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Re: [TCML] Racing sparks - question
JavaTC calculates the k of my current coil at 0.13 and I was getting racing sparks till I lowered it to about 0.12. Of course, who knows what it really is - the program output is only as accurate as the input you give and I didn't go meticulously measure every aspect of my coil. In other words, my model is probably off quite a bit, so I have to apply a tolerance factor to what's coming out of the code.
But generally, JavaTC has been correct for me as long as I give it the right numbers.
The thing I got out of it (and also by talking to Bart), is that my k was too high. So forget the actual number to the 4th decimal place - whatever my k was, it was too high. JavaTC said it should be around 0.137 and I think when Bart intervened it was over 0.137. So lowering it was necessary, and I could figure out the order of magnitude of how much to lower it by the numbers that came out of the program.
I wound up cutting out the inner 2.5 turns of my primary, and also raised the secondary 1/2". No more racing sparks. I was able to "simulate" the results with those modified numbers and it now says my k is around 0.12. So we're talking a change of about 15-20%. And I think you can get that kind of accuracy from JavaTC.
One other thing - I got this from Dan's book, and it worked true for me. Dan ran EM simulations to plot the field of a coil with single, and double toroids. The single toroid plot shows the maximum field gradient generally down and out from the toroid in a single toroid arrangement. In a double toroid arrangement it's sort of up and out.
When I was running a single toroid, 90% of all the strikes were to my strike rail. When I moved to a double toroid, the sparks go out laterally and upward.
Now - there's another phenomenon, too. With the double toroid, the top of the coil is (obviously) higher, and so farther from the strike rail.
One of those two things caused the sparks to go outward and upward in a much more fashionable and aesthetically pleasing fashion. IN any case I'll be running double toroids for a while.
On Aug 8, 2010, at 3:00 PM, otmaskin5@xxxxxxx wrote:
> Thanks everybody for your replies. To answer a few questions you guys raised:
> JAVATC calculates the coupling coefficient at .122k, below the recommended .137
> break rate is 206 bps
> I have handled the secondary without gloves to get it in place, but later wiped it down with rubbing alchohol
> the secondary 6.6" in diameter, winding length 29 7/8 inches of #26 AWG for 1650 turns
> At this point unless I hear any other ideas, I'll just continue to play with the secondary height and separation between toroids and see if I can work it out.
> Thanks again, Dennis Hopkinton MA
> -----Original Message-----
> From: DC Cox <resonance@xxxxxxxxxxxx>
> To: Tesla Coil Mailing List <tesla@xxxxxxxxxx>
> Sent: Sun, Aug 8, 2010 10:24 am
> Subject: Re: [TCML] Racing sparks - question
> If you have handled the sec without gloves on there is a strong possibility
> hat sodium salts from your skin may have been deposited on the wires thus
> ausing various conduction points along the coil. Some people have very dry
> kin so this may not be a problem, while some have more damp skin and there
> s a lot of conductive sodium in your sweat.
> If racing sparks have occured you now have very small "pinholes" in your
> nsulation which can lead to continuing problems. If only a few you might
> et by, but if there are a lot of them, sometimes so small you can't even
> ee them, or if they are on the inner side of the wire where you can't see
> hem, then rewinding is the usual solution.
> Best way to properly set coeff. of coupling is to use JAVATC to accurately
> alculate the k value. Keep it in the general range of 0.1 to 0.14. I
> sually find that 0.15 to 0.2 gives me the longest sparks. You should also
> se the "water heater element" method to measure the coeff. of coupling.
> ou can also small a small elec. heater --- anything that gives you a
> rimary current limit around 10 Amps will work fine.
> All of these issues need to be properly addressed to eliminate this
> roblem. With most high voltage systems, in which great stress is always
> resent, once sparking has occured it will continue. You may even have to
> ewind the sec coil is this problem continues to plague you.
> Best regards,
> Dr. Resonance
> On Sat, Aug 7, 2010 at 7:43 PM, <otmaskin5@xxxxxxx> wrote:
> Hi coilers. Life's been busy the last few months & not much time for
> coiling, although I still read the pupman postings. Anyway, I did find the
> time to roll out my coil tonight & run it, but I kept running into on an old
> problem I've had in the past. Using a screw or ball bearing for a breakout
> point, my 15/60 coil produces good sparks, and the coil runs well with no
> problems. If I remove the breakout, I still get sparks from the toroiod,
> but eventualy start getting racing sparks. Without the breakout point, the
> coil seems to have no trouble producing sparks from the topload even fairly
> lower variac voltages, but when I increase variac the voltage to the 120 or
> higher I eventually get the racing sparks. I've played around with
> raising the secondary to reduce coupling, but so far, I'm still getting
> racing sparks if I dont use a breakout.
> If it's just a matter of over coupling, I'll have no problem gradually
> raising the secondary to eliminate the problem. However this will be
> somewhat involved as I have to removing the secondary's end cap & adding a
> longer mounting bolt. Before I go much further, I wanted to see if any of
> you guys had other suggestions on what might be causing the racing sparks
> when I don't use a breakout. I'd really like to be able to run the coil
> without using a breakout.
> FYI, I have a 6 X 20.5 toroid and a 3 X 12 toroid underneath it.
> Thanks for any suggestions, Dennis Hopkinton MA
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