db's new MOT coil

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Daniel Barrett by way of Terry Fritz <twftesla-at-qwest-dot-net>" <dbarrett1-at-austin.rr-dot-com>


    Hi All-
    I just wanted to share some data on my first coil comming to life. Don't
have a website for it yet, but if anyone is interested in any
schematics/photos whatever, let me know and I'll send them. I'm looking for
some feedback about this design.

    For a power supply, I'm using a single MOT which feeds complementary
doublers which charge a 4-MOT-cap-in-series filter cap. This gives me about
+/- 8KV when loaded to 1.44 kVA. This feeds a 9H diffierential mode charging
reactor made from an old MOT core and 8lbs of #24 under a quart and a half
of mineral oil. Two strings of 40 each 75nS 1kV diodes are used for d-q-ing,
then it's off to the MMC. It's a 3x10 Geek Cap array for 45nF (center tap
grounded) at 20kV.
    The gap is also 'ballanced' - there is a gap between each +/- MMC output
and a leg of the primary. Triggering happens when the Ignition coil jumps a
third gap to the negative side of the primary, which avalances the first (+)
and second (-) main gaps. All three use 1/16 tungsten welding rod and are
staggered around a rather gnarly blower from a hand-held 'duster'. The
ignition coil fires from a PIC-based SMPS and trigger timer. BPS can be
varied from 0 to 500, but the 15A breaker pops past 300 BPS ;)
    Coil is standard- L=37.5", d=8.2" (quicktube concrete forming tube).
Wound with 1k turns of #20. Torroid is 19.5" by 4.5". F0 is 144kHz, primary
seems to like to be tuned at about 129kHz.

    I'm getting 60 inch streamers and 42" power arcs at 1.44kVA input (12A -at-
120V). MMC is charging to 17kV, so this is running about 6.5 joules/bang.

Can anyone who is running a coil in this power class tell me if this is a
reasonable output? I'm not sure how to interpret the standard spark length
formulae for a DC powered coil- The difference is that the BPS can be varied
independently of the joules/bang, unlike an AC coil. I seem to get the
coolest looking streamers at about 200, but the length is pretty much
constant from 60-300 BPS.

    Still working out the firmware details for how to play it from MIDI. It
has been fun getting a microcontroller to work correctly when it lives 6"
below a 25 megawatt pulse generator...
ESD and EMI/RFI seem to be an issue for some reason ;)


Comments invited-
db