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Re: SSSSTC Coil questions for Mr. Steve
Original poster: David Sharpe <sccr4us-at-erols-dot-com>
Hi Steve
Tesla list wrote:
> Original poster: "Steven Ward" <srward16-at-hotmail-dot-com>
>
> Okay Dave,
>
> Some of your ideas are a bit unclear, but i like the way you seem to
> envision much more which could be done with this design ;) I will answer
> what i can, and question what i dont understand.
>
> >I understand this now. A couple more power circuit questions:
> >1. What FET are you using?
<<SNIP>>
---------------------------------------
Thanks for FET info. Also, any idea what AC input current is on system
when developing 24" sparks (i.e. Power Input?)
---------------------------------------
> >2. What is size, type and voltage rating E storage cascade capacitors
> > are you using?
>
> They are 5uF 400VDC 40L G.E. polypropylene capacitors. High quality ones.
> So about .4j each at 400VDC (which i eventually plan on running the coil
> at). Now, we dont want these caps to discharge much at all on each cycle
> as i understand it... is this the correct way to think?
----------------------------------------------------------------
Yes, that is correct. What is your resonant frequency? If you know period
time, you could calculate a minimum capacitor value (minimal stored energy=
minimal capacitor package sizing) for a given allowable droop. I suspect
that even a 20% droop would have minimal impact in spark length...
I also simulated in Multisim a 3 stage setup with your current circuit
configuration with 1uF it worked as well. If you assume 100Khz, this
would be equivalent to 5 microsecond discharge time. If 10% of E
(40 millijoules) is removed in 5 us would be approximately 8kW (pk)
time number of stages (i.e. WAY oversized). BTW this would equal
about 20V drop across each cap during each discharge pulse.
-----------------------------------------------------------------
<<SNIP>>
>3. What blocking diode are you using (P/N, voltage current
fast recovery, etc.)?
>
> Hmm, im not sure which blocking diode your referring too. The only fet
> protection i have are the parallel ultrafast diodes. Here is the spec
> sheet for them:
>
> http://www.fairchildsemi-dot-com/ds/IS/ISL9R3060G2.pdf
>
> I also use them for the diodes that charge the capacitors for each stage.
> They seem like really nice diodes.
----------------------------------------------------------------
Sorry, you are correct, charging diodes are what I meant. Thanks.
---------------------------------------------------------------
<<SNIP>>
> >----------------------------------
> >Basically wind the primary ONLY on a ferrite toroid. Pass through the
> >window of the primary toroid a high current copper loop (1/8 to 1/4"
> >copper tubing is perfect). At each driver PCB have a toroid with number
> >of windings for each FET. Copper tubing would pass through each
> >of these FET drive toroids. The copper tubing makes a one turn loop
> >through the window of all the toroids. The GDT driver now drives the
> >entire high current loop, and thereby drives each driver board.
>
> WOW! I LOVE that idea! The only thing i worry about is the leakage
> inductance. I think it may be worth looking into. What about just making
> that copper loop THE primary? Though i suppose that would mean low voltage
> but very high current driving it. I doooo like the idea though, maybe i
> can test it out ;)
>
> >The advantage of this idea is one HUMONGOUS driver could drive 4X
> >as many drivers and they would be synchronized fairly well to each other.
> >This would simplify building the isolated gate transformers, and if the
> >copper tubing is passed through a thick wall PE tubing ( polyflow(R) )
> >through the interior of the toroid, very good HV standoff (perhaps
> >5kV or more) could be achieved, cheaply using off the shelf stuff
> >from Home Depot, Lowes, Wal-Mart, etc.
>
> Yeah. That would be exceptional isolation. Im still not convinced on the
> coupling and leakage inductance of such a design, ie, need to see it myself
> to believe it.
-------------------------------------
Yeak, 10-4 on leakage inductance. But if you have a large enough driver, and
low enough system frequency, shouldn't present that big a problem. OBTW
this is technique used to generate isolated control voltages for high power,
HV power converters, modulators, SG replacements, etc. So it is proven
technology (at least at 25-50kHz regime). LFSSTC gate control... IDK
but might be worth a shot, could greatly simplify making a truly modular
high power driver system... Big boys (Powerex, et al) are getting Vholdoff
of up to
50kV using this technique, and I've seen radar modulators capable of 100kV+
holdoff (oil immersed) using this technique.
--------------------------------------
> >-------------------------------------
> >Ok, imagine your circuit, but build a mirror image with bottom 4X drivers
> >tied to (-) power with neutral (+). Tie together at a terminal with two AC
> >caps. Repeat on other side of bridge. While one diagonal pair of drivers
> >are discharging (driving) the load, the opposite pair are charging the
caps,
> >Diagonal drivers swap, now vice versa diagonal pair is driving (in opposite
> >direction) while previous discharging drivers are now charging.
> >Vo-N = V*4stages *2 (+/- pk). So if you doubled number of existing
> >stages on your current design, voltage would be doubled (at load) but
> >each driver would still see 4X Vin stress; but most importantly 2X the
power.
> >Can sketch up a drawing a Excel to clarify. I also ran a manual switch
> >simulation in Multisim and it worked no problem... :^)
>
> I would really like to see a drawing of this. I just cant make it out in
> my head what you mean. I thought i WAS using an h-bridge, but i guess not?
> Please, drawing would be excellent.
------------------------------------------
Will try to post a simplified "switch stick" conceptual circuit on my nest on
Hotstreamer by
weekend... Your present circuit is working like a full bridge based on
simulation. By
modifying design by adding a +/- 170V PS and (-) charger/discharger you double
voltage (theoretically quadruple power) across load beyond your present
condition.
Negative is it takes double the parts and a bipolar power supply. On second
thought
might be better to use fractional transformer (much simpler) to get voltage
gain
versus
additional switch (and GDT) stages.
------------------------------------------
> I also dont understand how the drivers are seeing 4X Vin stress? Maybe i
> need to see your scheme to understand.
-------------------------------------------
Steve, sorry I was confusing. The voltage stress seen by each driver is
the same,
but
pk to pk voltage is 4X Vin. (based on circuit above)
-------------------------------------------
> > > >Another possibility is build a "voltage adder" circuit using multiples
> > of this
> > > >circuit to drive a driver transformer cascade. Imagine what could
be done
> > > >with 30-60kV pk going into base of resonator like a magnifier!
> > >
> > > Im not sure what a voltage adder is, example?
> >
> >Look up "Fractional Turn Transformer" in Google. Imagine 4 large identical
> >toroids. Wind 1 turn from you present driver (4 in parallel) around each
> >toroid.
> >Then wind 'X' turns around _ALL_ four toroids. Vo ~Vin * 4 * Xturns. Dunk
> >whole assembly in oil. Now what's limiting your drive output voltage?
> >This
> >technique is used for linear accelerators, and Klystron drivers. This
"drive"
> >transformer Vo could directly feed the base of the resonator.
>
> This is truly insane ;-) I DID look up fractional turn transformers and
> was blown away by the concept. Now my question. MUST they be toroids? OR
> would something like an oversized flyback core work? Perhaps if the gap was
> removed? I suppose even still ive been seeing large ferrite rings on ebay
> for not too much (in sets of 4). I really just cant imagine feeding the
> resonator so many kv! And the fractional turn transformer makes it...
> possible! The only thing im unsure of, is saturating the cores. Now, if i
> was to run some math on this, would i add up the dimentions for ALL 4 (or
> however many) cores together and say there is 1/4 turn on it? Or does it
> somehow still count as 1 full turn? I guess i need to think about it more,
> but the idea is really something else.
---------------------------------------
I suspect that ferrite ring(s) will be needed. I know Duane Bylund in early
90's built driver transformers using ferrites. With single turn on each
ferrite
(and dividing current by 4) you will _significantly_ reduce risk of saturation
since you are making the equivalent transformer "bigger", plus you are
going to be running at a fairly high frequency. It will probably be a
"build it and try it" situation. Watch for heating in ferrite rings, oil
cooling
is probably an excellent idea, not only for Vholdoff improvement.
Worse case, a slot will have to be cut in ferrite ring(s) to prevent
saturation.
---------------------------------------
> Dave! why arent you building some of these ideas! And if you have been,
> can i see?
>
------------------------------
Been working on several projects here trying to clear to way for some of these
ideas to be built... I'm contemplating how to "package" this system into a
truly
modular, expandable system. The more modular the system is, the lower the cost
to make (and expand).
--------------------------------
>Best Regards
> >Dave Sharpe, TCBOR/HEAS
> >Chesterfield, VA. USA
> >