Re: tesla coil power ?! (fwd)

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Original poster: Steven Roys <sroys@xxxxxxxxxx>



---------- Forwarded message ----------
Date: Wed, 26 Sep 2007 13:23:54 +1200
From: m.j.watts@xxxxxxxxxxxx
To: High Voltage list <hvlist@xxxxxxxxxx>
Subject: Re: tesla coil power ?! (fwd)

HI Chris,

> Date: Sat, 22 Sep 2007 12:23:59 +0100
> From: Chris Swinson <list@xxxxxxxxxxxxxxxxxxxxxxxxx>
> To: High Voltage list <hvlist@xxxxxxxxxx>
> Subject: tesla coil power ?!
> 
> Hi all,
> 
> After messing around with many coils, I found that some of my secondary 
> coils were sparking when near my tesla coil in operation. After some 
> tinkering about I managed to light up 3 100watt lamps from 3 secondary coils 
> placed about 1 meter away from the tesla coil. The lamps did not dim as each 
> one was lite so appears to be a fair amount of RF radiated there.

How were they positioned relative to the transmitting coil? Equally spaced around 
it? You can demonstrate the effects of directors such as you find on yagi 
antennae by placing receiving coils in a line. I did that using a metal bench as a 
ground plane (a long time ago).
 
> Though trying not to get shot down here, but it was only a 500w tesla coil 
> in the first place, I did not have enough room to physically place anymore 
> secondary coils there but this suggests that 3 more coils would output 
> 600watts ?!

Have you measured the actual input and output power of your transmitter or are 
you going on transformer faceplate ratings? Beware of non-sinusoidal waveforms 
messing up readings on multimeters.
 
> I spent a while lot of time crunching this , even with low power testing on 
> 12V coils. From what I can work out, from a transmitter coil to the receiver 
> coils there seems to be over 90% loss in voltage. However moving the 
> receiver coils closer to the transmitter starts to drag down the voltage, 
> though does not seem to effect it more than 1% or so. Moving further away 
> the voltage drops but the 100watt lamps remain lite until all of a suddon 
> the lamps just go out just over about 2meters.
> 
> Even though I can't measure the voltages, I would guess that 10KV impressed 
> upon the receiver coils would have to have 10mA of current, for 0.01A x 
> 10,000 = 100watts. If we take the transmitter power as 100,000volts then we 
> have lost like 90% of the voltage. So this must mean 90% loss ? on this 
> basis the transmitter would have to output 90times higher the wattage ?!  if 
> we have 10,000watts and loose 90% then we only obtain a few watts output 
> kind of thing.

Since the above is based on speculation rather than measurement I think few 
conclusions can be reasonably drawn.
 
> Further to the problem, adding 2 more receiver coils does not seem to effect 
> anything. If power must divide between coils like a regular transformer then 
> the wattage on the transmitter would be near unthinkable.

Some real measurements will show where the truth lies. Using the brilliance of 
lightbulbs as a measure is a rather dubious proposition. It is a very popular 
technique on Keelynet-type expts. 
 
> Going to a small 12V test. I can obtain about 0.1V output per receiver, 
> actually this supports my post on plasma globe power also. where you can 
> draw about 0.1mA per receiver but only the first receiver coil drops the 
> voltage on the antenna. Adding more coils has no effect on the transmission 
> voltage.
> 
> Going back to the tesla coil testing again, each time you actually add a 
> receiver coil, you would assume it would shunt the transmission , like a 
> faraday cage. Though it actually boosts the transmission "range" by about 
> 25%.

An unloaded resonator has a high Q. If you place one some distance away from 
the transmitter and then pop another in between the two you increase the couple 
of the transmitter to the first.

> The problem is with these results is the more receiver coils you add, the 
> stronger the transmission actually seems to get. Running 2 coils side by 
> side or any point around the transmitter has no effect on anything ?!
> 
> If there was 50% coupling to the transmitter then once the second 100watt 
> lamp was added the first one would dim, but it does not. As the voltage has 
> lost like 90% over the distance, then even 10% coupling over 2 receiver 
> coils is 30% loss overall, but the lamps did not dim.
> 
> I then obtained some X-ray machine diodes, had to have a long talk to their 
> sales guy first though :-(  Special HV HF diodes so I could convert the 
> 250khz AC to DC. I could run window wider motors there no problems. I then 
> also charged up a range of capacitors, much like my plasma globe tests. I 
> can't remember the values now, but after I crunched the numbers there would 
> have to be 100watts to charge the capacitor to a voltage over 20 seconds. I 
> got these figures verified by some people on the electronics forum and 
> several electronics engineers at the company I used to work with. So the 
> 100watts power seems to be real.
> 
> I ran out of space and funds so I could not try anything further :-(  Even 
> so 500watts input and 300watts output does not seem very exciting. Though it 
> makes me wonder how many coils could be powered in this way. As more coils 
> increase the transmission range then it seems to suggest the more coils 
> added , the more efficient the system becomes.
> 
> I plotted whole charts of data and gave up. In fact if you assume 10mA is 
> the baseline current figure then 10mA at 100KV is a lot of wattage. If the 
> receiver coils were coupled enough to obtain power then the lamps would dim 
> each time one was added. Though if the coupling is only like 1% then you 
> could have 10 receiver coils which would load in a way to output 90watts per 
> coil, which is 900watts x 10coils = 900watts. The problem is I was in 2minds 
> about posting this to the list, as it implies 900watts output with only 
> 500watts input.
> 
> I latter reversed the testing and ran on 250watts power. With this setup I 
> could  only light up 25watt lamps at best. So as the input was cut down by 
> 50% the output wattage was cut down by 4times. On this basis, if I increase 
> to 1KW input, then I would obtain 4times the output wattage.  Also 4times 
> the output also increases the range. I had problems with the 250watt system 
> as the receiver coils were coupling to the transmitter coil and causing it 
> to go off tune which messed everything up.
> 
> It is hard to work out what is going on here. has anyone here done anything 
> along these lines before ? I know Richie lite up I think a 25watt lamp via 
> RF, 2 people holding it at one of the Corby events I think. Though that was 
> a "untuned" setup. If you run the lamp between 2 toriods, one in the 
> "transmission range" and one outside (3 meters away) then you can light up 
> 25watt lamps. Though it works a lot better to ground one end of the lamps 
> and obtain 100watts output instead.

These are quite common little demonstrations of e.m. coupling. Recently some 
prof somewhere hit the headlines with a suggestion that HF RF could be use to 
wirelessly charge cellphone batteries etc. as though it were something new. I 
guess he forgot or never knew about Tesla. It was all near-field stuff as in fact my 
use of a local radio station to power a bank of LEDs in my study is. 
 
> I wonder if there is  a sub resonance between the transmitter and receiver 
> coils which is the reason the transmission range is increased. Placing 2 
> coils side by side is hard to work with due to the high voltage involved. It 
> was unclear if the lamps were brighter with 2 coils next to each other. 
> Though either way it seemed to have little effect.
> 
> Taking things a little further. I built a larger primary coil and placed 3 
> secondary coils inside. Each coil gave some good output , though I forgot to 
> document the results, but seemed to work very well for powering multiple 
> secondary's within the primary. Arcing between coils made testing very 
> problematic anyway.
> 
> If the transmitter is not coupled and has all these losses, then the 
> transmitter is not being loaded ? if so it would mean we could obtain 
> 100watts almost unlimited times ?!

Does that seem reasonable? An unloaded (uncoupled-to-load) transmitter should 
have few losses shouldn't it?
 
> I did some 12V testing again, over 15cm there was like 99% loss. Though 
> using a 1K resistance and measuring the voltage, I could obtain there was 
> about 0.2mA of current at about 0.1V. This was without a transmitter coil. 
> Actually I just ran a meter of wire from my signal generator and it 
> increased efficiency about 4 times.  I don't know how much current was 
> involved, but there was nothing connected to the signal generator other than 
> the cable. Each coil at 99% loss did not appear to load the antenna. At 
> least he voltage never dropped. Well it did a fraction but was so small was 
> not much. In anycase adding more coils did not appear to drain the voltage 
> any further.
> 
> While 0.1V is uninteresting at fractions of a milliamp, however at 1million 
> volts 0.1mA is 1KW. As my 100watt tests appear to operate at 10mA then as 
> the voltage increases then so does the amps. I plotted in that each time the 
> voltage doubled the wattage output would go up by a factor of 4.  In 
> anycase, it would seem at least 100KV is needed to obtain any sort of 
> results. Anything below 100KV you have to move closer to the transmitter to 
> obtain any power. Though anything closer than 1 meter starts to become a 
> real problem for many reasons. Though it appears to me that the arcing and 
> de-tuning are the main factors, not so much a drop in transmission power.
> 
> In fact if you move one coil  as close as you can get without the system 
> going out of tune, you can easily blow 100watts lamps. I had a box full of 
> blown lamps at the end of the week. Good thing is though they glow purple 
> when burnt out :-D
> 
> All being said and done, that's all the facts and figures in a "overview" 
> kind of way.  Figures are the best I can come up with to fit the results. 
> They could be totally wrong though even so I can light up 300watts worth of 
> lamps form my tesla coil. The interesting test would have been to add 3 more 
> coils, but something I just could not do unfortunately. So reason why I 
> posted my results to see if anyone else had done anything interesting along 
> these lines before ?

I think you should arrange things so you can take the expt. further. It hardly 
seems a satisfactory conclusion is reached when stopping at this point.

Malcolm