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Re: A LUA file for BELA (a help to build electrostatic model of TC)



Original poster: Finn Hammer <f-h@xxxx>

Mike.

What you are writing is sweet music in my ears. Is it possible to access pictures, drawings or even samples s,ince I could save myself a lot of experimentation that way.
Even just a lead to that flexible rubbery potting material would be nice.

Cheers, Finn Hammer

Tesla list wrote:

Original poster: "Mike" <induction@xxxxxxxxxxx>

Hi Terry, List,
Well, if I am following this line of logic about tight / high coupling or LERT right for the DRSSTC, why are people not using the method that RF induction heating output RF transformers, very well proven, use. I can see where using an iron core is a problem on the RF units but using a copper sheet secondary works great. At starting frequencies of 450 kHz and down into the 150 kHz range, this system runs hundreds of kW all 3 shifts in the CW mode. So, in the DRSSTC, you could run it backwards. Your one turn copper sheet with slot becomes the primary and of course potted between the primary and secondary. We use, build and fix these things (when a line breaks outside and the water shorts it all out) so we sort of do what Finn is talking about, only we usually make the primary from tubing 18 through 8 turns on the inside of copper shell /secondary and the copper sheet with vertical slot, with connection block and water cooling, drives the 1 or 2 turn work coil for pipe welding, etc. Regardless if the machine is a tube or IGBT unit running in the 200 kHz range, the current is stepped up by the turns ratio and the voltage of course stepped down by that same ratio. The "secondary" can be from 4 inches high (two slightly spaced and stacked for a N:2 ratio) or 8 through 18 or more inches high, again of course with that slot to make two live ends. We even place a tab halfway on the sheet for earth ground connection. These are tightly coupled, 3/16 through 5/8 inch primary to secondary and all in the vacuum pumped potting rubber material. RF transformers work fine with the primary on the inside of the shell and they are also done with the primary on the outside, though this tends to make less room for the work coil connections, so it's usually inside. I've run them backwards before, works great. I've also dumped large HV caps into the 15 turn primary (tubing) and got a 15 fold current gain on the shell /copper sheet secondary. Also done it backwards, dumped a large HV cap into the one turn copper slotted "now backwards primary" and saw one impressive voltage gain off the 15 turns. Watching the discharge on a scope, even a cap dump had no rise time issues in the typical TC frequency range. I found the noise from the 25 kV 100 MFD (pulse rated) cap spark gap less than desirable but the RF transformer, a stock commercial shell in the 300 kW class, worked fine. So, why can't you use this wide one or two turn sheet as your DRSSTC tightly coupled primary?
Can't get much tighter than that.
Scoped ring time through the transformer was about the same as a shorted to cap body spark gap shot though I think the ~ 31,225 J blast harsh on the ears. So why can't an IGBT in TC service pump such a wide and tight coupled primary, after all, IGBT's do it all the time in induction machines, just driven CW Vs pulse.
Normal or backwards, a transformer is a transformer.
Mike


----- Original Message ----- From: "Tesla list" <tesla@xxxxxxxxxx>
To: <tesla@xxxxxxxxxx>
Sent: Friday, December 16, 2005 9:39 PM
Subject: Re: A LUA file for BELA (a help to build electrostatic model of TC)


Original poster: Terry Fritz <vardin@xxxxxxxxxxxxxxxxxxxxxxx>

Hi DC,

They are trying to get high coupling with DRSSTCs to reduce the number of cycles and thus time it takes to bring the secondary voltage up. This helps to decrease the load on the IGBTs and gets a better LERT.

LERT is Load Energy Rise Time. The DRSSTC folks have found that there is an optimal time to energized the secondary to get the best sparks. This time is fairly fast and demands a higher coupling.

ScanTesla (the computer program) says that coupling otherwise does not matter too much and couplings like 0.13 might be just fine. But that is before this fast rise time effect is taken into account. ScanTesla can calculate LERT, but it does not really judge what is good or bad. LERT is a little to unknown right now to make "equations" but it seems to be a real important thing.

LERT might also be why coils with low surge impedance seem to do well. We really don't know right now what it all means...

Cheers,

        Terry

At 02:47 PM 12/16/2005, you wrote:


Has anyone tried purposefully reducing the coupling to see the results? I'm not sure why you need the increase the coupling so much more than for classic TCs. Some experiments along these lines might produce interesting results.

Dr. Resonance



<snip

<You don't really need to do heavy electrostatic analysis or differential equations to <get it right the first time!!

<snip

DC,

Your approach to Tesla Coil Design is fine for conventional disruptive coils. I have been here 8 years now, and have gained enough experience to acnowledge that. However, the electrostatic analysis i am playing with, is aimed at the new breed of coils.

The DRSSTC`s.

Those of us that have built this type of coil can witness to the fact, that flashovers from secondary to primary still is a limiting factor with these coils.

In an attempt to solve this problem, I have tried to add increasing amounts of dielectric in the space btwn. the 2 coils, only to observe that the problem got worse.
.......