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Re: 1st light on small MOT coil



Original poster: "Gregory Hunter by way of Terry Fritz <twftesla-at-qwest-dot-net>" <ghunter31014-at-yahoo-dot-com>

Hi Wells,

You're right about Marco and the level shifter--he
didn't "invent" the idea, but he illustrated &
explained it on his web site in a way that made it
popular with the mailing list crowd. I'm pleased to
hear you got the MOT supply working. I have a couple
of suggestions for improving performance. Since the
MOT pulser puts out modest voltage (~8kvac) at fairly
stiff current, a multi-gap might not be the best
choice. A single static sucker gap with a powerful
vacuum cleaner (some have even used a shop-vac!) will
allow you to close the gap down for reliable firing,
but still have adequate quenching. The TC output
getting weaker as you turn up the power is a classic
symptom of power arcing. You need a better quenching
gap.

Along the same lines, the medium voltage/high current
supply might give better performance with a bigger
tank cap. 3nF is pretty dinky. A bigger tank cap would
utilize the stiff current better by getting the bang
rate down and the bang size up. I tried my own
unballasted MOT pulser (sucking 20A from a 240V
outlet) with a 23nF and later a 47nF tank cap, and the
bigger tank cap gave longer, hotter sparks.

I like the jumper idea--pretty neat. Any hope we can
have some pictures of this MOT PSU & TC setup?

Regards,

Greg
http://hot-streamer-dot-com/greg

--- Tesla list <tesla-at-pupman-dot-com> wrote:
> Original poster: "Wells Campbell by way of Terry
> Fritz <twftesla-at-qwest-dot-net>"
> <wellscampbell-at-onebox-dot-com>
> 
> hello, 
> 
> in a recent fit of activity, I cobbled together my
> scrounged MO parts
> into a power supply, turned a cooler full of beer
> bottles into a cap
> and fired a small coil. 
> 
> The power supply is two small MOT's and a level
> shifter arrangement where
> the caps are in series with the HV transformer
> windings, diodes across
> the other side of the caps to ground, and diodes out
> each leg to the
> DC terminals. I believe the original to have come
> from Marco Denicolai,
> and websites and info from Gregory Hunter, Steve
> Young, and Richie Burnett
> were most helpful. 
> 
> I set up the power supply to be reconfigurable to
> Greg's other proposed
> schematic (I believe it is a full wave
> doubler/filter?) simply by changing
> a few jumpers. I'll send pics soon. 
> 
> Anyway, the PS in level shifter arrangement has four
> caps in series on
> each leg, which limits current nicely. The output
> looks alot like a medium
> neon transformer. Changing jumpers on the cap groups
> will increase current,
> keeping voltage in the same range. I could use
> several different arrangements
> to go from four caps per leg in series (.25 uF) to
> four in parallel (4
> uF) (though this would probably be too powerful). I
> ran low voltage tests
> to confirm the nature of the output (cheep DMM) then
> ran it through a
> copper cylinder type static spark gap (no cap) and
> got the familiar purple
> sparks, buzzing along at a clearly audible 60Hz. 
> 
> I couldn't wait on the caps to come at that point,
> so I took about an
> hour to cobble up a small saltwater cap with beer
> bottles and a cooler.
> 14 bottles in all. my meter says this is about .003
> uF, which if I remembered
> from my coiling in the past, would get me ballpark
> for a small coil.
> 
> 
> I then used an extra coil (3.5" by  16", 27 AWG ~
> 1100 turns) and magnifier
> primary (14" dia. cylinder shape) in a normal coil
> arrangement (my maggie
> secondary has no wire yet) and brought up the juice.
> the gap sparks had
> that familiar snap now with the cap, and-- the end
> wire of the secondary
> had a small purple fuzz to it! I retuned to about
> four turns, and the
> whole top of the secondary was haloed with purple,
> spiky little sparks
> about 3" into air. I quickly added topload, (alum.
> pot lid) retuned for
> about five turns, and got 4" spikes. A ground wire
> produced 6-7" point
> to point arcs which were a little brighter, and
> popped along with the
> 60 hz. buzz from the gap. Increased power actually
> reduced performance
> somewhat, as the cap would arc multiple times during
> the duty cycle and
> fire chaotically. Anyway. I'm quite pleased at
> having the ability to
> throttle down the power with no mains current
> limiting, and the general
> adjustability the design affords. 
> 
> I also hooked up a MOT and de-Qing diode, to see if
> the charging choke
> effect would work. I measured only about a 10 % rise
> in voltage in low
> power mode, and the output of the coil seemed to be
> about the same. I
> think that the pulses of the level shifter with no
> filter cap to supply
> a constant voltage is to blame, also no rotary gap.
> I will investigate
> this later, after I have built the maggie, and a
> rotary gap (gripe) 
> 
> Now I need to wind the magnifier secondary, add
> protection and bleeder
> resistors (some caps must be discharged by hand) and
> get a nice big tank
> cap. 
> 
> Thanks to those who supplied info, it was most
> useful. I'll keep updating
> and hopefully have some pics...
> 
> Anyway, the ozone smelled pretty fresh, after more
> than 3 years...
> 
> -- 
> Wells Campbell
> wellscampbell-at-onebox-dot-com - email
> (415) 430-2169 x3756 - voicemail/fax
> 
> 
> 
> __________________________________________________
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> 
> 


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