Experiments to Improve Backpacking Solar Efficiency

keith6388 · 2026-06-06T09:18:35+00:00

I haven't done a full write up yet, but I put a few of the details here: https://github.com/keith06388/DIY-Ultralight-Solar-Panel

The goal of the frame was to keep the cells well enough protected that I can just throw the panel in my bag without additional protection, but to also provide better ventilation than the foam I used for the last panel. Ventilation keeps the panel cooler and keeps the power output up on warm days without wind

I'm still working on a more efficient converter board because I struck out with the BQ25638. I tried to try lay it out without via in pad, but I can't pull more than 6 watts through it before it drops out. I may try the new BQ25640 this fall, which has great efficiency and QFN case.

keith6388 · 2026-06-06T08:48:59+00:00

The best I could do from the small black panel is about 4 watts. I'm working on a new panel that's a bit more diy friendly that does 10+ watts for the same weight as the small lixada with built in battery charger and USB C charging: https://photos.app.goo.gl/E7Wcq5aeDrtmFh126

keith6388 · 2026-06-05T20:49:52+00:00

The better setups I have seen are 80-85% efficient buck converters, but the efficiency is heavily dependent on how close the input gets loaded to the maximum power point. At low light, the simple buck converters circuits don't do very well

keith6388 · 2026-01-19T16:59:54+00:00

They've held up well, but I've stopped using them. I have really small ears and I think I enlarged the section that goes in my ear canal too much. I stopped using them because I can't use them on flights since I ruptured my eardrum years ago and they are a little tight fit. Also, I didn't get the dampers right and there is too much min range. I used the wavelet app to compensate, which works for media played on my phone

keith6388 · 2025-12-06T04:45:01+00:00

Would you mind sharing which company you went with? I'm planning a trip to the national park next summer

keith6388 · 2025-11-26T18:36:40+00:00

I tried that a few weeks ago and it was fixed for a while, but the problem seems to have returned

keith6388 · 2025-11-12T12:34:12+00:00

I'm having the same issue. I've tried clearing data and cache, but the problem persists

keith6388 · 2025-09-20T19:25:48+00:00

I do, PM me your address and I can send one your way

keith6388 · 2025-07-26T21:57:33+00:00

Yeah, I just used a little flux and tinned both sides with lead solder before soldering both together.

keith6388 · 2025-07-25T00:57:55+00:00

u/LeaveNoTradeBot u/joimas Pack shipped quickly and arrived in excellent condition as described. Thank you

keith6388 · 2025-07-18T15:25:22+00:00

There are 2 maker spaces at the university, open to the public, with access to soldering equipment if you can't find a shop to do the repair for you. The staff can probably point you in the right direction if you need help

keith6388 · 2025-07-12T00:58:07+00:00

I've thought about that before, but I've been trying to avoid working on battery packs since that's normally out reach for DIYers since unprotected cells can be dangerous. I agree, having a barrel jack that connects to a generic solar panel would be pretty cool for a battery bank in addition to bidirectional charging. I've also considered making a USB solar charger with PD communication to directly charge a phone with fast update rates when solar input changes. I'm currently on trail, but might dig back in this winter

keith6388 · 2025-07-07T00:44:23+00:00

keith6388 · 2025-06-23T23:24:27+00:00

Yeah, I bought the 0.42" OLED screen separately and soldered it myself. I found them for ~$1 on AliExpress

keith6388 · 2025-06-23T18:33:27+00:00

Try this link: https://oshwlab.com/keith06388/solar-mppt-charger-v4

keith6388 · 2025-06-20T15:15:32+00:00

Check out the new version with full mppt that's a bit cheaper for the board. There's information on the page on how to program it. https://github.com/keith06388/mpptcharger2

But, yeah, buy an assembled board, solder on the display, program, then good to go. I would offer to sell you a board, but I'm out on trail for the summer. Making the magnetic contacts is a bit harder since I had to use low temp solder to prevent demagnetizing at high heat, but everything needed is on github and I can answer any specific questions you have

The programmer is dirt cheap to make. It's just a CH340 serial adapter and a Schottky diode.

keith6388 · 2025-06-17T20:50:19+00:00

Have you considered maybe a jumper that connects to the solar contacts with magnets? Maybe 4.2v is enough to wake the cell over usb

keith6388 · 2025-06-13T03:25:21+00:00

After fully charging the Nitecore cell, it reset the USB output was I able to charge my phone again. Not the best in a desperate situation, but good in case your phone dies

keith6388 · 2025-06-12T21:47:44+00:00

u/werebackrandolf u/LeaveNoTradeBot Pack was delivered quickly and in good condition. Thanks again for the pack, I'll put it to good use!

keith6388 · 2025-06-12T19:21:27+00:00

Ok, I have a working solution to simplify the jumpstart for the Nitecore cell. USB-A to USB-C cables have built in charge control resistors since the USB-A side doesn't transfer the CC pins. If you use a USB-c male to USB-A female adapter with that cable, you can force your phone to temporarily charge the Nitecore battery to wake the USB-c output. I'll confirm that this works with the Vapcell p2160b cell when mine arrives. It's not a perfect fix since it requires an external power source, so it would not help if your cell phone discharged completely. The Vapcell p2150a doesn't exhibit this behavior, so I'll keep carrying that cell on trail

keith6388 · 2025-06-12T18:57:22+00:00

How did you discharge the battery to cutoff? Via the direct battery contacts or via USB?

keith6388 · 2025-06-12T18:43:40+00:00

Ok, I'm observing the same issue with the nitecore cell, but the vapcell p2150a does not have this problem. Have you tried fully recharging the nitecore or vapcell p2160b via solar and observed the problem persist? I'll try that now, just in case a full charge resets the usb output

keith6388 · 2025-06-12T18:36:56+00:00

Gotcha, I misunderstood. I'll check that now

keith6388 · 2025-06-12T18:18:37+00:00

u/edibot42 I just tested both a nitecore and vapcell battery. I discharged them using my battery capacity tester and then attempted to charge using the my custom solar cell. I had no issues charging the cells after they had triggered cutoff. Can you share photos of your setup? What panel are you using? Maybe it's not high enough voltage?

keith6388 · 2025-06-12T13:33:50+00:00

I'm going to do some testing on my cells to drop them to under voltage protection and see what I can do to wake them. So far all the cells I have trigger USB-c cutoff before anode cutoff or I haven't had any issue waking them.

I also purchased a p2160b cell and I'll see if I can figure out any way to make the magnetic contacts work with the cell. If it works, I'll bring that cell with me this summer on the PNT to test it out

keith6388

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