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Re: LTR Pig Project -biggg coil
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.
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 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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