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Right now I am using nine components intended for home air ionizers in parallel, I'd like to build one big one. I've heard that if one keeps the discharge voltage at -4kV, this produces negative ionization with a minimum of ozone, but I'd like to know more than that, e.g., where that voltage arises from, whether and how it changes with temperature and/or current applied, et cetera. And I'd like to keep it as simple as possible, though I probably can still pull out my long-ago calculus if I must. Suggestions?

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  • $\begingroup$ How close are your needle points (ion emitters) to other items that are more positive than the points? Too close, and that'll generate more ozone. $\endgroup$ – Mike Waters Sep 19 '19 at 13:39
  • $\begingroup$ The emitters are in the form of the ends of carbon-fiber brush bristles. That is a very interesting datum. Can you direct me to a discussion of its causality? $\endgroup$ – Jonathan Brickman of Topeka KS Sep 19 '19 at 16:59
  • $\begingroup$ I will if you buy my negative ion generator business. :-) $\endgroup$ – Mike Waters Sep 19 '19 at 17:38
  • $\begingroup$ Look up field emission in a physics book. That is the principle that all high-density corona-discharge negative ion generators are based on. $\endgroup$ – Mike Waters Sep 20 '19 at 2:16
  • $\begingroup$ 4 kV is a good number, provided that the emitter points stay sharp. Our first ionizers used just above that voltage. You could even raise that a kV or two with sharp points kept far enough away from other surfaces. You'll have to experiment with your emitter configuration. $\endgroup$ – Mike Waters Sep 21 '19 at 21:46
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AFAIK generate your 4kV using off the shelf components. The trick is getting the electrons off the wire, and into the air. Sharp points are your friend here. An electron at the tip is repelled by all electrons on the surface of the point behind it.

In practice, the more common practice is to use a very small diameter wire. The tight radius of the wire gives the same effect. See the guts of a photocopier.

Actual current is tiny. Parasitic losses of your circuit, and fans to move the ionized air will be much larger.

Thoughts on removing ozone:

  • This is a ppm problem. Would introducing a small amount of hydrocarbon along with a UV light source cause the ozone to recombine? Do the reaction in a mirror chamber so that the light has many chances to excite an ozone molecule.
  • Ozone is used for water purification. Implication is that it is soluble in water. Don't know how the solubility compares to that of oxygen. Use something the the stack scrubbers on power plants, where the air rises through a rain of water droplets just barely large enough to fall.
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  • $\begingroup$ Yup. Probably going to use a carbon fiber brush, have found a few varieties. Won't have to worry about a fan, because the application is an engine air intake. But I do want to rigorously minimize ozone. I have found off-the-shelf DC-DC converters, some which do a fixed 4kVDC, others which are variable from 100VDC to 6kVDC (and many other variations), and thus am wondering what environmental parameter(s) might determine the precise voltage needed to keep that ozone minimized. Humidity? Temperature? Other? Or is there something other than voltage I need to control for this? $\endgroup$ – Jonathan Brickman of Topeka KS Sep 9 '19 at 1:51
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    $\begingroup$ Read up on electrostatic precip. I know that humidity and temperature are both considerations. Charge bleeds off in humid conditions faster -- water is a lighter molecule? Polar? Why is ozone a consideration for an engine intake? $\endgroup$ – Sherwood Botsford Sep 9 '19 at 13:25
  • $\begingroup$ Electrostatic precipitation, got it, I will. Ozone is a consideration principally because of its corrosive and poisonous nature. Before the consumer standards were set, consumer air ionizers used to corrode themselves to death quite routinely. Not so much since. $\endgroup$ – Jonathan Brickman of Topeka KS Sep 19 '19 at 17:02
  • $\begingroup$ Added thoughts on ozone removal. $\endgroup$ – Sherwood Botsford Sep 20 '19 at 19:29
  • $\begingroup$ One problem we've found with a corona wire is that they have to be kept clean to maximize the electron emission. Under .005" diameter, they emit electrons from their entire length, even with a sharp point on one end. But I suggest that you try it! You can buy small spools of it. They usually have a coating with a low work function. $\endgroup$ – Mike Waters Sep 21 '19 at 21:59

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