Hi
If you know anything about this topic, or the design of electron gun
accelerator electrodes, please repond. After four posting in the
electronics newsgroups only three kind souls replied. This is why I'm
cross-posting. Someone out there must know something - or are you all
busy selling negative ion generators? :-)
I've managed to build myself a negative ion generator and am currently
evaluating it to see whether it really does help to lift my gloom at
being in an office that's effectively underground - No sunlight, no
visible sky :-(
Don't bother sending lots of flak about this - even if it doesn't
work, assuming I don't produce lots of ozone, it won't do any harm!
I'm using the usual Cockcroft-Walton voltage multiplier giving (I
think) about -3.5KV and feeding this into an array of needles.
I discovered along the way NOT to build the voltage multiplier on
phenolic PC board. The voltage output was way down - fibreglass board
is better. I guess at the voltage levels involved, what is normally
considered an insulator may not be!
The generator has a chain of 15 multiplier stages (230Vac in) using
1N4007 diodes and 0.01uF 1KV ceramic capacitors feeding into four
needles via a 4.7M resistor.
When I get within about 4 - 5cm of the needles it starts to hiss -
faintly but audibly, and at night I can see tiny pin-pricks of blue
light. They're so faint that it's impossible to focus on them!
- Is the hissing normal?
- How can I tell if I'm producing any significant amounts of ozone?
Is a voltage on the end of the chain of 15 multiplier stages (230Vac
in) likely to generate ozone? or is it not just the voltage but also
the sharpness of the point? I'm using sewing needles sold as "sharps"
but I've no idea of their end diameter (although they are sharp :-).
I really would appreciate some direction - the physics texts in a
university library are not very helpful when you need practical
guidance!
Thanks
Giovanni
PS: If you have a few minutes, could you skim the following detailed
description and let me know your thoughts?
*************** More detailed description of generator ****************
and accelerator electrodes follows
To detect any ion output I'm using the usual neon and capacitor detector:
%%%%%%%%% .015uF %%%%%%%%%% <--- Square of PC board about 1" x 1"
%%%%%%%%%----||----%%%%%%%%%% 2.5cm sq
%%%%%%%%% %%%%%%%%%%
%%%%%%%%%---neon---%%%%%%%%%% <- hold or Ground this end
%%%%%%%%% %%%%%%%%%%
Pad A Pad B
place near
needles
I can't measure the voltage on the needles as the output impedance is
so high, a 100Mohm Fluke 40KV probe loads it but the neon detector
works ...
BLINK RATE:
No accelerator - at 15mm away - once every ten seconds
No Hissing at any distance
With accelerator - at 15mm - once every 3.5 seconds.
35mm - once every 10 seconds
The accelerator is a small block of aluminium with conical holes and
has about -1500V on it - it's connected 10 diodes down from the high
voltage end.
The accelerator was made by drilling conical holes with a lathe
centering bit about 1/4" (7mm) in diameter so that the side view is:
______
accellerator -> |____/
needle -------> ----------
The bottom is the same shape (eg 45 degree cone) but I can't draw it
using ascii graphics. The 4 needles are spaced about 20mm apart (0.8")
and protrude about 4mm (1/6") past the end of the 1/4" cone.
With the accelerator in place, it will start hissing at me if I get
within about 5cm of the needles - before I put it in its box. Boxing
it seems to dampen things down a bit. The black plastic box has holes
drilled in it as an approximate continuation of the flare of the
conical shape of the aluminium accelerator block which is screwed to
the back of the front panel.
It's definitely got some ion wind but how much? How I can measure the
output (ions/cc) or alternatively (and much cheaper) what's the blink
rate from a commercial unit of known output with the type of neon
detector described above?
You can probably calculate the ion output (at least within an order of
magnitude) by assuming that "if so much current is going in and
nothing's getting hot" then that current - "in ION form" - is coming
out the other end, but I've not looked at my physics texts for years
as you can probably guess by that handwaving logic!
The shape of the accelerator is also a bit of a mystery. The 4mm that
the needles now protrude is simply what "looked" reasonable. The conical
shape is simply because I had the lathe centering bits.
What's the desirable shape? - probably exponential :-(
Obviously they'll be a relationship between the flare angle, how far
the needles poke out beyond the end of the accelerator, the voltage on
the accelerator and that on the needles ...
Any info or readable references? (eg those without triple integrals :-)
Any thoughts would be very much appreciated ...
Thanks
Giovanni
__________________________________________________________________________
Giovanni Moretti "WHATEVER YOU CAN DO, OR DREAM YOU CAN, BEGIN IT.
Computer Science Dept BOLDNESS HAS GENIUS, POWER AND MAGIC IN IT" Goethe
Massey University Ph +64-6-3504184 Fax +64-6-3502259
Palmerston North, NEW ZEALAND G.Moretti@massey.ac.nz ZL2BOI
Date: 23 Jul 1996 12:42:35 GMT
Original Subject: Negative Ion Generator: should my homebrew one hiss and glow in the dark?