Re: Piezo HV Power Supply

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

Original poster: "Ed Phillips by way of Terry Fritz <twftesla-at-qwest-dot-net>" <evp-at-pacbell-dot-net>

Tesla list wrote:
> 
> Original poster: "Jan Florian Wagner by way of Terry Fritz
<twftesla-at-qwest-dot-net>" <jwagner-at-cc.hut.fi>
> 
> > Have any of you made a Piezo Electric HVDC power
> > Supply?
> Well I once considered making a piezo powered coil (piezo from gas lighter
> ignition), but the output current is so low that, taken the tank capacitor
> leakage current, you'd probably be crunching that piezo crystal till
> doomsday.

	Over last weekend I tried rectifying the output of a piezo stack from a
gas stove igniter.  (Kind that goes for about 3 bucks at the hardware
store.)   The setup was extremely crude and haywire. Here were the
results of charging an 0.001 ufd 30 kV mica capacitor with various
numbers of "clicks":

CLICKS   VOLTAGE   COULOMBS   JOULES

  10       7500     7.5E-6     0.028   

  20      11300    1.13E-5     0.064

  30      13800    1.38E-5     0.095

  40      15200    1.52E-5     0.116
 
  50      17100    1.71E-5     0.146

The voltages are the average of 10 runs, and might be good to perhaps
10% at best.  One thing which surprised me was the rather large spark
length I could get when I brought a grounded lead up to the HV
terminal.  Both the lead on the terminal and the ground lead were #24
wire, cut with a pair of dikes.  For the 30 click run the sparks were
about 3/8" long, far more than the 1/4" I get when I just form a similar
gap between the ends of the stack. 

	In each case I was pushing the button on the igniter with my thumb and
holding the other end with a finger.  Tried pushing against something
much harder but got the same results.  More than once I got a spark
between my thumb and my finger, and it gave me a real jolt!

	I haven't thought about this enough to draw any conclusions except that
this isn't the way to power anything useful except a night-vision
imaging tube or similar very low current device. I should mention that
when I tried running the same experiment with a disk ceramic capacitor
marked "18 kV, 0.001 ufd" I got somewhat higher apparent voltages, which
I attribute to the possibility that the capacitance is substantially
less than 0.001 with high voltage across the thing.  I looked up similar
capacitors on the web and found typical capacitance at rated voltage is
from 10% to 50% lower than at low voltage, with the difference probably
due to different ceramic formulations.

Ed