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I'd like to use a nice, thick otterbox defender style case, and keep wireless charging, but not shell out almost $100 for the actual otterbox defender case.

Those cases are sturdy and protect the phone well, but are typically too thick to charge wirelessly.

Here's what I'm wondering -

  1. do chargers with higher output (e.g. 30 watts) emit a stronger magnetic field? Does that translate to a larger field, as in one able to travel the additional 2 or 3 mm resulting from a thicker case?

  2. Would it help to put some very thin rings of ferrous material that matched the shape and dimensions of the transmitting and recieving coils in between the layers of the case? or perhaps a few other 'mini-coils' of copper wire like the ones in the charging pad and the phone itself? part of me guesses that they'd be induced into being temporary magnets and would, hopefully, be able to induce the next ring, and so on, until some portion of the original field actually reaches the receiving coil and induces a current.

Any other ideas? Thanks!

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Those cases are sturdy and protect the phone well, but are typically too thick to charge wirelessly.

Hm, theoretically Qi chargers are supposed to work up to 40mm coil-coil separation, if at reduced power, if I remember correctly[citation needed].

do chargers with higher output (e.g. 30 watts) emit a stronger magnetic field? Does that translate to a larger field, as in one able to travel the additional 2 or 3 mm resulting from a thicker case?

Possibly. Probably not enough to compensate the distance to the fourth power loss of transferable power through wireless charging. So, not a route I'd recommend.

Would it help to put some very thin rings of ferrous material that matched the shape and dimensions of the transmitting and recieving coils in between the layers of the case? or perhaps a few other 'mini-coils' of copper wire like the ones in the charging pad and the phone itself?

The ferrous metal almost certainly would be counter-productive (you don't want to heat up some iron, you want power to be transferred).

The coil idea might work, you might want to build a tuned circuit with a capacitor, if things still work out from a charger trying to determine whether there's actually a receiving coil (and not some much larger or smaller load) point of view. So, your mileage might vary, and you need to try.

Note that wireless charging (at least s usually seen in phones) happens with a complex handshake and control protocol – to avoid, for example, frying your Rolex the moment you put it on the charger on your nightstand. That might be smart enough or not to detect that there's some extra coil in between that's "dumb".

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  • \$\begingroup\$ Thanks. I think it's distance cubed, but I get the idea. I forgot that the receiving coil has to talk back to the transmitter, so it's not just a power issue, it's also a communication issue. \$\endgroup\$ Oct 23, 2023 at 5:26
  • \$\begingroup\$ That doesn't seem to make the tuned circuit idea any more likely, not that I would know how to do it. phone has max wireless charge of 7.5 W, chargers go up to 65w. 40mm sounds theoretical, guess I'll find out. FWIW 5mm is the largest gap I've heard. 'm going to try those old add-on qi receivers for iphone 8's IF nothing else works, I'm going to cut a hole in the back of my case big enough for the little magsafe things to poke through - as a woodworker, that's much more my speed. \$\endgroup\$ Oct 23, 2023 at 5:36

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