Running heavier wire for solar panels

[kmacafee]

I have searched high and low in advance to see if anyone has run heavier gauge wire from the roof to the battery box. Currently, the camper has 12 ga installed and I am thinking of going to 10, maybe 8 ga. So far I have not found any references.

I know where the box is in the ceiling and I know the wires run behind the front lift panels and down to the battery box over the water tank. Its the section between the ceiling box and the front panels that I am unsure about -- is it run thru conduit (unlikely) or just bundled and zip tied to roof supports? I am hoping I can get some info from Brenda at FWC but was hoping someone here might have attempted it.

Currently, the camper has 12 ga installed and I am thinking of going to 10, maybe 8 ga.

Thanks in advance for any help.

Cheers

 

[pods8]

How many amps are you trying to carry? Even with a pair of 100watt panels you'd have ~11amps max in the wire and it'd be starting around 17-18volts, you'll have about 5% voltage lost. That's still plenty of voltage going into a PWM controller which is just chopping it down and wasting off the extra voltage. If you have an MPPT controller you're only casing a couple % of efficiency. Hardly seems worth trying to swap the wire out in the roof after the fact, 12ga isn't too bad up there.

 

[JaSAn]

Can't help with the routing, cuz my Grandby is OLD. But I ran AWG 4 gauge wire from solar to batteries based on length and amperage:
http://circuitwizard.bluesea.com/#

The explanation of my solar setup is in post #3:
http://www.wanderthewest.com/forum/topic/9972-renovating-sk%C3%B6ldpaddan-%E2%80%93-1977-grandby-interior-build/

 

[pods8]

But I ran AWG 4 gauge wire from solar to batteries based on length and amperage:

You have a PWM controller, it chops down the excess voltage that gets to it, really anything over 12ga wasn't needed. That said running 8 or 10ga on a new installation sure doesn't hurt for the little extra cost. 4ga seems to have crossed into extra money and having to deal with stiff/bulky wiring for no real need. Not trying to attack, just confused.

 

[kmacafee]

In talking with many people who are very knowledgeable about solar, they are unanimous in their opinion that 10 ga wire is the minimum that should be used for almost any 12 volt solar setup and 8 is preferable. Even for 100-200 watt panels, the voltage drop can be significant.

I was checking to see how easy it would be to run new wire. Brenda at FWC says that the wire from the ceiling box to the front of the camper runs thru a channel but I have not heard how it runs back under the bed to the battery box. I may just live with 12 ga which I agree, is not the end of the world. And if/when I do wire, I will use welding cable which, even in 6 and 8 ga forms is quite flexible.

 

[JaSAn]

pods8: Being a Mechanical Engineer, I just went with what the 'sparkies' told me

The 'experts' I followed: HandyBob, MaineSail, Jack Meyer, insisted that one of the biggest mistakes made in solar installations was undersizing the wire from panels to battery. (Going from memory) for panels in parallel, HandyBob recommends AWG 6 minimum, Jack Meyer recommends no smaller than AWG 8.

I ran my refrigerator all last summer. Every time I looked, I was at 100% by noon; usually earlier. I think my system works well.

I did oversize the wire for the possiblity of adding more panels if needed.

kmacafee: I'd hook them up and see if they will keep the batteries charged. Worst case is you will have to rewire.

The 4 gauge welding wire I used was like a wet noodle, very flexible.

Another possiblity is running another set of 12 gauge wires in parallel and combining them at the controller.

 

[Fallbrook]

12 gauge is all you need!

 

[Advmoto18]

I am by no means an electrical or solar SME!

But, having worked with such SMEs in remote locations, they had different length and gauge wire bundles to select from based on...
Solar panel array output voltage.
Total amps the solar panel array produced
Length of run from panels to controller anf to batteries

While using a heavier gauge wire then needed will not have adverse effects, you will be toteing around a lot more weight in copper wire, perhaps reducing your loadout of other needed supplies.

 

[ntsqd]

The thing to consider is NOT the ampacity of the wire. If you do you will end up with too small of a wire gauge. If you use the vastly common National Electrical Code based ampacity charts you will for sure be undersized as due to the cooling effect from the reversing polarity AC power is much different than DC power with regard to wire size.

The thing to consider is voltage drop, ideally you don't want any!

Search generically and specifically for the "Handy Bob" blog both here and on the greater net. Jasan gave some other, supporting author's names as well. There isn't universal agreement, but there is a trend that is pretty obvious.

In that searching I hope that you find the argument against paralleled smaller gauge wire. I wish that I could recall the details, but there was stated a good reason not to do this. The counter argument is/was that the stated reason isn't universal in application, so some can probably do it and have it be OK, while others can not.

 

[jha6av8r]

I'm a mechanical engineer and by no means an expert in electrical set up, but DC voltage drop calculations for wire lengths of 20' or shorter are less than 0.5% for 12 gauge wire and less than 0.1% for 8 gauge are larger. Seems like a lot of work to rewire for minimal return.

For me it's like spending more for an MPPT over a PWM controller for small systems. The bang for the buck just doesn't seem justified. Handy Bob puts out a lot of good information which would be beneficial for building a system from scratch. However if 12 gauge wire is already in place, I fail to see how a properly sized solar pane/array (150 to 200 W), PWM controller, and a pair of deep cycle batteries will not meet the electrical needs most of us have.

I would install using existing wiring and see how it performs first. Rewiring would only be done as a last resort. Anyway, just my two cents.

 

[pods8]

Run some numbers and think about things, not just "follow" advice. When you say panels to batteries you're ignoring there is a controller in the middle. What kind of controller do you have? IF MPPT then you would see the benefit of the slight bit of lower voltage drop, if PWM you will not reap any benefit. If you're not familiar a PWM controller chops down the voltage, it does not convert it.

Take a typical 100watt solar panel. Watts = Volts x AMPs. A typical panel makes 100watts at something like 17V and 5.8amps. With a PWM controller your batteries will NEVER EVER see close to 100watts because it does not covert the voltage it chops. If you're in bulk charge and its say 14.4V and you have 100% efficiency on amps then that means 14.4V at 5.8amps goes to your batteries 83watts (keep in mind there are other efficiency issues being ignored here). Off hand I'm not sure how much extra voltage is needed into the PWM controller before the chopping but even with a 10% voltage loss in the line you're looking at 15.3V and I'd bet it would still work just fine.

That said in a new installation sure it doesn't hurt to oversize the wire within reason, I know I plan to. However I certainly would not go digging into a finished camper to remove 12ga wire. Even keeping to a 5% voltage loss that gauge wire could service 200watts for ~25' of wire.

Now lets say you have MPPT and 200watts going 25'. The 12ga is 5.3% lost, 10ga is 3.4%, 8 is 2.1%, etc. So in a perfect efficiency world the BEST case is 8ga gets you an extra 6.4watts over 12ga. Things are not perfect and in reality you may see a couple tenths of an amp extra into your batteries with 8ga, 200watts, and a MPPT controller. If you don't have MPPT you are completely wasting your time/money to change it.


One area I do agree that minimizing voltage drop to as little as practical would be between the EDIT (for brain fart) BATTERIES panels and controller. If the controller is wisely mounted within a few feet of the batteries then you still don't even need much in terms of wire gauge but it certainly does not hurt to upsize (again I plan to, within reason).

 

[DrJ]

There have been some great posts on here. Thanks.
I am a big fan of solar. I have it on my camper and my travel trailer. I have portable panels when that's not enough. I've even had an iphone case/charger that was solar - nearly worthless by the way.

I currently have 340 watts - 1.5 times - what you are thinking about using, on my hawk with the stock 12 gauge wiring.
I have a MPPT controller and frequently see amps around 10-15 charging my battery (verified by my trimetric). I also have monitor at the controller that tells me the voltage and amps from the panel. So I know what is coming in and what is going to the batteries.

There is very little voltage drop going to the batteries at 200 watts - even in perfect sunlight. I would not even consider the hassle of removing their wiring to go to 8 AWG. If I didn't have wiring already and was sizing it or having it custom made that is a different story.

Handy Bob and Jack are sizing big motorhomes with huge battery banks and solar often above 500 watts. The wiring size in that system is critical. In a FWC with 200 watts and probably not much more than 200 amps hour battery, it's not that big of a deal.

Here's my recommendation - if voltage drop is a big deal to you, buy a larger panel that has a higher maximum voltage. The higher voltage means less voltage drop at your controller. It will require a MPPT controller but it definelty works better.

I orginially installed a 100 watt panel and then went with 2 more 120 watt panels. They had higher maximum voltage and were more efficient for my system.

I would go even higher if I had to do it again.

Compare these two units:
http://www.ebay.com/itm/Semi-Flexible-100-Watt-Solar-Panel-12V-High-Efficiency-Sunpower-Marine-Rated-/131424858972?pt=LH_DefaultDomain_0&hash=item1e9988335c

http://www.ebay.com/itm/Semi-Flexible-135-Watt-Solar-Panel-High-Efficiency-Sunpower-Marine-Rated-/141262084821?pt=LH_DefaultDomain_0&hash=item20e3e05ad5

For only $40 more you would get 35 more watts of power and the voltage would be 24.9 vs 17.8.
More power and more efficiency.
Same wiring.

 

[billharr]

Dr J at 340 watts you are at the top end of what most have on pop up campers. Most are at 100 or 200 watts. I have a 100w on top and a 120w solar in a bag that I had first. I like the new flex panels for weight. The $40 price difference you show between the two also requires a MPPT controller. I have a 30 amp PWM no question it is not as good as a MPPT but for the difference in price to go to a MPPT controller I could buy another 100w panel. I am with Solar Bob's opinion, if you are not over 300watts no need for a MPPT.

 

[pods8]

I am with Solar Bob's opinion, if you are not over 300watts no need for a MPPT.

and in turn no need to freak about voltage drops (within reason) prior to the PWM controller either.

 

[kmacafee]

Thanks to everyone for their input. I should have mentioned that I have read almost all the material referenced in the various posts as well as most of the info here on WTW. I have also spoken with a number of electrical engineers and other folks in the solar industry. There are many, many different opinions on everything related to solar so it can be a challenge sifting thru all the "talk".

I have done quite a bit of 12 volt wiring in both the marine and automotive worlds and while solar presents a few unique challenges, the size of the pipe the current runs thru isnt one of them. Since I am keeping my solar panel small (under 200 watts) and due to the complexity of replacing the existing wiring, I may have to live with whats there for now. I really just wanted to check and see if someone had done it already.

Not to stir the pot but I will share some info I have on the flexible panels that so many of you are using. I, too was sold on them for their light weight and low profile. But in talking with some friends with boats who have used them for years, have decided to go with a rigid panel based on their experiences, for several reasons;
1) heat -- even in marine environments, panels apparently need airflow underneath them to maximize efficiency. I know this has been discussed on WTW but the only info I saw that stated otherwise came from Renogy, the manufacturer.
2) cell cupping -- apparently, no matter how well you glue down the edges, the panels and their cells start to cup over time, reducing panel efficiency. In several instances, the cupping got so bad the panels had to be replaced, not a fun process given the adhesives that are typically used.
3) Durability -- the surface is much more prone to scratching and scuffing than a rigid panel. Granted, ours are on the roof but low branches could easily run across the surface.

Ill just need to hit the gym harder to work on my overhead presses.

Cheers

 

[pods8]

I have done quite a bit of 12 volt wiring in both the marine and automotive worlds and while solar presents a few unique challenges, the size of the pipe the current runs thru isnt one of them. Since I am keeping my solar panel small (under 200 watts) and due to the complexity of replacing the existing wiring, I may have to live with whats there for now. I really just wanted to check and see if someone had done it already.

I'm still unclear why you think you would even gain anything by changing it?

 

[ntsqd]

When I ran the numbers for our current 100W panel the 10ga. wire it came with was marginal re: voltage drop for the total length of the run. Do not forget the length of the ground wire when figuring this length. I recall being surprised at how long the circuit was after measuring it. My guess of the length was far off.

I ordered two 100W panels not knowing if one was going to be enough. It has been. Had it not, and being forced into 10 ga. because of the panel wiring, I'd have gone to series wiring of the panels and an MPPT controller. At 200W parallel the voltage drop with 10 ga. was more than I was willing to accept.

I get that a PWM is like a child playing with the light switch, but I don't see how less line loss is not a good thing. That isn't to say that 4/0 is necessary for a 200W system, but that 6 ga. or 8ga. is worth looking at for such a system.

Would I rewire a system with pre-existing 12ga.? Very likely, after cursing whomever made that poor decision. That isn't to say that's for everyone, but it is what I would do and thus my advice.

One of the things that I gained from Handy Bob was a distrust of RV oriented solar "experts." I've seen exactly that situation in the past in several different & totally unrelated fields. Folks who don't truly know, but have been thrust into a guru position and have come to believe their own press. Their chafe is easy to sort because I never acquire it.

 

[kmacafee]

I'm still unclear why you think you would even gain anything by changing it?

The ability to expand the system down the road, a higher level of efficiency and peace of mind. I've seen winch installs that have used 8-10 ga wire -- the manufacturer says its fine but IMHO, they are trying to save a few bucks providing a less than optimal solution. FWC should be using at least 8 ga in running these solar systems and ideally 6 but my guess is their decision is based on economics. They are a for profit business so I get it but at least provide a way for the owner to upgrade on their own or provide it as an option.

 

[pods8]

When I ran the numbers for our current 100W panel the 10ga. wire it came with was marginal re: voltage drop for the total length of the run. Do not forget the length of the ground wire when figuring this length. I recall being surprised at how long the circuit was after measuring it. My guess of the length was far off.

Often the calculators ask for one way distance, 100watt from the panel for 25’ in 10ga is about 1.7%, I have no idea why you would call that marginal.

When I ran the numbers for our current 100W panel the 10ga. wire it came with was marginal re: voltage drop for the total length of the run. Do not forget the length of the ground wire when figuring this length. I recall being surprised at how long the circuit was after measuring it. My guess of the length was far off.

This makes no sense, you are saying you'd be forced to abandon the PWM controller to go MPPT because there was too much drop, right? 25' of 10ga for 11.6amps is 3.4%. So your starting ~17V is 16.4V at the controller and then chopped to charging voltage. You actually had quite a bit of margin left.

I get that a PWM is like a child playing with the light switch, but I don't see how less line loss is not a good thing. That isn't to say that 4/0 is necessary for a 200W system, but that 6 ga. or 8ga. is worth looking at for such a system.

Would I rewire a system with pre-existing 12ga.? Very likely, after cursing whomever made that poor decision. That isn't to say that's for everyone, but it is what I would do and thus my advice.

Its a "it doesn't matter in the end" thing as long as you're delivering something like 15V to the controller in the end. Not saying I'm going to pick a wire gauge with 10% loss or anything but wire cost, connections, and tools for the connections, wire flexibility, etc. ALL factor in picking a wire to snake through a popup camper. 12ga is PLENTY. I have no idea how one would credibly say whomever make that decision make a poor one.

One of the things that I gained from Handy Bob was a distrust of RV oriented solar "experts." I've seen exactly that situation in the past in several different & totally unrelated fields. Folks who don't truly know, but have been thrust into a guru position and have come to believe their own press. Their chafe is easy to sort because I never acquire it.

I totally agree on that. A friend came back from one of the overland expos talking about some guy selling folding solar panel kits. He was advertising his 100watt system would deliver 8.33amps to the batteries (ie 100watt/12V) which is the biggest snake oil salesman pile of horse crap I've ever heard. Liar or idiot?

The ability to expand the system down the road, a higher level of efficiency and peace of mind. I've seen winch installs that have used 8-10 ga wire -- the manufacturer says its fine but IMHO, they are trying to save a few bucks providing a less than optimal solution. FWC should be using at least 8 ga in running these solar systems and ideally 6 but my guess is their decision is based on economics. They are a for profit business so I get it but at least provide a way for the owner to upgrade on their own or provide it as an option.

Winches pull 100s of amps yes larger guage is VERY warranted there. On a FWC its completely unwarranted in my mind to say 12ga is subpar for their typical customer who would normally run a 80-150watt panel, even with 200watts up there 12ga is PLENTY. I laid the numbers out above for 25' of wire (plenty) and 200watts, you gain nothing with a PWM controller and with a MPPT controller you at MAX save ~6watts in going 8ga. In no way is that a copout on the part of the manufacturer to run 12ga wire which can handle 200watts at ~5% loss. Their customer base isn't going to typically run 200+ watts of solar on the roof and if someone knows they are going to then ask about UPGRADING when ordering. I see ZERO credible basis on why one would say FWC should run 6ga solar wiring. Have you ran some numbers rather than taking ques from larger system designers?

 

[kmacafee]

Often the calculators ask for one way distance, 100watt from the panel for 25’ in 10ga is about 1.7%, I have no idea why you would call that marginal.



This makes no sense, you are saying you'd be forced to abandon the PWM controller to go MPPT because there was too much drop, right? 25' of 10ga for 11.6amps is 3.4%. So your starting ~17V is 16.4V at the controller and then chopped to charging voltage. You actually had quite a bit of margin left.


Its a "it doesn't matter in the end" thing as long as you're delivering something like 15V to the controller in the end. Not saying I'm going to pick a wire gauge with 10% loss or anything but wire cost, connections, and tools for the connections, wire flexibility, etc. ALL factor in picking a wire to snake through a popup camper. 12ga is PLENTY. I have no idea how one would credibly say whomever make that decision make a poor one.

I totally agree on that. A friend came back from one of the overland expos talking about some guy selling folding solar panel kits. He was advertising his 100watt system would deliver 8.33amps to the batteries (ie 100watt/12V) which is the biggest snake oil salesman pile of horse crap I've ever heard. Liar or idiot?


Winches pull 100s of amps yes larger guage is VERY warranted there. On a FWC its completely unwarranted in my mind to say 12ga is subpar for their typical customer who would normally run a 80-150watt panel, even with 200watts up there 12ga is PLENTY. I laid the numbers out above for 25' of wire (plenty) and 200watts, you gain nothing with a PWM controller and with a MPPT controller you at MAX save ~6watts in going 8ga. In no way is that a copout on the part of the manufacturer to run 12ga wire which can handle 200watts at ~5% loss. Their customer base isn't going to typically run 200+ watts of solar on the roof and if someone knows they are going to then ask about UPGRADING when ordering. I see ZERO credible basis on why one would say FWC should run 6ga solar wiring. Have you ran some numbers rather than taking ques from larger system designers?

So, while this has been an interesting discussion about FWC's business practices, wire size and voltage drop, it is irrelevant to my original inquiry -- has anyone upgraded the solar wiring in their camper? And after sifting thru all the various opinions here, my conclusion is that it has not been done on newer campers. Thanks again to everyone for their input.