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Coil Meeting...
Hi All,
We had a most enjoyable Tesla coiling meeting today. I brought my coil
and stuff to an area where had that had lots of room (unlike my low ceiling
basement lab with high speed Internet links in the ceiling :-O ). I was
able to really let it rip.
My little spark gap that, I made the tungsten electrodes for, overheated
the electrodes and they melted the poly disk. I need to think more about
thermal cooling there but it was a great data point and the damage was
minimal. I wonder if the tungsten has a higher resistance that causes
extra heating? I resorted to my old big sync gap which performed well
throughout the rest of the day. However, I am starting to LOVE using drill
chucks to attach rotor disks to motor shafts...
My EMMC cap performed flawlessly. I am very pleased with it. I ran my
EEMMC cap to destruction. It failed at around 18kV (it was rated for 6.4kv
:-)). It certainly failed due to over voltage rather than over current.
The caps blew apart very cleanly. I felt the temperature of the two
strings immediately after it blew and the lesser damage ones were still
cool!! I ran it up slowly so it has plenty of time to heat but apparently
heating of these mini poly caps is a very minimal problem. I personally
think you can run them fairly safely to 1.5 times the DC voltage rating but
to each there own there. MMC caps are definitely the future of Tesla coil
caps. They can handle very heavy currents. I think the amount one spends
on caps of the future will be dictated more by current handling rather than
voltage standoff. I don't think it really quite sunk into the others at
the meeting just how much power and current those 50 little caps where
handling. For the big secondaries they were probably stone cold. For the
small secondary with small top terminal they would have seen much higher
currents and were still happy as could be. I blew a nice arc through my
primary coil base of 1.5 inch thick wood, but a simple wire rerouting fixed
that right quick.
One thing I was VERY interested in testing was this. My computer models
told me that I would dissipate the same power in the output arcs with a
small torroid as a large. But the smaller secondary would deliver less
power than the large secondary coil. As far as I can tell this was
TRUE!!!. I will post more on this very important thing once I have more
time. There may be something very important going on there. I mentioned
this in the "LTR Coil Power Calculations" post of 6-14-99, I got no
responses, but I didn't word that very well either... Once again the
computer told me something I would not have seen otherwise :-)) I will
repost that old post at the end of this for reference. I really think this
is super important!!!
My new control box worked very well. I have trouble knowing where the
variac was in low light but the addition of a dimple would allow me to us
the "braille" approach at feeling where the pointer location is (the
thermal breaker told me this day :-)) The 10 amp breaker tripped a few
times but it tripped right when it should have (like when I turned the dial
up too far :-)). I will post more on this in the future.
So how did the old LTR perform. VERY WELL!! It wash throwing mean 4 foot
arcs and would have thrown larger ones with a larger torroid. Even though
the small and large torroid seem to be running the same output power, the
larger torroid seemed to channel that power to a smaller number of larger
arcs. The small torroid had many steamers but seemed overwhelmed with the
power going into it. It was almost glowing with corona. My coil seemed to
be begging for a larger torroid still!! For just being run off of a 15/60
neon it was darn nice!! Everything seemed to be just as the computer
predicted. This LTR stuff is definitely the way to go even if it is much
more complex technically. The output arcs frightened me a few times :-)))
My new filter circuit performed just as expected! I got a chance to test
those ball bearing spark gaps I sweated over so much and they fired at the
perfect time with no problem. My 5K resistors were dissipating 100 watts
and seem to get hot as expected but not too excessive. Apparently, these
big power resistors are supposed to run about 350 to 400 C at full
power!!!! I think those that thought they are getting too hot just don't
realize how hot those darn things are designed to run. Mine didn't seem to
be getting "red hot" but more just "nice and hot" :-))
Everyone was very interested in the AC motor I converted to a salient pole
sync motor. My normal sync motor is not salient pole so I had to adjust it
every time I restarted it which got VERY old. I am looking forward to
converting to salient pole. I wonder if I removed too much metal. The
current draw is 5.25 amps which is it's rating but it has really good
torque (Chip Atkinson put on his welding gloves and tested it). I think
one could go for less torque and less heating but it still works fine. I
think I would go to the edges of the poles instead of the centers for the
amount to grind. Or grind to one less pole width. Perhaps Bill Wysock and
other super experts on this could give more info on how much to grind to
get a good balance between torque and heating.
There was one thing that surprised me. We stacked me small coil on top of
my large coil with the large torroid and got super good output sparks.
Since the secondary inductance was higher I would expect this now. However
we then moved the third coil off to the side to play with the magnifier
type setup. I thought the original tuning would still work. However, we
were unable to tune it at all. I will have to think more and have the
computer help me understand what was going on there. Apparently extra coil
system require more than just trivial thought to get them to work...
So it looks like LTR coils with BIG secondary coils and BIG torroids can
really perform well. MMC and even EMMC caps perform with no problem.
Salient pole sync rotary gap with very good heat dissipation are the way to
go. I am going to get the gap problems solved (design the ULTIMATE gap)
and maybe look into a bigger inductance secondary and larger torroid for
the future. Then I may even try getting another 15/60 transformer for even
more fun :-))
Some day I hope to extend all this "pure science" stuff to a PT or PIG
system that will REALLY perform. But I need to get this "low power" stuff
figured out first. :-)
I see there are a lot of posts about timing lights and such for sync gaps.
I'll have to wait till tomorrow before getting back into that. Tiered now
:-))
Cheers,
Terry - Putting tons of theory to the test :-))
Old post for reference...
=====================
Hi All,
I have been running my new coil through MicroSim to see what kind of power
throughput my new coil will have. Here are some of the details...
The primary cap (27.9nF) is charged by a 15kV/60mA neon transformer. The
firing voltage is 21kV with the gap (sync) being set to fire 1.324mS (29
degrees) after the voltage peak (LTR coils like late firing). That is 6.17
Joules per bang.
The power distribution in the system is as follows:
Neon Primary = 30.6 watts
Neon Secondary = 38.87 watts
Filter Resistors = 98.4 watts
Spark Gap = 386.5 watts
Secondary Losses = 54.4 watts
Power to Arc = 283.5 watts
Total Power = 892.3 watts
I then calculated the power to the arc with different coupling:
K = 0.201 301 watts
K = 0.171 290.4 watts
K = 0.145 285.1 watts
K = 0.123 281.1 watts
K = 0.108 268.4 watts
K = 0.089 227.6 watts
This is interesting since it suggests that the coupling is not very
critical. I may be able to back off the coupling to get a better quench
without too much real loss of power. I suspect the lower couplings have
longer transfer times that allow more time for the primary circuit to burn
up power.
I then calculated the power output using two coils (large and small) and
two torroids (large and small).
Large Coil with Large Torroid
Lp = 121.7 uH
Ls = 75.4 mH
Cself = 15.7 pF
Ctop = 29.0 pF
Power to Arc = 286.9 watts
Large Coil with Small Torroid
Lp = 71.6 uH
Ls = 75.4 mH
Cself = 15.7 pF
Ctop = 11.0 pF
Power to Arc = 278.4 watts
Small Coil with Large Torroid
Lp = 34.12 uH
Ls = 22.1 mH
Cself = 10.0 pF
Ctop = 35 pF
Power to Arc = 183.75 watts
Small Coil with Small Torroid
Lp = 18.55 uH
Ls = 22.1 mH
Cself = 10.0 pF
Ctop = 14.5 pF
Power to Arc = 184.1 watts
This is really interesting because the torroid size does not seem to matter
but the coil size does. I suspect the larger coil gives lower primary
current which reduces the primary system losses. The small torroid seemed
to give slightly better arc power. Much to ponder and much to test...
The MicroSim 8.0 model of this is at:
www.peakpeak-dot-com/~terryf/tesla/misc/LTR6-14.sch
Cheers,
Terry