[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
RE: [TCML] Faraday Cage Safety
This interesting discussion has gotten me thinking of how to design a small coil where no conductive part would need to breach the wall of the cage. It would be a SSTC, the low voltage signal generator located outside the cage and then feeding through a fiber optic hookup (the fiber optic cable being the only item going through the cage wall) to a battery powered unit inside the cage.
I have yet to build a SSTC but have experimented with 555 timer chip astable circuits to make LEDs blink at different frequencies and duty cycles. Somewhere along the line I heard such a driver could control power flow from a couple of 6 volt lantern batteries to an older type auto ignition coil with an external condenser, and from there have the single terminal HV out charge the tank and then have the rest of the secondary and topload in the cage as well? I could even have the 555 signal be 50 or 60 Hz with a 50% duty cycle to simulate what AC would deliver, making the math for the rest of the coil design easier, then probably a cascade multiplier to step up the voltage to an IGBT - but then ignition coils are designed to run at 12 volts, so maybe I should try to increase the amperage instead? I have run an ignition coil by itself as described with 2 lantern batteries 6v each, a couple switches and a relay wired to act like a 'buzzer' (analog infinite loop).
Has anyone tried that full design as I describe? Parts of it? I might try it, but wonder if it would be worth attempting such a coil design, then if it works, to contain as much RF within a cage a possible, no back feed into the home power line etc, so any advice there is welcome (if the idea for an auto ignition coil as an HV source for a SSTC branches outside of the faraday cage discussion then feel free to change the subject line)
----------------------------------
Brian Hall
> Date: Mon, 12 Aug 2013 02:14:28 +0200
> Subject: Re: [TCML] Faraday Cage Safety
> From: susax2@xxxxxxxxx
> To: tesla@xxxxxxxxxx
>
> That's right, 2 different situations, one with a large coil and people
> who'd insist on the close up experience, the other with a small coil next
> to a computer.
> But my question is answered with the 1/10th wavelenght thumb rule.
> Thanks
>
> Mark
>
>
> 2013/8/12 dave pierson <dave_p@xxxxxxxxxxx>
>
> >
> >
> > > I've got some questions I was hoping you or someone else could answer
> > > about Faraday cages:
> > >
> > > What would be a safe mesh size to catch streamers from entering the
> > > cage?
> > Leaving?
> > Any reasonable _mesh_ from 1.5" 'chicken wire on down to
> > window screen. Or an array of bars.
> >
> > > More important would be, what mesh size should one use to have a
> > > Faraday cage that's effective to keep interference within?
> > Keeping RFI/EMI inside also depends on handling all
> > wire penetrations correctly: filters 'in' the
> > 'wall', 'bonded' to the wall. This becomes more
> > critical in dealing with the VHF range strays, rather
> > than the 20/50/100KHz/whatever 'fundamental'.
> >
> > Planning for some debug/test/rebuild time is
> > desirable..
> >
> > > I only presume it has got something to to with the wavelength
> > > of the emitting device?
> > Yep. The rule of thumb i was familiar with was openings
> > to be smaller than 1/10 the wavelength. This is simple
> > at the '50 KHz end', may take some attention at the VHF
> > stray end. A subtlety is that this measure applies to
> > the single longest dimension of an opening: picture
> > a solid copper room, with a solid copper door. close
> > the door and its still a 6 ft opening, unless some
> > bonding/finger stock is provided. (OK: likely
> > not relevant to most cases here.)
> >
> > best
> > dwp
> > _______________________________________________
> > Tesla mailing list
> > Tesla@xxxxxxxxxx
> > http://www.pupman.com/mailman/listinfo/tesla
> >
> _______________________________________________
> Tesla mailing list
> Tesla@xxxxxxxxxx
> http://www.pupman.com/mailman/listinfo/tesla
_______________________________________________
Tesla mailing list
Tesla@xxxxxxxxxx
http://www.pupman.com/mailman/listinfo/tesla