Not So Smart Harvest
Building is one thing, and testing is another. With the Intrepid’s solar installation complete, I moved onto running it to see how it fared. The rooftop system, some 360 watts of panel powering a Morningstar TriStar MPPT 45A solar controller, ran like a refrigerator from the get-go. The Outback Smart Harvest MPPT 20A ran fine for a day, but then combining the two controllers to run simultaneously for a total of 560 watts seemed to freak out the Smart Harvest. Voltage at the battery sailed from 13.4-16 volts, throwing the unit into a momentary over-voltage stop before resuming its roller coaster ride. Okay. So I tried it solo again. It ran fine for a day or two, and then suffered the same symptoms and series of warning lights all by itself.
As I wrote in Intrepid Solar, Part 1, I’d already been disappointed that Outback offers no remote temperature sender for this new series of controller, even though the unit itself has the capability. A call to Outback Tech netted a replacement shipment, my controller’s serial number apparently being within a bad batch. That was slow to ship – a delay I don’t need at this stage. The weather has been unseasonably warm in the Yuma Arizona area, and the corresponding March temperatures are in basic agreement. I should have departed by now.
So, controller received and installed, I fired it up solo, which revealed none of the shenanigans of its predecessor. Good. Hook ’em both up and see what happens. The result of that was a circus again, forcing even the TriStar into over-voltage shutdown this time. That’s because the Smart Harvest was pushing voltage from 13.8-16.1 volts. The TriStar’s overall response is to shut down and step out of the picture so that the batteries aren’t harmed. It waits until battery voltage settles down to a normal range for awhile before it turns itself back on. The Smart Harvest did the same – sort of. Now running solo with me having unplugged the roof panels, it stayed on the same roller coaster of voltage, the problem being that its protective shutdown was only momentary. Once battery voltage cascaded down out of the cutoff limit, it instantly went back to work and repeated the loopy cycle of doom. Unlike the TriStar, unplugging its panels blanks its LEDs and it apparently no longer monitors battery status.
Ostensibly, the problem should be a mismatch between the two controllers in what voltages they expect to see during each stage of charging. From past experience with Morningstar controllers, the unit dealing with the worst panel output of the two simply backs down and lets the other controller drive. The two controllers need to be approximately matched as to how they respond to different voltage levels, so that one is not continually rendered useless by the other. The Smart Harvest’s voltage expectations are within a tenth of a volt of the TriStar’s, so there shouldn’t be a big problem. But there is, and at its much lower price level, I have to think that the Smart Harvest 20A is simply not sophisticated enough to play well with others. Once it goes nuts, it stays nuts until manually forced into a reboot by unplugging its solar panel input. It would be nice if, like the TriStar, it waited and calmly reset itself without breaking any connections, but it does not.
For my purposes, what this does it to prevent all 560 available panel watts from coming into play at once. That isn’t much of an issue when the Intrepid is parked under a tree with the ground panels out in the sun, or parked in the sun with the unneeded ground panels stowed away. But it is an issue when parked in the open under dark skies for days, when there’s some 416Ah of battery capacity to deal with and the compressor fridge has used the reserve. Unfortunately, there is not enough time remaining to resolve this lack of full panel power. Unlike Morningstar, Outback’s user manual is merely a few cryptic symbol diagrams on one letter-size sheet, rather than a 68-page manual. And unlike Morningstar, there are no inferences or other references as to tandem use. In fact, Outback’s website does not acknowledge the Smart Harvest’s existence. This replacement Smart Harvest, having been sent direct from Outback’s USA office/warehouse, presumably works as intended, hopefully being part of a known good batch. The good news is that it works to specification, guaranteed for three years by Outback Power Inc. The bad news is that its internal design is unsuited to tandem use, which is certainly a reflection of its relatively low cost.
Ultimately, it will need to be replaced with a more suitable product. Until then, I’ve decided to live with it and examine just how the either/or panel usage works out in practice over the summer. That will mean pulling the roof panel fuse every great now and then when the ground panels are out, but that access is very easy. I hate to have yet another post which in essence says, “Don’t do what I did here”, but in this case, it’s true. Recharging one battery pack with two controllers and sets of panels is frequently done, and as long as the cycle voltages are comparable between the two, is no big deal. In this instance, the lesson is a little different. Oh well. On to making usable space where there is none left.
Great article as usual, keep us posted on your solar electric project.
Thank you, Joe!