Solar Panel for USB devices

Hi all,

It is a significant challenge on extended trips to keep devices such as my Samsung Galaxy S2 mobile phone charged. I carry spare batteries and have even begun using high capacity batteries that make the phone less slim-line. However, no matter how big the battery, it is going to run out sooner or later. Tricks like turning the device into flight mode, ensuring bluetooth is off and using apps like Juice Defender do lead to longer run times but all things come to an end.

The biggest demand when using the phone in the field is running GPS applications – especially if having track logging on. Trekbuddy is lighter on the juice than Androzic, but both certainly consume. Also, if I am in mobile range and on a Summits on the Air activation, I try to also use an APRS app on the phone so people can track my progress towards the summit so they then have some idea when I am likely to come on air. I need a solution if I go on a week long SOTA trip and I would still like the phone alive at the end.

Solar Charging Panel

On a trip last year with Glenn VK3YY, I saw him using a small solar panel on the top of his pack. I looked around on ebay, but most USB solar charging devices really are just a (not always so) big external battery with a small solar panel. I would think many of the panels would be around 1 watt or even less.

Glenn alerted me to a 2W 6V solar panel on ebay. The seller provided a Schottky diode and a female USB socket. Upon receiving it, I soldered the diode and the socket on, and found the voltage was 6V up to 6.5V in the sun. The phone refused to recognise it.


Separate to this, I purchased a 12V to 5V regulator with a USB socket. This was so I could charge phones in the car, but also in the field off LiPO batteries. I put Anderson Powerpoles on the 12V side. Here’s a pic of the device:

12V to 5V (USB) regulator

12V to 5V (USB) regulator

This device works quite well with a 12V input. My experience with similar buck regulation devices is that they tend to hold the output voltage even when fed something only a small greater input voltage, meaning that I should be able to get 5V out with 6V in. I removed the USB socket from the solar panel and made up a about 5cm of conductors to put a set of Anderson Powerpoles on. I left the Schottky diode in place, so that the solar panel would not be exposed to any voltage coming up the other way.

I put a small amount of duck tape on the outside of the panel to protect the edges, and here is the finished product:

Completed Solar Panel with Anderson Powerpole connector

Completed Solar Panel with Anderson Powerpole connector

Testing even in fairly low sunlight showed that the phone accepts charging from this setup. I’ll have to see how it goes in the field on a trip, but it is looking good. I’ll be interested to see if I get something like the 2W out of this panel in good sunlight – however being near winter, we might only really know in 6 months.

73, Regards, Wayne VK3WAM