Re: 4 Inch tesla coil - Inquiries

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: nancylavoie@xxxxxxxxxxx 

I agree with Bart on the tywrap deal,they always seem to allow the 
primary to shift around.I've had good luck with those tack down 
coaxial cable clamps.They fit 1/4 copper tubing perfectly as well as 
working as a fool proof spacer between turns.You can pick up a jug of 
them at the local Home Depot for about $10.And no, the tiny nails 
that hold them down do not effect anything whatsoever(I was kind of 
uncertain about trying this for fear of sparks or inductive 
heating  etc.).Wyatt

-------------- Original message --------------
From: "Tesla list" <tesla@xxxxxxxxxx>

> Original poster: "Barton B. Anderson"
>
> The coil has even lower coupling that I thought due to the secondary
> height above the primary plane (near 0.06). Rebuilding the primary
> would be a great idea. You could even use the same acrylic. Just
> drill the tywrap runner holes inward for inside turns (assuming the
> center hole was not cut out). You could then cut a center hole about
> 1/2" larger than the secondary form and slide it down from the top.
> Although you could use the same tubing, it would be best to use a new
> one without the hardened bends (to make it perty).
>
> One problem I see that you did on your tywraps is to drill 2 holes to
> hold down the winding. This almos t always results in a very loose
> primary, and no matter how tight you make the tywraps, they won't
> hold the primary in position. What I do if using tywraps is to drill
> a single hole where I want the primary to be tied. I slide the tywrap
> up through the hold, then around the tubing, and back down the same
> hole finally fastening it on the bottom.
>
> For 1/4" tubing, the holes are distanced 1/2" from one to the next.
> When starting the hole pattern, mark the center in the acrylic. Then
> mark your first tywrap hole (turn 1) at the distance you decide on.
> For the remaining runners, you need to add a distance to ensure a
> fluid growing of the primary. Divide the center spacing by the number
> of runners to find how much to add from marking the inner holes. For
> your 4 runner primary and assuming you want 1/4" spacing using 1/4"
> od tubing, the center to center spacing is 1/ 2". So, 0.5/4=0.125, so
> add 1/8" inch more from the center of the acrylic for runner #2, and
> so on. After your 4 inner runner holes are marked, then simply mark
> off 1/2" from each inner hole outward where the tywraps will be
> placed. Here's a pic of something similar.
>
> http://www.classictesla.com/photos/tgk/21.jpg
>
> But, you may want to do something other than tywraps. Look around at
> what others have done and find what you think you would like to do.
> Tywraps are pretty easy, so I used them in the past simply because of
> that. But lately I am fond of using non-conductive runners where the
> primary can be snapped in and held in place. A bit more work on the
> design and requires more work to make, but it does look good (well,
> after a few trial and errors, it will look good). But for quick and
> easy primary's, tywraps are hard to beat.
>
> T he spa rk gap is as I imagined it. Build a large pipe gap. The
> sphere's are going to heat and pit the brass spheres due to your cap
> energy (your bang energy is high and based on the cap voltage and cap
> size). Your gap would probably do ok for a low energy coil, but not
> for the energy your running. You want to dissipate and stabilize that
> heat. To do that, you need a material that is quick to heat and to
> cool. The thin walls of a copper pipe have little mass and are quick
> to heat. But, they are also quick to cool, so using forced air
> through those pipes will cool them easily. You then find the amount
> of air needed to keep the pipes relatively cool. Usually, guys just
> throw a fan at it and call it done. Most of the time that's ok.
> Sometimes, there's just not enough air for the pipe sections used. If
> the pipes get hot, increase air flow. I personally like large 1.25"
> pip es ins ide a cylinder and then I suck the air through the pipes.
> Here's a pic.
>
> http://www.classictesla.com/photos/ba45/s2752.jpg
>
> All I did there was epoxy a 4" cut of 4.5" pvc to the open hole on
> the squirrel cage fan (and painted green since that was the only
> color in the cabinet). I then used a slightly smaller pvc form (just
> happened to fit nicely inside the epoxied pvc form on the fan) to
> epoxy the copper pipes into place. Pretty simple to make. Note the
> solid brass section in front of the copper pipe section. The brass
> sucked! The copper pipes are far superior at thermal stabilization.
> What is nice about a gap like this is that the white pvc can be slid
> out easily (which is nice for testing various gap styles and really
> why I did it like this). Also, the white portion was actually a pvc
> cap. I simply cut a hole in the bottom leaving a 1/4" lip t o set the
> copper pipes onto for positioning. Too much lip will hinder air flow
> (the brass section actually had too much lip, but this is actually
> the first of two brass sections where I used a small lip on the
> second, but the brass still did not do well). The gap could be
> improved by adding a center plastic baffle between the pipes which
> would further force air over and through only the pipes, but I didn't
> find that necessary once I used the large copper sections. I actually
> did that when I tested the solid brass gap, but the brass itself
> simply maintains the heat (which is the whole problem). You just can
> cool it down with air flow like a pipe gap can be cooled.
>
> Take care,
> Bart
>
> PS. Sorry to be long winded.
>
>
> Tesla list wrote:
>
> >Original poster: "Hydrogen18"
> >
&gt
; > I now have some pictures at:
> >
> >http://www.hydrogen18.com/projectlogs/hivolt/4inchtesla/
> >
> >and in response to your concerns:
> >
> >Primary to secondary coupling - I think I should rebuild my primary
> >to locate the first turn of both coils as close together as possible
> >without the risk of arc over.
> >
> >Spark gap- My current spark gap is an improvement over previous
> >designs(
> >http://www.hydrogen18.com/projectlogs/hivolt/3inchtesla/IMG_6748.jpg
> >) but is still poor. I was noticing heat buildup while running the
> >coil on 4/2/2007. Would adapting the 1/2 copper pipe up to 3/4 inch
> >and then putting pipe caps on function better than this setup? I
> >presume I could drill holes in it to allow for more airflow throughout it?
> >----- Original Message ----- From: "Tesla list" < BR>> >To:
> >Sent: Sunday, April 01, 2007 8:29 PM
> >Subject: Re: 4 Inch tesla coil - Inquiries
> >
> >
> >>Original poster: "Barton B. Anderson"
> >>
> >>Hello,
> >>
> >>Lot's of detailed information and annotation regarding your coil.
> >>Thanks for that. I think most would agree that the spark gap is the
> >>biggest are of concern, but I'd like to intersperse comments. See below.
> >>
> >>
> >>Tesla list wrote:
> >>
> >>>Original poster: "Hydrogen18"
> >>>
> >>>I've got a 4 inch tesla coil that I've pulled out of storage and
> >>>set about improving and trying to make into a more logical setup.
> >>>Specs are as follows
> >>>
&g
t; >>>Secondary - 4 inch Schedule 80 pipe, 1500 turns 28 awg, 18 inches long
> >>
> >>
> >>If it's 28 awg magnet wire, it's about a maximum of 1230 turns if
> >>closewound with no winding error for an 18 inch winding length.
> >>That is based on thin insulation as well. If it were double or
> >>triple insulation, the turns would be even less. Not a big deal,
> >>but I do like to note discrepancies. To verify, mark off 1 inch of
> >>winding and count the turns in that 1 inch space (I like to simply
> >>use masking tape to mark off the 1" area). You should count about
> >>68 turns for 1230 turn coil.
> >>
> >>>Primary - Coil of 1/4 inch copper pipe, about 13 turns worth. laid
> >>>out flat and zip tied to plexiglass. 1/4 spacing between turns.
> >>>about 2 foot overall diameter. > >>
> >>
> >>Wow, that must be quite a large inner primary hole (3.25 inch
> >>spacing between primary and secondary). Yields a low coupling. If
> >>you even rebuild the primary, you could certainly tighten that up
> >>to about 1" to 1.5" spacing).
> >>
> >>>Spark gap - Static style, 1 inch spherical brass drawer pulls
> >>>mounted to 1/2 inch copper pipe. This can be adjusted really
> >>>easily. A cheap blower supposedly running at 25000 rpm blows alot
> >>>of air in an uncontrolled fashion across these. They get pretty
> >>>dang hot, but the arc seems to be quenched pretty well, although I
> >>>have no first hand experience with spark gaps outside of my own design.
> >>
> >>
> >>Biggest problem is the spark gap. The brass drawer pulls are often
> >&

gt;sol id brass. Once they heat up your discharge voltage across the
> >>two sphere's will decrease and output will suffer dramatically,
> >>even with a fan across them. You would probably gain the best
> >>performance rebuilding the spark gap to maybe a heavy duty static
> >>gap such as a RQ/TCBOR style (pipes mounted inside a PVC tubing
> >>with a goodly fan either sucking or blowing across the pipes). I
> >>recommend large 1.25 inch diameter pipe segments (available ready
> >>to go in 3" or 4" segments at most hardware stores). They will cool
> >>much faster and will maintain a steady state temp with proper air flow.
> >>
> >>>Topload - 12 inch toroidish thing with a section of 4 inch dryer
> >>>duct stacked around it. Seems to discourage primary strikes pretty
> >>>well, although it was designed for such
> &gt
;>
> >>
> >>Should be fine.
> >>
> >>>Tank Cap - 942C20P15K's(2000 VDC 0.15MFD) in strings of 8, up to 3
> >>>strings of these in paralell(plenty more strings ready to be
> >>>assembled). Mounted in a wooden box but the capacitors themselves
> >>>are in 180 degree sections of PVC pipe for insulation. Connection
> >>>is made at all junctions to the strings by means of 1/4-20 brass bolt.
> >>
> >>
> >>This is fine to. The full cap bank capacitance is 0.0563uF. Based
> >>on your system, you are probably tuning in about 5 turns. The cap
> >>size explains the narrow tuning range as well. I'll comment 
later on that.
> >>
> >>>Power supply - 4 MOTS producing around 9500 volts RMC AC, current
> >>>is limited by 10 lbs 10 AWG wrapped around a 3 inch piece of
> &

gt;>>Schedule 80 with an adjustable iron core(I have also left the
> >>>shunts in the MOTS, as I see no need to drive them as hard as some
> >>>people do; mine are not under oil but epoxy potted). Driven by a
> >>>30 Amp 240 VAC outlet, I do not feel this is the limitation in my setup.
> >>
> >>
> >>Should be good for lots of current. No problems there.
> >>
> >>>So far my recent attempts have yielded point to point strikes of
> >>>28 inches or more; longer arcs accounting for the bend. That was
> >>>with 2 capacitor strings. Attempting to use 3 capacitor strings
> >>>seems to make finding a tuning point impossible, all I suceeded in
> >>>doing was getting the primary so hot I burned myself(this was in
> >>>just a second or so of having the spark gap firing). I am dumb
> >&

gt;>tuning this coil, just starting at turn one and moving out until I
> >>>get a large response, and then making smaller movements from
> >>>there. I've made the following conclusions:
> >>
> >>
> >>Yes, less capacitance will increase the range of tuning. There's a
> >>ratio of C and L for any given resonant frequency. The more C you
> >>have, the less L you have to play with.
> >>
> >>>- Steel anywhere in the primary circuit basically destroys
> >>>performance and likes to get really hot.
> >>
> >>
> >>It can if it's close enough to the field.
> >>
> >>>- Tuning seems to be very pecuilar on a lower coupling coil(I had
> >>>3 inch coil in the past with 'high' coupling between the primary
> >>>and secondary, you could make turns of adj ustmen t to the primary
> >>>without noticeable output in spark).
> >>
> >>
> >>It's not the lower coupling, it's the fact that the tank cap value
> >>is so large compared to the inductance required to tune into the
> >>resonant frequency of the secondary. If the cap were 10 times
> >>smaller, your tuning sensitivity would decrease by the same amount.
> >>
> >>>- The charging current available to the coil doesnt seem to affect
> >>>things much, other than the spark gap getting louder.
> >>
> >>
> >>The charging current, as long as it is beefy enough to charge the
> >>caps within a decent time frame will never be problem. But if a
> >>weak tranny were used, you would then experience charging problems.
> >>
> >>>- This spark gap is better than the last, be cause I don't have to
> >>>wait for it to cool down between runs. It takes a very long time
> >>>run time for the initial breakdown voltage to change due to
> >>>tempature of the electrodes. They are hotter than a car brake
> >>>rotor at the parts you can observe, but I suspect where it matters
> >>>they are remaining cool. They also dont require a resurfacing
> >>>every 30 seconds of runtime.
> >>
> >>
> >>Still a problem. Solid brass will not perform as well as properly
> >>designed copper pipe gap unless something special were added to
> >>them to allow quick dissipation of the heat. Of course, it's very
> >>easy to build a poor copper pipe gap as well. Large radius, proper
> >>spacing, and well designed air flow are the main ingredients for a
> >>nice running pipe gap.
> &gt
;>
> >>>And I've got these concerns:
> >>>
> >>>- My primary is very poor. The spacing is nonuniform. I think
> >>>tuning is changing because the turns are not held very securely.
> >>
> >>
> >>Nope, tuning is not changing. A primary with a lot of gap to gap
> >>differences will only look ugly, it will still perform just as well
> >>a nicely wound primary. The only time it might cause a problem is
> >>if two segments were close enough to arc together. Tuning will not
> >>change unless the caps were heating up and changing their value.
> >>Most likely, primary and gap heating is simply changing the arc
> >>voltage and decreasing performance. Easy to identify: basically, it
> >>starts out good and after a little while of running, sparks start
> >>diminishing in length.
> >&

gt;
> >>>- Should I add another gap to my static spark gap? Are there any
> >>>telltale signs of an overloaded static power gap? I know that the
> >>>signs of a 'power arc'(the deep orange-reddish arc that does not
> >>>quench) or rapid electrode erosion are two to look for, and I 
have neither.
> >>
> >>
> >>Look for heat. If their getting hot, your definitely going to have
> >>problems. I would rebuild this part of the system first. A lot of
> >>people here have built a lot of different gap types that work well.
> >>Almost anything would beat the brass sphere's on a coil like yours
> >>which has a big tank cap and lots of energy.
> >>
> >>>- I have a safety gap on my transformer, so I'm not concerned
> >>>about opening my spark gap up too much. But is there a primary
> &g
t;> >side side RMS VAC that I shouid aim to have the spark gap breakdown at?
> >>
> >>
> >>Opening the gap will increase the voltage required to arc the gap.
> >>This won't help and only puts the MOT stack at risk. For 1" brass
> >>sphere's, about 0.18" is about right for 10500V output. I wouldn't
> >>go beyond 0.2 myself.
> >>
> >>>My questions are from here:
> >>>
> >>>- Should I bother improving the primary? I'm not getting turn to
> >>>turn arcing, it's the inconsistency of the shape that's my concern.
> >>
> >>
> >>I would. Mainly for raising the coupling. Again, the shape is not a
> >>concern, but low coupling can be if it's too low and your energy is
> >>large (which it is).
> >>
> >>>- What's the maximum size capacitor for t his co il I can reasonably
> >>>expect to run?(I know my limitation is the spark gap, and probably
> >>>will be for all my coiling years given the easy availability of
> >>>large dangerous HV transformers)
> >>
> >>
> >>Well, actually, depending on the MOT's, you could probably go to a
> >>larger cap size. The problem is that the coil is small for such
> >>energy and a larger cap is unnecessary for spark lengths. Your
> >>better working on reducing the thermal losses.
> >>
> >>>- Why is my primary getting so darn hot? Is off resonance driving
> >>>of the coil the cause of this?
> >>
> >>
> >>Well, first, the primary tank energy is high. You are dumping a lot
> >>of current into the primary. Secondly, the coupling is quite low.
> >>This can be similar to run ning the primary without a secondary in
> >>place (which is a big no no). You need a load to dump the energy
> >>to, otherwise, the primary has to get rid of all that energy somehow.
> >>Heat is natures backup mechanism. I would lower the capacitance
> >>from your two strings of 8 to two strings of 16 for .0188uF. This
> >>will increase the primary tap requirement to about 8 turns with
> >>your primary as is. A few reasons is you will put more L into the
> >>circuit, decrease that energy to something the coil would be happy
> >>with, and your peak voltage out the tranny is nearing 15kV (the 8
> >>string is good for 16kV which is a little close). Adding the extra
> >>caps per string will help the voltage rating of the cap bank.
> >>
> >>>- Is there a better(intelligent, mathematical) method of tuning
> >>&gt
;the c oil I can employ?
> >>
> >>
> >>Use a design program would be beneficial so you know at least the
> >>ball park for any given configuration.
> >>http://www.classictesla.com/java/javatc.html
> >>
> >>Also, you could employ a generator and oscilloscope to do the same.
> >>
> >>>- What kind of spark length performance should I expect from this coil?
> >>
> >>
> >>Far better than your getting. There are just too many losses
> >>throughout the system robbing all your power. For reference, here
> >>is a similar coil in size but only uses a 12kV 60mA NST. This one
> >>also uses a .0188uF MMC.
> >>http://www.classictesla.com/photos/ba45/ba45.html
> >>
> >>>- Any other obvious mistakes?
> >>
> >>
> >>Heat is th e obvi ous problem. That's the thing to work on. Also, if
> >>you do use a smaller cap size and you want to rewind your primary,
> >>remember 1 to 1.5" clearance.
> >>
> >>Take care,
> >>Bart
> >>
> >>
> >>
> >
> >
> >
> >
> >
> >
>
>
>
>