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Re: LTR Pig Project -biggg coil
Original poster: "Malcolm Watts by way of Terry Fritz <twftesla-at-uswest-dot-net>" <m.j.watts-at-massey.ac.nz>
Hi Kevin,
On 18 Feb 01, at 14:13, Tesla list wrote:
> Original poster: "Kevin R Eldredge by way of Terry Fritz
> <twftesla-at-uswest-dot-net>" <kreld-at-juno-dot-com>
>
>
>
> All
>
> I just picked up on this post, and wanted to clarify several things
> that might help out. LTR or not? I won't guess, it works, and I'm
> happy. (:D The Biggg Coil project was a "everything new
> from the start" project. That is, all components involved were not
> used on any other of my Coils, except for a contactor and fine tune
> inductive ballast. This made things a lot harder to find initial
> problems, but thanks to John Freau for guiding me the right way on the
> break rate.
> The whole project evolved around the purchase of two 0.376 uF
> cap's which are wired in series (0.188 uF approx).
>
> The only math involved was for basic resonance,ie..secondary,
> primary, capacitor parameters. Problems were many. Initialy the
> sync. Rotary was at 480 BPS. This pulled 300+ amps from the 245 volt
> mains, and only 14' sparks. Ballast adjustment made no difference.
> Removing gap electrodes for 240 BPS operation made things better,
> current down, sparks longer, but still not right.
> Finally running 120 BPS, current came down to 110 amps, at
> 300 volts at the pig's, 24' sparks. This was new, 300 volts AFTER
> the inductive ballast, 240 volts before the ballast. I unfortunately
> did not measure the actual 245 volt current into the control cabinet,
> this Spring I will.
Your ballast is resonating with the primary cap.
> As John stated, the external ballast gets real hot, smoking hot.
> However, the ballast is a 15 kVA transformer with the secondary
> shorted, so this creates most of the heat, the shorted winding.
> This too will be addressed this Spring with a new ballast.
> The internal switchable ballast, runs only warm, it's simply
> #10 wire wound on a steel torroid.
The smoke represents copper losses and core losses.
Regards,
malcolm
> The coil has been dormant this winter, but as weather warms,
> the coil will be brought out to play again. Simply getting things to
> work was the goal last year, this Spring will bring a new 10 x 10 x
> 16' building to keep the Coil in a ready to fire state. Also the
> rotory will be rebuilt with on the fly phase adjustment to better tune
> while adjusting reactive ballast for maximum spark.
> An old tube scope is being modified to accept high voltages
> directly to the CRT's deflection plates through a resistive divider.
> This will allow more accurate P-P voltages in the Coil while
> running....hopefully anyway. Power factor correction may also be
> tried depending on how things go.
>
> I'm open for suggestions on any improvements, or experiments
> if anyone has any.
>
> snip...
> >> >Consider Kevin's coil. His pig combo rating is 14.4kV at 20kVA.
> >His
> >> >cap is 0.138uF or something similar. He draws 100 amps from a
> >> >240 volt line. He runs at 120 bps. I just did the calcs, and a
> >> >matched sized cap for Kevin's coil would be 0.31uF or so, and a
> >> >typical LTR sized cap would be about 0.6uF or so. This is huge
> >> >cap, and I don't recommend anything that large. His cap seems to
> >> >be less than 1/2 the resonant size. (If you calc the reso-size
> >> >based on the pig's specs.) You may want to check my calcs here
> >> >in case I made an error. But if his reso-size would be 0.31uF, I
> >> >certainly would not suggest using anything larger than 0.375uF or
> >> >so. Since Kevin's cap may be about 1/2 the reso-size, it's
> >> >possible that his power factor might not be that good, but I have
> >> >no real idea if it is or not. It is also
> >
> >> >possible that Kevin's coil may work much better with a 0.375uF
> >> >cap, if it greatly improves the power factor. It's too bad we
> >don't
> >> >know what the power factor is on Kevin's coil. Then again, it is
> >> >possible that a reso or LTR cap is NG for a big coil. It may
> >hurt
> >> >the quenching too much or something, who knows. Maybe
> >> >someday someone will build a big coil with LTR.
> >>
> >> Forgive as I think out loud about Kevin's coil...
> >>
> >> 240 volts at 100 amps gives us 24000 watts. We'll assume we can
> >add power
> >> factor caps until the PF is good and we can use all 24kVA.
> >>
> >> 24000 / 120BPS gives a 200 Joules per bang. The firing voltage
> >> for
> >a
> >> 14.4kV transformer is 14400 x SQRT(2) = 20365 volts. 200 Joules =
> >>
> >1/2 x C
> >> x V^2 so the LTR cap size is 964.5nF. Yeah!! :-))
> >>
> >> If his present coil is running 138nF then he would have to
> >> increase
> >the BPS
> >> to match the LTR case. 120 x 964.5 / 138 = 839BPS. However that
> >is async!
> >> There for he instantly has to double that to match the sync case
> >for 1677
> >> BPS (async gaps deliver 1/2 the power of sync gaps of the same BPS
> >>
> >do to
> >> firing on less than full voltage).
> >
> >You're assuming that his firing voltage will remain constant
> >regardless
> >of the cap size. If this were true, Kevin's coil (0.138uF) would be
> >drawing only about 3430 watts at 120 bps, (not counting losses). Yet
> >his coil
> >
> >draws 24kVA or so! To me, the only explanation is that his firing
> >voltage must be much much higher than 20365 volts, due to a ballast
> >setting that gives some degree of resonant charging. Although the
> >power factor may not be perfect, I don't think the true watts drawn
> >is only 3430 watts. If he was using only 3430 watts now, I don't
> >think he would be getting 24 foot sparks. So to me, this is a
> >reality check.... his caps must be firing at a much higher voltage
> >than 20365. I believe that resonant charging must often be
> >considered when analyzing low bps pig powered coils. Otherwise
> >things just don't add up.
> >
> >Kevin is using a combo of two ballasts, I believe, and it is possible
> >that the ballast is lossy. I know that when I used a variac as a
> >ballast on my small coil, it doubled the input VA, for the same spark
> >length. I think Kevin said that his ballast gets quite hot, so it
> >may be burning some power, but I have no idea how much. If we assume
> >that his ballast burns up 3000 watts, and his other wiring and xfmer
> >losses are 5% more or another 1000 watts, then he'd be supplying
> >still about 20kVA to the system. If the power factor is only 70%,
> >then his true wattage would be about 14kW. This would mean that his
> >bang size is 117 Joules at his present 120 bps. This is much larger
> >than the 28 Joules that is predicted if one uses 20365 volts as the
> >firing voltage. Now if one uses 37kV for the firing voltage, then a
> >figure of 97 Joules per bang is obtained, which seems to fit his
> >situation better. It's still not 117 Joules, but his losses may be
> >even higher than I figured, which would explain the difference. Or I
> >may have made a mistake, and his total input VA may be 20kVA, not
> >24kVA. If this is the case, it would drop his bang size to 97
> >Joules, which would match up with a 37kV firing voltage. Another
> >thing that makes me think that my analysis is correct, is that it
> >agrees with Greg Leyh's results. Greg has posted his firing
> >voltages, etc., so we kind of know the bang size vs. spark length
> >relationship. We know for instance that 3430 watts cannot give 24
> >foot sparks at 120 bps.
>
>
> Freezing in Oklahoma
>
> Kevin E.
> >
> >
> >
>
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