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.
> 
>