to do it right. IMO they are "best in class" in the RV world in all things electrical. Including the big busses.

 

I'll use my system as an example. 4x305 panels at 36 volts. In parallel through a combiner to a MidNite Classic 150. Properly wired. (Really, overwired). Proper disconnects. Proper lugs crimped correctly. Proper heat shrink. Magnum Hybrid 3012 inverter. Trimetric battery monitor (my choice - the normal would be a BMK). Progressive Industries hardwired EMS. 4xL16 Fullriver AGM battery bank for 1200 Ah. (Next year we will start doing LFP).

 

So, it CAN be done "right". It just is rarely the case.

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That is good to hear.Seems like the clock is running on other manufacturers since Solar is here to stay. When someone buys a trailer and turns on a faucet onnly to get a trickle they know the plumbing does not work and be in the dealers face.. But solar is indirect usage with battery and AC backup. Folks who camp a couple weeks a year would have no clue if it was not functioning properly. I still maintain most dealers wrongly claim they are selling something solar ready. At a minimum they need an asterisk stating the specs and the size of a system that can be supported.

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Dave, lots of issues and info floating around here, I'm trying to keep up lol

 

1) "They were telling me that a 450 watt system with 17 voltage, 27 total amp with 3 panels, pwm controller AND 10 gauge wire would work."

 

Okay, when you hear me speak of the 125% rule, that concerns max continuous sustained current. NOT ALL loads are considered by the NEC as max continuous, you have to look up the definitions. HOWEVER THAT BEING SAID even if the NEC didn't consider the 27 amps as max continuous sustained I STILL WOULD NEVER USE 10 GAUGE WIRE FOR MORE THEN 80% X 30 OR 24 AMPS. In other words if there is 27 amps as they say, I (a retired Electrical Engineer) WOULDNT USE LESS THEN 8 GAUGE WIRE REGARDLESS.

 

ALSO that's is NOT even computing VOLTAGE DROP which can make things worse which is yet another reason to up the wire size to 8 Gauge or larger SUBJECT TO WATTS AND VOLTS AND DISTANCES!!!!!!!

 

 

2) "They do not even offer higher voltage panels as options and no m ppt controller as an option".

 

You can still get to the higher voltage option if you series connect the panels as opposed to parallel ASSUMING YOU HAVE MORE THEN ONE PANEL!!!! You mention 600 watts which could be six 100 watt panels or perhaps four 150 watt panels or three 200 watt etc. So to the extent possible Id use series and where necessary series/parallel configurations so your system is at least 24 and up to say 48 volts. And as you well know, higher voltage = less current down to the controller which means smaller wire can suffice.

 

3) "I know I can make a system that works but they insist this design works which makes me doubt the whole company and product. I want at least 600 watts. I will need to go with higher voltage panels and mppt butt hate the idea of series because of shading problems"

 

I would NOT use PWM but an MPPT Controller,,,,,,,,,,Run at higher voltage,,,,,,,,,,Use series connections where possible so voltage is increased,,,,,,,,,,,,,,

 

Once more, to calculate the wire size from panels down to controller you need the total watts,,,,,,,,operating voltage,,,,,,,,,,,,,,distance to controller and NOT what they say will "work" even if it will work yet under perform...

 

No more sense in guessing and speculating until your design is complete. Then with the total watts and operating voltage and distances I can compute voltage drop and recommend wire size, be it 10 or 8 or 6 gauge or whatever.

 

I will try to keep up and offer advise but we have slow internet here at Yeehaw Junction Florida Bluegrass Festival for which I apologize

 

John T Retired Electrical Engineer

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Regardless of the outcome from this discussion, I'd RUN from this manufacturer, and post the name here, for their attitude toward the customer. If you want a purple 17ga run, and are willing to pay any real extra cost, they SHOULD be jumping with joy to do it. That's why I didn't buy a new Lazy Daze, I wanted a component left out, I was still willing to pay for it, but their response was I could remove it after I bought it.

 

Sorry for the hijack, but consider how they will treat you a few months down the road?

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