DIY magnet-based charging system is possible, but not perfect

A few days ago I had an idea. My generic rubber case has plenty of space between the phone’s battery cover and the actual case, due to being stretchy and being forced on a phone with a 2000mAh extended battery kit. I was thinking of how to use that space, and then a thought struck me: what I I soldered magnets to a PCB, wired those magnets to a small microUSB connector, thread the magnets through the case wall, and made a matching wall/desk holder? The idea being that the phone would snap on the holder, stay there, and get a charge through the magnets. A couple of days and a working prototype later and I can report on where the system works, and where it fails.

It didn’t take long to make a prototype. I have microUSB ports made for DIY use, magnets, and everything else such a system needs. I made the microUSB connector as small as possible, soldered the power wires to magnets, and made a corresponding US-to-magnet cable for plugging into USB power. After testing it out on some LEDs to make sure I had it wired correctly, I moved on to pluggin it into my Galaxy S II, and the phone happily started charging through the magnetic connection. Not that it was surprising that it would work, after all magnetic charge connectors are not that uncommon, though it’s been a while since we’ve seen them in phones (think back to the HP Veer) thanks to that (in my opinion) horrible microUSB initiative.

There are however two problems that I encountered. First of all, even when I shaved as much off the microUSB connector as I could, this will add some lip to it. I would probably shave even more off it if I really sat down and really tried, so this isn’t a huge dealbreaker, and I managed to get the connector down to where it’s a heck of a lot smaller than what you’d normally see.

The second issue is of graver concern however: the magnets’ impact on the phone. No, I don’t think it will erase data, I know what flash memory means. There are however magnetically sensitive parts still in the device, specifically the compass. Using a compass app I saw major interference with the magnets being even 10 cm from the phone, so whether or not I switch out the phone side of the magnetic connection system with something that is passively magnetic isn’t going to put the magnets far enough from the device to eliminate this effect. Devices that have integrated magnets from the factory have been developed for it, with magnets that fit the purpose 100%, and engineers that know for a fact if it will hurt a device or not. I don’t have that luxury, and to make matters worse, the fumbling for my phone in its holder at night due to my dependence on contact lenses (and hence inability to see much without them) means that I chose this size of magnet for a reason.

I need to do some research on whether or not there’s any real issue here, and whether or not it’s something that I can live with or not. I can live with the compass not working while the case is on, I can’t live with it never working again because the case has been on. Unfortunately it’s not easy finding proper information about such things online, where most discussions on the matter are back at the magnetic storage misconception, and if you’re lucky, have barely moved on to the lithium battery + magnets debate. Discussion after discussion between people who think a magnetic flap on a case can damage a phone (they can’t) is not going to be very helpful when the question is if much stronger magnets will affect the phone’s sensors.

I don’t know where if I will continue this project or not, but I definitely won’t do so without a definitive answer to whether there’s a danger to the phone’s sensors. If someone reading this has that answer and can say so with an engineering background and not just guesswork based on myths and misconceptions, I would love to hear it. My perfect ending to this project would be a slightly thicker phone with a tiny bump sticking out the microUSB port and four magnets sticking trhough the back of the case, and a device that charges when these magnets snap onto a desk holder.


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Andreas Ødegård

Andreas Ødegård is more interested in aftermarket (and user created) software and hardware than chasing the latest gadgets. His day job as a teacher keeps him interested in education tech and takes up most of his time.