Earlier this year, within the concluding post of a multi-part series that explored a not-as-advertised portable power generator, its already-broken-on-delivery bundled solar panel:
and the second solar panel I’d also bought for the setup (and subsequently also returned):
I discussed the primary options (serial and parallel) for merging the outputs of multiple solar panels, the respective strengths and shortcomings of the two approaches and, in the parallel-connection case, the extra circuitry that (unless already built into the panels themselves) would likely be necessary to prevent reverse-current hotspots in situations where one or both panels were in dim light-to-darkness.
Since both panels I’d bought, plus the portable power generator they were intended to “feed”, were all based on Anderson Powerpole PP15-45 connectors:
the parallel combiner I’d also bought from (and subsequently also returned to) Amazon had Anderson Powerpole connectors on both input ends, plus the output:
What if anything was inside it beyond just two pairs of input wire, with like-polarity cables soldered together and to an output strand, all within an intermediary watertight compartment? And if more, why? Here’s what I wrote back then:
Assume first that the combiner cable simply merges the panels’ respective positive and negative feeds, with no added intermediary electronics between them and the electrons’ intended destination. What happens, first, if all the parallel-connected panels are in shade (or to my earlier “dark” wording surrogate, it’s nighttime)? If the generator is already charged up, its battery pack’s voltage potential will be higher than that of the panels themselves, resulting in possible reverse current flow from the generator to the panels. Further, what happens if there’s an illumination discrepancy between the panels? Here again there’ll be a voltage potential differential, this time between them. And so, in this case, even if they’re still charging up the generator’s batteries as intended, there’ll also be charging-rate-inefficient (not to mention potentially damaging; keep reading) current flow from one panel to the other.
The result, described in this crowded diagram from the same combiner-cable listing on Amazon:
is what’s commonly referred to as a “hotspot” on one or all panels. Whether or not it negatively impacts panel operating lifetime is, judging from the online discussions I’ve auditioned, a topic of no shortage of debate, although I suspect that at least some folks who are skeptical are also naïve…which leads to my next point: how do you prevent (or at least minimize) reverse current flow back to one or both panels? With high power-tolerant diodes, I’ll postulate.
Those folks who think you can direct-connect multiple panels in parallel with nothing but wire? What I suspect they don’t realize is that there are probably reverse current-suppressing diodes already in the panels, minimally one per but often also multiple (since each panel, particularly for large-area models, is comprised of multiple sub-panels stitched together within the common frame). The perhaps-already-obvious downside of this approach is that there’s a forward-bias voltage drop across each diode, which runs counter to the aspiration of pushing as much charge power as possible to the destination battery pack…
If you look closely at the earlier “crowded diagram” you can see a blurry image of what the combiner cable’s circuitry supposedly looks like inside:
And I closed with this:
Prior to starting this writeup, I returned the original combiner cable I bought, since due to my in-parallel return of the Duracell and Energizer devices, I no longer needed the cable, either. But I’ve just re-bought one, to satisfy my own “what’s inside” research-induced curiosity, which I’ll share with you in a teardown to come.
That time is now. Since I strongly suspected my teardown would be destructive, I picked up the cheapest combiner I could find on Amazon. This one, to be precise, from the same supplier I’d chosen before (therefore presumably with the same “guts” in between the output and inputs):
In this particular case, the combiner was intended for use with Jackery portable power stations (historically based on, as I’ve noted before, either a DC7909 or DC8020 connector depending on the model), so it included native-plus-adapter support for both plug standards. Today’s patient was “Amazon Warehouse”-sourced, therefore $3.20 cheaper than the $15.99 list price. And again, I assumed it wouldn’t live past my dissection of it, anyway. Speaking of which, here it is:
Now freed, along with its associated output adapter, from clear-plastic captivity and as usual accompanied by a 0.75″ (19.1 mm) diameter U.S. penny for size comparison purposes:
Input(s) end:
Middle thirds, top and bottom:
And output end, both “bare” and adapter-augmented:
Back to the middle third for a side view. Look, it’s an ultrasonic welded seam all the way around!
I’m glad to see that at least some of you enjoyed my attempted (successfully, so, albeit not cleanly) breach of an ultrasonic-welded wall wart case at the beginning of last month.
To the Hackaday crowd: No, it wasn’t intended as an April Fools’ joke. I had no idea what day Aalyia was going to publish it, although in retrospect, excellent choice, my esteemed colleague!
This time I decided to downscale my “implements of destruction” somewhat, downgrading from a 2.5 lb. sledge to a more modest ball-peen hammer, and to a more diminutive but no less sharp (unfortunately, this time absent a “hammer end”) paint scraper:
I’d also like to introduce you to my equally diminutive, recently acquired vise, the surrogate for the Black & Decker Workmate I used last time. Isn’t it dainty (albeit surprisingly sturdy)?
It took a few more whacks than I would have preferred (or maybe I was just being cautious after last time’s results), but eventually I got inside, and cleanly so this time, if I do say so myself:
The other side…not so much, although still not bad (and yes, to several readers’ suggestions, I also own a hacksaw, which I’ve used before in similar situations; I was just angling for variety):
All that was left was a flat-head screwdriver acting as a lever arm to pry the two halves apart:
And we’re in:
This initial perspective is of the bottom of the device:
Note the thick PCB traces and their routings. Keep this in mind when we flip it to the other side:
Speaking of which, let’s next remove those two screws:
And the PCB’s now free:
Here’s the bottom side of the PCB again, now absent the case half that previously surrounded it:
And here’s the now-exposed top half, blurrily glimpsed earlier in one of the “stock photos”, that we all really care about:
Zooming in a bit:
And now even closer, courtesy of my crude, inexpensive loupe-as-supplemental-lens setup:
Those are indeed “high power-tolerant diodes”! Specifically, they’re multi-sourced (does anyone there know if the first line “LGE” mark refers to LG Electronics?) MBRD1045 Schottky devices, variously referred to both “diodes” and “rectifiers”, the latter because their Schottky-derived low forward voltage loss makes them amenable to use in (among other things) full-wave rectifier circuits like the one seen in last month’s “wall wart”. In actuality, the two terms refer to the same thing, as a discussion forum thread I came across in my research made clear. This memorable phrase in one of the thread’s posts cracked me up (no, I won’t reveal if I agree!):
EEs are not known for consistency and precise language.
Admittedly, a circuit diagram I found in several suppliers’ datasheets gave me initial pause:
Two anode pins? Were the same-polarity outputs of both solar cells combined ahead of the diode? And if so, why were there four diodes in the design, instead of just two?
Eventually, even before doing the math and calculating that the spec’d 10 A of peak per-diode forward current would barely-at-best enable free flow of even one solar panel’s electron output (thereby, I suspect, being the primary cause, vs the slight forward voltage drop across the diodes, of my previously mentioned inefficiency results noted by some combiner users), far from two panels’ aggregate load, I’d also realized that such a setup would only achieve one of the two desired combiner objectives. It would indeed prevent this scenario:
What happens, first, if all the parallel-connected panels are in shade (or to my earlier “dark” wording surrogate, it’s nighttime)? If the generator is already charged up, its battery pack’s voltage potential will be higher than that of the panels themselves, resulting in possible reverse current flow from the generator to the panels.
But it would do nothing to current flow-correct this other key potential “hotspot” scenario:
What happens if there’s an illumination discrepancy between the panels? Here again there’ll be a voltage potential differential, this time between them. And so, in this case, even if they’re still charging up the generator’s batteries as intended, there’ll also be charging-rate-inefficient (not to mention potentially damaging; keep reading) current flow from one panel to the other.
So, four diodes total it is, two for each panel (one for the output and the other for the return), with both anode connections of each diode leveraged for a common input, and the two panels’ respective positive and negative pairs combined after the multi-diode structure. This “digital guy” may yet evolve embryonic-at-least analog and power electronics expertise…nah. C’mon let’s get real. Delusions are inexhaustible, don’cha know. Regardless, did I get the analysis right, or have I missed something obvious? Sound off with your thoughts in the comments!
—Brian Dipert is the Editor-in-Chief of the Edge AI and Vision Alliance, and a Senior Analyst at BDTI and Editor-in-Chief of InsideDSP, the company’s online newsletter.
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