I can explain the principle, but explaining every detail would take too long and it would still be hard to follow. It is easier to show someone. I have been wanting to put together an informational brochure with CAD drawings and maybe a video on CD on how to build a cold corona unit for less than $100. But I have to find someone that can do CAD, and I have to find the time.
A hot corona system is much easier to build, but you can only use it externally. You will need a wire tube brush like the ones they use to clean gun barrels. But you need a stainless steel one. Then you will need glass tubing with an inner diameter the same size as the outer diameter of the brush. You can find glass tubing at scientific supply houses or from a neon supply company. The longer the brush the stronger your unit will be. A brush 4 to 6 inches should work fine. Cut the handle off the brush. Cut about 6 inches of stranded 16g copper wire, strip the ends and attach one end to the brush.
Cut the glass tubing a half inch longer than the brush. I use a Dremel power tool with a diamond blade for this. Put the brush in the tube so it is an equal distance from each end. Use a small amount of a silicone glue like Goop to lock it in place.
Take some aluminum tape and wrap it around the glass making sure that you leave a quarter of an inch of the each end of the glass tube uncovered. The reason for not taking the metal brush or the aluminum tape to the end of the glass is to prevent an arc over between the electrodes. This could cause a fire if this happens. Now cut another 6 inch length of the copper wire and strip each end. Unravel the strands one end of the wire, and spread them out so they are flat. You are going to attach this wire on the OPPOSITE end of the tube from where the wire is sticking out. Except the wire will not be attached to the brush. Instead you will be attaching the end of the wire to the aluminum tape. To do this cut a piece of aluminum tape about an inch long. Lay the unraveled flattened end of the wire on the aluminum tape so the rest of the wire is facing straight out the opposite direction of the wire attached to the brush. Then take the small piece of aluminum tape and tape the wire down to the rest of the aluminum tape. Rub the tape over the wire to make sure it is well fastened. If done properly it will look something like a candle with a wick on each end.
The next step is not necessary, but I do it anyway just as a redundant precaution. I take electrical tape and wrap the glass from end to end. Start from the edge with the external wire and wrap around the tube under the wire first, then as you come around go over the wire and keep winding it around at a slight angle all the way to the other end. Again this will help to prevent arc over.
At this point it would be a good idea to check the tube function. So hook up a neon transformer 7,000 to 10,000 volts 20 to 30ma. The higher the voltage the more ozone out put you will get. To hook it up just attach one of the output leads from the transformer to one of the wires from the tube, and the other transformer wire to the other tube wire. PUT THE TUBE UP ON A BLOCK OF WOOD. Do not let the tube or tube wires touch any conductive surfaces, including a cement of stone tile floor as this will cause arcing. Plug the transformer in to a power strip so you have an off and on switch. Turn the power on. You should hear a nice even buzz, no crackling. If there is cracking then you have a problem. It could be arc over, a crack in the glass, or something in the tube that should not be there. If you turn off the lights you will see a purple corona inside the tube. Remember to keep a little distance from the transformer and tube. The electrical current can sometimes jump about an inch. It won't kill you but I can tell you from experience it hurts.
Turn off the power and disconnect the transformer and tube wires. If the tube was working ok then move on to the next step.
The next step is the hardest. You need to find a PVC pipe that has a slightly larger inner diameter as the outer diameter of your glass tube. You will also need two end caps and two nylon threaded 1/4" hose barbs. Cut the PVC pipe to the same exact length as the glass tube. Put a thick layer of silicone glue around the center of the glass tube and slide the glass tube in to the PVC tube, then let it dry. You will then need to apply more silicone between the ends of the PVC and glass to seal the gap. This is to force the air or oxygen though the center of the glass rather where the corona is rather than outside the glass.
Now, drill holes in the end caps large enough to allow the wires to pass through. Drill them on the side near the top of the cap at a 45 degree angle inward. You also need to drill holes large enough to screw the hose barbs in. I highly recommend step bits for this purpose rather than normal drill bits. Step bits make a really clean cut, and they don't grab like regular drill bits so you can use a hand drill if you do not have a drill press. The drawback to step bits is that once the hole is large enough on one side you will have to flip the cap over and drill the hole from the other side so both sides have the same diameter. After both caps are done cut the threaded ends of the hose barbs down only leaving a 1/4 inch of the threads. I use a Dremel with a cut off blade for this. Glue around the remaining threads with PVC cement and twist the hose barbs in to the drilled holes. Once dry take a cap and push the end of one of the wires through the smaller hole drilled in the end cap and push the cap while pulling the wire all the way until the cap id to the edge of the PVC pipe. Put some PVC cement on the outside of the end of the PVC pipe and push the cap on the end of the pipe. Then put a dab of PVC cement on the hole where the wire comes through to seal the hole. Repeat the same procedure with the other cap. That was the hard part.
Because the tube wires will be carrying high voltage and they are not insulated properly for that I cut some 14"OD tubing about 1/4 inch shorter than the wires. Then I slide the tubing over the wire and but it up to the PVC tube. The stripped end of the wire should be sticking out of the tubing when it is pushed all the way on. This will give the wire much more insulation, which will reduce the risk of shock or arcing.
Reattach the transformer wires to the tube wires and put electrical caps on them so there is no exposed wire.
Cut two small lengths of 3/8"OD X 1/4"ID tubing and push them on to each end of the hose barbs. Next cut several pieces of 1/4"OD tubing. One piece should be no more than six inches. The second piece I would cut about 2 to 3 feet long. Push each of these smaller tubes in to the each of the larger tubes connected to the hose barbs.
Attach the smaller, shorter tube to an aquarium pump. I let the pump run a few days to dry the glue that gets inside the tube and to blow out all the fumes.
That's it, your ready to go. Turn the power on while the pump is running and you should smell ozone coming out of the longer 1/4" hose. A stronger pump will allow a longer hose to be used. And if you want to reduce the pressure for ear insufflation you can add a gang valve in line between the pump and the discharge tube. Just divert some of the air out in to the room to drop the air level actually going though the discharge tube.
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