Gags, Humor, and Solar Power
I recently managed to replace the misbehaving Outback SmartHarvest 20A MPPT solar charge controller with a proper Morningstar controller, and now all is right with the world. The Outback was exceptionally naughty right out of the box, and its replacement was no better. The USA office of Outback appeared to be manned only with sales types and customer service reps, with no technical staff on board. The sole solution seemed to be trying another unit. So I did, but opted for the Sunsaver. Since I could not in good conscience sell or even give the SmartHarvest away, it is now residing in the local landfill, where it belongs.
With Morningstar’s remote temperature sender attached to one of my batteries, the Sunsaver now operates in tandem with their TriStar MPPT 45A. The Tristar handles everything coming in from the 360W roof panels, while the Sunsaver serves to feed power in from the 200W ground panels via the external rear wall plug that comes standard with the Four Wheel camper. (A simple internal wiring harness change was needed to feed both of these units to the same battery pack for my installation.) Four Wheel uses the less expensive “PWM” version of the Sunsaver in production, since most buyers who use solar install one panel on the roof, and/or plug in a ground panel. As long as the total input doesn’t exceed 6.5 amps, you’re good to go and no harness changes are needed.
PWM solar charge controllers are normally the way to go for most installations, since they do the job at much less cost. As long as the panels are joined positive to positive and negative to negative (a parallel connection) and the wire gauge and lengths are able to handle the resulting amperage without too much loss from resistance, it’s the smart way to go.
My setup, however, would throw way too much amperage through the standard 10Ga roof wires and the 20-foot ground wires when connected in parallel, requiring heavy cables to avoid the big resistance losses that would result. Since I was not about to replace the roof or ground wiring with heavy cable, I chose MPPT controllers that would allow me to add panels without stressing the wiring much. This is done by connecting each of the two panel sets in series, which boosts voltage instead of amperage. They each mimic those old D-cell flashlights, where the batteries are stacked in series to power a higher voltage bulb. The key is that standard 10Ga wires can handle high voltage, but not high amperage. Boosting voltage does not aggravate losses in wire efficiency, and allows much longer runs of thinner wire without sabotaging panel power output. The TriStar is adjustable in its charging voltages, so it was an easy matter to match it with the charging routine of the Sunsaver. I turned off equalization on both controllers (a once-a-month charging routine to slow battery sulfation) to avoid competition and because I use a dedicated desulfator, the Battery Life Saver (BLS-12/24C, due to my pack’s capacity rating. The BLS-12N is good up to 200Ah).
So, I’ve got about 72VDC coming in from the roof, and 36V coming in from the ground panels, each leading to a dedicated controller. MPPT controllers are the only type that can deal with such high voltages, since only they can convert the voltage into charging amperage. The only heavy wiring needed is between the controller and the batteries, which is a universal need anyway. In particular, stringing two sizable ground panels together in parallel over 20-foot wires would be quite a wasted effort due to the losses from electrical resistance. The only ways around this are to either bulk up the wire gauge to heavy cable, or shorten the ground wire lengths to just a few feet, which negates the whole point of having ground panels that can be placed out in the sun some distance away. Adding more panel wattage to compensate simply aggravates the inefficiency problem. Better to keep the amperage to that of a single panel, and wire them together such that voltage is ramped up instead. This makes keeping lightweight 10Ga wiring practical.
Now, two MPPT controllers obviously cost a heap more than one, which points out the liability of high voltage series wiring. That is, shading one or more panels with this system can pretty much collapse the output of the combined panel array. So, parking in the cool shade and setting out the ground panels with everything connected to one controller doesn’t do much for you. What helps is having two independent charging systems, one for the ground panels and one for the roof panels. Park under a tree, and while the roof system becomes nearly useless there, the ground panel controller is still sawing away with whatever panel wattage is connected to it, out in full sun. In my case, that’s 200 watts. That may be too little power to fully recharge 420Ah of batteries, but it’s still a definite help.
Similarly, parking the rig under overcast skies calls for maximum charging power, since the roof’s 360 watts of power will not be adequate to recharge that much battery capacity after a long night of raiding the 12V fridge and watching Ernest Saves Christmas several times. In that case, deploying the ground panels will display a total of 560 watts of panel potential. Naturally, both overcast and the inability to aim the Intrepid’s roof-mounted panels toward the sun takes its toll on power output, but you get the point. However miserable or good the charging conditions, two independent charging systems allow for some flexibility in maximizing whatever charge is available, and making those MPPT systems allows for retaining practical wiring gauges and lengths. It’s all good, if you have a big battery pack and can handle the initial cost.
Now if you’ve suffered through all this, here is your reward, though some may not think it so. It’s a short clip from Ernest Saves Christmas, with the late Jim Varney in his “Ernest P. Worrell” persona. There are three other very different but carefully crafted characters he does in the same movie. The “Ernest” character makes one assume that Varney was a one-trick pony based on goofy slapstick, but in truth, he studied Shakespeare at the Barter Theatre in Abingdon, Virginia and was considerable in his adaptability to varied roles. By age 17, he was performing professionally in nightclubs and coffee houses. The Ernest P. Worrell character simply caught on (along with his “Auntie Nelda” character), and he made more breakthrough commercials than you can shake a stick at before beginning a TV series and then moving on to some awful but fun movies. Enjoy.