Re: Twin coils 180 degrees out of phase : Weird happenning (fwd)
---------- Forwarded message ----------
Date: Fri, 10 Jul 1998 10:15:55 +1200
From: Malcolm Watts <MALCOLM-at-directorate.wnp.ac.nz>
To: Tesla List <tesla-at-pupman-dot-com>
Subject: Re: Twin coils 180 degrees out of phase : Weird happenning
> From: ESchulz531-at-aol-dot-com [SMTP:ESchulz531-at-aol-dot-com]
> Sent: Friday, July 03, 1998 6:45 PM
> To: tesla-at-pupman-dot-com
> Subject: Twin coils 180 degrees out of phase : Weird happennings
> I made two identical secondary. Same inductance 20 mh,
> only 0.2% off. But my toriods are different. One is 5" aluminum
> duct about 17 pf and the other is 7" about 22 pf. The primaries
> are connected in series. Same inductance in each. Using
> Medhurst formula I get a self capacitance of 11 pf. So the additive
> capacitance would be 28 pf and 33 pf. So the frequency for each
> coil should be 213 kHz and 196 kHz. With the coils alone I
> measured them to be 216 kHz and 198 kHz.
> OK that's all great. Now's the weird part
> Now with the coils together I measured a 176 kHz frequency on
> the 7" and 353 kHz on the 5". ? What in the world? By the way
> 176 * 2 = 352. I couldn't find any second harmonic on the 7" but
> I found a 2,3,4 harmonics on the 5". The voltage on the 5" was 3
> times greater than on the 7"
> I measured the frequency with my o-scope and a RF generator.
> The primaries in series and no primary cap. Normally my scope
> only loads my coils by about 0.7% By load I mean change the
> I imagine everything will go back to normal when I get identical
> toriods but what's going on here?
I suspect the two coils (made dissimilar by the different toploads)
are beating with each other and producing the odd frequencies you are