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My project for this week: turn this warning lamp thing in a small solar charger / battery pack combo. Let's see if I find a way to make that happen...Permalink On twitter.com
❤️ 6 Favorites Mood -3 🙁
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They normally run on these big chunky 6V batteries, but I'll try to replace them with 18650 Li-Ion batteries, probably 3S for nowPermalink On twitter.com
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The screw holding that thing together is a funny one. Should be a hex thing on the front, but I didn't have anything that fit, so it's this hack instead 😆Permalink On twitter.com
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Let's take this this apart a bit more. Take off the lenses first, which has just a few regular screws.Permalink On twitter.com
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First side is off, the back side slides out easily now as well. This pole in the middle here has two LEDs in the top part, one of each side. That's the light you see usually. There's another LED (I think) down below and a photodiode to figure out when it gets dark.Permalink On twitter.com
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That whole thing pops out of the base, including the battery connector in the base, and that leaves me with a quite dirty piece of plasticPermalink On twitter.com
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Probably a good idea to give it a rinse and come back to it later🚿Permalink On twitter.com
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While that's drying, there's some electronics work to do. I don't want to build my own battery pack quite yet, but use these battery holders instead. I can sandwich two of them together for a 3S2P battery, so there are two cells in parallel, and three of these pairs in series.Permalink On twitter.com
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How do we charge these? I would've liked to go with one of those cheapo PWM solar chargers from China (got of few around like this one), but while you can dial in their cut-off voltages a bit, they won't adjust far enough for Li-Ion 3S. So DIY it is (for now).Permalink On twitter.com
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I decided on using instructables.com/ARDUINO-SOLAR-CHARGE-CONTROLLER-PWM/ as a reference, but I'll change quite a few things around probably. I don't have the exact same MOSFETs, the voltage dividers don't work for what I'm doing, and I want an OLED display. And who knows what else. So let's do some sketchingPermalink On twitter.com
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I don't seem to have any P-channel MOSFETs, and neither does the parts library at @munichmakerlab. So I guess I'll have to order a bunch of stuff again, which will take a week. Damn 😕Permalink On twitter.com
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Put together the battery pack with its battery management system. Only populated one side for now, but it looks like it's working 💪Permalink On twitter.com
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Ok, on to the charge controller. This little display seems to have a non standard I2C address configured, but after some fiddling around, I managed to get it to work 🎉Permalink On twitter.com
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Next step: adapt the firmware to that thing. The instructable this is based on used a normal LCD, but that's too bulky for the lamp. So need to adjust it to work with the OLED screen. Again a bit fiddly, the libraries are only somewhat compatible. But we got text now 😬On twitter.com
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After tweaking some settings it's actually charging 🥳 only a beat-up lead acid battery so I don't start any fires, and off a tiny solar panel, but I still can't quite believe this actually works 😬Permalink On twitter.com
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Ok so switched locations to get some real sun on that panel, and the whole thing went crazy. Did some more code magic that I don't quite understand and it sort of works. Still not sure if this is all like it should be, but hey, we're still getting some juice into the battery 🤷♂️Permalink On twitter.com
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The serial plotter baked into the @arduino IDE was really helpful figuring this out, but it was really hard to find some good documentation on it. Maybe I should do a small blog post about that thing 🤔Permalink On twitter.com
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Did a bit more testing over the past week, with a new watt meter I just got. And realized I need to fix the wiring job, and also need to make a proper test setup to compare the charger against the cheap off-the-shelf charger. More here: hackaday.io/project/178837/log/192259-solar-charger-testing-the-prototypePermalink On twitter.com
