Hi all. Chinese USB soldering irons appeared quite a long time ago and they already have a million reviews. But in this article, instead of a review, I will tell you how to easily and simply attach a PWM power regulator to a soldering iron.
The soldering iron is actually quite good. It heats up very quickly, it's light, it's small, and it can be powered by anything that has a USB connector. For example, from a smartphone charger, from a charger through a cigarette lighter in a car, or from a power bank. I don’t recommend powering a soldering iron from a computer’s USB connector.
But most owners of these soldering irons encountered problems with their operation, namely:
The listed problems lead to the fact that using a USB soldering iron is inconvenient and sometimes impossible to use.
Naturally, people tried to fix the problems. I found some of the most popular ways to modify soldering irons:
I didn’t like the first method because although the soldering iron starts to turn on and off when you touch the sensor, it will still be extremely difficult to control the desired temperature so that the soldering iron does not cool down or overheat.
The second method has the same disadvantages as the first. By the way, the Chinese, having not found a better solution, have already started installing buttons instead of a sensor. These simplified soldering irons are sold with a gray cap instead of a yellow one and the words “Press Switch” instead of “Touch Switch” on the packaging. You are such a soldering iron you can't change it under PWM regulation. 
The third method involves the presence of a “sleep mode”. When a person touches the ball, the soldering iron heats up to a temperature of approximately 250 degrees in 20 seconds. Another touch - the soldering iron heats up to full within a certain time. There is an article with this modification on Muska -. I consider the disadvantage of this method to be discrete control - either 250 degrees or 500. There is no intermediate temperature. Well, complexity of course. Not everyone has a programmer at hand.
Since I didn’t like any of the existing modification options, I decided to go my own way.
Below you can see a diagram of a USB soldering iron. The circuit was made by user JVX79 with drive2. 
The diagram shows that the NE555 timer is used to turn on and delay turning off the heating in the soldering iron. What else is this timer used for? For PWM regulation! That is, you already have almost everything you need to modify your soldering iron!
All you need to do to modify your soldering iron is:
The most difficult thing is to find and place a variable resistor in the small case of a USB soldering iron.
I took the resistor from the volume control of old headphones. I didn’t take a photo of the volume control, so I’ll attach a photo from the Internet so that you understand what I’m talking about. 
The resistor was placed in the center of the case above the timer chip. In the upper half of the case I made a small cutout for a variable resistor.
Photo of the modified soldering iron
Assembled. The resistor wheel protrudes onto the edge of the housing by several millimeters. 
View with the cover removed. 
Reverse side of the soldering iron board. 
Slot in the upper half of the body. 
After assembling and testing the soldering iron, I determined the heating range - from 230 to 500 degrees. At 230 degrees, pos60 solder already melts and you don’t have to worry about the safety of the tip, and at 500 degrees you can solder and desolder even large elements.
Well, the most important thing- you can set any temperature within the specified range for soldering elements of different sizes and heat capacity.
I also advise you to watch a video demonstrating the operation of a soldering iron and a detailed description of the operation of the PWM regulator.
I hope that the information provided in this article will be useful to you. And let me remind you again - make no mistake when buying a soldering iron. You need to take the version with a yellow cap and the inscription “Touch Switch” on the packaging.
I think there is no point in presenting this interesting tool. Repeatedly described here in reviews.
Received today from Mongolia Post :) very quickly. Tried. Certain advantages and disadvantages of the product were fully confirmed.
The main advantage is fast, almost instant heating. And this advantage immediately turns into a disadvantage - without sufficient heat removal during the soldering process, the soldering iron overheats terribly.
Control over maintaining the temperature is provided by turning on the heating when you touch the sensor on the body.
Also, if the soldering iron is left alone, the timer will turn off after (in my copy) 45 seconds. approximately.
What we see in practice:
- the sensor (again, in my copy, at least) is terribly sensitive. It works not just by touching, but by bringing your hand 10-15 cm closer to the soldering iron!.. That is. the soldering iron will turn off only if you leave it completely alone and remove your hands
- due to the very fast heating of the tip, the delay in turning off the soldering iron is ~45 seconds. very(!) big. During this period, it is guaranteed to overheat.
I don’t know to what extent the described parameters of the soldering iron’s automatic power supply are typical for products in general, but the fact of problems with overheating is mentioned in other reviews.
Based on the above, it is advisable:
- reduce the sensitivity of the soldering iron sensor to the level of reaction to direct finger touch
- reduce the timer delay after releasing the sensor to prevent uncontrolled overheating of the tip.
These problems can be solved quite easily
Reducing sensor sensitivity:
solder the capacitor between the sensor contact and ground. The power bus can be used equally, which is preferable for ease of soldering. I used a 2.2nF capacitor to eliminate interference and ensure reliable finger triggering
- reducing the delay: we reduce the value of the timing SMD resistor in the NE555 timer circuit. The denomination was set to 200k, in parallel with which (just for convenience) I jammed 47k
In the end it looks like this: 
Working with a soldering iron becomes convenient. You can control the heating as you use it, avoiding idle overheating. Which, by the way, will extend the life of the heater.
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Once, while walking through the expanses of Aliexpress, I saw a USB soldering iron on sale. I was surprised. Can a normal soldering iron be powered from USB, where the supply voltage is only 5 Volts? But out of curiosity, I still ordered this copy.
Convenient small soldering iron. Fits perfectly in the hand.
You can look at this soldering iron for yourself this link.
Weighs only about 20 grams
The kit includes a 1.5 meter cord with the following connectors at the ends:
as well as a stand for the soldering iron itself
All assembled it looks like this:
USB power supply: take a power supply that produces a current of at least 2 Amps
In order to find out the power consumption of USB consumers, I have this device
I connect the soldering iron to the block through this device
When you turn on the soldering iron, the red LED on it lights up
So, the voltage supplied to the soldering iron is 4.9 Volts
The current consumed by the soldering iron is 1.44 Amperes
Therefore, the power consumption of the soldering iron is: P = IU = 1.44 x 4.9 = 7 Watt with kopecks.
This soldering iron heats up very quickly due to its small dimensions. The fireproof thin nickel tip will serve you faithfully for a long time. As a last resort, you can buy it on Aliexpress without any problems.
The solder melts once and twice!
And of course, the best feature: automatic shutdown. If you do not touch the soldering iron, it will automatically turn off after 25 seconds! As soon as we want to pick it up, the contactless sensor on it is triggered, and the soldering iron is ready for battle again. Well, honestly, I didn’t expect this from the Chinese.
Well, what else can you say about this soldering iron? It is unlikely that you will be able to solder large parts, but various small things will work just fine. Can it be powered from a USB computer or laptop? Mmm... Well, I plugged it into a laptop and it worked fine for me, but I strongly do not recommend doing this! Still, it is better NOT to use the USB ports of your computers to power the soldering iron. As you remember, they are intended for other purposes. If you buy a Power Bank in addition to it, you can solder even in an open field. This is much more convenient than using a bulky and smelly gas soldering iron.
Such a soldering iron will be an excellent purchase for young radio amateurs, since many of them forget to unplug the soldering iron from the outlet, and also in such a USB soldering iron there is no voltage of 220 Volts, which in itself is considered unsafe. So, parents, if you still want to buy a good soldering iron for your child, take a closer look at this USB soldering iron. I've been using it periodically for a month now. He showed his best side. Reviews on the Internet about it are also good. Further use will show what this soldering iron is capable of in terms of longevity;-)
I want to talk about the modification of this soldering iron, or more precisely about why it failed.
I must say that this soldering iron is really very decent in appearance (if you don’t pay special attention to the use of the audio connector at a current of ~1.5 A) and even seems to solder. Of course, I wouldn’t plug it into a computer’s USB port (since, with its eight watts of power, it obviously doesn’t support USB Power Delivery), but with an adapter or powerbank it works great. The only negative that I was going to fix was the touch button. The fact is that it is not implemented in a human way, using the method of measuring capacitance, for example, but in the way they liked to make touch switches in very ancient years - on the principle of receiving interference. That is, it is assumed that on any conductive object (including a person) there is an induced interference voltage, which is used to determine the fact of touch; in this case, to restart the power control of the monovibrator heater, assembled on a 555 timer.
There are several disadvantages here. First, I am not a fan of relying on factors that are not consistently reproducible. What if, for example, I go with this soldering iron somewhere out of town, where there is not even electrical wiring, there is relative silence on the air and induced interference will be much less - the soldering iron will not turn on at the moment when it is most needed?
Next, turning off the power by timeout is, of course, good. The only thing is that after this very shutdown you have to wait until the soldering iron warms up, and, in addition, many powerbanks tend to turn off when there is no load.
In addition, I am not a fan of using touch buttons in such cases, since they are too easy to touch accidentally. Thank God, no one has yet thought of installing touch keys on industrial hammer drills, for example.
In general, the direction of improvement was clear - replace the sensor with a button, solder ATtiny13 (whatever was suitable) instead of 555 and make sure that during idle time the power was reduced, for example, to 25% of the maximum, and pressing the button raised the power to maximum for example, three minutes. I must say that I, of course, am not the only one so smart - we have already installed tiny13 in this soldering iron. But normal PWM is not used there, the sensor is left, and the code, how can I say it...
I took it apart and soldered out all the unnecessary parts (that is, almost everything).
I soldered ATtiny13 in place of 555, wrote and uploaded the firmware...
And nothing worked. And very strangely it didn’t work. I even began to suspect that I had come across fake tiny13. However, later, after a day of continuous soldering of parts and painful tests, I came to a simple conclusion - apparently, when using PWM (even low-speed, with a frequency of about 300 Hz) to control the power of the heater, the ATtiny13 simply resets regularly due to power supply interference , since the native board was naturally routed without taking into account the fact that a controller would be installed on it.
Moral: to radically improve this soldering iron, it makes sense to make a new board. Maybe I'll do this someday. In the meantime, I came to the conclusion that it would be best to remove the electronics from there altogether.
And now - some music in honor of the anniversary of my master's thesis. It was on this day exactly a year ago that my student life ended, taking with it many hopes and plans...
Chinese goods have long conquered the Russian market and are gradually displacing well-known electrical products from other manufacturers. However, due to the difference in standards and other features of Chinese production, the Russian user constantly has to make adjustments to the design of the purchased products.
Particularly pressing in recent years are the problems associated with the modification of Chinese soldering irons, taking into account all the shortcomings found in them (including the small temperature control range).
A modern Chinese soldering iron with a temperature controller has certain advantages, along with which it often has some shortcomings. The latter manifest themselves, as a rule, not only in the high cost of this product, but also in its fragility and insufficient accuracy in adjusting the main operating parameter - temperature.
Soldering irons from China with a power of over 40 watts are very rare, although it is often necessary to work with parts of non-standard sizes. Most users who want to purchase such devices at an affordable price are forced to put up with these shortcomings. On the other hand, any attempts to independently remake these devices encounter certain difficulties, which are especially noticeable in areas remote from regional centers.
In the simplest case, adjusting the temperature (and therefore the power) comes down to changing the supply voltage, which outside the city limits is not particularly stable anyway. That is why, if you want to modify Chinese products, you must act very carefully, trying not to disrupt the normal functioning of the soldering iron.
Refinement of the power regulator
A homemade contact sensor is made from an old Soviet capacitor and balls from a bearing. The device is placed on the factory board without modifications to the case. When the soldering iron is placed on the stand with the tip up, the sensor opens the circuit and the heating temperature decreases. When we start soldering, the contacts inside close and the tip warms up to the set temperature in accordance with the position of the regulator.
Let's look at a few more examples of such modifications in relation to various models of soldering devices.
The classic Chinese-made model has a power of 60 Watts and is designed to operate from a standard household network of 220 Volts. The delivery set includes a very inconvenient adapter for a plug with flat contact legs (it always gets stuck in the recess of the sockets).
Therefore, many users begin modifying this model by changing the power cord (or at least its final part). After switching to a Russian standard plug, working with such a soldering iron becomes much more convenient.
A lot of complaints about this model are caused by the sting, which is not at all suitable for dismantling work. Its tip, coated with a protective compound, takes a very long time to heat up, and the sensor built into the soldering iron does not react to temperature, but temporarily and constantly turns off the device. Because of this, when soldering particularly difficult areas that require good heating of the surfaces, it is necessary to raise the temperature with some reserve.
However, such a soldering iron often overheats and often turns off. As a result, many craftsmen immediately after purchase replace the “native” tip with any other one they have in stock. When studying customer reviews, we often encounter complaints about poor quality of contact at the point where the power cord is connected to the heating element. In this regard, it is advisable to replace it with stasis after acquisition.
A USB soldering iron with this name provides very fast heating of the tip, which ultimately turns into a disadvantage, since the soldering iron overheats greatly. Its design provides temperature control, which can be controlled by touching a sensor built into the body of the handle. If you hold such a Chinese soldering iron in your hand, the regulator maintains the set mode, and it continues to heat up.
After it is placed on the stand, the timer should disconnect the device from the network (after about 40-45 seconds). In fact, the following phenomena are observed:
In this regard, immediately after purchasing a Chinese product, it is necessary to reduce the sensitivity of its sensor, and also try to reduce the time interval after which it disconnects from the network. This will require some reworking of the circuit.
Many people do not want to tinker with the device and ask the seller to send a replacement, explaining the problem.
Very often at home you have to repair small parts, which are most conveniently processed using low-power soldering devices. Miniature gas soldering irons are ideal for these purposes, which, however, need some modification. Its essence usually comes down to changes in design that reduce fuel consumption during the soldering process.
To do this, you can take a number of actions of the following nature:
After such modification, gas consumption is significantly reduced, especially when processing heat-shrinkable tubes.
To summarize what has been said, we note that modification of inexpensive Chinese products used for soldering at home can significantly improve their parameters. For a number of people who like to make things with their own hands, this activity turns into a kind of “hobby”.
