# Re: [TCML] Secondary self frequency

Has it been verified that the toroid was connected during measurement? I remember Andrew specifically mentioning selfC (which I personally always refer to as the sec without other components).
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But with everything installed, yes, likely 320kHz or in the neighborhood.

Regards,
Bart Anderson
Modesto, CA USA

Quarkster wrote:
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```Ed -

Andrew's secondary dimensions are 4" OD, with a winding length of 22".

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With his 4.5" X 18" diameter toroid installed, he is measuring a resonant frequency of around 515KHz.
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This seems far too high a frequency for a coil of these dimensions WITH the topload installed; something appears to be wrong.
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Regards,
Herr Zapp
----- Original Message ----- From: "Ed Phillips" <evp@xxxxxxxxxxx>
To: "Tesla Coil Mailing List" <tesla@xxxxxxxxxx>
Sent: Saturday, July 04, 2009 9:28 AM
Subject: Re: [TCML] Secondary self frequency

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Late message because I've been out of town. I use a home grown program to calculate SRF and here's what I get, based on a winding factor [turns / turns with no spaces] of 0.98:
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Diameter = 4.5 "
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Winding length = 18" [You didn't say whether the 18" was winding length or total form length]
```SRF = 555 kHz
Self capacitance = 7.6 uufd
Top load capacitance = 19.4 uufd
Loaded resonant frequency = 295 kHz
Turns = 653
DC resistance = 12.4  ohms

Not too far from what you got so your results don't sound strange to me.

Ed

Andrew Robinson wrote:

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Does this sound strange to anyone. A 4" OD x 22" (windings) secondary using 22 gauge wire with a 4.5" x 18" spun alum toroid having a self res freq of around 515kHz? I ran the tests in the lab today and thats what im getting. For some reason though, I had reason to believe it was going to be much lower. I'm gonna resubmit this email next Thursday when I get a chance to get back in the lab and im gonna take a video of myself taking the measurements. Maybe im just doing something wrong.
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Regards,
Andrew Robinson
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