RE: silly question

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Loudner, Godfrey by way of Terry Fritz <twftesla-at-qwest-dot-net>" <gloudner-at-SINTE.EDU>

Hello Peter

Power transformers are designed so that the coefficient of coupling between
the primary and the secondary is closed to 1. This makes power transformers
efficient. This is done by placing the copper of the primary and secondary
in closed proximity to each other and to the core. The proximity problem is
burdened by insulation and heat sinking requirements. The usual design
equations are for idealized transformers that are 100% efficient, and they
work well on power transformers. When the coefficient of coupling is
lowered, the idealized equations begin to fail. In this case, one can fall
back on the equations which contain a description of the magnetic field of
the core. These equations are too complicated to solve for analytical
solutions, and computer application is needed to provide a numerical
solution in each individual design problem. This is already beyond the
resources of most, if not all tesla coil builders.

In the case of NSTs, the design features are to reduce the amount of
magnetic flux that can pass through the HV coils. One way to do this is to
place the primary and secondary at opposite ends of the core, and to place
inside the core window magnetic shunts to interrupt the flow of magnetic
flux through the core. The cross section of the core can be made smaller
than what you expect to further reduce the flow of magnetic flux. These
actions reduce the coefficient of coupling, and hence the applicability of
the formulas for idealized transformers. 

There is one way out of all these complication to a tempered degree. Start
with an excellent core that is capable of the KVA required. Use the
idealized formulas to compute the number of turns in the primary for input
voltage and secondary voltage desired. Make sure that the primary wire is
capable of carrying the current at the KVA level chosen. Then construct the
primary and install it on the core. Using the wire and insulating material
you have chosen, make a small secondary with a few layers and install it on
the core in the same location where you are going to place the final
secondary. Measure the performance of the small secondary. This should give
you enough information to scale up to desired output. As long as you do not
exceed that KVA level of the core, you can expect a linear scale up. If the
scale up exceeds the KVA level of the core, saturation of the core will come
into play and the scale up will no longer be linear. If you want build in
current limiting features, use a large square core and locate the primary
and secondary at opposite ends of the core. 

Godfrey Loudner     

> -----Original Message-----  From:	Tesla list [SMTP:tesla-at-pupman-dot-com]
> Sent:	Thursday, September 27, 2001 3:09 PM
> To:	tesla-at-pupman-dot-com
> Subject:	re: silly question
> 
> Original poster: "Peter Lawrence by way of Terry Fritz
> <twftesla-at-qwest-dot-net>" <Peter.Lawrence-at-Sun-dot-com>
> 
> 
> I'm not making much progress (lot of other more important things than
> TC'ing
> lately) but I am making a mechanical transformer coil winding machine. By
> mechanical I mean that is uses gears and lead screws to position the wire
> while the bobbin turns to take it up. When I get it finished and have
> wound
> a coil I'll try to post some pictures.
> 
> On the other hand Terry Fritz has made an electro-mechanical one (stepper
> motor to turn the lead screw) and he has pictures of it somewhere in his
> web page.
> 
> http://hot-streamer-dot-com/TeslaCoils/Misc/Winder/winder.html
> 
> I would appreciate if anyone that has taken appart an NST could supply the
> NST ratings and the dimensions of the steel core that goes through the
> coils. There seems to be a large difference between the core cross section
> used for a shunted/current-limited NST verses that used for
> non-shunted/non-
> current-limited power transformers and so the standard engineering
> equations
> and table for designing a power transformer are not quite right for an
> NST.
> 
> -Peter Lawrence.
> 
>