Re: [TCML] Thumper, the worlds most advanced tesla coil.

[Michael Twieg <mdt24@xxxxxxxx>]

Thanks for the link, it was a really good read.  The mechanical design of
the tuning is incredible.  In a design I'm currently testing, I'm
implementing a phase lead using an all pass filter (can be tuned with a
potentiometer), so we should be able to get the same results as adding a
series inductor with the burden resistor.  However, I've had some issues
getting it working properly.  Our control scheme has two current
transformers on the primary, one of which is burdened with a resistor (for
measuring current) and the other is burdened with clamping diodes (only for
zero-crossing detection).  When detecting the clamped-diode crossings, the
thing works fine, but when I try to have it trigger off of the burden
resistor waveform, it always starts oscillating at a very high frequency,
causing everything to freak out (not fatally, though).

I'm almost certain that it's due to the emi from the bridge transitions
coupling back into the circuitry and fooling it into thinking a zero
crossing has happened. Thing is, I've already shielded the electronics
pretty well, and my PCB layout was meticulously designed to prevent this, so
I'm having trouble getting around this issue.  Did you have any issues with
preventing false zero-crossing detection in your circuit?  It doesn't look
like you used any hysteresis on your comparator.

-Mike

On Tue, Jun 8, 2010 at 4:37 AM, Finn Hammer <f-h@xxxx> wrote:

> On Tue, 08 Jun 2010 06:03:24 +0200, Michael Twieg <mdt24@xxxxxxxx> wrote:
>
>  Looks excellent!  For the predikter driver, did you just put a phase lead
>> on
>> the current waveform prior to zero-crossing detection?  Or did you do a
>> more
>> sophisticated method, maybe with PLLs?
>>
>> And how do you vary the tapping on the primary?  Brush contacts?
>>
>> -Mike
>>
>>
> Mike,
>
> Sometimes keeping it simple is the key to success, so an inductor in series
> with the burden resistor did the trick.
> With regard to the tapping, you really should go to 4HV for full details of
> a custom 5kA spring loaded Brush trolley riding the primary.
>
> The Predikter driver and the rest of the coil build is generously text and
> photo documented on 4HV.org.
>
> With 142 posts as of now, and with constructive input from Coiling Experts
> like Steve Conner, Richie Burnett, Steve Ward, Aron Koscho, Chris Hooper and
> many others, It is a very good read.
>
> Go spend some time here:
> http://4hv.org/e107_plugins/forum/forum_viewtopic.php?68820
> The whole story is there, It is like a manual, you could build your own
> from it! And I invite you all to plagiarize from it, I would feel honoured
> if you went and did.
>
>
> Cheers, Finn Hammer
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>
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