Many claims have been made for the beneficial attributes of negative atmospheric ions on human and plant life. Studies have shown that negative ions promote physical and mental alertness and well-being, while positive atmospheric ions (such as in polluted air) cause discomfort and llassitude.
The surrounding air, after a thunderstorm smells clean and fresh due to generation of negative ions from lighting. The negative ions attach to smoke, dust, and pollen particles, bringing them to the ground to discharge, leaving fresh, clean air. That's why a cool room with a breeze is invigorating compared with one that's stiflingly heated. Cool air is generally negatively ionized, whereas heated air is generally positively ionized.
Negative ions are air molecules with one or more excess electrons, and can produced artificially by a low-power, high voltage (about 5 to 14-kilovolt) DC supply. The positive terminal is grounded, and the other (the emitter) is a needle exposed to air. Extra electrons on the emitter's surface produce a high local electric field owing to its pointed shape. The electrons exit the emitter needle's surface due to the polarization of surrounding air molecules between the emitter needle and ground. The electrons collide with the air molecules and produce negative ions.
What actually causes electrons excitation (corona) is the high electric field at the tip which is directly proportional to the voltage and is enhanced by sharpening an electrode tip to a fine point. The high electric field strains the air molecules polarizing them by a phenomenon called dipole polarization. Air molecules are forced to accept electrons creating negative ions.
The negative ion generator described here is low-cost and easy to build. It generates high voltage, but at very low current. However, safety precautions must be taken, as for any high-voltage device.
The negative ion generator circuit
The negative ion generator is based on cascaded half-wave voltage doublers. The biggest advantage to using voltage doublers is that they use inexpensive low-voltage parts. The basic half-wave voltage doubler is presented in Figure 1.
Figure 1. Half-wave voltage doubler
Regarding Figure 1, we'll assume that C1 and C2 are initially discharged. During the first half-cycle shown in a, the upper input terminal is positive and the bottom negative, so D1 conducts and Cl charges to about V*√2 =170volts peak. Diode D2 can't conduct, since it's back-biased, so C2 discharges through RL. In the second half-cycle (b), the analysis is similar, except that D2 conducts and C2 charges.
The circuit is really a transformerless voltage amplifier. While T1 can provide isolation, as well as increase the AC voltage initially going into the doubler, the amplification due to the doubling action would occur without it. When the polarity reverses, both the input voltage and the charge across C1 are in series like two batteries, producing about 2*V*√2=340 volts peak. The half-wave doubler can't be used with a load that draws much current.
A negative ion generator can be built using cascaded voltage doublers, as shown in figure 2 and adding one (or more) sewing needle(s) as an emitter to generate "corona wind."
Figure 2. This 25-stage voltage doubler can be used as a Negative Ion Generator
The circuit delivers 3.75 kilovolts DC when powered from 120 volts AC, 7.5 kilovolts DC when powered from 240 volts AC, and 12.5ΚV when powered from 400V AC. The output of the cascaded voltage doubler should be terminated with at least 2 megohms, and only then be al lowed to extend beyond a protective plastic case, for safety.
Due to the high voltages some safety precautions must be taken. For instance, if you face any problems with the circuit in Fig. 8 (or any other high-voltage circuit), you must discharge every capacitor before you check for malfunctions. To properly discharge capacitors, disconnect the circuit from the power line and short circuit every capacitor or discharge all capacitors directly to a cold water pipe (as earth ground with good electrical connection). Discharge all capacitors twice, since they generally either hold charge, or tend to recharge from other capacitors. Do not use an AC line ground or a chassis ground instead of an earth grounded water pipe, or you may blow a fuse or damage parts.
Cascading transformers for raising voltage
If you can not find a 220-450V secondary winding transformer, you can build one by cascading two ordinary power transformers as shown in figure 3.
The first transformer (T1A) is a 5V/1A secondary winding transformer, and the second one (T1B) is a 220V primary - 9V/2A secondary winding transformer. By connecting the 15V winding of the first transformer to the 9V winding of the second one, about 360V ΑC will be available at the second transformer’s 220V winding. If powered from 360V AC, the negative ion generator will deliver about 11.5ΚV at the needles.
Figure 3. Cascading transformers for raising voltage
For even higher voltage, try to cascade an 18V/1A secondary winding transformer, with a 220V primary - 9V/2A secondary winding, transformer. That configuration will give about 440V at the second transformer’s 220V winding and about 15ΚV at the sewing needles.
Warning!! This article deals with high voltage circuits! Do not attempt to implement or use the information contained herein, unless you are experienced and skilled on building high voltage circuits. Please, use the information provided here at your own risk. We do not disclaim any liability for damages or injuries, whether caused by or arising from the lack of completeness, inaccuracies of the information, misrepresentations of the directions, misapplication of the information, or otherwise.