UV LEDs for air Ionizer? - Page 1
Forum section: electronics / beginners

author: m.m.m
author_rank: Regular Contributor
timestamp: June 17, 2015, 08:29:43 pm
content: Hi, first of all I have made a cockraft-walton generator air ionizer and I realized that these air ionizers make ozone and that's not good, so I came with the idea of adding some UV LEDs to destroy (or whatever you call it in chemistry) the ozone to oxygen atoms, and also to kill the bacteria in the air. I wanted to know that is this possible with 10 5mm UV LEDs?thanks a lot.

author: Sigmoid
author_rank: Frequent Contributor
timestamp: June 17, 2015, 08:37:47 pm
content: I'm pretty sure UV lightcreatesozone from molecular oxygen rather than destroys it...https://en.wikipedia.org/wiki/Ozone#Ultraviolet_lightIt would seem that if you don't have arc discharge in your device, then it mostly just ionizes air, and arc discharge (which of course generates UV light) creates ozone. So I think adding UV is a really bad idea if you want less ozone as opposed to more.https://en.wikipedia.org/wiki/Air_ioniser#Ions_versus_ozone

author: m.m.m
author_rank: Regular Contributor
timestamp: June 17, 2015, 09:26:50 pm
content: Quote from: Sigmoid on June 17, 2015, 08:37:47 pmLol now I see why my marks were bad in chemistry, so how can I reduce Ozone? Also did you mean that I have to have an arc discharge for the air ionizer to work? I.e I have to put a ground wire near the high voltage line to get sparks?Again thanks a lot.

author: Paul Moir
author_rank: Frequent Contributor
timestamp: June 17, 2015, 09:28:31 pm
content: Germicidal action doesn't kick in until UV-C ~ 250nm, so don't expect anything from a UV LED.

author: helius
author_rank: Super Contributor
timestamp: June 17, 2015, 09:49:49 pm
content: Laser printers generate ozone from their corona discharge. They filter it out of the exhaust air using a paper filter coated with activated carbon.

author: Zero999
author_rank: Super Contributor
timestamp: June 17, 2015, 10:43:39 pm
content: Quote from: Paul Moir on June 17, 2015, 09:28:31 pmUse an aluminium nitride LED.http://www.hexatechinc.com/uv-c-led.html

author: Paul Moir
author_rank: Frequent Contributor
timestamp: June 18, 2015, 02:36:00 am
content: Ah I had forgotten(?) about those. Used in those little sticks you can put right in a glass of water for sterilization I presume.

author: LukeW
author_rank: Frequent Contributor
timestamp: June 18, 2015, 06:08:55 am
content: Quote from: m.m.m on June 17, 2015, 09:26:50 pmHit it with some 1950s hairspray?Anyway... UV LEDs have a wavelength that's too long. What you want is a "hard" UV source, like a mercury vapor UV tube used for germicide/sterilisation applications or for erasing EPROMs. The kind that will burn your eyes/skin.And yes, a UV source like this willmakeozone. These lamps generate that distinctive ozone smell when they've been operating for a while, just like a corona discharge.

author: Zero999
author_rank: Super Contributor
timestamp: June 18, 2015, 07:27:46 am
content: Quote from: LukeW on June 18, 2015, 06:08:55 amNo, the common cheap UV LEDs off ebay which give out more visible violet than UV won't do, but it's now possible to get UVC LEDs, see my previous post.

author: m.m.m
author_rank: Regular Contributor
timestamp: June 18, 2015, 10:33:49 am
content: thanks everyone, I didn't get it, do I have to put a spark gap or something in my air ionizer to work?I mean the one I built has some sharp tip wires with high voltage (around -2kV) in front of a fan and there's a grounded aluminium filter about 30cm away. Is this OK?

author: rs20
author_rank: Super Contributor
timestamp: June 18, 2015, 10:49:47 am
content: The amount of ozone you're making is going to be tiny, most likely harmless, but it's so reactive that you just have to push it through a filter made of any of a multitude of substances (even ozone will react with ozone, which is why you can't buy a tank of the stuff and it has to be generated on site). As mentioned earlier, carbon seems like an excellent choice, since it just turns into CO2 and it'll take you millenia to react any visible piece of carbon away.Also, in the interests of promoting scientific accuracy, when you do the whole blowing air past a corona wire thing, what you're building should not be called an "air ionizer". Why? Because the air leaving the device* is not ionized. If you get it wrong, you've built an ozone generator, if you get it right, you've built anelectrostatic precipitator, or perhaps more consumer-friendly,air purifier. Makes dust particles briefly ionized so they stick together and neutralize, clump up and fall out of the air (/stuck to a metal surface in the device). Popular at power stations, rather less proven in the home.Shameless not-entirely-relevant plug:my blog post on beeswax candles and their claimed "ionizing" properties. Relevant discussion in the comments about electronic air ionizers.* Note the careful choice of words!

author: m.m.m
author_rank: Regular Contributor
timestamp: June 18, 2015, 07:07:58 pm
content: Quote from: rs20 on June 18, 2015, 10:49:47 amThanks!so if I put a carbon(like graphite) in the air flow path it will make CO2 (I don't think that's a big deal since I've got some flowers in my room) in addition to electrostatic charging the particles in the air? also there's another thing, I've got a lot of allergy to these moving particles so it will help me with that, right?

author: rs20
author_rank: Super Contributor
timestamp: June 18, 2015, 10:41:18 pm
content: If you just blow the air over a lump of charcoal, 99.9% of the molecules will never hit the charcoal. Making filters is harder than that :-)