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RE: Gary Lau's gap
When I have this problem, my gap is ususally set to 0.25 in or less. My
coil really likes the faster firing rate, until the gap stops quenching.
For power, here's my best data. I use resistive ballast only. My PT would
put out 15.4 kV open with no ballast. By calorimetry, my ballast bank
dissipates about 2.5 kW, so "at unity power factor" I would have about 80V
on the PT primary and 5600 V rms out. Depending on the PF that could be
more. My dvm is hopeless to measure V and I directly. According to my dvm
the capacitor is 0.017 uF, but that dvm is not always consistent when
measuring C.
I considered putting caps on the copper pipes and drilling them, maybe mash
a bearing ball into the hole to chamfer the inner edge. Maybe its better to
use a brass fitting ? Or a copper bushing with one end rounded off ?
Will
> ----------
> From: Tesla List[SMTP:tesla-at-pupman-dot-com]
> Sent: Tuesday, November 03, 1998 00:27
> To: tesla-at-pupman-dot-com
> Subject: RE: Gary Lau's gap
>
> Original Poster: Gary Lau 02-Nov-1998 2252 <lau-at-hdecad.ENET.dec-dot-com>
>
> >Original Poster: "Payne, Will E" <will.e.payne-at-lmco-dot-com>
> >
> >I switched to a Lau Gap with good results. I have 40 in sparks using
> 0.017
> >uF SW caps and about 1.3 kW input. However, with close spacing, I will
> >suddenly lose breakout, followed by an audibly "faster" sounding SG
> >discharge which continues to increase until its almost a continuous
> sounding
> >arc. Obviously at this point quenching is virtially non existent. Input
> >power rises and I have to shut down. Running of the airflow with no SG
> >discharge for 10 s to 1 min seems to clear the problem for a while, but
> its
> >getting worse. Reducing the power by opening 3/4 of my ballast switches
> (HW
> >elements) will not restore quenching once its lost. Wider gap is less
> >sensitive, but mine will not fire at the lowest power setting.
> >
> >I'm using 3/4 Cu pipe end to end with no fittings. I thought ionized air
> >was being trapped in a boundary layer and killing the quench, but I have
> to
> >shut off HV for much longer than I would expect for this failure mode.
> My
> >Cu electrodes are becoming dark and eroded which may be a factor. RIght
> now
> >I'm down because the washtub sprung a leak, when I'm up agin, I hope to
> be
> >instrumented for measurements thanks to Terry and his excellent Mk I
> fiber
> >optic VI probes. Y'all missed the bargain of the century.
> >
> >I still want to know if I'm in the ballpark with 40 in from my SW cap
> >system, running from a 70:1 PT, about 1.3 kW thru the xformer, maybe 2-3
> kW
> >in ballast.
> >
> >Will
> >
> >ps Gary is it OK with you to post this type gap on my site ?
>
> Hi Will:
>
> No problem posting your gap, I doubt I'm the first person to use a
> single gap.
>
> I suspect that your use of 3/4" pipe with no fittings may be making your
> quench worse, due to the sharp radius of curvature on the ends. This
> will cause sparks to break out prematurely and to power-arc. See my
> recent post about safety gap experiments! With my main single gap, I
> made sure that the arcing surfaces were as flat and blunt as possible.
> What was your gap spacing and what is your PT voltage?
>
> Regards, Gary Lau
> Waltham, MA USA
>
>