Re: measuring secondary parasitic capacitance?

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

Original poster: "Antonio Carlos M. de Queiroz by way of Terry Fritz <twftesla-at-qwest-dot-net>" <acmq-at-compuland-dot-com.br>

Tesla list wrote:
 >
 > Original poster: "Laurence Davis by way of Terry Fritz 
<twftesla-at-qwest-dot-net>" <meknar-at-hotmail-dot-com>
 >
 > just out of curiosity i tried to measure the capacitance of a secondary.
 > my meter kept giving the out of range error, then at one point started
 > to give a reading. it wasnt stable.  the lowest I read was .150 nf.
 > I didn't do the tesla calc thing on the secondary, but I would expect
 > two things.
 >
 > should be .015nf (or 15pf) or rounds 'bout there.

The out of range error in a capacitance meter usually means that,
or the capacitance is higher than the limit of the range, or there
is a DC patch in parallel with the capacitor. In this case, the
wire of the coil is a possible candidate, depending on how did
you try to make the measurement.
The "self-capacitance" of a coil can't be measured directly with
a capacitance meter, since it is a function of the voltage
profile along the coil when it is operating.
An approximate value can be obtained by suspending the coil at
some distance from the ground and measuring the capacitance between
the coil and the ground. As "ground", your body is enough. Discount
the reading obtained with the leads of the meter in the position
used in the measurement, but not in contact with the coil.
This measures the "body capacitance" of the whole coil, that is
very closely twice the "self capacitance" of the coil with one
side grounded.

Antonio Carlos M. de Queiroz