Inductive cellphone charging without voiding warranty

[Derek Hughes] wanted to use inductive charging on his cellphone without voiding the warranty. He picked up a Pixi charging backplate meant for a Palm Pre and scavenged the coil and regulator circuitry from it. To make the electrical connection with his HTC HD2 he removed the mini-USB plug from a charging cable and connected it with 30 gauge wire. The whole package will fit beneath the back plate for use with a Touchstone charger (as we’ve seen with the HTC Evo) but there was one problem. The metal backplate from the HD2 interferes with the inductive charging. For now he’s using tape to hold everything together while searching for a plastic case replacement.

He walks you through the hack in the video after the break. We’re usually not worried about voiding warranties, but a phone like this takes a lot of abuse and having warranty protection or even a service agreement isn’t a bad idea.

Comments

  1. andrew says:

    Why would a phone like that take a lot of abuse?

  2. Travis Deyle says:

    Been there, done that. A while back we built a wireless charging system that just provided USB power to _any_ device:

    http://portal.acm.org/citation.cfm?id=1586646.1588250

  3. MS3FGX says:

    Yeah, I don’t understand that logic either. What makes this phone more likely to be abused than any other?

  4. liam says:

    Is the backplate ferrous metal then? Aluminium might be a suitable substitute. Easy enough experiment to do, just cut up a coke can.

  5. Mike Szczys says:

    Perhaps a poor choice of wording. I meant cell phones in general, versus other electronics like a laptop.

  6. toaste says:

    Even non-ferrous metals could be an issue: the alternating magnetic field from the charger’s coil would induce eddy currents in any conductor which in turn produce magnetic fields opposing the source. If you doubt it, drop a magnet down a copper pipe and observe how slowly it falls despite copper being non-ferromagnetic. http://regentsprep.org/Regents/physics/phys08/clenslaw/default.htm

  7. alfcoder says:

    @Travis Deyle: me too :)

  8. fartface says:

    Bah, why cant phone makes pull their heads out of their butts and put this in the phones?

    We should have had this cince 1985.

  9. Regulus says:

    Awesome!
    This is a hack I can stand behind.

  10. Whatnot says:

    Lol at the tape, it’s so white and tawdry, such an ad hoc fix.
    Quite amazing too that he has clue what he’s doing it seems.

  11. Whatnot says:

    What I don’t get is why they don’t use the same system on cellphones that they use on classical wireless phones in the home, 2 large metal contacts on the bottom and you put it in the stand and it recharges without fiddling with plugs or slotting it into a small connector.

  12. nighthawk says:

    the little microusb board sticking out is… kinda impractical, isnt it? you cant really put that into your pocket or anything…

    and @alfcoder
    where can I get the schematic or guide to make that, thats pretty sick.

  13. bob says:

    I wish I could find some info on that wireless charger. How is a DC current generated? Is there a transformer on the board connected to the induced coil? I’m assuming that an AC current is being induced in the coil, which wouldn’t be able to charge the battery.

    • Rick Astley says:

      DC Power Supplies use step down transformers, rectifiers, filters, regulators.

      To charge a battery you just need a step down transformer and a full wave rectifier. A filter would be nice.

  14. roswellaliens says:

    lol.. i had this idea a few weeks back because my nokia el cheapo phone had a flaky unreliable charging connector.

    one thing that might work is some shapelock carefully formed into a copy of the unusable backplate, then if you want mix in some of that “Heat-it-Up” black pigment.

  15. D_ says:

    Rough finish, but a good proof the hack is functional. Personally I’d like to see drop in charging bases be made available. Inductive charging is far out, but I wouldn’t want my wallet with numerous magentic strips near them, and I like to keep my wallet where my check book, phone,keys HT, and pocket knife are kept by the door.

  16. stacyD says:

    Hello there bob,

    Actually there is a small circuit attached to the coil via an f-pcb. It is a relatively straight forward chip-based, surface mount circuit that they conveniently covered in black epoxy.

    I did the same thing to my EVO, although I did mine internally and with a PIXI backcover….guys you can pick up the PIXI back covered at many radioshacks right now for $6 with tax. I really should have bought more of them so that everything could be made inductive!

  17. Travis Deyle says:

    For people looking to understand the circuit, here’s a fair overview:

    http://www.hizook.com/blog/2008/10/07/wirelessly-powering-swarm-robots

  18. Curt says:

    Order a double capacity battery off of Ebay.. It comes with a plastic back that is a little deeper. Shouls accomodate the whole setup :)

  19. Simon Chester says:

    “He picked up a Pixi charging backplate meant for a Palm Pre”

    Shouldn’t that be:

    “He picked up an inductive charging backplate meant for a Palm Pre”?

  20. ansil says:

    you know i see this and i was wondering is the battery in this phone internal and not removable. cause otherwise why not buy another battery and just add this to the battery itself. i have about 50 different battery packs that all charge in different ways and built a diy charger for them very crudely. however when i saw afroman’s inductive article i was playing with my Lg Chocolate and did it to a separate battery.

  21. gripen40k says:

    @bob

    I built a super cheap wireless charger from pretty much scrap parts I had laying around. All it requires really is an oscillator and some caps.

    Check it out (sorry about the ible, need to move to a new site)

    http://www.instructables.com/id/Low-Power-Wireless-Charging/

  22. Mike says:

    “a Pixi charging backplate meant for a Palm Pre”
    No, it’s a Pixi charging backplate meant for a Palm Pixi. No Pre parts.

    Good work for adding inductive charging, but I would worry about that snagging that little dongle sticking out of the bottom. Even when you get a good plastic back, the cable part sticking out from the bottom will be your weakest link.

    @fartface: Palm did!

  23. djrussell says:

    @whatnot: my blackberry 8320 has that. the base is extra though.

  24. Jeff says:

    Can anyone help me out with figuring out what circuit is required to wire this directly to the battery so the plug does not have to stick out? I am attempting this on my Dell Streak.

    I know the phone wont recognize the charger by going this way, but I would expect I would need some form of power management so as not to overcharge the battery. Or is this already built into the Pre’s induction piggy-back circuitry with the coil?

    I would love to be able to internalize this in a simple way where I wouldn’t have to solder to the PDMI connector on the mainboard.

  25. FoxxCommand says:

    What would happen if he hooked up the + and – cords to the + and – terminals on the battery? could he use it like that

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