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Measuring Secondary Coils




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From:  Malcolm Watts [SMTP:MALCOLM-at-directorate.wnp.ac.nz]
Sent:  Sunday, August 23, 1998 4:38 PM
To:  Tesla List
Subject:  Re: Measuring Secondary Coils

Hi Chris,

> From:  chris.swinson [SMTP:chris.swinson-at-zetnet.co.uk]
> Sent:  Friday, August 21, 1998 12:31 PM
> To:  Tesla List
> Subject:  Re: Measuring Secondary Coils
> 
> Hi All,
> 
> 
> -----Original Message-----
> From: Tesla List <tesla-at-pupman-dot-com>
> To: 'Tesla List' <tesla-at-pupman-dot-com>
> Date: 21 August 1998 05:45
> Subject: Measuring Secondary Coils
> 
> 
> >
> >----------
> >From:  RWB355-at-aol-dot-com [SMTP:RWB355-at-aol-dot-com]
> >Sent:  Thursday, August 20, 1998 5:18 PM
> >To:  fwd
> >Subject:  Re:Measuring Secondary Coils
> >
> >---------
> >From:  chris.swinson [SMTP:chris.swinson-at-zetnet.co.uk]
> >Sent:  Wednesday, August 19, 1998 7:44 AM
> >To:  Tesla List
> >Subject:  Secondary Frequency
> ><SNIP>
> >
> >Hi Chris, all !!
> >
> >Chris
> >
> >I hope you are not thinking of just "plugging" a capacitor and/or
> inductance
> > meter across your secondary coil and then just reading what the meter
> tells
> > you. That doesn=B4t work !! The measuring frequency of these meters is =
> way
> too
> > low to give an accurate reading of the inductance (capacitance) the coi=
> l
> has
> > at "our" operating frequencies. Typical DMM=B4s run at about 200Hz bett=
> er
> ones
> > at 400Hz or 1000Hz. I don=B4t know, however, if there are RF "adjusted"
> meters
> > that would be able to really measure the values correctly.
> >
> 
> Humm, I've not had problems like this before, I know that DMM's can lie
> though at times.  Only thing which troubles me is the fact I have a curre=
> nt
> limiting chart which tells you in steps of 1 amps the inductance.  I trie=
> d
> this out with a few TR's and the meter aggreed with the table which sugge=
> sts
> that the meter is correct.  I have treid lots of calculations and they al=
> l
> say about 30mH, But the meter says 11mH.

I wouldn't trust a DMM with reactive components hooked to it. You can 
safely bet that Wheeler's formula gives a pretty close figure for  
the inductance. You can cross check by calculating your secondary 
capacitance using Medhurst's formula, measuring its resonant 
frequency without a topload, then calculating the inductance using 
those two knowns.

Malcolm
<snip>