Faraday cage for cells with charging

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Faraday cage for cells with charging

Postby Aknz » July 27th, 2015, 5:58 pm

Hi all,

I've been building some different Faraday cages to put my phones in. They work well, but here's the tricky challenge; I want to be able to charge the phones while they're in there (they're always out of battery and it would be cool to charge them while they're having their 'time off' in the cage).
However, even in the most effective cages I've made, when I bring the charging cable in there in acts as an antenna and the cells recieve signals again. I know that's logic, but does anybody have an idea how to get electricity in there without breaking the cage? I mean, there are people who construct complete rooms as Faraday cages. I guess someone has tried (and maybe succeeded) to get power access in there as well…
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Re: Faraday cage for cells with charging

Postby k-ww » July 28th, 2015, 3:55 am

The faraday cage is for keeping out electromagnetic fields, not magnetic ones - try some of the wireless charging rigs.
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Re: Faraday cage for cells with charging

Postby asheets » July 30th, 2015, 1:40 pm

It is probably not a standard thing, but a company I worked with had a Faraday room for work with cell phone gear. It was really nice, and everything was copper or foil lined to minimize leakage. The innards of the room were powered by a huge Telco battery bank. Between testing cycles, we'd run a line from the outside through the access door to charge the batteries back up.
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Re: Faraday cage for cells with charging

Postby k-ww » July 30th, 2015, 2:01 pm

[kicking self] - I forgot that a Faraday cage would act like a 'shorted turn' to the wireless charging rig, and couple little or no energy.

I forget which post it was, but I remember suggesting a solar charging setup on the inside, and a quartz lamp on the outside of the Faraday cage.

Not too efficient, but if the cage is a wire mesh, it should let enough of the light thru.
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Re: Faraday cage for cells with charging

Postby st2000 » July 31st, 2015, 6:15 am

Are you doing this just to stop inbound calls?

FYI: Many phones can be turned off and the PMIC (Power Management Integrated Circuit) still works to charge the phone.

Regardless, I think you want a tempest room (https://en.wikipedia.org/wiki/Tempest_%28codename%29). Some place that you can go and work that is isolated. Which, I think, is way over kill for what you want. But does do what you want. Heavily filtered power lines. I think, for starters, I'd loop the USB charger cable through 1 or 2 ferrite beads. Maybe one just before and one just after the skin of your cage. That should attenuate high frequency radio signals to some extent. How much I'm not sure.

BTW: I'm second guessing what the phone's SW does. But if there is a small or no signal, the phone may step up its game and burn power searching for any signal.
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Re: Faraday cage for cells with charging

Postby jongscx » August 1st, 2015, 12:36 pm

I'm willing to bet the antenna is grounding through the USB cable. Isolate just the + and - wires so the usb cable shielding inside is isolated from the outside.

You may need to also extend the Data+ and Data- or your charge rate may be limited.
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Re: Faraday cage for cells with charging

Postby d-prinssi » June 16th, 2017, 8:19 am

jongscx wrote:I'm willing to bet the antenna is grounding through the USB cable. Isolate just the + and - wires so the usb cable shielding inside is isolated from the outside.

You may need to also extend the Data+ and Data- or your charge rate may be limited.


Could u explain this idea like I was five? Cheers!
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Re: Faraday cage for cells with charging

Postby void » July 13th, 2017, 8:36 am

d-prinssi wrote:Could u explain this idea like I was five? Cheers!


If I understand him correctly, what he is saying is this.

a standard USB cable has 4 wires in it. +5V, D+, D-, and Ground. the D+ and D- lines are the lines used for transmitting data. while the other 2 actually provide power. if you make a custom USB cable, you can omit or ground the data lines and the phone will still charge off of the power lines. I make power-only USB cables all the time for various projects, just pick up some microusb connectors (i use these ones https://www.amazon.com/gp/product/B00OK ... UTF8&psc=1) and then just take some 22 or 23 guage wire and solder it onto the appropriate pads on the connector. you can connect the lines directly to a 5 volt power supply (a cheap one that I like to use for my 5 volt needs is https://www.amazon.com/gp/product/B00DE ... UTF8&psc=1). then just make sure to connect the power supply's ground to the faraday cage. If for some reason you are still getting a trickle of signal through the +5V line, add a large capacitor between the 5V output on the power supply and the power supply's ground and that should eliminate it. if you are STILL having problems, replace the 22 guage wire with shielded coaxial cables, and connect the coax shielding to the faraday cage. By the way in this scenario, the power supply would be outside the faraday cage.
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