Re: Coupling

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: "MIKE HARDY" <MHARDY@xxxxxxxxxx>

Sorry about getting back to you Bart almost 2 months after this kind reply.
It's been hard to find a decent day wheather wise to run my coil. I moded
the sec mounting to adj the sec heighth with threaded rod.I'm getting my
best results with the bottom of sec 1" above the center of the pri. I'm
tapped at 6 turns, with a 0.066uF tank cap. I'm pushing about 4 kVA, and
getting HOT consistant 6 foot arcs, some 7, and a few probably close to 8
feet. I was able to set the coil up in my buddies pole barn and there had
the time to tweek it properly. I find that small stuff, like setting the
toroid as close to the sec as possible can have signifigent affects. Anyway
thanks forthe help.
----- Original Message -----
From: "Tesla list" <tesla@xxxxxxxxxx>
To: <tesla@xxxxxxxxxx>
Sent: Wednesday, November 16, 2005 12:02 PM
Subject: Re: Coupling


> Original poster: "Barton B. Anderson" <bartb@xxxxxxxxxxxxxxxx>
>
> Hi Mike,
>
> Yes, I really meant that the primary would be 1" above the bottom of
> the secondary winding. Racing sparks are caused by poor tuning and by
> a coupling coefficient overly tight (energy transfer is too fast
> causing a voltage stressed secondary winding). The vertical position
> of the secondary affects coupling and also affects the proximity of
> primary to secondary voltage standoff (we don't want to arc from
> primary to secondary, which is a different mechanism than coupling).
> You have a 1.25" gap between the secondary and primary when the sec
> bottom turn is even with the pri inner turn. For your coil, that's
> about perfect in my mind. As the primary inner turn is moved
> vertically up and beyond the bottom sec turn, this 1.25" gap is
> maintained. You should not have arc over. However, coupling will
> change as a result of adjusting the primary to secondary vertical
position.
>
> The reason your coupling was so low, is because the primary was 2.5
> inches below. This is a large distance. As you decrease the inductive
> proximity (bring the coils inductively closer together, coupling will
increase.
>
> I used Javatc to calc the coupling coefficient. It is more accurate
> than you can measure. There are a few programs out there which
> perform this degree of accuracy. Javatc, Fantc, ACMI, Paul's TSSP
> software, and I believe Antonio's INCA program. ACMI was the first to
> do it and was developed by Paul Nicholson. There were numerous
> measurement vs. program projects to make this happen. Eventually,
> ACMI could predict better than we could measure (due to error within
> our instruments). Javatc includes this portion of ACMI (among other
> things). What is different about Javatc is that it is a "Tesla Coil
> Design" program. It's not just a program for inductance's and
> frequency's. When coilers have questions such as yours, it's really
> the perfect program to answer questions.
>
> I use it because I can input nearly all parameters which I know are
> taken into account. For example, you just mentioned you tap that 10
> turn primary at 8 turns. That information makes a difference, not big
> difference, but there is a change. So now I can easily recalc and see
> what changes.
>
> This tap position changes your current k to 0.081 (slightly lower). I
> can then just enter 0.15 into Javatc's "Desired Coupling" input box
> and re-run the program. Ok, now I see 0.15 k in the output. I can
> then go up to the primary and look at the primary height input values
> and compare to the secondary bottom height value. The difference is
> 0.935 or nearly 1". I used a base height value of 20" off the floor
> for the bottom turn of the secondary, thus, your primary was 2.5"
> below this at a height of 17.5". The program now shows the height at
> 20.935", indicating that for a coupling of 0.15, your primary must be
> 0.935" above the secondary bottom height.
>
> It's kind of strange for me. For a long time, we could only measure
> coupling and guess during the design process. Since ACMI and the work
> performed by Paul, Terry, myself, and others, coupling is now one of
> the outputs which carry's the highest accuracy (thanks Paul :-) ).
>
> When Javatc adjust the "desired coupling", it actually equates
> coupling at the original values. It then takes half steps and re-runs
> the program, over and over until a desired degree of accuracy is
> found (which is something like 0.1%). The half steps are changes to
> the primary height positions. The reason is raises the primary
> instead of lowering the secondary is to prevent super-excessive
> computation time. There's no reason you couldn't simply lower the
> secondary to achieve the same result. For the program, it's just
> faster to compute the primary positions.
>
> Hope this helps,
> Take care,
> Bart
>
> Tesla list wrote:
>
> >Original poster: "MIKE HARDY" <MHARDY@xxxxxxxxxx>
> >
> >I'm tapped at about 8 turns. I plan on a bigger topload once I get the
bugs
> >out. Do you really mean to put the primary above the bottom turn of sec?
> >Won't this cause racing sparks? How did you calculate the coupling from
my
> >measurements?
> >----- Original Message -----
> >From: "Tesla list" <tesla@xxxxxxxxxx>
> >To: <tesla@xxxxxxxxxx>
> >Sent: Monday, November 14, 2005 10:36 PM
> >Subject: Re: Coupling
> >
> >
> > > Original poster: "Barton B. Anderson" <bartb@xxxxxxxxxxxxxxxx>
> > >
> > > Hi Mike,
> > >
> > > Your coupling coefficient is currently at 0.083 and could certainly
> > > be adjusted. I usually like to start out at 0.15 k. If you position
> > > your primary 1" above the bottom secondary, this will get you to
> > > nearly 0.15. This is assuming the coil is tapped at 10 turns which
> > > indicates a pretty good size topload.
> > >
> > > Take care,
> > > Bart
> > >
> > > Tesla list wrote:
> > >
> > > >Original poster: "MIKE HARDY" <MHARDY@xxxxxxxxxx>
> > > >
> > > >I know that tweeking these coils is how we figure this stuff out,
> > > >but getting educated opinions doesn't hurt. I finally got to fire up
> > > >my new coil.
> > > >
> > > >6" O.D. sec., wound for 32", about 1000 turns
> > > >3/8" cu tube, spaced 3/8" for 10 turns
> > > >sucker gap
> > > >right now 30 nF 35 KV maxwell
> > > >14400V  PT running @ 1800 W -125 MA
> > > >
> > > >I'm not getting the performance I expect. Right now about 52"
strikes.
> > > >I suspect the coupling may be a little loose. The first turn of
> > > >pri.is 1-1/4" from sec, and first turn of sec. is 2-1/2" above the
> > > >pri. Tomorrow I may try to find some longer nylon screws, and raise
> > > >the primary.
> > > >So what do you think, am I too loose? Should I bother doinng this?
> > > >
> > > >