You can make a welding machine from a microwave transformer. Do-it-yourself spot welding from a microwave diagram and description

Lately, I have been seeing quite a lot of lithium-ion batteries in various devices. Sometimes it even came to assembling batteries, and I connected the elements by soldering. However, I wanted to take a more correct path and use a resistance welding machine for this.

Buying a ready-made welder, even on Aliexpress, has choked me to death, since I very rarely need to weld batteries, and the device is expensive. Therefore, I decided to assemble such a device myself, and at the same time enjoyed the process.

There are many methods for assembling a resistance welder with your own hands. You can use a car battery, or a transformer from an old microwave. There are also various ways to control the welding current and the duration of the welding pulse. In the simplest case, you can simply connect two thick wires to a car battery, make electrodes from copper wire, connect it all together and weld it manually, measuring the time “by eye.” You can make control based on Arduino or a specialized time controller, a relay from a motorcycle, etc.

Well, I decided to make a welding machine based on a transformer from a microwave oven (microwave). In any case, it will be more compact and lighter than a car battery. And I bought a controller that doses both current and pulse duration on Aliexpress, because it is inexpensive, and it is a ready-made product that you do not need to assemble yourself.

I bought an old 750-watt microwave transformer on Avito for 600 rubles.

I also bought 1 meter of multi-core power cable with a cross-section of 25 square meters at the market for 125 rubles. More precisely, I took 2 meters (with a margin), but one is enough.

On Aliexpress I bought: a controller with a 40-amp triac (no more needed for welding 18650 batteries), a 9-volt AC transformer to power the controller, a foot pedal for convenient control, and also the most expensive thing - wires with connectors (on this part it was possible to save money by making electrodes from thick copper wire and connecting them, for example, through a terminal block to power wires) + electrodes (copper needles). In general, from what you bought on Ali, you only need a controller and a 9-volt AC transformer, the rest is optional.

AC Transformer:

Foot pedal:

Cables with connectors and handles with collet clamps:

The first step is to get rid of the secondary winding of the transformer. It is located at the top and is wound with a thin wire. You just need to saw off the winding with a hacksaw.

After this, the remaining wires can be easily drilled out with a thick drill.

If your transformer has such additional packages of metal plates, they also need to be removed.

Now you need to take a thick cable and insert it into the place of the former secondary winding, making two turns. Thus, we will get a step-down transformer from a step-up transformer. The output voltage is now only about 2 volts, but the current has increased many times - tens or perhaps even hundreds of amperes. This voltage is safe for humans, and it’s okay if you accidentally touch the powered electrodes with your hand.

The ends of the cable are clamped into terminals and insulated with heat shrink.

We connect cables with handles to them.

Now, according to the diagram, you need to assemble the rest of the electrics.

The foot pedal comes with a 10 cm piece of wire, so I replaced it with a long one so that the pedal could be placed on the floor.

The power wires were connected using a terminal block. It was possible to sleep.

The wires were connected to the transformer through removable terminals so that it could be easily disconnected.

Well, I simply soldered two wires to the controller, although it would have been better to screw them onto screws and round terminals, but I didn’t have those on hand, unfortunately.

In general, the circuit is assembled and can be connected to the network. Please note that the controller is powered by an AC transformer, not a DC transformer.

When turned on, the digital indicator and various LEDs light up.

The left knob sets the pulse duration (from 1 to 50, each unit is equal to 20 milliseconds). The right knob sets the power, ranging from 30 to 99%.

When you press the pedal, the circuit is turned on for a set number of milliseconds.

To weld the tape to the battery, you need to press the electrodes tightly against the surface. The surfaces of both batteries and tapes must be absolutely clean, without dirt, glue, oxides, etc. Otherwise the tape will not be welded.

I didn’t have any experience in resistance welding, so I had to select all the parameters experimentally, training on an unnecessary battery. A properly welded tape holds well and comes off when force is applied, leaving a small piece on the battery. The pulse duration and current strength depend on both the power of the transformer and the thickness of the nickel tape - possibly also on other conditions.

Traces of experiments:

I began to get more or less correct welding with parameters 35/70. But I think it would be better for me to take a more powerful transformer; it would be possible to shorten the pulse duration and there would be less overheating. However, we still need to experiment.

After watching interesting videos on YouTube, and also being inspired by this topic on ChipMaker, I also really wanted to make spot welding from a microwave with my own hands.

To make welding from a microwave, I purchased a transformer from a microwave, a 50 sq. mm stranded copper wire. about 2 m long, but this turned out to be a lot... As electrodes for spot welding, I used tips from soldering irons with a diameter of 13 mm; I could not get another copper rod in my city.

So, how I made spot welding from a microwave transformer.

How to make a transformer

First I sawed the transformer to remove the secondary winding, and I will repeat again:

Please note that a microwave transformer is dangerous to life! Those. it should not be connected to the network for testing until the secondary winding is removed, because The voltage on it is about 2000V and it can kill a person from a distance!

From copper wire to 50 kV. mm I removed the insulation because... it is too thick and is designed for 600 volts, and spot welding has a voltage of 2-3 volts in total.

As experienced people joke: Enough papyrus for insulation 🙂

I made the new insulation from fabric insulating tape, the wire turned out to be noticeably thinner, as a result, 3 turns of wire fit onto the transformer - this is already good, with the original insulation only 2 turns fit.

Things to consider when winding the secondary winding of a transformer for spot welding:

• the thicker the wire you use, the less it will heat up and the more current you will get in the secondary winding, it’s even better to use 70-100 sq.mm. The whole problem is that the window for winding the wire in the microwave transformer is not as large as we would like. But if you use another transformer with larger iron, for example OSM-1, then you can push in a thicker wire.
• The more turns you wind, the greater the voltage in the secondary winding will be, I got 2.5 V, i.e. 0.8 V per turn, and the higher the voltage, the longer the wires can be made to the electrodes, because There is a voltage drop in the wires.
• For the highest welding efficiency, the wires to the electrodes must be of a minimum length; in wires a couple of meters long, you will already receive a significant voltage drop; you should also fill the magnetic circuit window with winding as much as possible.

After winding the secondary winding of the trans, I glued the core together with epoxy resin.

Next, I soldered copper tips to the ends of the wire from the transformer, soldered them with a gas torch, first tinned them, and then inserted them into the tips and added solder until the tips were completely filled with it. Then, after cooling, I pulled the heat shrink on them, which was previously put on the wires. On the one hand, I stripped the tips down to copper to avoid unnecessary losses due to solder resistance. Although there will already be losses in the soldered connection, nothing can be done about it...

Manufacturing of spot welding electrodes

Also check out these articles

For the electrodes, as mentioned above, I used 2 tips from soldering irons, sawed off the necessary pieces, drilled 7 mm holes in them and cut an M8 thread.

Then I made copper studs for them, from two more tips from soldering irons with a smaller diameter of 9mm - I cut M9 threads on them, then M8 threads to get the studs of the required diameter. The studs are screwed into the electrodes, the terminals from the transformer are put on them and secured on top with a washer and a regular nut, not copper, so I got good contact with low resistance between the terminals from the trans and the electrodes.

I sharpened the electrodes for my spot welding like needles, and then made a third electrode, which I did not sharpen - with such an electrode it is much more convenient to weld wire, and with two sharp ones it is more convenient to weld sheet steel.

Microwave welding housing

I then made the body from 16mm plywood and the top cover from 1mm steel.

A computer fan with a separate transformer and a 12-volt diode bridge for it was also installed in the case; if you have a 220-volt fan, then of course an extra transformer is no longer needed. I just made it from available materials.

The legs of the case are the legs from the computer system unit.

On the back wall of the case I also placed a two-pole 20 A circuit breaker.

On the front panel of the case I installed 2 lamps - red - the device is powered on, green - welding is in progress.

Welding pliers

The pliers for my microwave spot welding were made from a 15 mm profile pipe; a support from a piece of profile was installed at the bottom of the lower part so that the device would not tip over when pressed hard.

The handle is a piece of a 12 mm hexagon and a file handle. Fastening the pliers - 2 corners, purchased at a hardware store.

By the way, the electrodes are specially attached to the pliers at the corners so that their angle of inclination can be changed.

Welding switch

A microswitch from a microwave oven was used, which supplies 12V to the control coil of the REC-77/4 relay. Because my welding consumes current up to 18A, I decided to use such a relay, it has 4 pairs of contacts, each of which is designed for a current of 10A, and I connected them in parallel and got a 40A relay (thanks to a user from the ChipMaker.ru forum).

Thanks to this relay, I didn’t even bother to heavily insulate the switch, because... it only has 12V and a small current (you can use any microswitch), and not 220V if I used a switch without a relay, especially since the switch is designed for a maximum current of up to 15A in total.

The relay is connected to the primary winding of the transformer, because It seems unrealistic to use a relay in the secondary winding due to the high current...

What did I get in the end?

The power of my microwave spot welder during welding is about 4150 W, current consumption after 2 seconds. welding is about 18 A, the voltage on the secondary winding is about 2.5 V, the approximate current in the secondary winding is 1650 A.

The device welds 3 mm wire very quickly, even melts it if you overexpose it... It welds sheet steel 2 pieces of 1.5 mm each perfectly, and also welds: 2 pieces of 1 mm, 3 pieces of 1 mm, I haven’t tried it yet, I think that it will be able to weld steel up to 2 mm (2 pieces of 2 mm each).

The secondary winding heats up after about 7-10 points.

How can you improve microwave welding?

• you can add a time relay to it, i.e. you can set the exact welding time, this is convenient when welding many identical parts.
• It is possible that it is worth adding a thermal relay to it, so that when the transformer heats up, the device turns off before it cools down, like in an iron

P.S. I wrote the article rather chaotically; I didn’t consider all the points, because... there are quite a lot of them, I rebuilt the device 3 times within 3 months, so in the future the article will be supplemented with new details and photos.

The nice thing is that I made a completely working spot weld from a microwave with my own hands, although it’s impossible to say what kind of thing it is, because... It took about 2 thousand for materials, but a real plushkin will find all these materials in his reserves :)

Photo of spot welding from a microwave:

Video about spot welding from a microwave transformer:

The device has been in use for 5 years now, and by the way it works well, although the CA is not used very often. The transformer from which the welding machine is made was torn out of a rather strong microwave oven, as was the fan that was installed to cool the windings. The secondary winding has been removed from the transformer without affecting the network winding (). The next step to take is winding the new secondary winding with a thick cable (under 10 mm in diameter).

Both the transformer and the fan are screwed to the plywood. A board with two holes is attached in front of the transformer, through which both ends of the secondary winding are inserted. Plywood is also a kind of screen that stops cold air from the welding site. Next to the transformer, as can be seen in the photographs, a timer is used to adjust the power-off time.

The transformer is turned on using a foot pedal - then the operator will have both hands free to work with the electrodes and the part. The electrodes are made of an 8 mm copper rod, which is threaded. The cable clamp is made from cut copper tube.

Welding machine in action

The fan starts working from the very moment the plug is inserted into the socket, since the transformer becomes very hot during operation. Next, we install two electrodes opposite each other, press the pedal, switching the voltage on the timer, which gives it some more time to supply the trans. Here this switch is used only for unintentional long pressing of the pedal or unwanted blocking of the button.

Select the cross-section of the secondary winding, or more precisely the number of coil turns, experimentally. When powered by 220 V, it does not blow out fuses (even 10 A) and does not cause the light to blink at startup.

Naturally, the welding voltage is low and the electrodes can be handled with your bare hand, but it is better to wear protective gloves, since the electrodes heat up from long-term operation.

The power of the welding machine depends on the transformer - a microwave oven usually has 800-1200 watts, so the larger the transformer, the better. When welding, a large current is created - 1-2 kA or more at a voltage of 1-8 V. The higher the current, the better the connection, because the welding time is very short, and when it comes to long-term welding with low power, the result will be a blackened place.

Spot welding, as you know, is performed on specialized equipment, but such a device can not only be found in a serial version, but also made with your own hands: for this, a transformer taken from an old microwave oven is useful. The resulting device will give you the opportunity to perform high-quality spot welding using alternating current, the strength of which is not adjustable.

The transformer is the most important element of any such spot welding device: its task is to increase the input voltage to the required value. To effectively cope with this, the device must have a high transformation ratio. Large microwave ovens are equipped with such transformers, and you need to find one of them. When you find such a microwave model, you will need to very carefully remove the transformer from it.

The technology for assembling a spot welding machine can be seen in more or less detail in the video below. An example of this homemade device will help us illustrate the process of creating a point. For more details on the assembly details, read the entire article.

Removing the transformer from the microwave oven

If a homemade spot welding machine uses a transformer with a power of 700–800 W, then with its help you can join sheets of metal whose thickness reaches 1 mm. Such a transformer is included in the category of step-up devices; to provide power to the magnetron, it is capable of generating a voltage of 4 kV.

The magnetron that any microwave is equipped with requires high voltage to operate. In this regard, the transformer connected to it has a smaller number of turns on its primary winding and a larger number on the secondary winding. At the latter, a voltage of about 2 kV is created, which is then doubled due to the use of a special doubler. There is no point in checking the performance of such a device by measuring the voltage connected to its primary winding.

The transformer should be removed from the microwave carefully. Do not pick up a hammer or other heavy objects. Its base is unscrewed from the microwave, all fastenings are removed, and the transformer is carefully removed from its installation site. In the device removed from the microwave oven, you will need, firstly, its magnetic circuit, and secondly, the primary winding, which, compared to the secondary, is made of thicker wire and has fewer turns.

Due to its uselessness, you will have to dismantle the secondary winding, for which a hammer and chisel will come in handy. It is very important not to damage or crush the primary winding, so you must act with the utmost care. If, when dismantling the secondary winding, you find shunts in the transformer used to limit the current, they must also be removed.

The secondary winding can be cut with a chisel

If the magnetic core of the transformer is not a glued structure, but a welded one, then it is better to remove the secondary winding from it using a chisel or an ordinary hacksaw. If the winding is very tightly packed into the window of the magnetic circuit, then it will need to be drilled or picked out by cutting the wires. This must be done very carefully, since the magnetic circuit may collapse due to such manipulations.

After dismantling work, a new secondary winding should be wound. To do this, you will need a wire with a diameter of at least 1 cm. If you don’t have such a wire in stock, you will have to buy it. In this case, it is not at all necessary to purchase a solid stranded wire of this cross-section; you can also use a bundle of several individual conductors, which together will provide the required diameter. After installing the new secondary winding, your upgraded transformer will be capable of generating current up to 1000 A.

If you want to make your spot welder more powerful, then the technical capabilities of one transformer may not be enough for you. Here you need to use two such devices (respectively, by disassembling two microwave ovens).

Subtleties of upgrading a transformer from a microwave oven

To make a secondary winding, you need to wind 2-3 turns on the core, which will ensure an output voltage of about 2 V, and a short-term welding current of more than 800 A. This is quite enough for the effective operation of the spot welding machine. Winding this many turns can be difficult if the wire used has a thick layer of insulation. Solving this problem is quite simple: you need to remove the standard insulation from the wire and wrap it with electrical tape that has a fabric backing. It is very important that the wire used for the secondary winding has the minimum possible length, which will avoid an unreasonable increase in its resistance and, accordingly, a decrease in current strength.

If you need to weld metal sheets up to 5 mm thick, keep in mind that this will require a spot welder with more power. To make it yourself, you need to use two transformers connected in one circuit. It is imperative to follow the appropriate rules when making such a connection. If you make a mistake and incorrectly connect the terminals of the primary and secondary windings of two transformers, a short circuit may occur. The correct connection of the windings, if there are no markings on their terminals of the same name, is checked using a voltmeter.

After correctly connecting the same terminals of two transformers, it is necessary to measure the value of the current that they jointly generate. As a rule, homemade transformers intended for spot welding machines, which are planned to be used in home workshops, are limited in current strength - no more than 2000 A. Exceeding this value will provoke interruptions in the electrical network not only in your home, but also in your closest neighbors . And this, naturally, will lead to conflicts. The value of the current produced by the connected transformers, as well as the presence of a short circuit in their circuit, is checked using an ammeter.

Another example of spot welding assembly is shown in the video below:

What results can be achieved if, in accordance with the rules, two transformers that are not very powerful are connected? If you take two identical devices with the following characteristics: power - 0.5 kW, input voltage - 220 V, output voltage - 2 V, rated current - 250 A - then by connecting their primary and secondary windings in series, you will get the output double the rated current, that is, 500 A.

The short-term welding current will increase in almost the same way, but during its formation significant losses will be observed, which is due to the high resistance of such an electrical circuit. Both ends of the secondary winding - wires Ø 1 cm - are connected to the electrodes of the spot welding machine.

Connection of 2 transformers according to scheme No. 1

If you have two powerful transformers at your disposal, but their output voltage is not enough for a homemade device, you can connect their secondary windings in series, which should have the same number of turns. This measure is resorted to if it is impossible to simply wind up the turns on the secondary winding due to the insufficiently large size of the window on the magnetic core.

With such a connection, it is necessary to ensure that the direction of the turns on the secondary windings of the connected devices is consistent, otherwise antiphase may result, and the output voltage of such a combined device will be close to zero. To experimentally determine the correctness of the connection, it is advisable to use thin wires.

How to determine the terminals of transformers of the same name

If the terminals of the windings of the connected devices are not marked, then it is necessary to identify among them those of the same name in order to connect them to each other. This problem can be solved in the following way: the primary and secondary windings of two or more transformers are connected in series, voltage is applied to the input of such a combined device, and an alternating voltage voltmeter is connected to the output terminals (terminals from series-connected secondary windings).

Depending on the direction of connection, the voltmeter may behave differently:

• show one or another voltage value;
• show no voltage at all in the circuit.

If the voltmeter produces any voltage, it means that there are opposite terminals in the connection circuit of both the primary and secondary windings. When the windings are connected in such an incorrect way, the following processes occur in them: the voltage supplied to the input of the primary windings of two connected transformers is reduced by half at each of them; The voltage increase occurs on the secondary windings, each of which has the same transformation ratio. The output voltmeter will register the total voltage, the value of which is equal to twice the input value.

If the voltmeter shows a value of “0”, then this means that the voltages coming out of each of the series-connected secondary windings are equal in value, but have different signs, thus they cancel each other out. In other words, at least one of the pairs of windings combined into a circuit is connected by terminals of the same name. In this case, the correct connection of the circuit elements is achieved by changing the order of connecting the primary or secondary windings, focusing on the readings of the voltmeter.

Electrodes for homemade spot welding

When choosing electrodes for a spot welding machine assembled with your own hands from a microwave, you should pay attention to the fact that their diameter matches the diameter of the wire to which they are connected. Copper rods can be used as such elements, and for low-power devices, tips from professional soldering irons are suitable.

During operation, spot welding electrodes wear out actively. To correct their geometric parameters, they must be constantly sharpened. Naturally, over time, such elements will require replacement with new ones.

The wires that connect the electrodes to the spot welding machine must be of a minimum length, otherwise they will lose significant power from the device. Power losses will also become serious if there are many connections in the electrical circuit “electrode - spot welding device”. If you want to increase the efficiency of using your homemade equipment, then it is better to solder copper tips onto the wires that connect the electrodes. Using such tips, you will avoid power losses at the contact points due to the increased resistance of crimp or any other connections.

The wires connecting the electrodes to the spot welding machine have a fairly large diameter, so special tips, pre-tinned, will help make their soldering easier. Since the electrodes for such a device are removable, soldering is not performed at the points where they are connected to the tips. Of course, in such places, which are constantly exposed to oxidation, there is also a loss of power, but they are much easier to clean than crimped tips.

Installing electrodes on the welding machine

As already mentioned above, the electrode for resistance welding can be made from a copper rod or a tip from a professional soldering iron, if the power of the device is low. The wire from the device is connected to the electrode using a copper tip, which is connected to it by soldering.

The tip is combined with the electrode using a bolted connection, which must be very reliable so that an increase in resistance at the point of unreliable contact does not lead to a loss of power of the spot welding machine. To make such a connection, holes of the same diameter are made in the electrode and tip.

The bolts and nuts with which the electrodes and lugs will be connected to the wires are best chosen from copper or its alloys, which have minimal electrical resistance. Elements of such connections, which greatly simplify the maintenance of the resistance welding machine, are not at all difficult to make with your own hands.

Homemade spot welding controls

Operating a spot welding machine (especially one made from a microwave oven with your own hands) is not particularly difficult. For this, two elements are sufficient: a lever and a switch. The compression force between the electrodes, for which the lever is responsible, must ensure reliable contact of the parts being connected at the welding point. To meet these important requirements, the lever mechanisms of such devices can be supplemented with screw elements, which provide even greater compression force. Naturally, such an element of a spot welding device must have very high reliability.

On serious production equipment, which is used to join sheets of steel of considerable thickness, compression elements are installed that create pressure from 50 to 1000 kg, depending on the need. And on spot welding machines used for irregular and simple work in a home workshop, it is enough for such a mechanism to create a pressure of up to 30 kg. For convenience and ease of operation of the spot welding machine, its clamping lever is made longer; this will also increase the compression force to the required value.

For a homemade home device, a lever with a length of 60 cm is sufficient. Using such a lever, you can increase the applied force by 10 times. Accordingly, if you press the lever with a force of 3 kg, the electrodes and connected parts will be compressed with a force of 30 kg. To prevent such a lever from moving the device itself when pressed, the base of the equipment must be securely fixed to the surface of the desktop using a clamp.

The switch, which is responsible for supplying current to the device, is connected to the circuit of the primary winding of the transformer, the current in which is significantly less than in the secondary. If you connect the switch to the secondary winding, it will create additional resistance, and its contacts will be tightly welded under the influence of strong current.

If a lever is used as a clamping mechanism, then it is better to place the switch directly on it, then the second hand will be free (it can be used to support the parts being welded).

The peculiarities of working on homemade spot welding equipment are that current should be supplied to the electrodes only when they are in a compressed state. Otherwise, you will encounter intense sparking of the electrodes and, as a result, their active burning. You can get initial experience in working with such a device using a training video.

The electrodes of spot welding equipment actively heat up during operation. In addition, the transformer and conductive elements of such a device are subject to intense heating. To avoid too much heat, which can lead to the failure of the spot welding equipment, a simple cooling system should be provided. A regular fan is often used for this. You can also take breaks in work necessary to cool the elements of the device.

The holding time of the electrodes under current in a compressed state during the welding process can be controlled visually, focusing on the color of the point at the junction, or you can use a special relay for this.

Obviously, making a spot welding machine based on a transformer from a microwave is not at all difficult, after carefully studying the presented videos and photos of the assembly process and taking into account the recommendations voiced.

(votes: 6 , average rating: 4,83 out of 5)

Let's continue the cycling topic.
When I rode a bicycle to work, it was inconvenient to carry it in a backpack - my back sweats. Carrying it on the trunk is inconvenient - the package slips and tries to get into the spokes. You need a small basket for the trunk that would keep small loads from falling. Since they don’t make such small baskets, I decided to make them myself. To assemble such a basket you need resistance welding, which can also weld batteries.
The process of assembling the trunk basket, batteries, and welding itself is described below.

"Weld body"- transformer from a microwave oven.
The secondary winding was removed with a hacksaw, and the plates between the primary and secondary were removed. I recommend a hacksaw; a Dremel or grinder can easily damage the primary winding, but it is still needed. A PV3 wire of 70 square millimeters was inserted (stuffed, hammered) into the window of the secondary winding in 4 hands, 1 meter is enough. The wire goes very hard, it took two people to refuel.
Tinned copper lugs were soldered onto the wire with a gas torch; it was not possible to solder pure copper ones. Electrodes are attached to the tips - 10 squares of copper for welding batteries and rectangular ones for welding rods or sheets.



In the case of rectangular electrodes, they allow you to weld both wire, if the electrodes are placed plane to plane, and a sheet if you turn the top electrode at an angle, as in the photo.
Rectangular electrodes are plates from the installation kit for current transformers; they were not useful during electrical installation, but here they are.

"Welding Brains"- a homemade timer on the PIC16F628A microcontroller, the link to which is in the title of the review.
I purchased it from the Chinese Super Electronic market, it’s not the first time I’ve made it there, and I don’t think it’ll be the last. When ordering $15-30, it is sent by mail with a normal track, well packaged, and does not mess with the package. Moreover, his prices are usually minimal or close to them.
In addition to picukha, it was purchased
- , 10 items, 5 pieces each - $2.7 lot 50 pieces.
- 50 pcs $1.28
- 10 pieces 4.8$
- 10 pcs 1.6$
- - 10 pcs 13.8$

Based on the diagram from

The power part was taken from the circuit, and it was decided to write the firmware myself.
I didn’t like the use of two buttons in the circuit - it’s faster and more convenient to control the encoder, the shutter speed range is small.

I have already reviewed the power supply; a 5V stub has been added to it. Two supply voltages 5V main and 12V control go to the controller. When the power is turned off, the 12V voltage begins to drop first; it goes through a resistive divider to the controller leg (blue trimmer, set to 3V). The controller sees zero on the leg, saves the parameters and goes to sleep.

The output of the PIC leg gives a signal to the optocoupler, the optocoupler opens the thyristor, which in turn turns on the trans primary. No heating of parts was noticed. It is possible to use a solid state relay, as in the previous article on this resource. In my previous welder, I also used a solid state, but the optocoupler + thyristor is smaller and cheaper when purchasing 10 pieces.

The encoder was purchased
It already has pull-up resistors, the encoder not only rotates but is also pressed.
When you press the encoder, the number begins to blink smoothly (I changed the brightness according to a sinusoid) - it shows the number of pulses up to 9, that is, you can cook with a repeated or triple pulse, the pause between pulses is equal to the pulse duration, the duty cycle is 50% in general. When you press the encoder again, it remembers the parameter into memory (checks whether it has changed) and goes back to the operating mode.

Indication on two LED seven-segment indicators, dynamic indication.

When welding, you usually need both hands free; to start welding, a pedal was made - a bell button.

When turned on, the timer for 1 second shows and reminds the number of pulses.
Then the shutter speed indication
.2 -0.02sec
0.2 -0.2 sec
2.2 -2.2 sec.
maximum 9.9 seconds, minimum 0.01 sec.
When the pedal is pressed and the shutter speed is worked out, - - is displayed
The tweezers should not twitch when working out the shutter speed, it didn’t work out very clearly.
timer operation 1.33 min

Physically, the timer is assembled in the housing of the HP printer power supply; a board is used from it as a supporting element and a power connector, fuse and filter capacitors at the input.
Something is assembled on stands, something is glued with hot glue, in general, all the elements of the collective farm. Oddly enough, everything works.

The faint of heart and perfectionists should not look at photos of offal

Welding nails 4+4mm.

Welding result

Luggage racks, 1 kg of 3 mm galvanized wire was enough for both racks, price about $1.5-2
My cell is 4*4cm, my wife’s bike bag cell is 5*5cm

Welding batteries for screwdrivers

Galvanizing residues

UPD.
Added larger photo

Brief description of the principle of operation and assembly:
Resistance welding is the process of forming a permanent welded joint by heating the metal with an electric current passing through it and plastic deformation of the joint zone under the action of a compressive force. (Vicki)
That is, a large current and compression force are needed. In industrial devices, the compression force and current are regulated electronically; there are welders with hydraulic compression. The simplest ones are those where they are squeezed with their hands, as in my version. Current is still needed. The transformer from the microwave allows you to replace the secondary winding; instead of the step-up winding, we put a step-down winding. The voltage does not matter much; the current is sufficient. When using larger transformers, damage to the wiring is possible; the primary winding currents in the microwave transformer are around 15-20 amperes, a good home option.
In addition to the power part, which provides current and sometimes pressure, sometimes an electronic part is needed. You can put a 16A circuit breaker in the primary winding, like in an access panel, and use it to set the time delay of the current effect with your hands “by eye.”
For example like this


If you want a little convenience, holding both with both hands, you can add a button. But not every button can withstand currents of 15 amperes; for this you can use a solid-state relay or a starter. If the starter coil or solid state relay input is low voltage, not 220V, then a power supply is needed. This option is in the next picture.


The power supply provides 12 or 24 or any other safe voltage, it turns on the relay/starter through the K button, it is convenient to press with your foot and the button does not burn out.
For long shutter speeds of the order of 2-5 seconds and large details, this is acceptable. But when welding batteries, plates 0.1-0.2 mm thick are usually used and short dwell times of about 0.01-0.1 seconds are required. Such shutter speeds are difficult to work out manually; exceeding the shutter time will burn out the plates, and sometimes the battery, and they are not cheap.
To ensure repeatability of the result, an electronic timer is installed, which generates the necessary short exposures.
The next picture shows a circuit with a timer.


In total, almost the most advanced option - a transformer with a replaced secondary, a timer button, a power supply, you can combine it to your taste. For example, if the timer is 220V, then a power supply is not needed, but your leg may get fried if there is 220V on the pedal.

Brief assembly instructions:
-Find a microwave, disassemble it, remove the trans (it is 2/3 of the weight of the microwave).
-Check whether the primary winding is alive, it is usually wound with a thicker wire, ring. Don't turn it on! High voltage may appear on the secondary winding and transformer housing.
-Carefully remove the winding with the thinnest wire, if the thick one is live. Clamp it in a vice, cut it with a hacksaw or any other not very powerful tool, the remains will be knocked out.
-Remove the shunts (plates between the primary and secondary windings).
-There are several more turns of the filament winding. It can also be deleted.
-Wind the secondary winding into the vacant window. For welding batteries, 35 squares of copper are enough, for thicker materials 70-100mm. You may have to remove the factory insulation and insulate with heat shrink/duct tape. Two or three turns is usually sufficient. The wire is called PV3*70 or welding wire. Maybe PV5*70, but I haven’t seen those.
-End the wire. Typically, tinned copper lugs and copper lugs are used. You can crimp or solder them or both.
-Attach electrodes to the ends of the wire. For welding batteries, 10 squares of copper (PV3*10) are enough. For thicker metals, electrodes are made from large-diameter copper rods, sharpened at the ends. The better the connection between the electrodes and the wire and the shorter the wire, the greater the current and the better the welding.
- Add a timer, button, body to taste. You can add an LED to the upper electrode arm to illuminate the work area. You can add another winding of 3-5 turns and solder a 5V buzzer to it (the white wire is in my photo), it will beep when welding.

Link to firmware

RV2 adjust to 3v, lower log. 0 and the command goes to save to memory.
Motor-encoder, two buttons to turn it, a trigger button and an encoder button
ports B for indicator - ABCDEFG-2345610
I have sc56-11gwa indicators, that is, a common cathode.

Oscillograms
The title shows the shutter speed in seconds.
In the first, the shutter speed is 0.01 sec, pulses one by one manually, to the right 5 pulses of 0.01 each
the rest are all 5 impulses automatically after a pause equal to the shutter speed.

Welding an electric bicycle battery