faraday cage leakage

I am trying to charge my device in a faraday cage. The cage works well without the cord plugged into the device. When I have it plugged into the charge cord radio waves penetrate the cage. Do the waves travel through the cord? Any suggestions allowing me to charge and prevent waves at the same time?

Reply to
Scotty
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Your tinfoil hat needs polishing. Assuming you're in the northern hemisphere, do be sure to polish counterclockwise, or you'll suffer gravitational collapse due to mismatched Coriolis tensors.

Or are you trying to do something reasonable? If so, please explain.

Cheers

Phil Hobbs

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Dr Philip C D Hobbs 
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Reply to
Phil Hobbs

Any idea of the frequencies you want to keep out? There are all sorts of RFI filters. (L/C pi or Tee's mostly.)

George H.

Reply to
George Herold

What manner of "device"? A cell phone?

Yes. The charger cord makes a tolerable antenna.

Add a clamp on ferrite bead over the cable at the point of entry.

I can't offer a specific material recommendation because you didn't offer any clues as to the frequencies of interest. This mighth help:

If that doesn't do it, use two feed through capacitors and ferrite beads, one for each lead.

For more detail, look at how some of these RF shielded boxes work:

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Jeff Liebermann     jeffl@cruzio.com 
150 Felker St #D    http://www.LearnByDestroying.com 
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Reply to
Jeff Liebermann

If the cord is going into the cage then yes, it could be conducting radio- frequency energy in -- basically acting as a combined antenna/ transmission line.

What are you trying to do? We can give more concrete help if you give more concrete information.

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www.wescottdesign.com
Reply to
Tim Wescott

If your device can be charged via USB: Charge a 12 V sealed lead-acid battery outside the cage. Then put that battery inside the cage with your device and a "cigarette lighter plug to USB power" adapter.

Depending on the capacity of the battery built into your device, you can probably charge your device from 1 to 5 times before the sealed lead-acid battery needs recharging.

This is not the most efficient process in the world, but that doesn't seem to be a primary concern.

Matt Roberds

Reply to
mroberds

If your 'device' does DC/DC conversion on the input power, it's oscillating during charging. It isn't clear 'radio waves' are penetrating the cage, your charge circuit inside the target device could be generating the RFI.

Reply to
whit3rd

What battery (batteries?) does your device use and how easy is it to change the battery? If it is easy, why not buy a spare set and charge that. Then just replace the battery when the original runs low. Then charge that, and replace the spare battery, etc.

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Jeff
Reply to
Jeff Layman

On a sunny day (Thu, 09 Apr 2015 01:37:02 +0000) it happened Scotty wrote in :

If the charger itself is _in_ the cage, then all bets are off, as the thing will generate RF at the switching frequency and its harmonics, plus the rattle from the mains rectifier, plus what comes in via the main lead.

If the charger is _outside_ the case, note that the DC from a charger is by now way clean, and due to that silly Y cap or whatever it is called any RF on the mains is also passed to the DC side.

In that case:

----------------- | | |C | + -- L-===-- + | | battery | - ------0--- - | | | | | ---------------- cage

'C' is a feedthrough capacitor. You may need several LC sections in the + before the feedthrough cap. If you want to keep '-' insulated from the cage, then you need a similar filter and feedthrough cap in the -.

An other way is to have a huge light bulb outside, and a solar penal inside the cage...

I'm sure there are other ways too....

Reply to
Jan Panteltje

If your goal is to prevent Apple from downloading new sw into Your device against your wishes while it is charging. The easier Why is to put two entries into the hosts table of your router to Map the server sites to dead ends.

I don't have the deails handy right now, but you can prob Google it.

Mark

Reply to
makolber

Good one Phil. ;) Based on his lack of response, I think he may have got his Coriolis tensors in a bunch.

Hey OP, Try wrapping your charging cable around one of these a few turns and let us know how it works.

formatting link

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ChesterW 
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Reply to
ChesterW

Ideal: sharge from a secondary battery (eg load-acid) iside the cage, charge, or swap, the battery between experiments.

almost as good: charge from a dynomotor with a shaft or belt that penerates the cage.

probably good enough: fit chokes to the feed wire near where it penetrates the cage

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umop apisdn
Reply to
Jasen Betts

on 11/04/2015, Jasen Betts supposed :

For a good cage the belt hole will let enough leakage in.

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John G Sydney.
Reply to
John G

Looks like we chased the OP away.

Though badly worded, his question is not unreasonable. My guess(tm) is that he's using an RF shielded enclosure to work on some radio device in the presence of strong on-frequency signals. This is a common problem while trying to tune or test transceivers, cell phones, and broadband hardware. The signal from nearby transmitters can be stronger than the test source without really good shielding. The usual practice is to shield part of the building, but that's often not practical, especially for small repair stations.

RF shielded enclosures come in various shapes and sizes:

Power to the device under test is usually supplied through RF filtered feed throughs. My guess(tm) is that his RF shielded enclosure isn't wired for whatever power he needs, or that there are too many possible charging sources (117VAC, 12V, 5V USB) needed. Running the power cables through the door or cable entry is going to leak RF and won't work.

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Jeff Liebermann     jeffl@cruzio.com 
150 Felker St #D    http://www.LearnByDestroying.com 
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Reply to
Jeff Liebermann

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