RE: [TCML] Terry Filter Resistors

["Lau, Gary" <Gary.Lau@xxxxxx>]

What are the dimensions of these resistors?  My 6"x28" secondary coil's inductance is only 89mH, so 145mH seems huge.  Granted, the resistor is wound with much finer wire with more turns, but it'll make an interesting sanity check to see how many turns a secondary wound to the same dimensions as your resistor would require to achieve 145 mH.

Regards, Gary Lau
MA, USA

> -----Original Message-----
> From: tesla-bounces@xxxxxxxxxx [mailto:tesla-bounces@xxxxxxxxxx] On
> Behalf Of bartb
> Sent: Wednesday, January 28, 2009 9:17 PM
> To: Tesla Coil Mailing List
> Subject: Re: [TCML] Terry Filter Resistors
> 
> Hey Gary, Matt,
> 
> Confirmed today at 145mH on todays reading (leads). Also measured 992
> ohms. Measurements with 27XT.
> 
> I think Matt is correct and it's logical. If I do the math (noting that
> the 27XT frequency is 1kHz):
> 
> Z = 145mH x 6.28 x 1kHz = 910.6 ohms.
> 
> XL = sqrt(992^2 - 910.6^2) = 394 ohms (note R-Z due to -sqrt).
> 
> L = 396 / (6.28 x 1kHz) = 62.7mH
> 
> Still significant, but then these are rather large wire wound resistors,
> so not overly surprising.
> 
> Regards,
> Bart
> 
> 
> Gary wrote:
> > Please confirm "I just checked the resistor in question and it measured 146mH at
> 1kHz."  146 mH sounds about a million times too high for the inductance of a
> wirewound resistor.
> 
> > Matt wrote:
> > I think part of the problem is that most LC meters don't measure Inductance
> directly. They actually measure the Z of the device and assume Z=XL, and
> therefore L=Z/2pif, which for most inductors is close enough. For a wire-wound
> resistor though, this is not a good approximation, since actually Z=sqrt(R2+XL2),
> and R is no longer negligible. You could use the L?shown by the meter to calculate
> what Z it actually read by Z=2pifL, then using the known resistance, calculate a
> corrected XL? from XL=sqrt(Z2-R2)and from that, determine the corrected L by
> L=XL/2pif.
> >
> > Matt D.
> 
> _______________________________________________
> Tesla mailing list
> Tesla@xxxxxxxxxxxxxx
> http://www.pupman.com/mailman/listinfo/tesla
_______________________________________________
Tesla mailing list
Tesla@xxxxxxxxxxxxxx
http://www.pupman.com/mailman/listinfo/tesla