[NewCandle] Schlicher 'drive'

[Keith Nagel]

Hi Kyle + John,

While FETs are great, they get pretty pricey when you are
trying to control large currents. The situation is somewhat
improved with IGBTs, but still you're talking about a
bit of cash ( but a good investment all the same ). SCR's
are the cheapest thing for the job, and for relatively
slow risetimes like what we have been discussing more than
adequate for the task.

Which brings us to your problem, getting them to turn off.
The trick here is to design the circuit around the SCR.
There are two issues here. First, your gate drive pulse
must be >10 times shorter than your power pulse duration.
This ensures that the gate is off when the time comes
to extinguish the SCR. Second, your power pulse voltage must
be near zero, or better, reversed. To achieve this, we
design the capacitor and the load resistor so that we
have either critical damping or underdamping.

So let's put some numbers to this. You tell me how long the
pulse needs to be, and I'll tell you what value cap you'll
need and how much resistance in the total circuit will
critically dampen it. That resistance value will only be
a guide, because at these currents the distributed resistance
of the antenna and the rest of the output circuit will be
substantial. I use a special low resistance meter to measure
such circuits, not sure how you're set for such things but
I'm guessing not? An ordinary multimeter _might_ be used
but most of the units I have seen only go to .1 ohm and
that's not very useful. Perhaps you can hit up the local
uni's ( U of R. or my old haunt RIT might be able to help )
or prevail upon some other local source for the meter.

Additionally, we have the inductance of the antenna.
This is what will cause the voltage to reverse if we
get below critical damping on the resistance. It's clear
a lot of the antenna design was intended to minimize both
parameters, which is a good thing, and I'm guessing we
won't need a ballast resistor at all so long as we
choose our cap wisely.

As concerns the capacitor, and oil filled cap would
be best suited for the application. Often these can be found in surplus or
at ham fests ( big one up in your area every summer, keep
an eye out for that ). Polycarbonate caps could also be used,
it makes sense to buy a lot of small units ( say .2 microfarad
@ 1KV ) and gang them up to get larger values of capacity
or voltage. You mentioned electrolytics; we _might_ be able
to use these, but again, you risk destroying that cap if
our inductance is too high and damping resistance is too
low. But given the cost, they're the cheapest solution and
I'm guessing you'll want to go with that. Best to spend
what money you have available on the switching circuit.
Try ebay for the SCRs, often those hockey puck kinds are
available at reasonable prices. For this application,
a _small_ capacity electrolytic will be preferrable to
a large one. The ones you mention are maybe too big for
what we are considering, but I'll know when you spec the
pulse width.

I'll post a bit later with a pic of what a typical SCR switch
looks like, along with a circuit diagram. It may take some time
as I have neither pic nor diagram at hand, but all my stuff is
unpacked now so at least the kit is at hand.

K.


-----Original Message-----
From: newcandle-bounces at ipdiscover.com
[mailto:newcandle-bounces at ipdiscover.com]On Behalf Of Kyle R. Mcallister
Sent: Tuesday, September 30, 2008 6:28 PM
To: New energy for the new world.
Subject: Re: [NewCandle] Schlicher 'drive'


Keith Nagel wrote:
> Hi Kyle,
> 
> Firstly, thanks for sharing the pics of John S.'s thruster! 

Not a problem. I enjoy this stuff very much, and am happy to contribute 
if I can.

> We all miss John S, he was quite a unique character and I for one
> had many a fine correspondence with him over the years. 

He was a very good person to speak with on scientific matters, and above 
that, a very close friend. I put science aside for nearly a year, after 
his death, as it was simply to painful to go through. It brought back 
memories. I devoted my time to writing science fiction (of which, even 
though I'm back in the saddle scientifically, I'm still writing).
But now, between the writing and 'real life', I'm ready to heat the 
soldering iron back up.

> On to the antenna. I agree with John Steck that the structure looks
> kind of floppy and with high current pulses there may be some
> shifting and distortion of the conductors. I have noticed from
> my work with high power pulse driven inductors that the most
> stable geometry is a loop. In a loop, the forces are such that
> the vector is always pointing from the center out, so failure
> causes the loop to burst. If the loop is compressed ( limiting
> condition being a straight line of conductor ) the forces
> will tend to act to press the broad sides out to form
> a circular loop. Another way to look at this is
> that the magnetic forces are always acting in such a way
> as to maximize inductance.

This is actually discussed in the patent; high currents can deform or 
burst a given antenna geometry.

> All that said, this is a big circuit, and with
> ~1000 amps those mechanical forces will likely be small.
> Hopefully small enough that you don't have mechanical
> knocking when the pulse hits.

I actually never noticed much, now that I think about it, even when 
doing make and break with a car battery. Of course, I *was* keeping a 
close eye on that battery, so I might have missed any slight twitching 
of the antenna wires. I did look carefully for thrust, and didn't see 
any deflection of the antenna, when held as a pendulum, however. John 
did say this wasn't a very good way to drive it.

> As you point out, the prism shaped inner conductors are the
> thing that most differentiates Johns circuit from the NASA
> replication. The patent only mentions them in the section
> on cryogenic conductors, yet the text indicates that these
> would be important for any implementation. Not critical, but
> clearly important, if the eddy currents do indeed help
> cancel the back reacting forces. If this circuit did work,
> then the null circuit would best be an identical copy without
> those elements. Removing the elements is the easiest thing, but
> I understand your reluctance to mess with something, especially
> if you get it to work! We'll cross that bridge when we come to it.

I'm not entirely clear myself as to exactly how they do what they are 
supposed to do. There is also a 'ferromagnetic flux nozzle' in the 
patent, which is not present in any real-life implementation of this 
thing, as far as I know. John's doesn't have one. I asked John about it, 
and he simply said that he didn't agree with Schlicher's theory about 
how the device works. Only that it did work. I guess he didn't think 
that the 'flux nozzle' was important. I do think that if we get this 
thing to work, and I definitely intend, with the group's help, to work 
on it, that we should eventually try putting this thing on some version 
of the antenna, and see what it does.

I am considering building, as per John Steck's suggestion, a smaller 
scale model of this thing. That one could be modified for 
experimentation purposes. The only problem is, it is gonna cost a bit to 
make, what with the copper involved. But I've got some rainy day money I 
keep stocked up, and add to regularly, so what the hell? I'm game to 
spend a bit. My wife actually insists that I get back into 
experimenting. Apparently I'm less depressed then.

> It's also worth pointing out the size difference. Johns is
> about twice the size of the NASA unit. While the frequencies
> contemplated are low w/ respect to the size, 
> 
> After reading the patent text, I think that to achieve the
> current pulses you would do best to follow the claims, which
> suggest a decaying pulse like what you would achieve with a
> charged capacitor and switch. As much as you hate SCR's, it's
> probably your best bet. They are cheap, high current, and
> for the circuit I have in mind, easy to trigger. 

Well, if you want me to try using SCRs, I will. But you might have to 
give me pointers along the way. My main problem was, I never could get 
them to go completely off in a capacitive discharge circuit. John 
apparently didn't like them much either, and tried steering me towards 
FETs. I do, however, use TRIACs all the time in my "po' man's" HV 
supplies. I should put some pictures of those things up sometime too, 
driving homemade cathode ray tubes made from wine bottles. Having a blue 
electron beam going down the center axis of a bottle previously 
containing Cabernet Sauvignon is impressive.

> My circuit
> would be different from the ones presented in the patent,
> and easier to work with. What I have in mind 
> is a DC voltage source with a current limiting
> resistor that charges your cap. The cap's hot side is tied
> to the input of the antenna, and the output of the antenna
> is tied to the hot side of the SCR. The cold side of the SCR is tied
> to ground. The SCR trigger can now be safely driven with
> a pulser referenced to ground. To make things very simple,
> just keep the rep rate of the pulser to say 10X the time
> it takes to charge the cap. You can use a ballasting load
> resistor between the antenna output and the switch, if
> you don't want a reverse voltage left on the cap, but SCR's
> are really good about that and it shouldn't be necessary
> if your DC supply is using a current limiting resistor and a
> series diode to prevent possible back discharge.
> 
> If this is foggy, tell me and I'll post a circuit diagram.

I think I understand what you are suggesting. A circuit diagram would be 
helpful in any case, of course, just to make sure we're on the same 
page. What size capacitor would you suggest working with? DC voltage?

By "rep rate of the pulser...10X the time...to charge the cap", do you 
mean, for instance, if the cap is charged in 100mSec, fire the SCR only 
once per second? Or have I got this backwards?

> Your description of your driver gave me a chuckle. Clearly
> you are a braver man than I, or at least you have better
> health insurance (grin). 

Heh, according to my wife, I'm simply crazy.
I've got affordable healthcare...aspirin and a couple bandaids.

> Did John mention anything about his driver? The ones described
> in the patent are nice but perhaps a little more complicated
> than what you might be comfortable with. I think you will find
> my driver to be v/ simple and applicable to many other experiments
> if this one doesn't work out. 

He suggested capacitor discharge circuits as one method, but mostly just 
used a toroidal pulse transformer that he made himself to do the job. He 
told me that the primary was switched with MOSFETs in one incarnation, 
and relays in another. I gather that the MOSFETs worked better, but he 
said the relays can be made to work. I vaguely recall that his primary 
was driven by 24 or 28 volts at a relatively high current. Might have 
been close to 100 amps. If transformed right, I guess that would give 
you the requisite 1kA at a couple volts.

Your driver does sound like an excellent place to start. We should 
discuss this and hammer out some details. Then I can start rounding up 
some parts, and getting some stuff done. This is working out pretty good 
so far: no politics, we're simply discussing getting our hands dirty and 
doing some research. I'm glad I joined this list.

Off the top of my head, I have a couple fairy decent sized electrolytics 
here. I figure they aren't the size you want me to use, but I'll give 
you the specs anyways. The first is about the size of a small soup can, 
Nippon Chemi Con, 2700uF 400VDC. The second is Aerovox Mallory, about 
twice the size of the first, 6000uF, 250VDC. Anything useful here, or do 
we need to go bigger?

--Kyle

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