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Re: Double Throw Spark Gap (fwd)
---------- Forwarded message ----------
Date: Tue, 16 Oct 2007 07:47:20 -0700
From: Barton B. Anderson <bartb@xxxxxxxxxxxxxxxx>
To: Tesla list <tesla@xxxxxxxxxx>
Subject: Re: Double Throw Spark Gap (fwd)
Hi Steve,
I understand the large capacitance in the filter caps and stored energy.
My point is that the stored energy will be dissipated over time through
the gap and the only thing that will recharge the DC circuit is the
transformer. The transformer will be able to keep up with the DC current
requirements or it will not.
When you say the charging is not affected by the transformer, that is
partially true in that the storage caps are providing the charge to the
tank. But if the transformer cannot keep up, the storage cap(s) "will"
loose energy over time. There's no way around that except to find a
firing voltage in which the current required to achieve the rate of that
particular voltage is capable of the transformers ability or to stop
firing for a time to allow the recharge.
Take care,
Bart
Tesla list wrote:
> ---------- Forwarded message ----------
> Date: Mon, 15 Oct 2007 23:11:10 -0600
> From: S&JY <youngs@xxxxxxxxx>
> To: 'Tesla list' <tesla@xxxxxxxxxx>
> Subject: RE: Double Throw Spark Gap (fwd)
>
> Bart,
>
> What you are missing in your understanding is that the DC supply has a few
> microfarads worth of filter or "reservoir" capacitance which allows many
> amps of charging current in the couple hundred microseconds of electrode
> presentation. So the charging current is NOT limited by the transformer
> current. Basically, because of the filter caps, the impedance of the power
> supply is MUCH lower than that of the transformer.
>
> My DC charging current is 138 mA at 8.1 kV and 200 breaks per second which
> yielded 78 inch streamers. Because of resonant charging, the 8.1 KV charges
> the MMC up to nearly twice that.
>
> --Steve Y.
>
>
>
> -----Original Message-----
> From: Tesla list [mailto:tesla@xxxxxxxxxx]
> Sent: Saturday, October 13, 2007 11:51 AM
> To: tesla@xxxxxxxxxx
> Subject: Re: Double Throw Spark Gap (fwd)
>
>
> ---------- Forwarded message ----------
> Date: Fri, 12 Oct 2007 22:36:08 -0700
> From: Barton B. Anderson <bartb@xxxxxxxxxxxxxxxx>
> To: Tesla list <tesla@xxxxxxxxxx>
> Subject: Re: Double Throw Spark Gap (fwd)
>
> Hi Bert,
>
> I don't think so. Are you saying your going to charge a 20nF cap in 69us
> from a 12/30 NST source? (or am I misunderstanding your derivation?). I
> realize the charging inductors peak current is V/sqrt(L/C), but that
> does not account for the impedance of the transformer. You've got 360VA
> to play with and nothing you do in the charging circuit is going to
> change that. The charging inductor and cap will require time, and with a
> 12/30 is going to require a lot of time. In a typical 12/30 system, a
> 20nF cap will require 40ms to fully charge. The charging inductor is not
> going to change that "unless" you have a non-limited source of current
> (which you don't).
>
> If I understand this scheme correctly, the charging connection is
> limited by the dwell time of the electrodes. That adds considerable time
> to the situation (it's worse than a typical AC system). There's
> something else which complicates the charging mechanism. If the rpm is
> slow, the dwell time per electrode is extended (charge will reach
> voltage with less passes). Increase rpm, and it will take more passes to
> reach breakdown desired). But, here's the gotcha, typically RSG BPS is
> based on timing. In this case, the gap distance becomes critical with
> rpm. It's an odd thing to say the least.
>
> In Steve's case, he has a hefty transformer (14/250) at 3500VA. He's
> using 12 electrodes at 1850 rpm with a 50nF cap. His dwell time is 470us
> per electrode and 5.63ms per revolution. When you factor in the
> impedance of the transformer, full charge time is 64.3ms. This will
> require 11.4 revolutions to fully charge the cap. He's running at 370
> ppr, but if he was to actually fire at 30KVDC, the actual firing bps
> would only be 32 (by my calculation). He is likely firing at about
> 17KVDC which is in the low 100 bps range and likely brought about by gap
> distance, electrode edge surface, etc.). Gap distance is going to play a
> significant role in these SPDT gaps.
>
> In Chris's case, there's a huge difference (3,140 VA).
>
> Take care,
> Bart
>
>
>
> Tesla list wrote:
>
>> ---------- Forwarded message ----------
>> Date: Tue, 09 Oct 2007 23:10:39 -0500
>> From: Bert Hickman <bert.hickman@xxxxxxxxxx>
>> To: Tesla list <tesla@xxxxxxxxxx>
>> Subject: Re: Double Throw Spark Gap (fwd)
>>
>> Hi Adam,
>>
>> I suspect the tank cap will charge almost completely. Let's plug in some
>> reasonable "guesstimate" numbers and see...
>>
>> Chris didn't indicate the size of his tank cap, so let's take an
>> educated guess that it's 0.02 uF. We can always change this to the
>> actual cap size Chris is using later if necessary. The starting voltage
>> on the DC storage cap (when driven by a 12/30 NST and FWB rectifier)
>> will be about 17,000 volts. With a 25 mH charging choke, the resonant
>> charging frequency of the combination of the charging choke (Lc), tank
>> cap (Cp), and DC storage cap (Cs) will be about 7300 Hz. If allowed to
>> fully complete, the charging current will be a half sine wave lasting
>> for 1/2 cycle, or about 69 usec, peaking at about 14.5 amperes. For
>> complete resonant charging cycle, we must see a minimum effective dwell
>> time of about 69 usec in th charging gap.
>>
>> Now, when the charging gap initially fires, the rotating contacts are
>> approaching each other. Let's assume that the gap fires when the
>> approaching electrodes reach a minimum separation of 0.25", the gap
>> electrodes are 0.125" in diameter, and the DC charging current arc can
>> be drawn out at least another 0.375" before being extinguished. YMMV.
>> With these parameters, the estimated total distance over which the
>> charging current would be connected (via arcing) would be about 0.75".
>>
>> Let's further assume that the ARSG rotor speed is 3000 RPM, and the
>> electrode radius of rotation is 4" (8" diameter for electrode rotation).
>> The effective "dwell" angle is about 10.7 degrees, and at 3000 RPM this
>> translates to about 42 usec of total effective dwell time versus 69 usec
>> to fully charge the tank cap. Does this mean that the gap will
>> prematurely interrupt the charging cycle?
>>
>> I suspect the answer is - NO.
>>
>> Since the peak charging current is a robust 14.5 amps, I suspect that
>> (at least for the relatively short arc distances we're discussing) the
>> gap will be unable to interrupt the charging cycle until the charging
>> current has dropped significantly - perhaps down to an ampere or less.
>> Instead of prematurely terminating the charging cycle, I suspect that
>> we'll see trailing arcs in the gap that effectively "stretch out" the
>> dwell time so that the tank cap can achieve nearly 2 x Vsupply.
>>
>> It will be interesting to see the actual results that Chris sees... :^)
>>
>> Bert
>>
>> Tesla list wrote:
>>
>>
>>> ---------- Forwarded message ----------
>>> Date: Tue, 9 Oct 2007 03:46:42 -0700 (PDT)
>>> From: Yurtle Turtle <yurtle_t@xxxxxxxxx>
>>> To: tesla@xxxxxxxxxx
>>> Subject: Double Throw Spark Gap
>>>
>>> I haven't really been following this thread, so
>>> forgive me if this comment has already been addressed.
>>>
>>>
>>> Regarding the following circuit:
>>>
>>> http://tangent.cluenet.org/~chules/hv/tesla/dtsg.html
>>>
>>> Does everyone think the cap can charge adequately in
>>> the same amount of time it can discharge? Without
>>> doing the math, I gotta believe that if one set of
>>> flying electrodes zooms around at several hundred rpm,
>>> the presentation time for the charging portion will be
>>> too short to fully charge the cap. After all, most rsg
>>> coils are charging the whole time they aren't
>>> presenting (well not exactly). I guess you gotta know
>>> the dwell time and the size of the pig feeding this.
>>>
>>> Adam
>>>
>>>
>>>
>>>
>>>
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