Hi, Cham. I'll try to distill HandyBob's info down for you (after 4 hrs and about 50 edits), having read his entire blog a dozen times at least, and after building my system using his blog as my bible.
I'm assuming you're using traditional "wet" batteries. The charging voltages are different for AGM/sealed batteries, which aren't worth the money IMO, unless you're forced to use them because of battery positioning issues. They have less capacity per pound, and charge at a slower rate due to the lower voltage requirements needed for a battery with no venting capability. People say "they don't gas", but that's only because you're forced to charge them more slowly at a lower voltage
to keep them from gassing. The chemistry doesn't change just because they're sealed, and as Scotty says, "I canna change the laws of physics." Try to charge them at the same faster-charging voltage recommended by wet battery manufacturers, and they
will gas, in fact they will gas themselves out of existence when they blow their safety valves. And since they're sealed you can never check the specific gravity of the acid with a hydrometer, which is the only way to be 100% sure of your state of charge. And since they charge more slowly, you're accomplishing less in the limited time you have each day to solar-charge. So they cost an arm and a leg for lower performance, which makes no sense unless, again, you're forced to mount them sideways or something. In my opinion it's very easy for AGMs to be LESS safe, because you're told by the salesman that they're "zero maintenance", so you install them in a hidden, unvented compartment, and never look at them unless there's a visible problem, and by then it's too late. And contrary to popular belief, you don't need to add water that often to regular batteries, nor do you create a Hindenberg in your battery box, both the need for maintenance and the "danger" is exaggerated in a well-set-up system. Everything below is based on wet batteries, but the only difference is in the charging voltages used, and the fact that you can't do any maintenance on sealed batteries.
1. Yes, you do need a solar charge controller, or there will be nothing to decrease the (probable) 18 volts coming from the panel (too much!), or turn off the charging current when the battery is charged, and it will overcharge. I don't recommend paying the money for an MPPT controller for such a small system, though. The extra you get isn't enough to make it worth the price, IMO (and Bob's). I have the Morningstar Tristar PWM 45-amp model ($150 or so), it works great charging my 4, 6v golf cart batteries from 2, 205-watt panels. It allows you to set the charging voltage high enough for "wet" batteries (14.8v), which most controllers don't (and no converters that I've heard of do, either). And it keeps the voltage at that level for several hours after the batteries reach it, which allows it to stuff every last amp-hour in to fully charge the batteries, which very few other controllers do, and again, no converters that I know of.
I wouldn't connect your solar panel through the 7-pin connector. The wires are too small, and it would add unnecessary length to your wires. There is also the problem of having to rig separate paths from the 7-pin to the batteries depending on whether you're charging from solar or from the tow vehicle (if you're adding that function). You'd need the controller in the path for solar charging, but out of the path for truck charging. Also, as far as I know, unless someone has added tow vehicle charging to their system, the only thing the 7-pin plug is supposed to power are the trailer exterior lights, not anything inside, so it shouldn't even be connected to the batteries in most cases (correct me if I'm wrong about that, Vik, I haven't worked on that many campers). Give the panel its own wire to the controller, and the controller its own wire to the batteries.
A ten-amp controller would be plenty for one 50-watt panel, which at 18v will max out at 2.8 amps from the panels (watts = amps x volts, or 50w = 2.8a x 18v). At 14.8v from the controller, it will put a max of 3.4 amps into the batteries (50w = 3.4a x 14.8v). If you plan on possibly adding more panels or batteries in the future however, you might consider something larger. Six hours max of sun per day in the summer (unless you're a lot closer to the Equator than I am) at 3.4 amps (if you're following the sun by angling and tilting your panel as the sun moves to keep it at max power, it'll be much less if it's mounted flat on the roof) is only 20 amp-hours per day that you can hope to replace (3.4a x 6 hrs = 20 ah). That's just one typical 12v incandescent light bulb running for ten hours (2a x 10h = 20ah). 50 watts isn't that much, frankly. It's more a battery maintainer/trickle charger than a robust solar charging system (sorry), which may be all you need if you're stingy on your electrical usage or go from boondocking a night or two to a hookup.
I also have a Trimetric battery monitor, which allows me to know the state of charge or the amps going in or out at the touch of a button, I would strongly urge you to get one of these, they are definitely worth the money. Trimetric has also recently come out with a charge controller, the 2030, which can talk to the monitor and has more features like data logging, but costs more. I'm on a severe budget, so I don't do "costs more". The meter gets its info from a shunt in the negative line from the battery, and it must have nothing connected between it and the battery in order to measure every amp in or out.
2. Converters are wholly separate from any other charging system you might have, and must be wired separately from the solar. They are basically for people who are on a hookup all the time (and therefore not using their batteries at all, really). They're basically just 12v power supplies to power your 12v stuff. They charge at too low a voltage (13.6-ish volts, not adjustable), and taper the amps down too early, to ever get your batteries to full charge unless they're plugged in
all the time, and that includes after you get home. If you're boondocking you can use them with a generator in an emergency to get back up around 80% charge, but it's more efficient to just go straight from the generator's 12v outlet to the batteries than to let that "smart" converter not charge them fully while telling you that it has. And I have a PD-45 just like yours (that I bought before I did the research). It's just sitting there in a box, not connected to anything, and probably always will be, because I expect to almost never use hookups.
3. Here's a wiring diagram for a simple solar system including a converter, charge controller, and battery monitor. Where any wires cross on the diagram, let me say that they are NOT connected. I was just too lazy to draw the little "hop-over" symbols you would see in a pro diagram that show wires crossing each other but not being electrically connected. And I forgot to draw in the main battery disconnect switch that I have between my batteries and the positive hub, I used a 300-amp switch from the auto parts store. I also forgot to draw the little fuse that goes on the red wire to the battery monitor, but that's in the instructions. Red's positive, black's negative, except I didn't separate the 110v shore power cord to the converter, or separate the four little wires that come out of the battery monitor (again, too lazy, with too shaky hands for the fine stuff). The circles are + and - connection hubs, in my case they are just stainless bolts through my mounting board that make it convenient to hook everything up. LOL I also should have drawn the short connecting wire between the two batteries on the terminals that are next to each other, but that's what happens when you're hurrying, and it's accurate either way.
One of the most important parts of building a solar system that works is to use large enough wires. The wires going from the controller to the batteries, from the batteries to the hubs, and from the hubs to any large draws like big inverters or 12v motors and heating elements, should be both short and large, to minimize voltage drops and wasted power. In my system they're all #4, and everything is within six feet of everything else, wire-length-wise. The wires down from the panels can be a little smaller because the voltage is higher, but I still used #6 for those to get every watt possible out of my panels. Check an ampacity table or voltage drop calculator to tailor it to your specific current and distance needs. If you divide the 50 watts of your panel by the output voltage printed on the back (18v, probably), you can calculate the max current they will ever generate and size your wires to fit that and the distance the wire has to run to get to the controller. Always err on the big side when picking wire sizes, especially if you might possibly add more panels or batteries later. No sense having to rewire after the camper's done.
And here's a shot of my electrical board. The gray box to the left of the charge controller is a 60-amp dual A/C disconnect, which fuses my solar both between panels and controller, and between controller and batteries. It allows me to pull one "plug" to entirely disconnect my solar system if I have to work on anything, and only cost about $20-$30. The big fuse in the homemade holder up top between the inverters is an ANL automotive-type. The clear plastic ANL fuse holder by the big inverter came with it, as did the larger cables, which are still #4, but heavily-insulated fine-strand cable (like welding cable) instead of the cheaper heavy strand wire that I bought for everything else, that's why they're so fat. The shunt for the battery monitor is lower right, and also acts as my negative hub. The wires for the monitor aren't connected in the pic, they go to two small screws on the side.
And buy a $5 hydrometer from the auto parts store, if you REALLY want to know how charged your batteries are.
I hope this make things more clear for you. If anyone has questions, feel free to PM me. Have fun!
