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Wednesday, June 22, 2016

Scotty, We Need More Power...Solar Power That Is! [Part 2]

New Install!
    Welcome to the second article in the series! In the first article I talked about replacing my existing semi-flexible, thin solar panels that are adhered to my RV roof, with the latest and greatest, most efficient panels now available. Last time we talked about how to get the old ones off and the new ones to stay up on the roof without resorting to screws or brackets. This time we'll look at the wiring. It's a bit more complex than the original wiring since there are six panels rather than three. Really, not all that difficult to make it all work, but required a bit of "fiddling." Let's take a look!

New Wiring Partially Fitted
 Typically, each solar panel has a junction box that takes the flat contacts from inside the panel itself and gives you terminals to attach wires to. My last two sets of panels had exactly that. Since I had already run duplex boat wire (That's just a fancy way to say it's two insulated wires within a UV and water resistant cover) I wanted to re-use those wires. Each of the original panels had a duplex wire run back to the charge controller. This time around two panels would have to share each run. I had to figure out how to make that happen. If you take a close look at the old junction boxes, they have 2 watertight screw down terminals for the wiring back to the charge controller from the roof. I had the duplex boat wire separated and inserted into these openings then crimped/soldered on two ring terminals that attached to the screw down terminals inside the junction box housing. Since the boxes were mounted on the panels and the wires from the panels themselves came up through the bottom of the box there wasn't anything left to do. The new panels have permanently attached junction boxes that are filled with waterproof epoxy. Even though the lid comes off, you can't access the terminals! So I couldn't simply run the wires the same way. Now what?

See The Second Section Of White Duplex Boat Wire
Well, the easiest and most efficient way to make this work was to remove and re-use the junction boxes from the original panels. This way I had a good solid waterproof connection from the roof to the charge controller inside already set up. Then I would wire each set of two panels into the junction box. These could be wired in series OR parallel. Huh? Simply put, if you wire from positive to negative (one panel to the other) and then one positive from 1 panel and 1 negative from the other into the junction box you get double the voltage at the same amperage. Just like putting two (or more) batteries in a flashlight, nose to tail.) The other way, parallel wiring connects both negatives and both positives together and then runs those into the charge controller. The Voltage remains the same, but the amperage doubles. Just like adding another 12V house battery will add more storage. Why does this matter? Which is best? It depends on your controller.

Finished Back Pair of Panels
In my case, I have an MPPT solar charge controller. This device is capable of taking in varying amounts of voltage (up to 105 Volts total) and converting it down to whatever your battery needs to charge. Around 12 to 15V usually. By increasing the voltage coming from the panels, you can reduce the thickness of the wires needed to transport that power without excessive losses. There is a point of diminishing returns though. The closer you are to the voltage needed to charge the batteries the more efficient the charger is. Let me put it this way; my two 12 Volt batteries are at 50%, the charger needs to put out around 14.7 volts to charge then dropping to 13.5 to "float" the batteries when charged. ("Float" just means keep them charged!) The closer to 14.7 V the panels are, the more efficient the controller is. MPPT controllers have a neat trick. They can take excess voltage and convert it to additional amps going into you batteries. Not a HUGE amount, mind you, but it could be 10% in hot weather and up to 25% in colder weather. With my new 600+ watts of panels, that could be an extra 60-150+ watts of power or around 5-15 additional amps. Almost like having a seventh panel! Result!
Watertight Wire "Hold Down" No Flapping In The Wind!
The only way I could make the wiring work with the old junction boxes was to drill 4 holes on the opposite side of the existing openings and insert the 2 negatives and two positives into the box. Then crimp/solder on ring terminals and screw them down to the terminals in the box. This works fine, but isn't all that pretty as I had to seal the small gaps around the new holes so water couldn't get in and corrode/short the wiring. A bit of silicone inside and outside and it should be fine. Then strips of EPDM tape to hold down the wires and tidy everything up. Next time(!) I will source different junction boxes. If I was to install this system on someone elses RV, I wouldn't have these issues as new installs are MUCH simpler and faster to do!

Of course, the wiring was done just as the sun was setting, so I have NO idea how well these new solar panels will perform. I would wager they will be MUCH better than the last set. I mean, technology marches on! If these panels test well, hopefully, I will get to test some Lithium Iron Phosphate batteries next. They are still quite expensive and no manufacturer of "plug-and play" 12V versions want to send me batteries to test. That is a red flag to me that they are "NOT ready for prime time." If you are a tech savvy experimenter they should work well enough, but if you just want it to work....maybe wait a bit longer.

Next week's article (Part 3) will put these new panels through their paces. Let's hope all is well and I am as enthusiastic about them AFTER the testing!

Be Seeing You...Down The Road,

Rich "The Wanderman"

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