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RE: [TCML] Coil V4 fail
Stephan,
I need to look through your figures and Richie's pages on this first, but I
think you will find that the formula Richie gives for the optimum C value
is based on an NST that has inbuilt inductance for leakage purposes, as
they don't need a ballast.
The 320nF is correct for the resonant value, but this assumes a static gap
where the cap (effectively) decides for itself at what point it discharges,
whereas with a rotary it is a different situation.
(Richie's, or anyone's, talk of optimum sizes, will of course always assume
the dwell angle of the RSG is capable of handling these sizes as well. The
geometry or size of yours suggests it will not however)
I'll get back to you
Phil
-----Original Message-----
From: tesla-bounces@xxxxxxxxxx [mailto:tesla-bounces@xxxxxxxxxx] On Behalf
Of Teslalabor
Sent: 19 October 2010 16:04
To: Tesla Coil Mailing List
Subject: Re: [TCML] Coil V4 fail
Hi Phil, David,
The way I came to the 240nF is by following design steps from Richie
Burnetts site. Firstly, I calculated the "matched capacitance" with C = I /
(2*pi*50Hz*U) where I is the short circuit current of the feeding PT's
(950mA) and U the open-voltage of them (9450 Volts). So I come accros
arround 320nF matched capacitance which would resonate at 50 Hertz.
Then, I used the formula Richie gives for optimal primary-capacitance:
C=150*(Cmatched / 200bps)
So I got 240nF.
And, when putting this 240nF and the ballast inductance reflected to the
secondary-side of the transformers (arround 31 Henry) into Richie's 200bps
simulation, I come along with 16kV equal bang size! When putting in 166nF,
then its 18kV bang size, only 2kV more. So from this side of view, the 240nF
should do the job?
Maybe my error is in the correct calculation of the ballast inductance?
The inductance of the ballast I calculated with: L = U / (2*pi*50Hz*I) and
multiplied this with 25^2 because the transformer ratio is 400V / 10000V = 1
: 25
I is the short circuit current through the ballast (23,85A measured) and U
the voltage I measure accros the ballast when the HV transformer is shorted
(U=380V). So when putting this values in the inductance equatation, I get
50,7mH, and this reflected to the secondary side of the HV transformer
(*25^2) is 31 Henrys...
Stefan
----- Original Message -----
From: "Phil Tuck" <phil@xxxxxxxxxxx>
To: "'Tesla Coil Mailing List'" <tesla@xxxxxxxxxx>
Sent: Monday, October 18, 2010 10:12 PM
Subject: RE: [TCML] Coil V4 fail
> Stephan,
> As has been pointed out your SRSG is just not quenching effectively. The
> size of the electrodes at 4mm for 10Kva is far too small. They need
> increasing to ideally 0.5 inch or 12 mm (As Dr R has said) and the heat
> sinking needs to be greatly increased on the stationary electrodes as
> well.
> Hot electrodes do not aid quenching, so yours are in definite trouble! I
> don't know what size your propeller gap is, but increasing the electrode
> diameter may also mean the dwell angle then suffers, in which case you may
> need a bigger RSG altogether: hopefully that won't apply. Big coils, big
> power, and big sparks mean big money as the peripherals soak up the cash.
>
> That drawback with propeller gaps is getting the large diameter rods in
> long
> enough lengths (if you are outside the USA); hence, the 13M type
> arrangement.
>
> In addition, your big cap is almost certainly not being fully charged,
> even
> with 950 mA available. I would have thought 150nF would be more than
> enough.
> Too big a cap, assuming it fully charges, will also affect the quenching
> as
> well. Other owners of coils your size will be better qualified on that
> point
> to comment maybe.
>
> The height of the secondary in relation to the primary sounds in the
> region
> of being 'normal' if there ever is such a thing.
> Put your coil into Bart's JAVATC and get the coupling figure from that.
> This
> will also tell you the best coupling figure to aim for as well. You can
> also
> play around with your primary turns in the program as well and this allows
> you to decide if you want to lower the coupling by raising the secondary,
> or
> removing an inner primary turn.
>
> There is also a lot of wood around that primary, so check you are not
> tracking anywhere. Wood is a next to useless as an insulator, varnished or
> otherwise. Tesla had no choice, but we do.
>
>
> Regards
> Phil
>
> www.hvtesla.com
>
>
> -----Original Message-----
> From: tesla-bounces@xxxxxxxxxx [mailto:tesla-bounces@xxxxxxxxxx] On Behalf
> Of Teslalabor
> Sent: 18 October 2010 15:22
> To: Tesla Coil Mailing List
> Subject: Re: [TCML] Coil V4 fail
>
> Hi,
> really no one has any thoughts about my new TC and its melting SRSG,
> because
> of its energy transfer problems?
>
> Here again two videos and the specs of the system:
>
> http://www.youtube.com/watch?v=3pUh3UVZdiE
>
> http://www.youtube.com/watch?v=Abr3rxYUH5o
>
> In my opinion the sparks should be far longer.
>
> Input: 0 - 400V 20A from variac
> Tank circuit: 4 PT's each 100V / 10000V. Connected in series on low
> voltage
> side and parallel on high voltage side. So if variac is on 100%, every PT
> gets 100V and delivers 10kV. They are ballastet on the LV side via a
> ballast
> inductor with air gap, so that the short circuit current without tank
> circuit is arround 950mA.
> Caps: 2 commercial BOSCH Pulse Caps each 25kV / 500nF in series, giving
> 50kV
> / 240nF measured.
> Gap: Propeller Gap:
>
> http://www.youtube.com/watch?v=O84SI50g0NY
>
> Secondary is 25cm diameter, 1,5m long
> and wound with 0,5mm wire + 0,4mm spacewinding.
>
> The following problems: I think the coupling is to tight. Actually the
> lower
> turn of the secondary is 3cm ABOVE the flat primary. When I put it lower,
> I
> get bad racing sparks on the secondary surface.
> Should I remove some inner turns of the primary, so that I can put the
> secondary lower? Would this prevent the racing sparks?
>
> Next possibility: Is 240nF to much capacitance in this TC? The matched
> capacitance for resonance at 50Hz are 318nF, so I actually run the system
> slightly STR. I have some more of the pulse caps.
> Should I put a third one in series? Then I would get 166nF tank
> capacitance.
>
> This would increase the bang voltage and so the bang size, of course I
> would
> have to change the firing of the SRSG some ms earlier. Would this decrease
> the gap losses and so solve the heating problem of the SRSG?
>
> Best Regards
> Stefan
>
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