Thanks for the schematic. I cannot believe I even considered buying this. Not even a fuse on the output or on the input. if you micro locks up, the iron becomes hotter than the sun. or if ESD kills Q2 gate. Not to mention all the routing and assembly problems. What a piece of junk.
I do think you're being a little harsh in your criticism and since I haven't contributed very much to these forums of late, I'll explain why and add a little balance to counter this criticism. Incidentally, do you have any reason to think the gate of Q2 is particularly at risk of ESD damage? It's location in the circuit, as far as can see, makes it no more vulnerable to ESD than anything else within that Faraday Cage enclosure, earthed or not.
It's true the control unit, as delivered, has some serious electrocution hazard risks due to the kakameemee diode heatsink choice and layout and absence of connection of the PE to the metal casing and ground bonding issues to the controller PCB but these are issues readily addressed by anyone buying one of these controllers as an upgrade to an existing soldering iron collection (and hey! at least the soldering tip is grounded making it ESD safe
).
Anyone who has had even just one previous experience of Chinese Kwality in regard of mains powered kit will be well aware of the need to open these things up to make sure that they're actually safe to use (either by them uncharacteristically already being safe, or more likely requiring a few simple alterations to ensure all the ESD, electrical fire and electrocution hazards have been neutered).
Such modifications are fairly trivial to apply and well worth the additional work by anyone into electronics and DIY repairs/modifications to get their hands on such cheap Chinese bargain versions of kit that could otherwise easily cost ten times as much from Western manufacturers (who can't always be trusted to employ even minimal safety measures - Weller being a case in point with at least one current model of soldering station that has no protective fusing whatsoever).
As for your "What if?" concern over the cpu locking up and the lack of protective fusing leading to the possibility of a T12/T15 tip glowing "hotter than the sun", that's always been an ever present but vanishingly small risk with any such control systems. The Lord Murphy is forever hovering in the background waiting His chance to punish Humanity for such hubris in believing they have made a totally safe and reliable 'gadget'.
Most sensible designers (but not the Chinese it seems) don't aim for complete perfection, just enough 'perfection' to avoid suffering punishment of the "Capital kind" at the hands of Our Lord Murphy (i.e. minimal fire or electrocution risk). The Chinese don't seem to be able to distinguish between the level of consequences from their carelessness in design and manufacture of such electrical goodies, hence the safety check on Chinese electrical gadgets being SOP for the seasoned purchaser of such items.
When you refer to the lack of fusing on the input and output, you neglected to specify the object in question. The PSU for all its faults, unlike the aforementioned Weller soldering station, actually has not one but two mains voltage fuses (a user replaceable fuse in the C14 socket assembly and the obligatory soldered in safety fuse on the smpsu board itself). Since smpsus typically incorporate overcurrent protection on their outputs, I can only assume you're reference is the controller board attached to the front panel itself.
If this is the case, this is a situation where it would be impossible for any simple fuse protection (on the input or the output of the controller board) to protect against "the iron becomes hotter than the sun." risk. Since it's extremely unlikely that the iron could reach a temperature in excess of 2000K whilst the Sun's surface temperature is reckoned to be three times this at 6000K, this hyperbole detracts somewhat from your expressed concern over the lack of such protection.
Quite frankly, the only situation where I can see such an event leading to loss of life or financial ruin is where the user needs to be under tight supervision by a competent adult. Making the reasonable assumption that any such soldering tools will normally only be used in a safe working environment by persons with a reasonable level of awareness of the risks in their inappropriate use, the worst outcome will be merely that of a ruined soldering iron. No biggy in the case of a cheap T12 clone and merely an annoyance in the case of an overpriced Hakko T12 or T15 tip - it's only money after all!
Personally, if I ever saw my clone T12 tip starting to glow bright cherry red, I'd make a grab for my camera and use the opportunity to record just where the heating element is placed within these "Direct Drive Cartridge Tips" before hitting the off switch. Sacrificing even a genuine Hakko tip is far cheaper than investing in a relatively low resolution infrared camera to obtain such information at normal soldering temperatures. Besides which, photographic or even movie evidence can be useful when making a warranty claim against KSGER or their sales agent.
Although power transistors have become somewhat more robust during the past half century, that truism about such semiconducting devices being defined as "Transistor - a ten dollar device designed to protect a ten cent fuse", still rings true today. Ordinary fuses, as I've already mentioned, don't offer effective protection against a lock up state that results in the iron overheating. Carefully crafted slow blow thermal fuses, accurately matched to the anticipated fault current in such a scenario could provide some limited form of protection against such an eventuality.
Considering the rarity of such events (I can't recall anyone reporting such an event with these KSGER soldering stations[1]), such provision of slow blow thermal fusing seems extremely unlikely as well as an unnecessary complication. It's a risk of failure I'm happy enough to accept, especially when I'm not going to be using the iron in such a way as to elevate such a risk to a life threatening level. I would be very surprised if other members contributing to this thread don't also take a similar view of this risk.
You seem to forget that this product is aimed at a market demographic that will not only be all too grateful to get their hands on such a cheap clone soldering station based on Hakko's T12/T15 soldering iron direct drive cartridge tips but also have the necessary skills to render it safe and reliable for everyday use by applying the most basic of remedial measures.
However, this does mean it can't really be recommended as a first time purchase to a soldering virgin without access to help from an experienced mentor, prepared to apply such remedial work on their behalf or to guide them in the necessary reworking by way of a practical lesson in soldering (using ordinary soldering tools of course!).
Your concerns may be genuine if a little misplaced. Regardless of whether they were genuine or not, I thank you for giving me the opportunity to laud both the vices and the virtues of KSGER's cheap T12 soldering station. There are plenty here who see more of the virtue than the vice to go beyond mere remedial work and into the realm of applying hardware modifications to improve on KSGER's own efforts. I think your concerns may have fallen on deaf ears in this thread since I appear to be the only one so far, foolish enough to go where Angels fear to tread and make a reply.
[1] I'd seen an "illuminating" video on Youtube recently which demonstrated the 'glowing red hot' T12 tip but this was the result of mis-wiring a replacement temperature control module inside one of those combined spot welder/soldering station controller units. It was "illuminating" in that it showed just how close to the end of the tip the heating element was (extending just under 20mm from behind where the tip proper starts - impressively compact and right up against the tip itself).
[Edit] It seems I'd slightly misremembered that youtube video demonstration as you can see here:
https://youtu.be/E9eZTspkV0I?t=241 Nevertheless, it was literally illuminating, demonstrating just how compact and close to the business end of the tip the actual heating element is. I noticed he was careful to use the most commonly supplied K tip which so many reviewers tend to disparage out of hand. Close inspection shows that the heat is somehow being concentrated over the last 8mm or so of the heating element section which may or may not be typical for the K type tips.
Since the K tip originally supplied with the soldering station appears to have become unstable and I'm now using the one from the pack of ten assorted tips I'd included in my initial order, I might sacrifice the original to a similar test run, seeing as I now finally have a Longwei 30v 10A bench supply to hand (after more than a month's wait for Banggood's "Priority Airmail" to belatedly fulfil its promise).
This might actually cure it of its instability (or, more likely, kill it). At the moment it's like Schrödinger's cat, neither dead or alive so I'd prefer to force the issue one way or another and this seems a more fruitful way to resolve it (kill or cure - either is good, as in "All's Well that Ends", there's no need for it to end "Well", just as long as it ends).
JBG
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