Ultra-budget spot welding of lithium batteries at home. Arduino based spot welding machine arduino spot welding

In the life of every "radio destroyer" there comes a moment when you need to weld several lithium batteries together - either when repairing a laptop battery that has died of age, or when assembling power for another craft. Soldering "lithium" with a 60-watt soldering iron is inconvenient and scary - you overheat a little - and you have a smoke grenade in your hands, which is useless to extinguish with water.

Collective experience offers two options - either go to the trash in search of an old microwave, rip it apart and get a transformer, or spend a lot of money.

I didn’t want to look for a transformer for the sake of several weldings a year, saw it and rewind it. I wanted to find an ultra-cheap and ultra-simple way to weld batteries with electric current.

Powerful low voltage source direct current, accessible to everyone - this is an ordinary used one. battery from the car. I'm willing to bet that you already have it somewhere in the pantry or you can find it with a neighbor.

I'm suggesting - The best way getting an old battery for free is

wait for frost. Approach the poor fellow, whose car won’t start - he will soon run to the store for a new fresh battery, and he will give you the old one just like that. In the cold, the old lead battery may not work well, but after charging at home in the warmth, it will reach its full capacity.

To weld batteries with current from the battery, we will need to give out current in short pulses in a matter of milliseconds - otherwise we will get not welding, but burning holes in the metal. The cheapest and affordable way switch the current of a 12-volt battery - an electromechanical relay (solenoid).

The problem is that conventional 12 volt automotive relays are rated for a maximum of 100 amps, and short-circuit currents during welding are many times greater. There is a risk that the relay armature will simply be welded. And then, in the open spaces of Aliexpress, I came across motorcycle starter relays. I thought that if these relays withstand the starter current, and many thousands of times, then it will do for my purposes. This video finally convinced me, where the author tests a similar relay:

In some cases, instead of soldering, it is more profitable to use spot welding. For example, this method can be useful for repairing batteries consisting of several batteries. Soldering causes excessive heating of the cells, which can lead to their failure. But spot welding does not heat the elements so much, since it acts for a relatively short time.

To optimize the entire process, the system uses Arduino Nano. This is a control unit that allows you to effectively manage the power supply of the installation. Thus, each welding is optimal for a particular case, and as much energy is consumed as needed, no more, no less. The contact elements here are a copper wire, and the energy comes from a conventional car battery, or two if more current is required.

The current project is almost ideal in terms of complexity of creation / efficiency of work. The author of the project showed the main stages of creating the system, posting all the data on Instructables.

According to the author, a standard battery is enough for spot welding two nickel strips 0.15 mm thick. For thicker strips of metal, two batteries are required, assembled in a circuit in parallel. The pulse time of the welding machine is adjustable and ranges from 1 to 20 ms. This is quite sufficient for welding the nickel strips described above.

The author recommends making a payment to order from the manufacturer. The cost of ordering 10 such boards is about 20 euros.

During welding, both hands will be occupied. How to manage the whole system? With a footswitch, of course. It is very simple.

And here is the result of the work:

Hello, brain! I present to your attention a spot welding machine based on the Arduino Nano microcontroller.

This machine can be used to weld plates or conductors, for example, to 18650 battery contacts. For the project, we will need a 7-12V power supply (12V recommended), as well as a 12V car battery as a power source for the welding machine itself. Typically, a standard battery has a capacity of 45 Ah, which is sufficient for welding nickel plates with a thickness of 0.15 mm. To weld thicker nickel plates, you will need a larger battery or two connected in parallel.

The welding machine generates a double pulse, where the value of the first is 1/8 of the second in duration.
The duration of the second pulse is adjusted using a potentiometer and is displayed on the screen in milliseconds, so it is very convenient to adjust the duration of this pulse. Its adjustment range is from 1 to 20 ms.

Watch the video, which shows in detail the process of creating a device.

Step 1: PCB Fabrication

Eagle files can be used for PCB fabrication, which are available at the following .

The easiest way is to order boards from manufacturers printed circuit boards. For example, on the site pcbway.com. Here you can buy 10 boards for about 20 €.

But if you are used to doing everything yourself, then use the attached schematics and files to make a prototype board.

Step 2: Installing the Components on the Boards and Soldering the Wires

The process of installing and soldering components is quite standard and simple. Install small components first, then larger ones.
The tips of the welding electrode are made of solid copper wire with a section of 10 square millimeters. For cables, use flexible copper wires with a cross section of 16 square millimeters.

Step 3: Foot Switch

For driving welding machine you will need a footswitch as both hands are used to hold the welding electrode tips in place.

For this purpose, I took wooden box in which the above switch is installed.

A friend came, brought two LATRs and asked if it was possible to make a spotter out of them? Usually, upon hearing such a question, an anecdote comes to mind about how one neighbor asks another if he knows how to play the violin and in response he hears “I don’t know, I didn’t try” - and so I have the same answer - I don’t know , probably "yes", but what is a "spotter"?

In general, while the tea was boiling and brewing, I listened to a short lecture that one should not do what one should not do, that one should be closer to the people and then people will reach out to me, and also briefly plunged into the history of car repair shops, illustrated by savory tales from the life of "bone cutters" and "tinsmiths". Then I realized that the spotter is such a small "welder" that works on the principle of a spot welding machine. Used to "tack" metal washers and other small fasteners to the dented body of the car, with the help of which the deformed tin is then straightened. Indeed, there is also reverse hammer” is needed, but they say that this is no longer my concern - only the electronic part of the circuit is required from me.

After looking at the spotter circuits on the network, it became clear that a single vibrator was needed, which would “open” the triac for a short time and supply mains voltage to the power transformer. The secondary winding of the transformer should produce a voltage of 5-7 V with a current sufficient to "seize" the washers.

To generate a triac control pulse, different ways– from a simple discharge of a capacitor to the use of microcontrollers with synchronization to the phases of the mains voltage. We are interested in the circuit that is simpler - let it be “with a capacitor”.

Searches "in the nightstand" showed that, apart from passive elements, there are suitable triacs and thyristors, as well as many other "small things" - transistors and relays for different operating voltages ( fig.1). It’s a pity that there are no optocouplers, but you can try to assemble a capacitor discharge pulse converter into a short “rectangle” that includes a relay that will open and close the triac with its closing contact.

Also, during the search for parts, there were several power supplies with output constant voltages from 5 to 15 V - they chose an industrial one from the "Soviet" times called BP-A1 9V / 0.2A ( fig.2). With a load in the form of a 100 ohm resistor, the power supply outputs a voltage of about 12 V (it turned out that it had already been redone).

We select triacs TS132-40-10, a 12-volt relay from the existing electronic "garbage", take several KT315 transistors, resistors, capacitors and begin to breadboard and check the circuit (on fig.3 one of the configuration steps).

The result is shown in figure 4. Everything is quite simple - when you press the S1 button, the capacitor C1 starts charging and a positive voltage appears on its right output, equal to the supply voltage. This voltage, passing through the current-limiting resistor R2, enters the base of the transistor VT1, it opens and voltage is applied to the relay winding K1 and as a result, the contacts of relay K1.1 close, opening the triac T1.

As the capacitor C1 charges, the voltage at its right output gradually decreases and when it reaches a level less than the opening voltage of the transistor, the transistor will close, the relay winding will de-energize, the open contact K1.1 will stop supplying voltage to the triac control electrode and it will close at the end of the current half-wave of the mains voltage . Diodes VD1 and VD2 stand to limit the resulting pulses when the button S1 is released and when the relay winding K1 is de-energized.

In principle, everything works like this, but when controlling the time of the open state of the triac, it turned out that it “walks” quite strongly. It would seem that even taking into account the possible changes in all the on-off delays in the electronic and mechanical circuits, it should be no more than 20 ms, but in fact it turned out many times more and plus, the pulse lasts 20-40 ms longer, and then for all 100 ms.

After a little experiment, it turned out that this change in the pulse width is mainly due to a change in the supply voltage level of the circuit and the operation of the transistor VT1. The first one was “cured” by mounting a simple parametric stabilizer inside the power supply, consisting of a resistor, a zener diode and a power transistor ( fig.5). And the cascade on the VT1 transistor was replaced by a Schmitt trigger on 2 transistors and the installation of an additional emitter follower. The scheme took the form shown in figure 6.

The principle of operation remained the same, the possibility of a discrete change in the pulse duration with switches S3 and S4 was added. The Schmitt trigger is assembled on VT1 and VT2, its "threshold" can be changed within small limits by changing the resistances of resistors R11 or R12.

When prototyping and checking the operation of the electronic part of the spotter, several diagrams were taken, according to which it is possible to evaluate the time intervals and the resulting front delays. In the circuit at that time there was a time-setting capacitor with a capacity of 1 μF and resistors R7 and R8 had a resistance of 120 kOhm and 180 kOhm, respectively. On figure 7 the top shows the state on the relay winding, the bottom shows the voltage at the contacts when switching the resistor connected to +14.5 V (the file for viewing by the program is in the archive appendix to the text, the voltages were taken through resistor dividers with random division factors, so the “Volts” scale is not true). The duration of all relay power pulses was approximately 253...254 ms, the contact switching time was 267...268 ms. "Expansion" is associated with an increase in the trip time - this can be seen from drawings 8 And 9 when comparing the difference that occurs when closing and opening contacts (5.3 ms versus 20 ms).

To check the temporal stability of the formation of pulses, four successive switchings were carried out with control of the voltage in the load (file in the same application). On a generalized Figure 10 it can be seen that all the pulses in the load are quite close in duration - about 275 ... 283 ms and depend on where the half-wave of the mains voltage falls at the moment of switching on. Those. the maximum theoretical instability does not exceed the time of one half-wave of the mains voltage - 10 ms.

When setting R7 = 1 kOhm and R8 = 10 kOhm at C1 = 1 μF, it was possible to obtain the duration of one pulse less than one half-cycle of the mains voltage. At 2 uF - from 1 to 2 periods, at 8 uF - from 3 to 4 (file in the application).

In the final version of the spotter, parts were installed with the ratings indicated on figure 6. What happened on the secondary winding of the power transformer is shown in Figure 11. The duration of the shortest pulse (the first in the figure) is about 50 ... 60 ms, the second - 140 ... 150 ms, the third - 300 ... 310 ms, the fourth - 390 ... 16 uF).

After checking the electronics, it's time to do the hardware.

A 9-ampere LATR was used as a power transformer (right on rice. 12). Its winding is made with a wire with a diameter of about 1.5 mm ( fig.13) and the magnetic circuit has an inner diameter sufficient for winding 7 turns of 3 parallel folded aluminum tires with a total cross section of about 75-80 sq. mm.

We carefully disassemble the LATR, just in case, we “fix” the entire construct in the photo and “copy” the conclusions ( fig.14). It is good that the wire is thick - it is convenient to count the turns.

After disassembly, we carefully inspect the winding, clean it from dust, debris and graphite residues using paint brush with a hard pile and wipe with a soft cloth slightly moistened with alcohol.

We solder a five-amp glass fuse to the “A” terminal, connect the tester to the “middle” terminal of the “G” coil and apply a voltage of 230 V to the fuse and the “nameless” terminal. The tester shows a voltage of about 110 V. Nothing buzzes and does not heat up - we can assume that the transformer is normal.

Then we wrap the primary winding with a fluoroplastic tape with such an overlap that at least two or three layers are obtained ( fig.15). After that, we wind a test secondary winding of several turns with a flexible wire in insulation. After applying power and measuring the voltage on this winding, we determine the required number of turns to obtain 6 ... 7 V. In our case, it turned out that when 230 V is applied to the “E” and “nameless” terminals, 7 V is obtained at 7 turns. When power is applied to "A" and "nameless", we get 6.3 V.

For the secondary winding, “very well used” aluminum tires were used - they were removed from an old welding transformer and in some places had no insulation at all. In order for the turns not to close together, the tires had to be wrapped with sickle tape ( fig.16). The winding was carried out so that two or three layers of coating were obtained.

After winding the transformer and checking the operability of the circuit on the desktop, all the details of the spotter were installed in a case of a suitable size (it seems that it was also from some kind of LATR - fig.17).

The outputs of the secondary winding of the transformer are clamped with M6-M8 bolts and nuts and brought to the front panel of the housing. Power wires are attached to these bolts on the other side of the front panel, going to the car body and the “reverse hammer”. Appearance at the home check stage is shown in Figure 18. At the top left are the mains voltage indicator La1 and the mains switch S1, and on the right is the impulse voltage switch S5. It switches the connection to the network or output "A" or output "E" of the transformer.

Fig.18

At the bottom are the connector for the S2 button and the outputs of the secondary winding. The pulse duration switches are located at the very bottom of the case, under hinged lid (fig.19).

All other elements of the circuit are fixed on the bottom of the case and the front panel ( fig.20, fig.21, fig.22). Doesn't look very neat, but here main task there was a reduction in the length of the conductors in order to reduce the influence of electromagnetic pulses on the electronic part of the circuit.

The printed circuit board was not divorced - all transistors and their “strapping” are soldered to breadboard from fiberglass, with foil cut into squares (visible on fig.22).

Power switch S1 - JS608A, capable of switching 10 A currents ("paired" outputs are in parallel). The second such switch was not found and S5 was installed at TP1-2, its conclusions are also paralleled (if you use it when the mains power is off, it can pass quite large currents through itself). Pulse duration switches S3 and S4 - TP1-2.

Button S2 - KM1-1. Connector for button wires - COM (DB-9).

Indicator La1 - TN-0.2 in the appropriate installation fittings.

On drawings 23, 24 , 25 photographs taken when checking the spotter's performance are shown - a furniture corner measuring 20x20x2 mm was spot-welded to a tin plate 0.8 mm thick (mounting panel from a computer case). Different sizes"pyatachkov" on fig.23 And fig.24- this is at different "cooking" voltages (6 V and 7 V). The furniture corner in both cases is welded tightly.

On fig.26 shown back side plate and it is clear that it warms up through, the paint burns and flies off.

After I gave the spotter to a friend, he called about a week later and said that he had made a reverse “hammer”, connected and checked the operation of the entire device - everything is fine, everything works. It turned out that long-duration pulses are not needed in operation (i.e., elements S4, C3, C4, R4 can be omitted), but there is a need to connect the transformer to the network “directly”. As far as I understand, this is so that with the help of carbon electrodes it is possible to heat the surface of the dented metal. It is not difficult to make the power supply "directly" - they put a switch that allows you to close the "power" outputs of the triac. A little embarrassing is the insufficiently large total cross section of the cores in the secondary winding (according to calculations, more is needed), but since more than two weeks have passed, and the owner of the device has been warned about the “winding weakness” and does not call, then nothing terrible has happened.

During experiments with the circuit, a variant of a triac assembled from two T122-20-5-4 thyristors was tested (they can be seen on figure 1 on the background). The switching circuit is shown in fig.27, diodes VD3 and VD4 - 1N4007.

Literature:

1. Goroshkov B.I., "Radioelectronic devices", Moscow, "Radio and communication", 1984.
2. Mass radio library, Ya.S. Kublanovskiy, "Thyristor Devices", M., "Radio and Communications", 1987, issue 1104.

Andrey Goltsov, Iskitim.

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