![A photo of [nanofix]'s bench including his FNIRSI soldering station.](https://hackaday.com/wp-content/uploads/2025/11/nanofix-phantom-voltage-banner.jpg?w=800)
Just because you are paranoid doesn’t mean people aren’t out to get you. Do you think your soldering iron is after you? Well, [nanofix] asks (and answers): Is My Soldering Iron Dangerous?
He has a look at his cheap FNIRSI soldering station and measures a “phantom voltage” of nearly 50 volts AC across the tip of his iron and earth ground. He explains that this phantom voltage is a very weak power source able to provide only negligible measures of current; indeed, he measures the short circuit current as 0.041 milliamps, or 41 microamps, which is negligible and certainly not damaging to people or components.
He pops open his soldering iron power supply (being careful to discharge the high voltage capacitor) and has a look at the switched mode power supply, with a close look at the optocoupler and Y-class capacitor, which bridge the high voltage and low voltage sides of the circuit board. The Y-class capacitor is a special type of safety capacitor designed to fail open rather than fail short. The Y-class capacitor is there to remove high-frequency noise. Indeed, it is this capacitor that is the cause of the phantom voltage on the iron tip.
He continues by explaining that you can install a 1M resistor across some pads on the high-voltage side of the board if you really want to get rid of the phantom voltage on your iron, but he emphasizes that this isn’t really necessary. And to finish, he demonstrates that a sensitive MOSFET isn’t damaged at all when it’s connected to the phantom voltage.
It is perhaps worth noting that there is a difference between phantom voltage (as seen above with negligible power) and phantom power. Phantom power can deliver non-negligible amounts of power and is often used in microphones.
I guess that’s what you get when you buy a cheap knock off instead of buying the actual one.
What is the actual one?
I’m not sure but it looks like a FNIRSI DWS-200 https://www.aliexpress.com/item/1005008483861861.html
So the same the guy in the video has and not a knockoff?
What moron would use MOSFETs when you can cheaply buy GaNs. It isn’t 2010 anymore bruh XD
And who the hell is using room temperature GaN and non-superconducting wires. Get with the LN2. It isn’t 2020 anymore.
It is 50V (ac) if you are in a 100V country. If you are in a 230V country it is 100V, and the voltage and current is absolutely high enough to destroy mosfets without protected gates, rf devices, and even some SOC’s.
Yes, that’s my experience as well. When using a USB soldering iron, don’t power it with a two prong USB power adapter. Always make sure the soldering tip is properly grounded.
Sometimes the grounding of the iron is the problem and can cause a spike if something you are soldering is connected to a device because you forgot to unplug it – I found, much to my chagrin..
Same issue why artists sometimes die from microphones, because if there is ground the time to be extra careful starts.
You should always use a soldering iron with a grounded tip when working on solid state electronics.
Just because the components don’t fail immediately doesn’t mean they aren’t being damaged.
Call it what it really is is: Leakage current. Not “phantom voltage”.
Measuring leakage current and ensuring it is below limits is part of the certification process by test labs, per IEC . The limit varies by intended application and fault conditions, from 10 uA for medical devices, to 0.5 mA for “household appliances”, to 5 mA in certain fault conditions. It’s intended to be a safe limit, but most people will complain loudly at 5 mA, where most GFCIs will trip. 100 uA is readily discernable, even annoying. 10 uA is detectable if you’re aware what it feels like.
The Macbook Pro was horrible in this respect: The two-pin “travel adapter” did not bleed the power supply leakage current off to earth, so when using it the metal chassis floated at 50-100Vac, and delivered 50-100 uA through your body. The tingly feeling you got while using it was not Apple vibes.
For leakage you can’t feel with your fingers, try touching whatever it is to the tip of your nose. That will tell you pretty quick if there’s any leakage to be had. Make sure you’re standing barefoot on damp concrete for maximum sting.
That reminds me of a while ago. We bought a bunch of embedded computers with big name brand 24VDC adapters to power them. 360W bricks. I thought I was going crazy, I kept feeling this tingling when I touched a computer but my colleagues said they didn’t notice anything wrong. Turns out, the big name brand 24VDC adapter put 120VAC with low amperage on the housing of the embedded computer. Sadly, these adapters were in a housing that couldn’t be opened within warranty (glued up housing shells) and even if you do open one up using some love from a hacksaw and hammer, the board itself is filled up with the typical black casting stuff they put in there (opened one up months later when one came back from a jobsite and was damaged.
We had all the adapters replaced but I sadly wasn’t able to physically inspect what went wrong.
I once measured the voltage from my cable ground to regular (spike-in-the-ground) ground and it was several hundred volts.. and when I moved to another town it was the same, so not a local malfunction.
My theory is that they are perhaps trying to prevent corrosion that way, although they should really remove it before it enters the home. It’s quite ridiculous.
“he measures the short circuit current as 0.041 milliamps, or 41 microamps, which is negligible and certainly not damaging to people or components.”
41uA at 50VAC is plenty to fry a MOSFET gate. For the current to flow there needs to be a ground connection from the device being soldered, though.
I find that surprising, but it’s good to know! Thanks.