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Re: Current in the Coil - was oil dielectric
Original poster: "Malcolm Watts by way of Terry Fritz <twftesla-at-qwest-dot-net>" <m.j.watts-at-massey.ac.nz>
On 15 May 2002, at 11:48, Tesla list wrote:
> Original poster: "David Thomson by way of Terry Fritz
> Hi Malcolm,
> >Agreed about the heating caused by current, but the current flowing in the
> wires of an air-cored transformer can easily be in the tens of Amperes
> range. Depends how much energy you feed in doesn't it? There must be few
> Tesla Coils out there with a milliamp or less flowing in their windings at
> some point or another.
> The transformer I'm using is a 15KV NST at 30mA short circuit. The
> transformer is rated for 250 watts. If I'm getting the full 15KV and the
> power output does not exceed 250 watts, then the average operating current
> can only be 16.7mA. If the primary has only 16.7mA, then with the 50 feet
> primary and 2000 feet secondary I should have a rough 1:40 step up ratio.
> At 600KV the secondary will have an average current of about .4mA. Even a
> power supply of 1000 watts will only output about an average 1.6mA in the
An average, yes. And it is the RMS current that causes the heating.
But the argument presented overlooks the fact that the duty cycle in
a disruptive coil is only a few percent at best. Most of the time
between gap fires, the coil is silent. People who press a secondary
which was previously used in disruptive running into CW running will
note some heating in that part of the coil carrying the highest
circulating currents. The peak currents aren't any higher but the RMS
currents are (in other words, the peak currents are occurring on a
sustained basis). I can state with confidence that none of the coils
I have built right down to the smallest have peak currents lower than
a milliamp and most currents are far higher. It is also of note that
current at the base is not the highest - it occurs some way along the
resonator. None of this is saying that resonator current is uniform
(which it is not) but the bulk of the windings will have considerable
currents flowing in them.
The secondary peak currents bear a relation to transformer
current that is at best, weak. The energy coming in from the power
transformer is stored in a capacitor prior to being delivered to the
For an example of a small coil which has secondary currents
exceeding 1mA (considerably so in fact) I refer you to the tssp
website which graphs current and voltage profiles for one such coil.
The modelling has been verified by measurement and has yet to be
demonstrated to be in error (unlike a plethora of past popular
theories whose non-conformity with both measurement and reason
aroused suspicions as to their veracity - in fact gave birth and
impetus to this wonderful project). These things need be mysterious
> Keep in mind that my coil has a flat spiral winding in the bottom quarter of
> the secondary. Flat spiral coils can handle tremendous current loads with
> no heating to the windings, transformer, capacitors, or spark gap. By the
> time the electrical energy is in the solenoid and getting its voltage
> increase, the current is not high enough to do any heating. Hence the coil
> runs cool even without being jacketed in oil.
> The reason for the oil jacket is to keep the voltage in the coil, which it
> does to perfection. This system is state of the art as far as efficiency
> goes. The problem I'm having is that the coil is so efficient that when
> tuned to output streamers, the streamers break out evenly over the surface
> of the terminal, instead of as one long streamer. So instead of getting one
> 8 feet streamer, I'm getting 8 one foot streamers. When the system is tuned
> to perfect resonance, there is no spark coming off the terminal even with
> all the top load removed. But the EMF field is very strong and tubes light
> bright 5 to 8 feet from the secondary.
> Another noticeable effect of resonance with a jacketed coil is that there is
> a very intense electrostatic field around the solenoid. It's almost like
> touching a wall of electricity about one foot out from the coil form.
> Point me to a Tesla coil that claims tens of amperes in the secondary. I'd
> like to check it out. I'm sure that's just the peak current near the base
> of the coil, but even still that's pretty high and would require a fairly
> large system. I don't think that is what Paul was intending to build.
> In my opinion, every serious coiler needs to build at least one oil jacketed
> coil. They're not that difficult and the rewards are better sparks.