[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: A question of coupling

Original poster: "Barton B. Anderson" <bartb@xxxxxxxxxxxxxxxx>

Hi Curt,
The coupling will be maximum when the primary is center to the secondary. As the primary is moved away from the center toward one of the ends of the coil (either end), the coupling will decrease. As the primary is moved even further below or above the primary (perpendicular), the coupling continues to decrease.
This occurs because mutual inductance is greatest when the coils are at their closest proximity, which for a 2 coil Tesla configuration is when the primary is centered to the secondary. 

As to your specific question:
Let's say you start with a config where bottom pri = bottom sec (as you mention). You will have "some" coupling value. As you move the primary up the coil, the coupling increases. When the primary is center to the secondary, it will be maxed out. As you go past center, the coupling will begin to fall as you near the top end. 

Your friend is wrong. Prove it to him (measure it).
I drew up a well known measurement technique and put up here (since my ascii art sucks). 

<http://www.classictesla.com/download/M_and_k_Measurement.gif>http://www.classictesla.com/download/M_and_k_Measurement.gif
Maximum coupling is a point I need to know for the program, it is not "best" for obvious reasons. For a program, I need to know when to stop raising the the primary to achieve a coilers "desired" coupling. Imagine if someone put in a coupling value of 1 and the max possible was say only .25, well, obviously, I need to know when to stop. This is "my" purpose for realizing and identifying a geometry's maximum possible coupling.
Your primary is well below the secondary. As you raise it (small 1/4" to 1/2" increments), your coupling "will" increase. Because it is helical, it will have a significant effect on coupling due to it's geometric relationship with the secondary. Probably sooner than later, you will begin to notice periodic racing sparks. As soon as that begins, you should try to retune before adjusting the primary back down (to maximize performance). The primary itself will change the secondary resonant frequency slightly, so retuning may improve the racing spark problems and allow a higher k. 

Take care,
Bart

Tesla list wrote:

Original poster: "C. Sibley" <mailto:a37chevy@xxxxxxxxx><a37chevy@xxxxxxxxx>

Mine is a solenoid (helical) primary.  Back to the
original question, if the secondary starts below the
botton of the primary, does that increase coupling,
and would it help comphensate for the loose coupling
die to the oversize primary?  According to JAVATC it
does, but my friend insists that I would get less
coupling...

--- Tesla list <mailto:tesla@xxxxxxxxxx><tesla@xxxxxxxxxx> wrote:
> Original poster: "D.C. Cox" <mailto:resonance@xxxxxxxxxx><resonance@xxxxxxxxxx> 
>
>
> Lay a straightedge across the top of your primary if
> it is a flat spiral ---
> this is the horizontal plane.  This does not apply
> to solenoid type primaries.
>
> Dr. Resonance
>
> > > I bet you need this size sec approx 1/2 inch
> above
> > > the horizontal
> > > plane of the pri
> >
> >What do you mean by horizontal plane of the
> primary,
> >the plane of the base or at the top?
> >
> >Thanks,
> >
> >Curt.
> >
> >
> >
> >
> >
> >--- Tesla list <mailto:tesla@xxxxxxxxxx><tesla@xxxxxxxxxx> wrote:
> >
> > > Original poster: "D.C. Cox"
> <mailto:resonance@xxxxxxxxxx><resonance@xxxxxxxxxx>
> > >
> > >
> > > You might consider a "test rig" setup using a
> small
> > > DC motor running
> > > a thick piece of tygon tubing to lower and
> elevate
> > > your sec coil
> > > while it is running.  A speed of 6-10 rpm will
> work
> > > nice.
> > > DC motor is reversable.
> > >
> > > I bet you need this size sec approx 1/2 inch
> above
> > > the horizontal
> > > plane of the pri for the best performance
> without
> > > flashover.  The pri
> > > is also too long.  It needs to be 2-3 inches
> total
> > > base to
> > > top.  Since it's only a 60 ma NST you could use
> 12
> > > awg scrap house
> > > wire for a test and then switch to #6 or 8 awg
> solid
> > > copper ground
> > > wire (Home Depot) for the final coil.
> > >
> > > Distance from pri to sec should be approx 2-3
> inches
> > > when the primary
> > > is shortened.
> > >
> > > With this type of solenoid coil you also need to
> > > avoid extra unused
> > > turns at the top as the "auto-transformer"
> effect
> > > will produce over
> > > 40-50 kV on the top turn of your primary.
> > >
> > > Dr. Resonance
> > >
> > >
> > > >The secondary is 2.25", and the primary is
> 10"...
> > > >
> > > >Pictures at <http://www.nationalvintageracing.com/temp>www.nationalvintageracing.com/temp 
> > > >
> > > >Curt.
> > > >
> > > >
> > > >--- Tesla list <mailto:tesla@xxxxxxxxxx><tesla@xxxxxxxxxx> wrote:
> > > >
> > > > > Original poster: "D.C. Cox"
> > > <mailto:resonance@xxxxxxxxxx><resonance@xxxxxxxxxx>
> > > > >
> > > > >
> > > > > What is the dia. of your sec. coil??
> > > > >
> > > > > Dr. Resonance
> > > > >
> > > > > >I completed my first coil this last weekend
> and
> > > did
> > > > > a
> > > > > >few unusual things in the construction.
> The
> > > > > helical
> > > > > >primary is much larger diameter than
> required
> > > for
> > > > > such
> > > > > >a small primary.  I used a secondary coil
> that
> > > I
> > > > > wound
> > > > > >in High School 25+ years ago, and intend to
> > > replace
> > > > > it
> > > > > >later with a large coil.  To help
> comphensate
> > > for
> > > > > the
> > > > > >loose coupling I moved the primary up a
> couple
> > > of
> > > > > >inches.  As I understand it, the maximum
> > > coupling
> > > > > >would be with the primary centered half way
> up
> > > the
> > > > > >seconday, but this location would result in
> > > > > >overcoupling the coil.  I chose a height
> that I
> > > > > >beleive was a good compromise.
> > > > > >A friend with a lot of tesla experience
> what I
> > > had
> > > > > >done and objected. He insisted that I
> needed to
> > > > > "drive
> > > > > >the coil from the bottom".  While tuning
> the
> > > coil
> > > > > we
> > > > > >ended up removing several inches of turns
> from
> > > the
> > > > > >bottom of the secondary coil due to his
> > > insistence.
> > > > > >Now that the coil is working, I'm
> considering
> > > > > moving
> > > > > >the secondary down to it's original
> elevation.
> > > Who
> > > > > is
> > > > > >right here?  Is there a reason (other than
> over
> > > > > >coupling and increased possibility of arc
> over)
> > > > > that
> > > > > >this should not be done?
> > > > > >Thanks,
> > > > > >Curt.
> > > > > >
> > > > >
> > > > >