turn counters was Re: Sewing machine motor

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

Original poster: "Jim Lux by way of Terry Fritz <teslalist-at-qwest-dot-net>" <jimlux-at-earthlink-dot-net>

A couple of thoughts:
1) There are cheap counters made for odometers on bicycles. Consumer 
products, etc.
2) Why would you want to count the number of turns, other than for academic 
interest? In general, once you've decided on a size of wire and 
corresponding winding pitch, the length of the winding will tell you the 
number of turns to within a few percent.  More to the point, I suspect that 
the inductance of the coil won't change very much if the number of turns is 
say, 5% different.

Wheeler formula is r^2 *N^2/(9*r + 10*l).. yes, there's a N^2 dependency, 
but, say you've got 1000 turns instead of the 1050 you planned on: a 5% 
error in the number of turns (but radius and length stay the same)... The 
inductance will be off by 10 percent...an amount easily accomodated in the 
tuning process.


Of course, having a turns counter makes it easy to calibrate your TPI on 
the first couple inches, before you fininsh winding all 60" of the coil, or 
whatever.



At 11:07 AM 1/13/2003 -0700, you wrote:
>I use a magnetic reed switch to trigger my electromechanical counter.  This
>involves mounting a permanent magnet on one of the winder's form end-pieces.
>
>
> > Secondly, I also purchased a resettable electromechanical counter to keep
> > track of form revolutions.  Anyone have any hints for me?