USB powered irons (Pinecil and similar)

[tony359]

Hi all,

I am taking a look at a Kaiweets USB soldering iron - which should be also sold with the FNIRSI branding.

One thing I am noticing is that I have 80V at the tip when referenced to ground - but I don't see any current flowing from it. I believe this is a by-product of the non-earthed USB power supply and I guess it's unavoidable?

My two questions are

1. Could this be even remotely dangerous? I know it's probably ok for most of the tasks, just wondering if there could be *that* special IC which wouldn't like it
2. Can someone with other irons - the Pinecil for example - try to confirm the same happens? To check, set the multimeter to AC or DC (I'd check both) then connect one lead to ground and touch the tip of the iron with the other lead.

Any thoughts?

[magic]

Switching power supplies usually come with few nF class Y capacitors between mains voltage and output ground, which are there for EMI control.

My experience shows that this can damage 2N7000 MOSFETs and some sensitive ICs when one pin is "grounded" to such a PSU and another pin to true earth, because the capacitor passes a small amount of AC current from mains through the circuit.

If no other pin is grounded than there shouldn't be a problem, but note that you can also capacitively ground other pins, for example by touching them (this adds ~0.1nF capacitance to real earth).

[tony359]

Thanks - yes, that is also my concern. "good for most of the tasks but..."

Still, on the Aixun T3A I could read up to 1.8A from the tip - on this USB powered one I cannot see a current flowing. Shouldn't I be able to measure some current as you said?

[shabaz]

I was interested in obtaining a few USB soldering irons (for use by kids) and eventually settled on "KSGER C210" it is slightly easier to ground that one compared to a few others I tried. All the irons I tried had various strengths and weaknesses, though. There's a short blog post about the KSGER C210 iron since I didn't find a review of it at the time.

[agent_power]

2. Can someone with other irons - the Pinecil for example - try to confirm the same happens? To check, set the multimeter to AC or DC (I'd check both) then connect one lead to ground and touch the tip of the iron with the other lead.

Any thoughts?

Hi, what do you mean by ground? With a Pinecil V2, if I connect one lead to the USB-C cable connector's outer shield peeking out and the other to the tip, I get 0.015 VAC and 0.15 VDC approx, with both values going up for a brief amount by around 50% every 5-10 or so seconds, in standby mode (iron not actively powered).
I have a two-pronged GaN charger

[shabaz]

Hi,
If you connect one end of your multimeter to ground/earth (i.e. for instance, the third pin on your mains sockets; even if your USB adapter has only two pins; you may even be able to simply that multimeter connection in your hand to see the problem), and then the other end to the iron tip, this will reveal the issue:

[ealex]

that's the leakage trough the filter capacitors inside the power supply - it's something normal
you can solve it with a grounded power supply or by adding extra connection from the iron to something that's properly grounded (through some ~ small resistor)

from the pinecil description page: https://wiki.pine64.org/wiki/Pinecil
"
6. Check that all 3 external screws are present

    One near the back of the screen (ground screw for optional ground wire)
    One at the front on top (to hold the tip in)
    One at the front on the bottom (to hold the case together, does not touch the tip)
"

another way - use with with an usb-c power bank.
this is how i'm using it - and i've never had ESD issues. (example: ip2368 module and a 4S2P made from some left-over INR21700 cells)

[agent_power]

Ah yes, in that case I've got around 70-80VAC. So to avoid any potential damage to sensitive components, I run a wire from the grounding point of the iron to mains earth?

[tony359]

from the pinecil description page: https://wiki.pine64.org/wiki/Pinecil
"
6. Check that all 3 external screws are present

    One near the back of the screen (ground screw for optional ground wire)
    One at the front on top (to hold the tip in)
    One at the front on the bottom (to hold the case together, does not touch the tip)
"

Ah, that's it, the Pinecil provides an optional ground connection

Ok, I think I got this clear. The only thing which is unclear is why I don't measure any current from the tip. Anyways the bottom line is: to be 100% safe, it should be grounded. This iron doesn't have a ground point so it would need a bodge wire (with resistor) around the tip, which is not great. 99% safe but I think it's important to mention that 1% of chances!

Thanks @agent_power for checking for me, you read the same I do on my Kaiweets.

[watchmaker]

When connected to 20V laptop charger, my Pinecil measures 43 V AC from tip to earth.

When I use the Pinecil power station, I get 3 mV AC tip to earth. FWIW, I chose their power station because it was the same price as other 4 or 5 port stations while it is far more aesthetic.

[tony359]

interesting @watchmaker, thanks.

@agent_power, were you using the Pinecil power brick when you measured? From online pictures, it's not grounded either so I am not sure why it would prevent this issue?

[agent_power]

interesting @watchmaker, thanks.

@agent_power, were you using the Pinecil power brick when you measured? From online pictures, it's not grounded either so I am not sure why it would prevent this issue?

I'm using some other charger, not the one from their store. When connected to a laptop charger with mains earth grounding, there's only around 1.5VAC on the meter

[tony359]

Very interesting, thanks - I'll test with my laptop chargers. Which are really not an option as the cable is not heat resistant but for a test it'll do.
I'm still puzzled that the Pinecil power supply does not show that issue as it doesn't seem to be grounded by the pics I see online.

[abeyer]

When I use the Pinecil power station, I get 3 mV AC tip to earth. FWIW, I chose their power station because it was the same price as other 4 or 5 port stations while it is far more aesthetic.

Did they fix the compatibility issue between them? They used to explicitly tell people not to use their power station w/ the pinecil because there was some known issue between them.

[JohanH]

Here's one solution.

In this case I don't know if it really was needed. This laptop charger doesn't seem to float, so I was only able to measure a few volt AC. Anyway I can disconnect and use the grounding adapter if it's needed in other situations.

[watchmaker]

I just rechecked my report;   Yes, the Pinecil station IS earthed; 3 prong cord.  That 42 v AC from the laptop charger is real and disconcerting.

To be clear, Pinecil on; one probe on tip, the other to the earth that attaches to my ESD mat; direct connection not through resistance.

The laptop charger is a cheapy from Amazon; 2 prong.

42 VOLTS!!!

[watchmaker]

When I use the Pinecil power station, I get 3 mV AC tip to earth. FWIW, I chose their power station because it was the same price as other 4 or 5 port stations while it is far more aesthetic.

Did they fix the compatibility issue between them? They used to explicitly tell people not to use their power station w/ the pinecil because there was some known issue between them.

They seem to recommend it:  https://pine64.com/product/pinecil-smart-mini-portable-soldering-iron/

Maybe it was the version 1 iron or maybe they revised the station.  But I am happy with the combo.

[Veteran68]

Did they fix the compatibility issue between them? They used to explicitly tell people not to use their power station w/ the pinecil because there was some known issue between them.

If you're talking about this one:



then its USB-C port claims to be PD65W compatible, which should be fine for v2 Pinecils. I believe v1 might have had some issues with power supplies. My problem with their station is it's only got one USB-C port but four USB 3.1/QC ports, which Pinecil recommends against using because they don't supply enough power.

I don't have a Pinecil but I do have several other USB-C based irons from Kaiweets, FNIRSI, and Sequre. I use this station, as I also have mostly USB-C devices now and wanted more of those ports. It supports 140W on port C1, and 100W on ports C2 and C3 (not simultaneously). I really like it, it works great for my needs, though it is about $20 more than the Pinecil station.

[tony359]

I just rechecked my report;   Yes, the Pinecil station IS earthed; 3 prong cord.  That 42 v AC from the laptop charger is real and disconcerting.

Thanks for that. Silly question: what is the "pinecil station"? Is it their own power supply?

[tszaboo]

I have one at home which is called T12 soldering iron. Which is a bad name for it but whatever. Here is what's inside. Does PD properly, unlike some cheaper irons. About 20 EUR.

[watchmaker]

I just rechecked my report;   Yes, the Pinecil station IS earthed; 3 prong cord.  That 42 v AC from the laptop charger is real and disconcerting.

Thanks for that. Silly question: what is the "pinecil station"? Is it their own power supply?

Yes, it is their own.

[tony359]

Thanks - would you mind posting a picture of the power supply you're using?

I think I've realised the Pinecil comes with NO power supply and they just recommend a PD one. The "Pine" power supply I found on their website is... just a power supply, not the one which comes with the Pinecil.

Thanks!

[watchmaker]

Here is the link:  https://pine64.com/product/pinepower-120w-desktop-power-supply-us-version/

It is the same as pictured in reply #17.

[rteodor]

Hi all,
...
2. Can someone with other irons - the Pinecil for example - try to confirm the same happens? To check, set the multimeter to AC or DC (I'd check both) then connect one lead to ground and touch the tip of the iron with the other lead.

Any thoughts?

20 minutes after I got the Pinecil combo (with silicon USB cable - important for flexibility) I put my old Atten away and never looked back for it.
A bit crappy 2 button interface but otherwise the iron was a generation step for me. I even 3D printed an adapter to a power tool battery.

Positive continuity test from USB cable shield (which I did not check but I think its common with USB GND) to earth. No galvanic connection from the tip to earth. The tip is connected to all 3 screws as described in documentation, the one near the display has the earth mark near it.

And obviously there is no AC leakage, neither from USB cable shield nor from tip. Cca. 100...150mVDC from tip to earth.

LE: all measurements were done on the combo: PSU + USBPD cable +iron.

[tony359]

thanks @watchmaker and @rteodor.

@rteodor, are you using the same PSU @watchmaker mentioned?