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.

> 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.

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.

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

Here's a good resource on mains power safety:

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