Today I’m putting the cheap STHOR 79371 hot-air soldering station, which I bought for just under 80 PLN from a friend from university, through its paces. I’ll be testing how it performs in practice, taking measurements of the actual temperature recorded by a thermocouple at settings of 100°C, 350°C and 450°C, and finally I’ll take a look inside and show you its construction. Unfortunately, I don’t have any unboxing photos this time, as the owner had already unpacked the station and disposed of the box.
So let’s start with the general information. The brand of this station is Sthor, manufacturer’s code 79371, although it is imported by TOYA. The rated power is 750 W, and the temperature can be adjusted from 100 to 500 degrees. Airflow up to 120 l/min. The handle features a brushless fan and a sleep sensor.
For around 70 zlotys, the set includes three nozzles, the station and a cable.
We also have a manual, which I can show you:
Now we can move on to the actual tests.
Practical tests
To start with, the first test – we take a board and heat it up. Without any additional aids and always starting with a cold nozzle, so as not to cheat. We also time it, use flux and check how quickly the component can be removed.
It’s not as silly a test as it might seem; I’ve tested quite a few of these hot air guns and I know that some simply don’t heat up – even on a low setting. An additional heater can be a good help here, but personally I successfully replace surface-mount components without one, so I do want that solder to melt...
I started with a test at 350 °C, an SOIC8 component, a narrow nozzle, and full airflow.
Failure – it didn’t budge, even when I switched to low airflow for a minute at the end. On my Sugon, this component would have come off ages ago, even with high airflow and at the same (or even lower) temperature setting.
Second attempt – 400 °C – SOIC8 – full airflow.
This is workable. It took 2 minutes to remove the SOIC8. Acceptable, so to some extent this station is useful.
Third attempt – 400 °C – large transistor with a massive heat sink
2.5 minutes. This was a slightly more difficult task, as the component has better contact with the board and dissipates heat effectively, but it was still possible to remove it. That’s good.
Fourth attempt – 400 °C – TQFP chip
In just under 3 minutes, the chip was successfully removed.
At this point, the impression is that the station is up to the task, although the temperature on the display is overestimated.
Measurements
I carried out the measurements using my kit described in a separate thread: OpenBeken configuration for hot air tests – MAX6675, temperature and power logging
I checked three temperatures – 100°C, 350°C and 450°C, each at full and half fan speed.
Interactive version: https://openshwprojects.github.io/hotair/STHOR79371.html
Well... my Sugon, set to 350 °, reached 320 ° on the probe; I checked this with the same fan setting as here, although I didn’t measure the actual fan speed. The STHOR is about 100° lower. At 450°, the situation is similar, with a difference of over 100° as well. Interestingly, the same thing happens even at the 100° setting. Reducing the airflow doesn’t help at all here.
Separately, I compared the unit to other tested models:
The same problem occurs here; the display readings are significantly higher than what is on the probe. What’s more, when compared to the classic 858, one could even say that 450 °C here is equivalent to 350 °C on the 858...
Interactive versions:
https://openshwprojects.github.io/hotair/version12/350c.html
https://openshwprojects.github.io/hotair/version12/450c.html
The power measurement also explains a lot – 700 W is only achieved right at the start, and then it is heated at a much lower power.
Interior
We’ll also take a look at the sticker with the manufacturer’s information. On the back, there is a socket and a fuse slot.
We unscrew the screws and remove the casing. Inside, it’s basically… very empty, which comes as no surprise. The station is very light.
So does it work fully on 230 V? Well, not quite – there is a tiny switching power supply in there. You can also see what is responsible for the digital control and the display.
The display is controlled by the TM1650, a controller with a protocol similar to I2C, but without addressing.
The MCU is a Puya PY32F002B, a tiny but already 32-bit microcontroller based on the ARM® Cortex®-M0+ core with 24 KB of Flash memory and 3 KB of RAM. These days, even 8-bit chips are slowly becoming uneconomical, as their 32-bit equivalents are just as cheap...
In the high-voltage section, we have a BTA16-800BW triac with a driver; it is used to regulate the heater power directly from the mains and is controlled by the MOC3041.
You can also take a look at this power supply section. At the input, there is a capacitor acting as a filter and a fuse resistor. The converter is based on the SN57CP.
The protective wire is connected to the hot air nozzle:
Summary
It works, but it’s nothing to write home about. The very fact that 450 °C on this station at full fan speed is the same as 350 °C on other models (such as the classic 858) already goes some way towards explaining the frequent misunderstandings and surprise among beginners that, whilst components come off the PCB easily for others, they have to heat and heat with no end in sight. One might say that it’s fine, that you just need to help yourself with a heat gun – and there is some truth in that, but it doesn’t change the fact that there are differences between stations, and this is clearly evident from my measurements. It’s also interesting that even reducing the airflow at 350 °C didn’t help remove the SOIC 8 chips from the board; it only worked at 400 °C (on the display). You also need to be careful with the airflow itself, because even in the manual I’ve provided photos of, you can see that the manufacturer recommends the highest airflow setting to extend the heater’s lifespan. Otherwise, the heater overheats more quickly. Personally, I wouldn’t really recommend this station, especially as when I tested the classic 858, it heated slightly better. It would probably need to be calibrated before further use, assuming that’s even possible over such a wide range. I suppose the only advantage is that low lower temperature range; you can also work with heat-shrink tubing.
Does such a simple hot air gun make sense for a beginner? Join the discussion
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