Build an Ioniser in Under $10 | Hacker News Reader

Build an Ioniser in Under $10

amaldev.blog

124 pointssthottingal39 comments

Just be cautious, while correctly working Air Ionisers are safe, poorly working or designed ones can produce Ozone which is unsafe (particularly over prolonged periods or high exposures). This article has more information (in particular citation 10 used in Adverse health effects):

https://en.wikipedia.org/wiki/Air_ioniser#Adverse_health_eff...

Personally I don't see the benefit over a HEPA filter on a standard electrical fan, or a commercial unit with a similar design. Yes, replacing filters is annoying/has a cost, but there's no health downsides to the design and it is effective at removing air particulate. Building one requires an off the shelf HEPA filter, an off the shelf fan, and a couple of rubber bands. It isn't "sexy" or technically sophisticated, but it works. Want it improve effectiveness? Increase the surface area/make it bigger/increase the airflow.

Let's also consider what both devices (when working correctly) do. An Ioniser gives particulate a charge causing it to be attracted to and stick on surfaces. A HEPA traps particulate within a filter membrane. Or to phase that differently an Ioniser causes the particulate to dust onto every surface within range, causing dirt buildup/stains, dust blooms when disturbs, and people may still contact the air contaminants (since they still exist, now on surface rather than in the air). HEPA allows you to simply remove the particulate from the environment, Ionisers just move it from one location (air) to another (surface).

Veritasium had a good video showing the test of ozone being produced by air ionisers: https://youtu.be/ZQ--scjcAZ4?t=663

(time-linking since the ioniser part was sortof hidden within a video debunking himalayan salt lamps)

Thank you, really enlightening video. I'm happy I bought a HEPA filter now, rather than an ioniser.

This is especially ironic in this case, because the entire premise of the article was: "I have always had the issue of dust settling in every week on everything if I open the windows. Cleaning that up every week is a pain."

They then proceed to build a device that will, if anything, exacerbate this exact issue.

The issue was "I have always had the issue of dust settling in every week on everything if I open the windows."

If the dust is airborne, it will naturally spread everywhere before it eventually settles. Making the dust settle early minimizes spread.

Another way of improving the homemade air purifier is adding an activated carbon filter (read: kitchen extractor hood filter)

Can't you collect the dust at a particular location by using an opposite charge?

Ozone is actually a useful disinfectant, just make sure to ventilate the room well after treatment. Obviously not the outcome anyone building an ioniser is after.

In addition to the health concerns, ozone attacks unprotected polymers causing them to quickly break-down and release additional toxins into the air. I run an ESD ionizer at my well ventilated re-work / soldering station and have had plastic storage bins on the bench crumble at the touch from the ozone exposure.

> dust blooms when disturbed

I don’t find that at all. The dust that sticks to surfaces in my apartment can’t be moved even by forceful blowing on it. It has to be wiped away.

Also, I notice that when I brush stuck-on dust off a surface (e.g. my coffee table), it’s still ionized—so it just either gets pulled back to the sides of the table, or to the floor.

As the former owner of a biggish HVAC-integrated electrostatic precipitator, these things are not really worthwhile. An ESP needs frequent cleaning to work well, in comparison to a plain old MERV 13 or so filter, which will work for quite a while with no maintenance.

An ionizer doesn’t need maintenance, but that’s because it deposits all the gunk nearby. Eww.

Please don’t build this. There are numerous ways to kill yourself with it. Especially the construction as described.

Could you elaborate a bit more? I am curious from the technical side.

Lap soldered mains connection (can break off easily). Not double insulated (think small children and fingers). Also the actual ioniser port is usually recessed to avoid accidental contact as it hurts if you touch it.

Also lots of hand soldered MLCC caps are high potentials. They like to crack and explode if you do that. They need to be machine soldered really.

Edit: also the design doesn’t use proper voltage rated resistors on the output. I haven’t checked the other parts but it’s probably marginal. You’ll get home one day and find your house burned down.

could do with a fuse to.

Those needles connected to active make me uncomfortable, though there's a 10M resistor, I'd have an isolating transformer on the mains - not an engineer though.

Fuse would be good. Here in UK there’s one in the plug. The 10M resistor will current limit. Or probably flash over here.

Isolation transformer is not required if the enclosure is better. It also doesn’t help you if you stick yourself across it somewhere, only helping yourself with respect to ground. If you’re testing it or doing development with it I would use one. But I wouldn’t build it.

I used to hang around inside old valve radios when I was a kid. You learn respect for high voltages very quickly.

Hey you guys, Author of the article here. Thanks for mentioning the issues. I never meant it to go this viral. Crashed my website in the morning. You seem to mention that the output resistor was wrongly chosen. Can you elaborate? I thought I designed it properly. This post was not ever meant to be used without using basic safety features in mind. (Like keep it away from children and all). I will explicitly mention that to be taken care of in the post. Happy to take any more constructive criticisms to make the post better.

Yeah no worries. We’re all hyper critical. Need to outline the dangers because people who are unaware of the issues working with mains tend to be the first to drop dead. This is followed by the people who suffer from Dunning-Kruger effect. Us amateur radio operators like to kill ourselves on vintage power amplifiers doing that.

The output resistor need to handle potential to ground so say 7kv across output to ground. Resistor is rated for 200V working voltage. Usually you use a chain of many smaller resistors here.

I haven’t reviewed the design entirely but the main problem is the enclosure and mains connection and the component choice. The mains connection should be clamped in the enclosure and either spade connections or screw terminals or ferrules. The enclosure should be double insulated. As mentioned a fuse would be a good idea as well.

Always design for worst case with these things.

Here's a good resource on mains power safety:

https://hackaday.com/2016/05/11/looking-mains-voltage-in-the...

It's 20M, which if connected directly across 240V causes 12uA to flow --- that's in the range of the natural leakage current in most SMPS, and not harmful at all.

http://www.aplomb.nl/SMPS_leakage/Doc_ie.html

Unless the resistors flash over their 200V rating at which point the current limit is void

> MLCC caps

what about "manual" solder paste reflow ? I think I saw a few vids where people hinted at the fact that it's uneven heat and physical stress from handling that caused damage

That’s better for sure. Hand soldering stuff tends to be the worst outcome.

The article mentions BigClive, and his YouTube channel does have a lot of stuff about ionisers, but his site has an article about them too: http://www.bigclive.com/ioniser.htm

http://web.archive.org/web/20191229051555/http://amaldev.blo...

He talks about carbon-fiber stuff to get lots of ionization points, but steel wool works great.

You will be able to smell if you are producing ozone, which you don't want unless you like permanent lung damage. The smell is sharp. like around electric sparks. If you get that, the voltage is too high. Just leave off a few voltage stages.

I love the smell of ozone though (not kidding!).

I think it's an association from dicking around with dodgy electric motors (that sparked in a cool way) when I was younger.

It's the same reason people like Lisp: it smells of youth.

All comments seem to recommend a good old filter over an ionizer. Would an ionizer in series with a filter (e.g. in air ducts ) be more effective than a filter itself?

For some uses. I have to recommend the commercial Honeywell units highly: they're excellent at pulling tobacco smoke and smell out of the air; and yes the area around them will catch all the other dust around too.

It is not healthy to breathe in high concentrations of ozone. It's difficult to make an "ionizer" that doesn't generate ozone.

Also, the health claims of ionizers are dubious. False claims about them (and ozone) bankrupted The Sharper Image

https://www.nytimes.com/2008/02/21/business/21sharper.html

> I these days use LCSC.com to buy all my generic parts. Great selection at a great price. It’s way cheaper than Digikey or Mouser.

That's a good one, thanks!

You can buy a ionizer for less than $10 on aliexpress and it might be less electrically dangerous.

However - DON'T DO IT. Many ionizers generate ozone which is unhealthy.

Also if the goal was merely to combat dust settling on the floor (rather that health), it will only make the problem worse.

During crop-burning season in India, when the air is hazardous, would an ionizer + ozone be a net positive?

Crop burn pics: https://www.theguardian.com/world/2019/nov/08/indian-farmers...

Interesting, we banned it in the early 90s in the UK (I used to love watching it).

https://www.eurekalert.org/pub_releases/2019-08/imaw-atb0807... suggests there are better alternatives that will yield better returns for the farmers; but I gather some UK farmers want to return to burning as it - in their eyes - reduces weeds and provides ash for tilling in to the soil. It's not a simply equation though, eg https://www.researchgate.net/publication/230319729_The_effec....

No: ozone only makes things worse. Plus, a lot of smoke from burning plants has large particles that can be filtered much better with hepa filters

An estimated power use of 4 kWh per year -- only costs 4 Rupees in Mumbai? (around $0.05 USD) That's surprisingly cheap power. The US average is 10x higher. ($0.13/kWh)

Still a small cost ($0.52/yr in the US)

Epic

$10 really means ripping apart and wiring up cheap Chinese consumer electronics. A PCB project is at minimum $100.

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