Chinook RV

Couple of notes.

Maybe they have changed the Compact panels. This is the label they were showing for them. This is the label that would normally be on the back side of the panel:
On the fusing, just keep in mind a couple of things. One is that a fuse is to protect the wire. So you can't always just up the size. I think the stock solar wire is 12AWG. If it's rated at 90ºC then you could fuse it to 40 amps, so not saying you are not safe there. Just something to keep in mind when changing fuse sizes. Also, for solar, go as large as you can to save on the voltage drop of smaller fuses. Voltage drop is the enemy.

Just for example, let's say one were to put two 100 watt panels on the original Chinook wire. Let's say you added ten feet of wire to get to the new second panel. That would be around 32' of 12 AWG, one way. Now let's say you run them in series and have 5 amps at 16 volts trundling along. The voltage drop would be 4.4% (not counting any additional wire such as battery jumpers). That would make your 16 volts into about 15.3 volts. But we also have a solar controller in there. So let's say you set your solar controller to absorb at 14.4 volts (that's a common spec for a lead acid battery in absorb). Now you have around 15' to the controller, so that voltage drop is a bummer, but doesn't actually affect your battery charging specs. It only causes you to lose some power that will never get to the controller.

But now the controller puts out 14.4 volts (if it's 77ºF) and that goes 17' to the batteries on the Chinook stock wire. That's about 2.3% voltage drop on that leg (controller to batteries). That means the 14.4 volts your batteries want (and that you set into the controller) will actually be 14.06 volts (about). That's a big difference for batteries.

None of this may matter to you. Many people just plan on replacing batteries every year or two (obviously buy relatively cheap ones) and that is a fine plan if it suits your attitude and the availability of batteries to you. Just something to be aware of.

Admittedly, I'm on the opposite end of the spectrum. I rely on my batteries for boondocking all the time, and I hate re-buying things. So I have my system set up for minimum voltage drop, have a temperature compensated controller, etc. But that's not the only way. The only time it kind of bums me out is if someone thinks they are doing "Way A," but without realizing it are actually doing "Way B." That can lead to frustration.

On the series pairs: I too always read the wisdom of not doing series if there might be any shading. However it was attractive to me for a couple of reasons: You can have longer and thinner wires (less voltage drop at higher voltage), fewer wires, and (theoretically at least), the panels will "wake up" sooner and "go to bed" later. The first advantage is huge for ground panels, as you can have a longer thinner tether for the same result. But also it's fairly easy to put them in the sun so not much to lose by going series and everything to gain.

But what about roof panels? Well, I took a pair of matching panels (135 watts each, 17.6 volts vmp) and set them out on a summer day at around noon. So good, predictable sun. I set them flat on the ground, like an RV roof would be. I hooked them up to my battery monitor and the display on my MPPT controller so I could get good info. I started up some big loads so the controller would have reason to give me everything the panels could. Then I started in with the shade. Various things I tried were thin branches about 15' away, falling in a line or two over the panels, large deciduous trees a few hundred feet away shading either small amounts of one panel or up to a third or half of one panel (more blob like shape), and then finally l placed a piece of cardboard over one or more cells on one panel.

Interestingly, the branches and the big far away trees only knocked out either part or all of the shaded panel. I was still always getting at least half of the amps coming in (i.e. the non-shaded panel's worth), and sometimes more. The only time it knocked out "more" than the one panel was with cells completely shaded (the cardboard right on top of the cells for 100% blockage). Some amps still came in, but only about half of one panel. I don't have much that could do that on my roof (the tree and branch scenario is more likely), so I will probably start with series pairs. But if one had something big and blocky (or like on a boat where there are SO MANY things to block cells) then ....?

Always good insight Blue and so very much appreciated!

I went searching even deeper on these panels. In this case, I sure hope you are wrong . This spec sheet corroborates what Renogy said on the phone at having optimum voltage of 17.9V: https://www.renogy.com/template/files/S ... 20spec.pdf
Now, to be cautiously optimistic, the panels will be here on Monday so I guess we'll use the sticker as our final judge. Just saying, I hope I win this one!

I did order all 10AWG wires to hopefully reduce any drops as per your suggestion to connect all the panels together and from the panels to the controller, even though the output cables on the panels are 12AWG. I went with a 20 amp inline fuse between the panels and the charger. Does that work with your calculations and is it okay? They are a simple click in affair so I can change one pretty easily, let me know your thoughts. I figured unless I get my Volkswagen to 80 mph like Clay did, I should be fine! The short circuit voltage for a 50W panel is 3.10A x 2 and a 100W panel is 6.24A for a total of 12.44 amps. If I got a spike, then 20amps should be okay wouldn’t it? Or is even going down to a 15A a better choice?

So my setup will be like this (See drawing). Furthest panel connected to the middle panel with 12AWG connector, hopefully close enough that no additional cabling is required except the stock wires on the panel which are 2 feet each. Then a 5 foot cable from the middle panel to the main 100W panel up front which will be 10AWG plugged into 12AWG panel wires. Five foot wires of 10AWG plus 2 feet of 12AWG panel wire equal a 7 foot length. Then, 10AWG wires from all the panels down to the existing charge controller location. From the charge controller down to the batteries is the stock wire at whatever gauge that is. So, if I am already maxed out on the panel wires in every way down to the charge controller, what improvements would you recommend from here? I am using the Sunforce controller so that stays.

Now, here’s the curve ball. The clown who did some electrical wiring before I got this Chinook, did not re-install the driver’s side fiberglass seat belt/post panel correctly. The panel edge is in front of the side wall panel and he didn’t tuck it in behind it so it is clearly not on correctly because he couldn’t get it to go. I might still have to remove the front driver’s seat again so will have the opportunity to really get it put in properly which will also allow me access to the wires inside should I choose to do this job vs. just leaving it alone. I believe this is where the wiring from the controller to the batteries is hidden so I might be able to change out the wires.

What gauge wire do you recommend if I were to take on this monstrous challenge?

HoosierB wrote: March 5th, 2019, 3:09 pm Thanks for the measurements and the illo of your roof layout. Very helpful.
What type of panel mounts are you thinking of using? Blue has great research on the topic and I believe even had some brackets custom made. After seeing several vids on the benefits of using VHB tape, I'm convinced that's the way I'll go when attaching the mounts to the roof.

Maybe time to start a new thread on your "Solar Upgrade"?

Hoosier...+1 on the VHB tape to mount, it sure looks like the correct way to go. Super strong, no holes, thanks for the tip!

After a few hours of calculations, my headache has returned!

I don’t really want to go through all the extra hassle of wiring and stuff but I think I have to, or SHOULD for safety reasons as well as performance regardless of where the charge controller is located.

The maximum amps for our original 50W panel is about 2 or 3, the current wire gauge installed in my rig is 12AWG and the distance is about 25-30 feet round trip which according to the chart, is within specs. (See below)

My new 50 watt panels run between 2.9 and 3.1 amps each. The 100 watt runs between 5.72 and 6.24.
All panels together have a total potential amp production of between 11.52 and 12.44 amps plus or minus. If I leave the charge controller in its original location, I really need to use 8AWG for protection up to 15 amps. This will also allow some performance enhancement to help with the dreaded voltage drop.

Whatever the situation, 12AWG is not enough in my mind at any distance given the power output of these panels. Am I wrong or am I doing the math correctly here?

There are two things that you are looking at here. One is efficiency, and the other one is safety. The table is to deal with the 3% drop in voltage for a 12 V system, for efficiency. For a 12 AWG system, you can use it up to 9.3 A for safety. Obviously, these numbers are rule of thumb, it also depends on the various other parameters like the temperature , etc., and Blue has mentioned it in other places.

Anyway, if you do drive your 12 AWG wire at 9.3A, the voltage drop will be more than 3% at 30 ft. The resistance is 1.59 milliohm per feet, and you can calculate the voltage drop from V=I*R=0.44 volt = 3.7%. It is "safe" to use the existing wiring for up to ~9A, but the tax on the voltage will make it not as efficient due to the length. If you do end up with 12.5A, then you should get at least a 10 AWG, but that is pushing the envelop of safety. 8 AWG is much better because it has reasonable voltage drop. If I have to go thru the hassle of rewiring it, I would go with possible future upgrade to 30A, and use the 4 AWG wiring, which has 1/6 of the voltage drop compare to the 12 AWG, or only 0.6% for ~10A. Even if you do end up with 30A, the voltage drop should be only about 1.8%.

HOLY GAWD!!
Hoosier; I LOVE that graphic, it represents exactly how I feel!

Chin; I don't know what you do for a living but that's an awful lot of SMART going on right there!

So, if I kind of understand your brilliant calculations (and they are brilliant) , 8AWG would be enough and would perform well? From what I can gather, 4AWG is too thick to attach to the controller and is probably more upgrade than I would ever do. SO, and I don't want to risk another Hoosier style head explosion here...

Can I just use 8AWG and get good performance with a 30 foot round trip and should I upgrade it for safety and voltage drop reasons?

chin_k is spot on as usual.

I'm going to add something. While normally you size for voltage drop in terms of less than 10% for non-critical loads, and 3% for critical loads, I go for 1% (or as close as I can get it) for solar. Why? Because tenths of an amp are important when charging batteries. Those get lost to voltage drop.

Couple of caveats though: If you are going with an inexpensive controller that does not have temperature compensation, then to my mind it doesn't really matter. That's because the voltages that are specced for what the batteries want are for 77ºF. If your battery bank is always at that temperature, then great. But they realistically won't be. As the batteries get colder, the voltage the batteries want to see gets higher. As they get warmer it gets lower. So 14.4 volts that they want at 77º could be 15 volts when they are cold, or 13.x when they are hot. Temperature compensation in the controller adjusts for this.

But what I'm getting at is that if you are getting a controller that doesn't have temp comp, then trying to get super precise with your voltage drop is less important, IMO (I haven't been completely following what you are buying because it goes very quickly and I can't totally keep up).

If you want to understand more about lead acid batteries and the charging thereof, Lifeline's Battery Manual is a great (and free) document (they make AGM batteries, but most lead acid batteries generally work on the same principles).

Likewise a really good controller may have a voltage sense wire. This allows it to "ignore" any voltage drop and send the precise voltage to the batteries (you would still lose power through voltage drop, but the right voltage would get to the batteries. But not all controllers have that. I'd say temp comp is more important, because you can size wires to avoid much voltage drop.

Back to using the Chinook wires: I didn't want to come across too "mean," but my opinion is that using the Chinook wires and controller placement for anything much more than they put up there to begin with is kind of throwing good money after bad. Why not just do it more right to begin with? Put the controller near the batteries, and put in good wiring, sized for your largest panelage. With the cabinets and TV area, there are plenty of places to tuck in wires. Solar is a fairly "weak" charging source, and our roof real estate is limited, so why not make the most of it vs. giving anything away with the wiring and controller placement (maybe put a thermometer there or something if you don't want to patch the hole?)

Speaking of which, I have removed my "pillars" and did not ever take the driver's seat out. So I think it can go back in correctly without removing that. What made the driver's side one a bear was a coax cable that ran behind that "flap" and tried to hold it out making it hard to get it tucked or untucked behind the wall. I moved it. Maybe you have that too.

PS: Some controllers don't allow for reasonably sized wires - a pet peeve of mine. If that's the case you may have to go to power posts right by the controller and then have little pigtails to the controller. Sometimes you can make the positive one a switch and at least gain something. There are certain features I give bonus points for in the various controller brands and models and being able to put adequate wire into them without a lot of faddle is one of those things.

Yes, you will have less than 3% drop with 8 AWG with 30 ft at 15A, per the table.

here is my comment:
1, you maybe able to shorten the path a little if you locate the controller in the right place. I have not think much about it yet, but I think some others had it worked out already.

2, if you do think you will upgrade to 30A, I would suggest you reconsider the 4 AWG. If the controller has issue accepting the thickness, but can handle 30A, then it is possible to add crimp or other adapter (e.g., lugs) to the wiring just before it enter to the controller. Considering the hassle of redo the wiring, maybe getting a new controller is easier for you when you are ready for 30A.

3, another reason for a larger gauge wire is that you will have better efficiency. I don't know how tight is your solar budget, but for some people, that extra 1% or so voltage drop can make a difference. If you don't get to go to 30A, you still can benefit from this right away.

This is a decision of time, cost, and utility. You are the one who pay the cost, and reap the benefit, so you got to decide how you compromise.