Wireless Mains Adapter-Frequency etc.?

[pwdrive]

I think we are digressing here, screened coils operating at RF eg: within a Faraday cage aren't a problem providing the cage is fit for purpose insofar that it contains the emission of both component fields.
My initial point was about transmittng RF between two points that are unscreened as a means of receiving meaningful amounts of energy wirelessly.

Lawrence.

[boiss]

I have seen a couple of tesla HV setups in action and many that are on the net, none of these has had any sort of faraday cage except maybe around someone who was part of the show. The musical setups must be very rich in IMPs.
I have made a test coil and once I power it up I will check out what it is radiating unloaded and loaded etc.
I wandered out in the street yesterday with my Sony 7600, the level of noise on LW and the low end of the MW was quite surprising. On SW the situation was somewhat better but there were still a lot of noises which I assume come from comms/PC equipment in the region below 5MHz.
I attach a pic of the coil, the centre section will be screened as this passes under the AF amp, the fact that the wires are all together in this area should also reduce radiation.
The underside of the coils can be magnetically screened and the battery cases also will act as a screen on the top side. I'm a bit worried about the effect of the shorted turn caused by the casing of the battery.
Mike

[boiss]

Knocked this up, It's a push-pull Hartley, had no joy with the Royer setups.
It's running at 82KHz, radiation on 2nd harmonic about 6mtrs on my Sony, 5th harmonic 2m, 10th <1m. I will compare it with a 500W PC supply tomorow.
I attach a pic of it running a 6V 3Watt bulb across 15mm of wood. the frequency of the Rx coil has not been optimized for resonance.
Mike.

[boiss]

One thing I noticed was that the Tx coil gets quite warm as does it's tuning caps,
polyester 2 x 0.33uFd. I will increase the number of turns on the Rx coil (14 at present) and reduce the C ( 2x 0.33uFd) and connect it to a bridge of schotky diodes to endeavour to get about 12V out to charge each battery.
Mike

[Nick]

Knocked this up, It's a push-pull Hartley, had no joy with the Royer setups.

Hmmm. The Royers can sometimes be tricky to start, but are normally very reliable.

Is this based on the 4HV thread? The heating effect may well be down to tuning...

[Skywave]

One thing I noticed was that the tuning caps., polyester 2 x 0.33uF., get quite warm.
Mike

Is that heat being absorbed by those caps. from an external heat source, or is it heat generated within the caps.?

Al.

[boiss]

Hi Gents,
No it wasn't from 4HV, I found it a while back. The problem is probably down to the coil form/layout, It just wouldn't start unless I reduced the gate biasing and then the waveform was very bad. I removed a few components so that it is a very simple Hartley and now it starts reliably and the output waveform is basically a sine wave.
I was a bit surprised with the heating of the caps, I had thought that the quality of them was quite good, they are rated at 600V and the frequency is quite low at 82KHz.
I can understand the coil getting hot as the wire is only 0.8mm dia.
Mike

[Skywave]

I was a bit surprised with the heating of the caps. I had thought that the quality of them was quite good; they are rated at 600 v. and the frequency is quite low at 82 kHz.
Mike

I see. So presumably the answer to my question is that the capacitors are being heated from within.
If you have the equipment, perhaps it's time to measure their E.S.R.

Al.

[boiss]

Hi Al,
I don't have anything to measure this, but I reckon you are right, it's to do with the internal resistance and the current flowing at resonance. There used to be a similar problem with the caps across TV LOPTs, they were around 10nFd but you couldn't fit any old cap. I would have liked a lower frequency but the cap value gets much bigger, 0.99uFd gave me about 60Khz, I'll have to dig around in all the old boxes I have knocking around to see if there is anything suitable to try.
Mike

[pwdrive]

Maybe polyprop instead of polyester?

Lawrence.