(Fwd) Prelim calcs on my work coil

To: tesla-at-pupman-dot-com
Subject: (Fwd) Prelim calcs on my work coil
From: "Malcolm Watts" <malcolm.watts-at-wnp.ac.nz> (by way of Terry Fritz <twftesla-at-uswest-dot-net>)
Date: Thu, 18 May 2000 07:42:09 -0600
Approved: twftesla-at-uswest-dot-net
Delivered-To: fixup-tesla-at-pupman-dot-com-at-fixme

*Earlier sent to R.Jones*

Dear All,
              Based on Robert's findings and wishing to dive in and do 
some reality checks, I did some measurements on my work coil 
yesterday and came up with the following results:

------- Forwarded message follows -------
From:           	Malcolm Watts <malcolm.watts-at-wnp.ac.nz>
To:             	"Robert Jones" <alwynj48-at-earthlink-dot-net>
Subject:        	Prelim calcs on my work coil
Send reply to:  	malcolm.watts-at-wnp.ac.nz
Date sent:      	Thu, 18 May 2000 11:43:27 +1200

Hi Robert,
                Based on your findings, I've done some calculations on 
my work coil to get a feel for Vout etc. This is the 10" coil I 
measured here yesterday.  I assumed no topload (so bare resonator 
C), a fixed shot of energy (3.5J which is roughly what will be getting 
into it) and a lossless resonator (well the measured Q is around 300).

- I calculated Zo = 25.92kOhms. This is significantly different (lower) 
  from that which you would calculate using Medhurst's C of course).
- I got a velocity propagation of 576 km/s (3 orders of magnitude     
below that of light in a vacuum)
- I calculated a peak base current of 17.6A or so
- I calculated peak Vout to be 457kV.

***Extra: both the current and voltages were calculated using (LI^2)/2
and (CV^2)/2  from a conservation of energy viewpoint and making 
the assumptions that there was a current maximum at the base and 
voltage maximum at the top and further assuming a cos, sin 
distribution respectively for each quantity.*

That last one is especially interesting. It is lower than the figure you 
get using Medhurst's C.  I like that for a whole lot of reasons. It 
seems to correspond to empirical observations of attached single 
shot spark lengths and it is not an out of this world figure in MV.

*Extra: I just cross-checked this result by multiplying the peak base 
current I calculated by the characteristic impedance of the coil and 
lo and behold, got the Vout that I calculated. I am reasonably 
confident that these results are true.*

       In the next few days, I plan to remove the topload and retune 
the primary to bring it back into resonance and do the following:

- Meter an accurate shot of energy in the primary
- Calculate the first transfer loss from pri - sec so I get a figure for    
  Esec (I can do this by monitoring scope waveforms - I figured out   
a method a couple of years ago)
- measure attached sparklength while observing the secondary E-     
  field to ensure near complete energy loss to the spark and   
calculate a figure for kV/in to see how real it is.

Retuning this coil is going to be a bit nasty - the primary only has 
four turns in it already with a substantial topload and primary Q is 
going to suffer badly. However, if I can retune it accurately (and it 
might be best to try this on another coil where Xp is substantially 
higher), I can calculate Esec quite satisfactorily.

Regards,
Malcolm

------- End of forwarded message -------