Kaiweets KOT936 Soldering Iron Review

I was approached by Kaiweets recently, asking if we'd consider reviewing their KOT936 Electric Soldering Station. We don't get requests like this often, and especially not for soldering irons. In 2005, Dr. Webster wrote a scathing review of the ColdHeat Classic. For years, it was a top Google search result for "ColdHeat", prompting ColdHeat and Weller representatives to register at Applefritter and post rebuttals in a long forum discussion full of ColdHeat criticisms. ColdHeat is no longer in business.

That's why I was surprised when Jane from Kaiweets wrote me, saying "I browsed your site carefully and I noticed that there're some posts about soldering and related tools. So I think it would be a perfect fit to get our product exposed there." How carefully did Jane browse Applefritter? Is she aware of our history with ColdHeat and that confident in the KOT936's abilities? I normally ignore emails like this, but I couldn't resist the opportunity to put another soldering iron in Dr. Webster's hands. I accepted, and gave Kaiweets the mailing address of our resident soldering iron torturer, Dr—"it's such a pile of junk it's unbelievable it's still on the market"—Webster. He received the iron for free. Kaiweets has had no other influence on the editorial process. Will he like the KOT936? Will he destroy another soldering iron company? Read on to find out! –Tom Owad


Kaiweets is not a household name; like many other electronics tool manufacturers based in China, its got stiff and better-known competition. The KOT936 is one of two soldering irons that the company offers. The other is the KETSO2 "digital" iron that contains all of its circuitry in the handle. The KOT936 is more traditional in that the power supply and circuitry is contained in a desktop base station, and the iron itself just gets hot. This makes it less expensive, but perhaps more desirable for its modularity (though read on to learn how this may be meaningless).

The KOT936 came packaged in a plain brown cardboard box. I'm not aware of any retailers that stock this product in stores; it's available from Kaiweets' website and Amazon, and when it comes to mail order, pretty retail packaging is a needless expense. The box contains the base station and iron, a stand for the iron with sponge and copper wick, a baseplate with attachable feet, two goosenecks with alligator clips on one end, another gooseneck with a magnifying lens, a set of additional tips for the iron, and a small tube of lead-free solder.

The goosenecks screw into the baseplate, which then turns into a "helping hands" apparatus useful for holding wires and components during soldering. There are notches in the baseplate to accommodate the feet of the soldering iron's base station. Leaving it there while using the goosenecks isn't practical, but it does allow the setup to take up less space when stored.

The base station is primarily made of plastic, but has a decent weight to it and won't slide around on your desk if the cable from the iron gets tugged. There's only a few notable features: a permanently-attached power cord, a simple rocker power switch on the right side, a 5-pin DIN socket on the front for the iron's cable; a potentiometer for controlling the temperature, and a single red LED.

The iron itself features a largely plastic construction. It doesn't feel cheap, but it doesn't offer the high quality finish and sense of durability that more expensive composite plastics do. There's a dense, rubbery grip, and while not plush, it's comfortable enough. Kaiweets advertises the iron as being ESD-safe, and indeed I was able to measure continuity between the tip and the base station's electrical plug ground pin. Securing the iron's tip is a typical sleeve with threaded nut arrangement: loosen the nut, slide off the sleeve, then the tip slides off the ceramic heating element.

A small pencil tip was pre-installed on the iron; in a vinyl packet were five more: Two additional conical tips in different sizes, along with medium-sized chisel, bevel, and knife tips. The first time I tried to use the iron, I attempted to "tin" the tip as one normally does, using standard 60/40 leaded solder. Strangely, none of the tips would take the solder -- it would just turn into little balls and roll off, with some of the rosin flux left burning. I tried using the lead-free solder included in the box, and had similar result. Cleaning the tips using alcohol wipes had no effect. Soldering without a "wet" iron tip is frustrating at best, so the test of this iron was not off to a good start.

Thankfully the tips are of a standard size, so ones from other manufacturers, such as Hakko, will work. They're not expensive items, typically running less than $10 each, but one should not have to replace a critical piece right away just to get the product to work. Perhaps there was a bad production run of these tips, and there are a number of positive reviews of the unit on Kaiweets' website, but as a reviewer I'm left skeptical.

This also made me suspicious of other aspects of the iron. Its cable contains a 5-position connector, which suggests that it's temperature-controlled. Basic irons, such as the cheap units that plug directly into mains voltage without a separate base station, simply operate on a fixed wattage, similar to how a hair dryer works. Slightly better irons allow some temperature control by varying the amount of power delivered to the heating element, but this is done in a continuous fashion. Temperature-controlled irons contain a thermal sensor inside the iron's tip and send that feedback to the base station—if the iron is straying from its target temperature, the base station adjusts the amount of power sent to the heating element in order to compensate. It's a nice feature to have, and makes soldering a smoother and more consistent experience.

Despite my skepticism, I read 55 ohms across pins 1 and 2 of the iron's connector, indicating the presence of a thermal sensor. Controlling the temperature is a rudimentary affair; the base station only has a single knob, with markings to indicate approximate temps in both Celsius and Fahrenheit. When the iron is operating, there's no feedback other than the single LED, and its operation is backwards from what I'd expect. When performing its initial heating (after being powered on), the LED glows solid; once it's reached temperature, it then blinks.

The KOT936 is a 65-Watt iron, just like the iron I compared it against, The Hakko FX-888D, which is very popular among enthusiasts. The Kaiweets costs less than half as much, so if it performs anywhere near as well it could prove to be quite the bargain, despite the drawbacks I've identified so far.

A word about testing methodology: I had difficulty accurately testing the temperatures of these irons. My first attempt was using an IR thermometer, but its "spot" where it could read was larger than the tip of the iron, so it always picked up the background (room) temperature instead. Ultimately I purchased a basic temperature probe with K-type thermocouples. While readout wasn't instant, it was much easier to ensure the tip of the iron was being measured. Notably, the set temp of both irons never matched what the probe reported, but I suspect this is related to the way the thermocouple works and the fact that it was measuring the "actual" temperature of the iron's tip, as opposed to the iron's built-in temp sensor which is usually embedded inside or next to the heating element (that is to say, it'll always measure hotter).

The first thing I measured was initial warmup time and temperature accuracy. The Hakko was pre-set to heat up to 400C (750F), and I dialed in the Kaiweet's knob to that same value. From a cold start, the Kaiweets took 55 seconds to reach the point where its LED indicated it was "ready", and the temperature probe read 238C (460F). I let it continue to warm up from there, and the iron reached its highest-reported temperature of 310C (589F) after two minutes total. For comparison, the Hakko went from cold to "ready" in 38 seconds, with a measured temp of 344C (650F); it took one minute and ten seconds total to reach 360C (680F) where it stabilized.

From there, I wanted to test thermal capacity. Thermal capacity is, essentially, how much heat an iron can maintain when placed under load. For simple soldering tasks, like simple joints, this isn't much of a factor; the joint is over and done with before the solder pad or component can wick much heat away. But a real-world example of where thermal capacity matters is when trying to desolder components' negative terminals, like the leg of a through-hole capacitor. Since these are connected to the ground plane of a PCB, and ground planes usually comprise a lot of the copper in a board, it can require a lot of thermal energy -- the good conductivity of the ground plane wicks the heat away before the solder can melt. Thus, an iron with good thermal capacity will have the "power" to keep putting heat into the joint.

I approached this test as follows: With each iron heated to its target temp from the previous test, I placed it on a small metal bracket to simulate a large thermal mass (i.e. PCB ground plane). The bracket was at room temperature prior to each test. Immediately after the iron's tip was placed on the bracket, I started a timer and began measuring the tip's temperature. I set one minute as the target mark.

The Kaiweets' initial 310C (589F) had sagged to 227C (440F) after a minute had elapsed, a drop of about 37%. The Hakko's initial 360C (680F)'s temperature had only fallen to 324C (615F) in that same time, though, a drop of 11%. This indicates that the Kaiweets struggles more with keeping the iron's tip hot under load. It's difficult to make a general statement about the practical implications of both these irons' performance as soldering can be a varied task, but as you might have surmised, the more thermal capacity, the better.

The final test was recovery time. This is how quickly the iron can return to its original temperature after the thermal load has been removed. In a real-world scenario, this can dictate how quickly the iron is ready to move on to the next solder joint, thus affecting your efficiency. Nobody wants to wait while their iron heats back up. I removed each iron from the metal bracket and timed how long it took to return to its previous temperature. The Kaiweets took about two minutes and 30 seconds, while the Hakko required 40 seconds. Thermal capacity and recovery time both measure how "powerful" an iron is, so it makes sense that good performance in one can mean good performance in the other.

Something that works against the Kaiweets iron is the design of its stand. It's made of metal, and has a plastic insert to hold the iron, similar to the Hakko's (and many other manufacturers). However, the loose copper braid included for cleaning the iron's tip -- which works well for that purpose -- is meant to fit into the cavity where the iron's tip inserts. This has the result of meaning that every time you put the iron into the holder, the tip is cleaned. Convenient, but since copper braid is also thermally conductive, it has the effect of drawing heat out of the iron's tip, meaning it isn't up to full temperature once you remove it.

The KOT936 and FX-888D have a wide gulf in their prices; the former sells for about USD$50, while the latter is about USD$115. If you can justify the cost, the Hakko is the better product in many ways -- not just performance but also build quality and, critically, parts and support. The Kaiweets iron, on its own, is a solid value for the money and a decent step up from cheap 20-watt fixed-temperature irons. Its major concern is simply one of its relative disposability -- if parts fail, finding replacements could be difficult if not impossible.

Thankfully, tips are interchangeable with those of other vendors (especially given the bizarre tinning problem mentioned above), but good luck if the heating element or something in the base station fails. I was unable to find replacement parts for the iron on Kaiweets' Web site, and exploring it also reveals that soldering is not a priority for the company; most of its products focus on electrical testing (multimeters), thermometers, and hand tools (pliers, crimpers, etc). Would they be able to furnish a replacement part after the unit is out of its 3-year warranty?

That said, clearly the KOT936 is not targeted at the professional market where reliability and performance are paramount; it's meant for hobbyists and its price point (which I've seen as low as USD$30 after coupon on Amazon) is very compelling in that context. With that in mind, it's probably worth the money -- just make sure you shop around for the best price, and don't forget to pick up a replacement, brand-name tip.

Kaiweets offered us a 15% coupon and a 15% commission, which I declined. You can find many such coupons by searching youtube for kaiweets 15%. At present, though, Amazon's price is much better. - Tom

Content Type: 


Nice review.  It looks like a decent unit.  Similar in a lot of wasy to the YiHUA 939D+ that I have.  The "helping hands" look convenient.  I have a separate "helping hands" fixture I use which also has a magnifying glass like the one on the Kaiweets.  I'm not sure whether having that integrated would be better or worse.  I'd have to try it to know I guess.  The YiHUA includes a copper tip cleaner, but it is separately located so it doesn't automatically cool the tip whenever the iron is in the holder.  Does the Kiaweets include a digital temp readout like the YiHUA?  That's a nice feature so you know when it is up to temp.  The tips look very similar to and probably compatible with the YiHUA supplied ones.  The grip on the YiHUA looks like it is 1/2 way between the two you compare.  It is a more hard rubber like the less expensive one, but more generously sized like the expensive one.


As for buying through Amazon, that's where I got my YiHUA.  It is similarly priced to the Kaiweets, maybe $5-$10 more, although I suppose if you include getting a separate "helping hands" the YiHUA would be more.


I am definitely happy I bought a soldering station vs. the smaller hand held irons I used to use.  It's been well worth the money.




The number "936" is not an accident; a whole industry of Hakko 936ESD knockoffs has prospered during the last 20 years. The widespread counterfeiting of this unit was one reason Hakko discontinued it for the much more distinct looking FX-888. But even it has been counterfeited.

These copycat devices are known for poor fit and function as well as being electrically unsafe.

While it is true that some copycat products are of poor quality, it isn't universally true.  I'm sure that the YiHUA that I have would be poo-pooed by anyone who is a fan of the similarly featured but 2x the price products from big name companies like Weller.  And I won't dispute that a lot of those products are indeed very nice.  But a lot of the Chinese makers have really upped their game on quality the past few years.  An example is the electric power tools at Harbor Freight a few years ago were generlly kind of poorly made.  However they introduced newer higher end brands like Bauer and Hercules which are much more comparable to the name brands like Makita or Ryobi.  And even their cheap brands like Chicago Electric seem to be much better than what they were selling 7-8 years ago.  I bought a couple of Chicago Tool angle grinders a while back that were $10 each on sale and I have used the hell out of them and they're holding up fine.  Are they DeWalt?  No.  But I couldn't buy a beat up used DeWalt angle grinder in a pawn shop for twice that.


Now, I do see what you are talking about as far as some very cheap products like this one:




or even more so this one:




At those price points maybe what you say might be true.


It will be interesting if Dr. Webster gives us an update after a few months or a year of using this soldering station and lets us know how it performs over time.  I'm willing to keep an open mind.



It would have been interesting to know how much power the soldering iron actually consumes when one of the "difficult" solder operation on a large area copper foil / ground plane is done. Maybe it never gets full power, thanks to inferior temperature controller electronics. Note that proper measurement of power consumed requires better instrumentation than these $10 Harbor Fright (pun intended) multimeters.


For me, the almost 50 year old Weller WTCP-S soldering station still is the gold standard to make good solder joints under any conditions. The "Magnastat" principle is super simple and it only has two modes of operation: full power or no power on the heating element. The sensing element is a special alloy cap on the solder tips, which attracts a magnet inside the soldering iron which closes a switch, giving full power to the heating element, until the temperature setpoint is reached, which is the "Curie" temperature of the sensor, where it loses its ferromagnetic properties and does not attract the magnet anymore. The switch opens, no power to the heating element. Tip temperature drops a little bit, until below the Curie temperature, when the ferromagnetic properties are promptly regained, the magnet is attracted again,  and the power is turned on again. This is a very simple and foolproof system. In the base station, there is only a switch and a transformer. No electronic components to fail.


When Weller introduced the electronically controlled soldering stations, we quickly found out that they struggled with the before mentioned "difficult" solder operations on large copper areas. The industry found out that the pace of hand soldering work had to be slowed down compared to the WTCP-S. Worse, the temperature control electronics in these early electronically controlled Weller stations often failed. So buyer beware, if you buy one of those off Ebay.


But the WTCP-S is practically bulletproof and most spare parts are still available. The "magnastat" tips with the excellent life time and excellent solder acceptance are still available and don't cost much. For leaded solder, alloy Sn60PbCu2, the #7 tips work best. They can also be used for some lead free solder alloys, but I avoid them, and use leaded solder only. Why ? Leaded solder gives you shiny, perfect, long lasting solder joints while lead free solder gives you dull, brittle, and tin whisker growing, crappy solder joints which don't last for long (more on this see footnote).


There is a general rule with tools: either get a throwaway cheap one which just gets the one task at hand done (even I use these sometimes), or, if you do the task often and want the best outcome, buy the much more expensive professional grade tools. If you can't afford them new, find a used on that is in reasonable shape and still works. Ebay and pawn shops are a good source for used, but high quality, professional tools at reasonable costs.


You can't enjoy a hobby of you are getting crappy results because of the use of crappy tools.


- Uncle Bernie


Footnote on leaded vs. lead free solder and the lead free solder scam


IMHO, the whole "lead free solder" scam was brought about because a) the patent holders for lead free soldering wanted to make bank, and likely bribed some politicians tolegistale a ban on leaded solder, and b) the consumer electronics industry wanted to have products which don't last, and fail after a few years. So you need to buy a new flat screen TV, a new dishwasher, or a new other electronified appliance at a faster pace, thanks to failing lead free solder joints.

The same type of scam is found with refrigerants and pharmaceuticals: once the patents expire, and competitors could make and sell a generic version at lower price, all of a sudden it is “discovered” that the now patent free product “may be”  hazardous for your health or for the environment, politicians and regulation agencies get bribed to ban them, and new, patented, expensive, substitutes are promoted. Which actually may be less efficient and more hazardous than the now patent free, older product.

So unless you are the type of hobbyist who actually plans to  eat  your finished printed circuit boards, you may use leaded solder with no regrets. No, you can't save the environment if you don't use leaded solder, because 50+ years of use of billions of tons of leaded gasoline have already polluted all the world, and lead now is everywhere, and won't go away. If you want to play it safe, get a solder fume extractor fan (recommended anyways) and wash your hands with D-Lead Soap when leaving the lab.

Tom Owad's picture

I think most lead-free solders, when soldered correctly, has a longer lifespan. Here's a graph comparing cycles to failure, from Comparing and Benchmarking Fatigue Behaviours of Various SAC Solders under Thermo-Mechanical Loading:

Comparing Sn63 with other alloys that contain silver could be misleading; a more relevant comparison would be with Sn62 (which does contain silver). It's no surprise that silver makes for stronger alloys. In fact "silver solder" properly refers to alloys containing predominantly silver, which have much higher melting points and are much stronger than electronic solders. The technique of using silver filler metal is called brazing rather than soldering (or "hard soldering" as opposed to "soft soldering" using tin) and requires torches or special ovens.

There aren't very many situations where bonds stronger than Sn62 provides are desired in electronics: one case would be attaching steel needles to an ionic generator for air purification. Because the needles are only soldered at one end and protrude out, they are subject to very high mechanical loading force. In almost all other situations, components are more or less evenly supported by pins or pads on all sides and loading force is pretty low.

The increased strength of 'SAC' alloys is frequently a source of problems, particularly with high-density interconnects such a BGAs. With higher strength comes lower ductility, and that leads to fractures underneath the BGA that are hard to detect. The techs who repair these BGA failures ("reballing") always use Sn63 solder balls.