[Imagine a giant disclaimer here that says I speak for RIM about BlackBerry officially only on matters of product security. Everything else, like this post, is just me as an independent maker, messing around on my own time, in absolutely no official/approved way.]
Before I headed out for a week of no-electrical-service camping at my super-fave, The Pinery, I picked up a project that had been sitting on the bench since last year: a solar USB charger. My goals were to be able to charge my awesome bike lights (front and back) from MEC as well as my BlackBerry 9790.
The result, shown above, is my sub-$50 solution: a flat-pack, 1” aluminum angle frame (fabbed with dumpster-recovered stock), four $10 12V solar panels from Canadian Tire, and some USB car chargers. In short: it works!
Before you click through for a few more build details, let me point out the solar aiming mechanism in the middle of this rig. It’s just a 2” piece of aluminum plate with a piece of white duct tape on it and a 1.5” #10-32 machine screw driven through it. The idea is to position the overall frame until the screw casts no shadow on the plate, at which point you can assume you’re more or less aligned to the sun and grabbing the most power in. To prop the frame in place after positioning, I’m using a 36”x1”x1/8” piece of aluminum bar stock and a spring clamp, visible at the top of the frame. Low-tech, but very flexible.
These solar panels were the spark for the project. I saw them for 70% off in the Canadian Tire flyer last year and picked up four of them. Reg $35 and on sale for $10. The panels put out a nominal 12V at 80 mA for a theoretical 1W of power per panel.
I guess the purpose of these is to trickle-charge 12V batteries on motorcycles, sleds, etc. The attraction for me was that they were both cheap and had 12V output.
Here’s my quick after-work-Friday proof of concept at home. Interestingly, this was a no-soldering-required project. I had been wondering if I needed blocking diodes or other voodoo, but in the end I just used the included alligator clips to go directly from panel, to USB car charger, to device-to-be-charged. The panels came with an ample amount of wire, keyed plugs, and an optional fused hunk of wire with ring terminal lugs for hard-wiring, in addition to the alligator clips. Pretty good deal for $10.
Here you can see my MEC bike lights in the upper left. They have a mini-USB connection to allow recharging and come with a 6” USB mini-to-Type A cable. I’ve got them plugged into two generic USB car chargers that I salvaged from some tech garbage. If you’re not a packrat, you can just buy these for $2 each. Basically all these devices do is drop 12V from your car’s cigarette lighter (I guess we call it an auxiliary power port now) down to 5V for USB devices, probably with a simple 7805 linear regulator and maybe a couple of caps. That takes care of voltage, and as for current, your car can provide many amps, but the solar panel can provide at best, a theoretical 80 mA (0.08 amp). All this means is a longer charge time on solar. Oh, and please note, the positive (red) clip goes to the end pin of the USB charger and the negative (black) clip goes to the side contact.
The BlackBerry charger at bottom left was a bit of a different story…
First of all, you can’t just use some generic USB charger where the D+/D- lines are shorted together (yes, I tried it). You need a car charger designed to connect to BlackBerry smartphones. So I tried the connection show above and it totally didn’t work. My 9790 would start off with the flashing lightning bolt I’m-charging symbol, but would then flip to the AC power symbol, which indicates not-charging. Thought about this. Talked to some friends (thanks, boys!) The consensus was that I probably was getting insufficient current from the solar panel, causing the charger and/or the 9790 to reject the charging set up.
I thought if one panel was giving insufficient current, then maybe all four panels in parallel might work better, and…
indeed it did. Here we are back in the woods, on the other end of the wire from the solar panel frame. To neaten things up, I tie-wrapped all the USB car chargers down to a scrap of peg board. A nice benefit of the alligator clips is that they allow me to easily reallocate current to any given charger with no tools. In this pic, I’ve got the four positive leads from all the panels ganged up on the BlackBerry car charger at right. Likewise with the ground leads. I threw the multimeter inline and it shows we’re charging at 0.25A and the BlackBerry shows charging successfully. It works! I charged my 9790 from 52% battery to 95% charge in about 3 hours in late afternoon sun.
A few notes:
Actual vs theoretical charging current – with 3pm direct sun I got as high as 290 mA with the four panels ganged. That’s lower than the theoretical 4 x 80mA = 320mA, but not bad at 90%.
Keep it in the shade – electronics don’t like heat and that goes for LiPo batteries too. I made sure when positioning the panel frame in the sun that I put the chargers and devices in the shade. Trust me and do it.
Aiming is important – I was hanging around the campsite anyway, so I took regular breaks from reading Good To Great, and repositioned the solar panel frame about every 20 minutes. Sometimes, I had to move it out of the shade of trees and always repositioning it to be directly facing the sun. This made the difference between 50mA and 250mA.
Really <$50? – ok, so I already had the BB car charger, the generic USB chargers, the aluminum stock, fasteners, tie-wraps, and spring clamp, but I’m sure you’re equally resourceful.
Felt good to be back in The Lab. Y’all thought I had abandoned making for photography, eh?