A brief look at a small soldering iron, plus a little theory.

Since I’ve touched on soldering in my reviews, I’ll use this one to talk a little about the radio amateur’s most important tool: the soldering iron.
This review won’t actually be about soldering itself—that will probably be the subject of another review. Here, I’ll talk a little about soldering irons themselves.

As I mentioned in the introduction, today I want to talk about soldering irons.
I won’t make specific recommendations like “buy this one and you’ll be happy.” I think you’ll understand why by the end of the review.

As it happened, I accidentally ordered a small soldering iron for review. It has no temperature control and runs directly from mains power.
In other words, it’s a very basic, no-frills soldering iron, just for occasional work on the go or as a spare in case all the soldering irons at home burn out (knock on wood).

To start with, soldering irons come in several types.
Indirect-heating irons are a separate type: the iron is heated by something else, and then used for soldering. I haven’t come across any of these, though.
Direct-heating irons:
1. The tip sits inside a heater made of nichrome wire, insulated with mica.
2. The heater is inside the tip and is usually ceramic. More precisely, the heating element is inside a ceramic tube.
3. Gas-powered soldering irons, for working where there’s no electricity.
4. Induction soldering irons.
5. Soldering irons where the heater also serves as the tip.
6. Other types, powered by batteries and so on.

The first and second types are the most common.
Also, sometimes the soldering iron tip and heater are combined.

There are basic soldering irons, temperature-controlled ones, low-voltage ones, and mains-powered ones.

I won’t go through every type in existence, since that’s a whole topic in itself and would take us well beyond the scope of this review. But here’s a link to a pretty good article covering the different types of soldering irons.

In this review, I’ll describe a basic soldering iron with no temperature control, a ceramic heater, and mains power.

As always, I’ll start with the packaging.
The soldering iron came in a blister pack. There’s no useful information on it, just some generic phrases and a brief description.


The soldering iron itself is small and fairly well made, but unfortunately it has a plug with flat prongs, which is a bit disappointing since I’ll have to replace it with a standard one.


The soldering iron’s name is printed on the handle. To be honest, it doesn’t mean anything to me.
There’s a rubber grip near the front of the handle.
The handle is one of the important things to consider when choosing a soldering iron, but unfortunately it’s hard to judge by looking at it.
First, ergonomics. It doesn’t matter much for occasional use, but it makes a big difference if you use the iron often. It should sit comfortably in your hand, and ideally be well balanced—in a perfect world, you wouldn’t even notice it in your hand.
Second, heat. If the handle is poorly designed, it can get quite hot near the heater. Older soldering irons with Bakelite handles were notorious for this, especially high-power models. It’s hard to work when you’re distracted by how unpleasant the iron is to hold.
I didn’t notice any heat buildup with this soldering iron, though most models work this way nowadays. I also had no complaints about its ergonomics or balance, but those are fairly subjective.


The heating element and tip. This soldering iron has a conical tip.
I’m not a big fan of this type of tip; I’m more used to a chisel tip (it looks like the tip of a flathead screwdriver). But I know a few people who prefer this type.
There are lots of tip shapes, though most are more specialized. The most common are the chisel and bevel tips.


Replacing the tip on this soldering iron is very easy, as it is with most modern soldering irons :)
There are two types of ways to attach the heating assembly to the handle
1. There are three mounting screws near the handle, and the heating element has three tabs to match. This mounting method transfers less heat to the handle, but is slightly less sturdy.
2. The heating assembly fits directly into the handle. Here it's the other way around: more heat is transferred, but the joint is sturdier.
In practice, there isn't much difference between them. I use both types, but I've never bent either one, and I judge them only by how hot the handle gets—the cooler, the better.
Unscrew the metal nut and you'll see the tip itself, the heater, a spacer that keeps the tip from slipping inside, and the housing.


Here are several different types of tips I've used and still use, for comparison.
The tip from the soldering iron under review (presumably HAKKO 900M-T-xxx).
A tip from a domestically made industrial soldering iron.
The tip on the soldering iron I currently use all the time (a Solomon with a 976T-3D tip).
A tip integrated with the heater and temperature sensor. I rarely use this one these days. The photo shows the tip from an Aoyue 2738 soldering iron. They look like Hakko T12 tips, but are a little shorter.
Another tip from a domestically made industrial soldering iron, as an example of tips with a larger point.

As for temperature control, the best results I've had were with a tip integrated with the heater.
Don't let the fact that the tip has only two leads put you off—temperature control is still possible. A temperature sensor usually has a pair of extra leads; here, it's connected in series with the heater, and the station measures the temperature during the pauses in current to the heater.


Judging by its dimensions, the tip looks very much like a standard HAKKO 900M-T-xxx series tip.
I say “looks like” because the external dimensions match. I don't know the internal dimensions, but I doubt they developed a special type of tip just for this soldering iron.
When soldering, I almost always use non-burning tips, with only a few exceptions, although I know some people don't like them because you can't always get solder to stick to them.
In my experience, that's not a problem. As I see it, this kind of tip simply lasts much longer than a regular copper one, but you do need to handle it more carefully—especially don't try to reshape it, or file it at all.


The soldering iron's heater is 3.77 mm in diameter. Naturally, the closer the tip's inner diameter is to the heater's outer diameter, the better :)


If you carefully pull on the heater while pushing the power cable inward, you can see inside the soldering iron.
There's nothing special inside either: a small circuit board, and the power cable is secured with a cable tie.


A few photos of the internals.
1. Heater.
2. Oddly, the heater is powered through a diode for some reason. That puzzled me a bit.
3. The underside of the circuit board is extremely basic; it's only there to hold the diode, secure the cable, and solder the wires.
4. The heater is 59 mm long overall.


Measuring the heater's resistance, however, surprised me a little.
The calculations give a power of—
230/1808=127mA
230x0.127=29 watts
But since the heater is connected through a diode, that works out to about 15 watts, even though 35 watts is claimed. We'll check the heating performance later, but for now there's clearly a shortfall in power.
I don't really understand why there's a diode at all. If the heater had originally been designed for 115 volts, then with this resistance its power would be just 7 watts, which is clearly too low.


Another important parameter is the soldering iron's weight.
If anyone says, “What's the difference? It's only plus or minus 20–30 grams,” I'd say: try working with a soldering iron for 8 hours straight and you'll understand :)
This soldering iron is very light, just 39 grams without the cable, which is definitely a plus.

The cable is important too. If it's too stiff, it'll be hard to work with, but there's another issue: thin cables usually don't have heat protection.
A good cable should be as flexible as possible and, ideally, impossible to burn through with the soldering iron. The softest and best-protected cable (though very thick) was on a domestic industrial soldering iron.
This soldering iron's cable has no protection at all, so if you touch it with the hot tip, it'll melt easily. That's a minus.


The soldering iron's length is just as important—not only its overall length, but also the length of the heating element itself. The farther the tip is from the handle, the harder the iron is to work with. It's like taking a pencil and trying to write while holding it near the middle instead of near the point. You can write, but it's very awkward.
On this soldering iron, the distance from the handle to the tip is 72 mm.
On the Solomon soldering iron, this measurement is 95 mm.
The soldering iron from the Aoyue station is only 40 mm, and in my opinion it's the most comfortable one I own in this respect.


Next, I decided to run a small test to check a couple more important parameters:
1. Temperature. This is critical for non-adjustable soldering irons, since with an adjustable one you can set the temperature you need.
2. How quickly the soldering iron heats up. I think that's important too.
Four soldering irons will take part in the test.
1. The soldering iron from my Solomon SR-976 soldering station, which I use all the time.
2. The soldering iron under review
3. The familiar ЭПСН-25
4. The soldering iron from an Aoyue 2738 station (designed for lead-free solder). I turned off the fume extractor so it wouldn't interfere with the test.


Measuring temperature wasn’t a problem: I just connected a thermocouple to the multimeter and took a reading after a while. But for measuring warm-up time, I wanted to get the result as a graph.
At first, I thought I’d simply record measurements by hand every 5 or 10 seconds, then put them in a table or draw a graph. But then I remembered that in my previous review of a DIY oscilloscope, I’d mentioned that it could be set to a long (or even very long) sweep time. The rest was simple: I connected the thermocouple to the oscilloscope, set the minimum voltage per division (10 mV per square), and adjusted the sweep so the entire screen would refresh in 4 minutes (12 divisions at 20 seconds per division).
By the way, in this application, this oscilloscope did something my DS203 can’t.
The DS203’s maximum sweep time is 1 second per division, while the DSO138 goes all the way up to 500 seconds.
At the same time, the minimum voltage per division is 50 mV on the DS203 and 10 mV on the DSO138.
Of course, 2 mV per division would have been better for a thermocouple, but you work with what you’ve got. So there you have it: a real-world use for a simple instrument that managed to do something its more expensive and complex counterpart can’t.

1. You can see how quickly the temperature-controlled soldering iron heats up, then switches to temperature regulation. The waveform shows some strong spikes. Both the soldering iron and the oscilloscope were powered by switching power supplies, so some interference occasionally got through.
The soldering iron under review. I mentioned above that its power is only 15 W, so I was surprised by its maximum temperature. As it turned out, it’s quite convenient to use, but the temperature is high—that’s undeniable. It might work well with lead-free solder, or when doing a lot of soldering, since the tip will cool down a little during use. But I wouldn’t use it to solder SMD components.


1. EPSN 25. This one really takes its time. It took more than 4 minutes to heat up fully. It’s not very convenient to use in practice, and I don’t like it: despite its 25 W rating, it’s impossible to solder anything even moderately substantial with it. I’d sometimes even warm it up with a lighter when I needed to solder something quickly. For all the glowing reviews saying “it’s a classic,” I think it’s junk.
2. The soldering iron from the Aoyue station. If it weren’t for its short, thick cable (and the fume extractor hose on top of that), I’d say it’s the best one I use at home.
It heats up incredibly fast, reaching operating temperature in about 12–15 seconds. There’s a small “hump” in the waveform: during the test, I asked my wife to raise the temperature by 50 degrees and then lower it again (my hands were busy taking measurements).
And that’s not even counting the fact that you can change its tip while you’re working…


Seeing such different temperatures, readers will surely want to ask two questions: why do different soldering irons have such different temperatures, and what temperature is optimal?
I'll answer in order:
Why the temperatures differ.
1. Solomon soldering iron: the temperature was set for soldering small SMD components; I don't need it any higher. With good solder, the results are excellent.
2. The soldering iron under review: in my opinion, the temperature is clearly too high. But after using it for a couple of days, I didn't notice the handle overheating, the tip burning, or poor soldering. However, if you use it often and leave it switched on for a long time, the tip will start to burn.
3. EPSN 25. You can really feel that it doesn't get hot enough. The thermometer shows a higher temperature than the Solomon, but because there's no temperature stabilization, it “dies” on any reasonably large component during actual use. Still, since the tip is copper, it doesn't “forget” to burn, so I keep it around just in case.
4. This soldering iron reads somewhat high and should be recalibrated, but I never get around to it. At the moment, it was set for large components (the original setpoint is 350 degrees). But below there'll be a photo showing an even higher temperature; sometimes, in particularly difficult cases (like desoldering components from motherboards), I have to set it that high.

What temperature is optimal?
Of course, you can look up recommended temperatures online, but there are a lot of factors that affect the choice, and that's why in most cases I don't bother checking the actual soldering tip temperature (though sometimes it's necessary).
1. The solder alloy (not all solders have the same melting point) and its diameter.
2. Tip mass. If the tip is massive, the temperature can be a little lower.
3. The heat capacity of the components being soldered. Soldering a small resistor is one thing; a power connector is quite another.
4. The type of work. When soldering large batches, I used to crank up the tip temperature. At high working speeds, this didn't harm the components at all, but it did let me work much faster. However, you need experience to work this way. If you're soldering at a leisurely pace, it's better not to use this setting.
5. Air temperature. Back in the 1990s, we used to install TV antennas. In winter, we had to heat the soldering iron in a ventilation duct because it had no temperature control (and there weren't many that did); otherwise, soldering was impossible. This is hardly an issue with temperature-controlled soldering irons, of course, but it's still worth mentioning.

Based on all this, I'd say practice is what helps most, since there are too many variables.
Just judge by the results: a good solder joint should be mirror-bright, with no “frosty” patterns or porosity. If the tip seems to “freeze” to the joint, raise the temperature. If the flux starts boiling and burning, the temperature is too high.
In my opinion, the optimal range is 280–330 for a temperature-controlled soldering iron and 330–380 for one without temperature control, but it all depends on the specific conditions I listed above.

For demonstration purposes, I set the temperature on the Aoyua soldering station too high; you can still work even at this setting.
The station does read about 25–30 degrees high, though.


An important factor is how well the tip wets with solder.
People often complain that you can't get solder to stick to the tips on soldering irons like these. I didn't have that problem with the soldering iron under review, but I think it could well develop over time. It depends on how you care for the tip and how you use the iron.


It sits comfortably in the hand, and the rubber insert makes it easy to hold.


And now, to answer the question: what kind of soldering iron do you need for the job?
The answer is simple: you need several soldering irons. Different jobs call for different tools.
Here’s what I have at home:
1. Aoyue, for lead-free solder and small jobs involving components with high thermal mass.
2. The one reviewed here, currently out of work.
3. A domestic industrial soldering iron (one of two) with temperature control. It was my main iron for a long time, but I retired it because replacement heating elements are no longer available.
4. Solomon, used with a small soldering station; this is my main workhorse.
I have two of them. I bought the second as a spare, but so far I haven’t needed it.
5. EPSN 25, used to be my “travel” soldering iron; it will probably be replaced by the one reviewed here.
6. I bought this one by chance at a market, just because of its unusual appearance. I planned to put it to use, but it’s still sitting in reserve.
7. EPSN 65. Because the tip is very short, it runs extremely hot. I fitted a switch with an indicator light to the power cord so I can switch it to a gentler mode. It turned out to be very handy for soldering wires: it heats the cable strands before the insulation starts to warm up.
8. EPSN 40, used for soldering large connectors, but I rarely used it.
I also have an EPSN 80 and an EPSN 100, but I used them so long ago that after moving I didn’t even bother looking for where I’d put them. The EPSN 65 replaces the EPSN 80, and I never really needed the EPSN 100.


Summary.
Pros
Good ergonomics
Lightweight
The tip holds solder well, although I don’t work this way; I feed the solder directly into the joint.
Flexible power cord.
The handle doesn’t heat up during use.

Cons
It overheats, so I don’t recommend leaving it switched on for long periods.
The power cord isn’t protected against burns.
The power plug has flat pins, just as shown in the store’s photo.

My opinion: I wouldn’t call this a bad soldering iron, but I wouldn’t particularly praise it either. It’s just an ordinary, perfectly usable iron, albeit with some drawbacks. It’s best suited to occasional small jobs: keep it in a drawer, take it out when you need to solder something, and put it away again. I wouldn’t use it for frequent or heavy-duty work, or for fine electronics—it’s simply not the right tool for that.
At first, I planned to write a guide to the basics and techniques of soldering, but this iron isn’t really suitable for teaching, so I decided to put that topic off until I find an affordable, convenient iron that’s better suited to beginner electronics hobbyists. I’ll probably combine that article with a guide to choosing the right soldering iron or soldering station (or possibly both), but not this time.

I hope you found this review useful and interesting. As always, if you have any questions or comments, leave them below. This review came together a little spontaneously, since I’d originally planned to cover something else—sorry about that :)
Just to reiterate, everything above is my personal opinion and isn’t meant to be taken as the absolute truth.

The product was provided by the store for review.