Great point!
As many people are purchasing the iron these days, it would be great to have a summary/guide of all the modifications at one place.
With the help of this thread, I removed the heatsink from the PSU, clipped the side of it, and removed the soldered legs. Now it has at least 3mm of clearance from the HV side. I also connected the chassis to the PE, and verified that the PE goes to the tip. It does, because the PSU's 0V output is tied to the PE, and the 0V is connected to the iron handle minus and Earth as well on the pcb.
According to the schematic published here, the iron actually has a separate GND and Earthing up to the controller. I think it would be great to separate those, and connect the chassis and controller board to the PE, but add a small resistor between the Iron Earth and PE, to limit the possible current. Does it make any sense?
Before purchasing mine last August from Banggood (who had uncharacteristically shipped it out to me from their Chinese warehouse - cheapest option- in just 8 days!), I'd looked at countless youtube review videos so was well prepared to tackle the remedial work on the PSU and that 10K R10 battery draining resistor (as well as the need to fettle the wiring of the supplied 9501 handle which had guided my choice of soldering station - the alternative handle options had all looked rather naff to my mind).
It turned out that this resistor had not been placed on the control board in mine, neatly explaining the 3.16v reading I saw when checking the plug in CR2032 cell which had been stuck to the side of the diode heatsink rather than jammed between the top of the psu transformer and the case lid - I relocated mine to the base of the case just under the LV end of the psu board, clear of any PTH wires.
Since I had a 180W Parkside soldering gun stored unused since I'd purchased it from Lidl a year earlier, I decided to put it to use to sweat the heatsink off the board and reshape all three fins that overhung the "Isolation Slot" using a junior hacksaw and file to provide a healthy airgap to that 340vdc trace coming from the BFO smoothing cap rather than just ease it up enough to slide a layer of insulation tape in between said trace and the heatsink fin. I didn't have any kapton tape otherwise I may have used that method instead. Either way works - I just happened to have a BFO soldering gun to hand is all.
Compared to that rather scary reliance on just a thin layer of solder resist mask to insulate the heatsink from a source of 340vdc, the 2mm creepage clearance between the retaining lug and mains voltage seemed positively generous so I left it alone. It's not ideal but the risk is low enough once the case is earthed.
However, I must admit that it hadn't occurred to me to check whether the aluminium case had any earth connection until seeing another video review shortly after getting it "all sorted" as I'd thought in a moment of hubris, so I landed up stripping it apart yet again to rectify that particular Chinese sin of omission. Then, a little later on again, I discovered that the oval TPH which the unsoldered rotary encoder retaining tabs passed through weren't actually connected to the groundplane so had to solder short straps to nearby grounded points on the board for good measure.
Which now reminds me that it might be a good idea to run an additional earthing wire from the soldered up retaining tabs as a belt to my braces soldering of an earthing strap from the PE tag directly onto the GX12-5 socket's barrel (I hadn't wanted to drill a hole into the case just to fit an earthing tag).
I'm not sure (I've lost track of all the various sources of such useful information on these mods) but this last one may have been a floobydust inspired mod since I think I did the ground bootstrap diode mod across the heater element suggested by him to suppress voltage spikes at the same time.
I used one of three BY298 diodes that I'd had in my parts bin for the past four decades just waiting to be put to good use - this seemed a golden opportunity to finally get some return on whatever my initial investment had been. Whether it makes any difference is hard to tell but I'm sure anything that suppresses voltage spikes on the input circuitry of an opamp dealing with mV level thermocouple signals is no bad thing.
The one constant in all of this was the fact that the soldering iron tip was always fully grounded via the PE connection in the C14 mains socket (the only thing in fact that
was actually earthed!). I know the idea of using a 1MR static drain resistance connection to the tip is largely deprecated by most, including myself but I can see where this could be useful in those rare usage cases such as working on ancient live telecoms kit running off 52 volt DC power to have an insulated tip with not even a static drain connection to ground for ESD protection. TBH, I can't see any such need these days with modern modular telecoms or IT kit nor with any other kit you might find yourself working with.
Unless you have an essential need to work on live low voltage kit, you'd be better off with a low resistance earth connection to the soldering iron tip and work on circuit boards only when they are disconnected from their power source. You could try fitting a 1MR static drain with a bypass switch to let you choose whatever option seems best but this does leave room for mistakes. If you are going to use a resistive connection to earth the tip, just ensure that everything else (0v rail and the case metalwork) remains connected to the safety earth (PE tag in the C14 socket).
I guess if such an option is desired you could use a two pole switch so you can light up a warning lamp to indicate when it's safe to use on live low voltage kit and when it's not safe. Even with such an indication scheme, the risk of getting the setting wrong still remains.
In this case, using a low voltage DC (or AC) supply to power the heating element allows you to use a lowish value resistance, such as 10KR to 100KR, in place of the more usual 1MR static drain to earth with an acceptably low risk of damage to any unpowered delicate electronic components you may be working with. You could embellish such an arrangement with a leakage voltage detector circuit to trigger a warning of the presence of any undesirable voltage on the tip that could arise out of a breakdown of the insulation between the heating element and the tip itself - your call.
The full earth contact to provide an ESD safe soldering iron is really an inheritance from soldering irons using mains voltage heating elements where the issue was not only one of ESD risk but also one of safety against the risk of electrocution.
In the case of this KSGER T12 soldering station, you have some freedom to DIY whatever ESD protection scheme you fancy but it's best to avoid unnecessary complexity. The general advice here is "Make it no more complex than it absolutely needs to be (and, ideally, less complex than that)", which usually boils down to in this case, leave it as it is (the tip stays directly connected to the PE tag on the C14 socket).
One alternative that could neatly address the occasional need to work on live kit is to add a socket so you can run the station off a 5s or 6s LiPo pack with the mains disconnected. Depending on your choice of battery pack, you could get several hours of use per charge, especially if you take full advantage of the low temperature standby and power down modes.
Unless I'm very much mistaken, the smpsu should tolerate the application of battery voltage on its output when powered off (disconnected completely from the mains), leaving only the need to use a suitable diode in series with the battery supply to eliminate the risk of accidental backfeed should you power it up from the mains without unplugging the battery pack.
If you use a 5s LiPo pack you could include a basic battery charging controller to let you use the smpsu to recharge the battery pack. You could do the same with a 6s pack but the charge controller will need to provide a small voltage boost which may make it a little more expensive an option. In this case, I'm assuming the use of a LiPo cell balancing and overcharge protection circuit in or attached to the battery pack.
I've seen several examples of such battery powered stations built from KSGER kits but I can't recall seeing any based on the addition of a battery pack to an existing mains powered station. It might be worth taking a look, even if it's just to get some ideas on how to provide a battery power option to the existing mains only powered T12 soldering station if such an alternative has any appeal (freedom to work away from the mains supply with no troublesome earth contact to interfere with low voltage live circuits).
JBG
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