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.

1-box.JPG

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.

2-contents.JPG

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.

2-setup.JPG

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.

4-iron.JPG

5-heatingelement.JPG

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.

6-addltips.JPG

7-solderwontstick.JPG

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.

8-hakkovskaiweets.JPG

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.

9-thermalcaptest.JPG

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.

10-ironinstand.JPG

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