Spotter for do-it-yourself body repair from a welding machine

In detail: a spotter for do-it-yourself body repair from a welding machine from a real master for the site my.housecope.com.

Spotter is a device that allows you to perform spot welding. This device is used to connect thin parts, and perform leveling work. Most often, the spotter is used in the restoration work of the car body part. Equipment of this type is used by employees of car services. But if necessary, you can assemble the spotter with your own hands from the welding machine.

A homemade spotter can be made from an old inverter. But for this you need to know what scheme the structure is going to use. Spotter operation depends on a number of mandatory components:

welding transformers;
primary winding;
diode bridge;
thyristor.

The equipment operation scheme is determined by two diagonals. The power of the transformer of the first diagonal is higher than that of the second. Therefore, it accepts voltage after turning on the device. Electricity flows through the secondary winding through a diode bridge and a relay into a capacitor. This system provides charging. In this case, the voltage is passed in the transformer and does not accumulate. With this triggering scheme, the thyristor closes.

Opening the thyristor is required to start welding. After disconnecting the charging of the capacitor, the secondary winding of the transformer will receive a sufficient current for welding... In more detail, you can consider the elements of the scheme in work on the plan.

When creating a homemade device, the body is selected. A dielectric plate acts as the base of the device. Parts made from other materials are not used for this purpose. The dimensions of the base are free to choose. It must be taken into account that all used components can be placed on it. At the same time, they must be placed so that during installation and, if necessary, free access to them is provided.

Video (click to play).

In order not to make a mistake in the calculations, a drawing is prepared in advance, including the components used.

A suitable option for performing the functions of a body is an old welding machine. Also, a microwave oven is used as a case. The fastening of the components depends on how the device is planned to be made: stationary or portable. When choosing the second option, the components are distributed evenly and mounted using fasteners. Handles for transportation are installed on the outside of the case.

Considering the weight of the equipment, place wheels under the base. Thanks to this, the device does not need to be lifted when moving.

The list of additional components consists of:

pistol - the working mechanism of the device;
welding cables - two pieces;
inopuller - a device also known as the "reverse hammer".

To connect the cables to the gun, terminals are used that are compatible with the threaded connections of the operating mechanism. On the back of the cables, the same components are attached, or mass is created using quick-clamping elements.

Without a pistol, the spotter will not perform its functions. This component is also known as stadder. The choice of a working mechanism depends on the intended purpose. Spotter pistols are conventionally divided into two categories:

To work with a high frequency of spotter use, factory models are purchased. Such devices are capable of providing sufficient performance for the assigned tasks for a professional welder.

A homemade spotter pistol is recommended for household work where a heavy load on the equipment is not required. As homemade working mechanisms are used:

glue gun;
semi-automatic welding machine.

To make a handle for a stadder, getinax or textolite is used. The thickness of the material ranges from 12 to 14 millimeters. Two rectangles of the same size are cut from it.

A niche is created in one of the segments to accommodate the fastener. This part of the blank is intended for fastening:

electrode - a copper rod with a diameter of 8 to 10 millimeters;
light bulbs;
buttons that turn on the backlight;
switch that gives an impulse.

The button must be placed strictly in the created recess. A homemade bracket is used as a fastening element. For its production, a pipe made of copper is used. It is necessary to get a section of a square or rectangular type.

When the spotter is in operation, the electrode must be replaced periodically. To make this task easier to perform, when designing the device, it is necessary to place the electrode so that replacing it does not require disassembling the entire structure.

The gun is connected to the spotter using a five-wire welding or control type cable. The veins are connected to:

switch;
backlight lamp;
light on the switch.

The end of the cable is placed in the hole in the bracket and fixed with a soldering iron... Before that, it must be cleaned.

An inopuller for body repair is an expensive device. But self-production is carried out according to a simpler scheme than assembling a pistol. This component is manufactured from an assembly gun. The reverse hammer and attachments are made step by step:

removal of the upper part for attaching a foam bottle or sealant;
welding of racks instead of them - made from rods with a diameter of 6 to 10 millimeters;
welding the ring to the posts - take as a basis the same rod that was used for the posts, and then fasten it into a ring with a diameter of 100 millimeters.

Then the welding ring is wrapped with electrical tape. Thanks to this, in the process of work, it will not accidentally weld to the working coating. The curved part of the gun is sheared off and a cable is attached in its place. The cut point is sharpened until it acquires the shape of a cone with a diameter of no more than 3 millimeters.

A spotter made from a do-it-yourself welding machine works with a transformer. The generation of welding current and the power of the spotter depend on the welding transformer. Such a device is difficult to find on the electrical appliance market, so the machine will have to be made independently in any case. The basis of the transformer is a magnetic wire with a cross section of 400 square millimeters.

Transformers are divided into two categories: plate and strip. Devices of both categories are produced in three forms:

w-shaped, also known as "armor";
o-shaped, also known as "swivel";
toroidal.

A suitable option for a homemade spotter is the third, since it is distinguished by the lightest weight and the minimum volume of the layers of the secondary winding. Transformers have a different number of turns on the body. The number of turns that the primary winding of the working device includes depends on the voltage received. When the winding is performed, test runs are carried out until the indicator reaches 1 volt.

A homemade straightening spotter has most of the functions of a professional apparatus. With his help:

a spot weld is created to connect parts;
working elements are warming up;
damaged areas of parts are cleaned;
fasteners are captured;
the dents of the car body are pulled out;
fasteners are removed;
the working surface is cleaned.

The use of the device does not require professional skills to use, since the spotter control circuit is simple. The device works in constant and short-term mode. With the help of additional elements, a forced cooling system is provided.

The spotter is a rather useful device that helps to significantly increase the efficiency and speed of work. for car body repair... But this unit has a fairly high cost with a simple design. Therefore, many craftsmen prefer to make a spotter from an old transformer or from a welding machine with their own hands.

When car body repairs, it is often necessary to remove dents, for example, after an accident. For this, various methods are used: pulling out dents with suction cups, aligning with hammer blows from the back of the part, etc. In the latter case, the part must be dismantled to eliminate the defect.

The use of a spotter can significantly speed up and simplify the alignment process of auto parts. This unit is a kind of spot resistance welding, with which you can weld washers, pins, bolts, hooks and other fasteners to damaged parts of the car body. In the future, various tools for leveling dents are hooked on them.

Also, the spotter can be used for soldering, heating, hardening and settling of the surfaces to be leveled.

The spotter consists of the following elements:

a welding machine, which can be of a transformer or inverter type;
cables (power cable and ground cable);
welding gun (studder);
electrode with an inertial hammer.

When the button on the stadder is pressed, current begins to flow to it. Depending on the selected mode, the current supply can be constant or in the form of one short pulse. Further, the current flows to the electrode, which can have tips of different shapes.

The device is working according to the following principle.

The place on the car body that needs to be leveled is cleaned of paint. You should also strip a small area for connecting the ground cable.
A fastener, such as a washer, is attached to the electrode of the spotter and welded to the straightening point.
The alignment tool clings to the washer and the dent is pulled out.

Pulling out dents can be carried out and without welding of fasteners... In this case, a pointed tip must be installed on the electrode with an inertial hammer. The electrode is applied to the desired location on the part and the tip is welded to it with a short current. Further, without removing the electrode from the part, blows with a hammer in the direction opposite to the tip, thereby pulling out the dent (you cannot use a reverse hammer on aluminum). After eliminating the defect, the welded end of the electrode easily breaks off.

The spotter transformer differs markedly from the classic welding transformer. In arc welding, the metal is heated by an electric arc, and in spot heat, it is released due to the transition resistance in the electrode-metal section. This occurs during arc welding if, for example, the wrong operating mode is set on the machine. In this case, the electrode sticks to the metal, which can cause damage to the device.

To prevent this from happening, spot welding is carried out in pulsed mode of current supply (up to 1 second). And since arc burning is not required for spot welding, the voltage in the spotter should be minimal (about 6 V), and the current strength should be high (at least 1000 A).

Making this unit from an inverter is impractical, if only because spot welding does not require a constant current. In addition, the transformer will have to be redone in order to achieve high current rates.With such success, you can make a spot welding unit from scratch. If there is an inverter device, then it is better to use it for its intended purpose, and adapt a conventional transformer welder for the spotter.

As for semiautomatic devices, all universal models of these units already have the function of pulse welding, and they will not need to be altered. But if a broken, ordinary semiautomatic device is available, then the transformer will need to be redone in it.

Semiautomatic welding machine Aurora

Alteration of the transformer consists in removing the secondary winding and winding a new one. The spotter requires a welding current of 1000 A. If, in the calculations, it is assumed that the current density is 8 A per 1 mm 2, then its cross section should be about 120 mm 2. But winding a wire of this cross section is quite difficult. Therefore, you can take a bus with a smaller section, for example, 80 mm 2, if the device will not be used in too intensive mode.

For determining the number of turns do the following.

Wrap any insulated conductor around the magnetic core. 10 turns will be enough.
Connect the primary winding to the network, and measure the voltage on the improvised secondary.
The result obtained must be divided by the number of turns, that is, by 10. As a result, you get a value that determines the number of turns to obtain 1 V voltage. But since a voltage of 6 V is required for the spotter, multiplying the resulting value, you can find out the number of turns.

Based on the diameter of the wire with the required section, it is possible to determine whether this winding will enter the free space between the primary and secondary windings of the transformer (not yet removed). If there is enough space, then the secondary can not be removed from the magnetic circuit, but a new winding can be wound over it. In this case, the welder can be used and for electric arc welding, and for point.

A modified transformer is not the only part required to make a spotter from a welding machine. To it you need to add discharge electronic control unit and a small transformer to provide power to the module. Below is a diagram of the block that controls the spotter.

This scheme works as follows.

When the circuit is closed by the switch S1, current starts to flow to the primary of the transformer T1.
Further, the capacitor begins to charge. It is connected through the closed contact of the switch to the diode bridge.
The output transformer T2 will be de-energized until the switch button S is pressed. After that, the voltage from the capacitor through the variable resistor will go to the control electrode of the thyristor. Further, the voltage will go to the primary of the output transformer, after which a pulse with the current strength required for welding will appear on its secondary winding.
After the capacitor is discharged, the module returns to its original state. To repeat the impulse, you must press the switch again.

After the control unit is ready, all components are placed in a plastic or metal case.

This device, made of a 12 V battery, is mobile and can operate regardless of the presence of an electrical outlet. The following components are required to manufacture the unit.

Standard battery for 12 V and 75 A / h and above.
Solenoid relay. You can use a relay from a car starter. It is desirable that it be collapsible for periodic cleaning of the contacts inside it.

Start button.

Terminal cables and welding gun.

The assembly of the apparatus is carried out according to the diagram below:

a ground cable is connected to the negative terminal of the battery, which must contact with the part prepared for repair;

the first contact of the relay is connected to the positive terminal of the battery;
a cable going to the welding gun is connected to the second contact of the relay;
a start button is installed between the first and third (connected to the battery positive) contact of the relay;
the solenoid relay must be connected to ground.

Read also: DIY tefal toaster repair

Incorrect connection of the windingsTo determine the desired ends of the windings, use a voltmeter. First, the voltage on one of the windings is measured. Then a second winding is connected to its end and the voltage is measured again. If it increases, then this means that the end of the first winding is connected to the beginning of the second.The beginnings of both windings are marked with a turn of colored electrical tape.Zero voltmeter readings indicate that the windings are connected by the ends of the same name. In a series connection, one pair of opposite ends is connected. The output voltage is removed from the free ones. When parallel, the same ends of both windings are connected. At the end, the terminals should be crimped with special tips (Fig. Below).Special lugs for wiresA short voltage pulse is required for welding. Therefore, a do-it-yourself spotter from a welding machine needs a control circuit. Due to the fact that the welding current is large, it is impossible to directly switch the output voltage. The control is carried out by applying voltage to the primary winding.The simplest circuit is shown in the figure below. The disadvantage of the circuit is that the button switches directly to the mains voltage, which is unsafe.Simple spotter control circuitIn addition, a strong spark is generated when the contacts are opened. If, instead of a button, we put a retractor relay from the starter, and in turn turn it on with a button, then such a scheme will be much more practical and safer. A combination of any automotive relay and high-power starter can be used. The relay is controlled by a voltage of 12 V. In turn, the relay contacts will control the contactor.The proposed control options for the welding transformer do not allow you to accurately maintain the required period of time. It will be possible to work normally with such a device only after acquiring the necessary skill. Those who are versed in electronics and are friends with a soldering iron can make a more complex circuit with their own hands and devoid of the indicated drawback (Fig. Below).Thyristor spotter control circuitIn this circuit, the primary winding of the transformer is controlled by a thyristor. The thyristor is turned on by applying voltage to the gate electrode. The capacitor (C1), when the button is released, is charged from the transformer (E1) through the diode bridge (V1-V4). When the button is pressed, the capacitor is discharged through the resistor (R1) to the control electrode of the thyristor, turning it on. The on time of the thyristor depends on the discharge time of the capacitor. This time can be changed by adjusting the variable resistor. For the next switch-on, the button must be released and pressed again.Making a spotter with your own hands is described in the video below.

Diy thyristor circuit with autostart for a spotter

The thyristor PTL 50 can be changed to PM 40, as well as to PM 80. You can draw up another circuit in which instead of the PTL 50 supplying the transformer winding, you can use a triac. The triac is controlled by an optocoupler, and the diode bridge is replaced with a stabilizer on the LM317 microcircuit. As a stabilizer, you can use any power supply that will give at least 10 volts. The variable resistor RP1 is installed in the circuit of the microcircuit wire, and it can adjust the voltage to charge the capacitor. This manipulation adjusts the pulse duration for welding. In case of short welding times, increase the capacity C4.

There are several options for how to make a spotter for body repair from old units that have served their purpose. Let's consider in detail the different assembly options.

In order to provide the spotter with a current source, we will need a transformer of about 1500 A, as well as a working tool that will directly be used for editing. If there is no such transformer, you will have to rewind it yourself.

Diagram of a spotter device for DIY body repair

In addition to a transformer and a reverse hammer (we will show you how to make it just below), you will need a control unit (it contains a 200 V thyristor), a diode bridge, a contractor (220 V), as well as a 30 A relay.

The biggest challenge in adapting a transformer for welding is increasing the output current to 1500 amps. To this end, experiment with a bus installed instead of the secondary winding. Rewinding the transformer is the most time consuming step. Usually, copper or aluminum wire is chosen for these purposes.

Copper wire winding of transformer for spotter

For your information! A cross-sectional value of at least 160 mm² is considered ideal, while the bus voltage should be 6 V.

To protect your spotter from sudden failure, and yourself from electric shock, the primary and secondary windings of the transformer are isolated from each other. Usually for these purposes they take varnished cloth or several layers of paper impregnated with paraffin.The magnetic circuit, which is the basis of such a transformer, must have a working section of at least 400 mm², and its dimensions are calculated taking into account the location of the windings.

For the W-shaped core, the primary winding of the transformer, consisting of 200 turns, is made of a wire with a cross section of 2.5 mm².

Types of construction of magnetic cores of transformers and their dimensions for calculating the cross-sectional area

The secondary winding has 7 turns, for which a wire with a cross section of 50 mm² or a bus of the corresponding cross section with insulation is used. The length of the outgoing ends of the secondary winding of the transformer must provide for the possibility of its connection to the output terminals, and the primary one - for connection to the electrical circuit of the apparatus. It is advisable to impregnate the transformer that you made with shellac.

The most important thing when assembling the control unit is to correctly connect the jumpers to break the contacts of the primary network. The simplest and more complex schemes can be used. We have given them above.

Fastening the jumpers on a 12 Ampere machine

Usually, wires are brought into the control unit to the start button and quick start switches, which are displayed on the case. Coolers are installed, if necessary, and also the ground wires are hidden.

There are many different types of spotter enclosures that can be used. Someone takes the case from a PC, this is convenient, since it already has the ability to install microcircuits and coolers, others make boxes from metal plates or even wooden blocks. The dimensions of the case are chosen arbitrarily, it all depends on the size and number of transformers and additional parts. At the base of the body, a dielectric plate is used, on which all working elements are attached. The main selection criterion is not the aesthetics of the structure, but the possibility of unhindered access to all elements.

Homemade spotter housings options:

Image - Spotter for DIY body repair from a welding machine

Very often there are cases from old microwaves, welding machines, batteries, system units. When choosing a welding cable, it is better to start from the following calculations: for 10 A of the maximum permissible current that the spotter produces, there should be 1 mm² of the cable cross-section. For mass, use a cable with a length not exceeding 1.5 m, for a worker - no more than 2.5 m. If you neglect these requirements and use cables of longer length, this will lead to significant losses in the strength of the welding current.

You can also do it yourself. Usually, copper rods of round cross-section, bronze or copper tubes are used, which are very convenient to connect to the current supply cable. On the side of the working part of the electrode, it is necessary to make a slot where the washer for welding will be inserted. If you use a tube to make an electrode, then its working end must be flattened, and only then make a corresponding slot on it.

The fixing of the components depends on whether it is a stationary device or a portable one. When choosing the second option, the components are distributed evenly and mounted using fasteners. Handles for transportation are installed on the outside of the case.

The welding gun is the main working body of the spotter. If you plan to use the device actively enough, then it is better to buy a ready-made sample. But for small-scale work, a home-made device is quite suitable. An assembly glue gun or a working part of a semi-automatic welding machine is used as a basis. We will present the easiest way to assemble a handle for a spotter with your own hands.

Spotter is a spot welding machine widely used for flattening automotive work. Very often, such work requires maximum geometric accuracy and knowledge of all body panels located on the car. And rarely when a high-quality straightening can be done without special devices, in particular, a spotter.

Today we will talk about how to assemble a spotter with your own hands and what is the scheme of its work. So, homemade spotters will save you a lot of money if you make them from a welding machine.

A device such as a spotter is used for the following needs:

body welding works;
straightening the body surface without disassembling the skin.

Especially the spotter convenient for straightening body parts, which are difficult to access due to certain design features. When repairing body parts using a spotter from a welding machine, you need to weld special fasteners to the deformed part, which, using a reverse hammer, pulls out the damaged metal. Also, the spotter is capable of heating it, so the metal quickly regains its quick rigidity and shape.

There are several electrical circuits of a spotter, which can be assembled not only from an inverter, but also from an old battery or transformer. Homemade spotter acts like a hammer, works in a dotted manner, but in the opposite direction. It looks like this:

the return hammer of the guide is fixed to the damaged area on the body;
only a hammer in the form of a washer can move along the guide, which applies force to the point of its fixation.

A common spotter has two modes of operation;

short-term, when the guide needs to be fixed at the desired point with special rings;
welding - welding is carried out at minimum power using a carbon electrode.

A spotter from a welding machine is the most common among home-made devices, despite the fact that there are other schemes for their assembly. So, do-it-yourself spotters can be assembled not from welding machines, but they will be less powerful.

The spotter is a branch of resistance welding, however, unlike it, the spotter design eliminates the presence of ticks, which is why this machine can be considered an analogue of an electric arc welding machine, where the voltage is passed through the car body. One contact is attached to the body, and the stem and nozzle act as the second contact.

Below we suggest that you familiarize yourself with the simplest spotter scheme based on a welding machine, which you can modify if you wish.

A do-it-yourself spotter from a welding machine includes two key elements:

welding inverter;
thyristor relay.

To assemble this unit yourself, you will need:

thyristor 200 volts;
a 12 volt step-down transformer for push-button control of the relay;
relay for 30 amperes;
diode bridge;
contact group (220 volts);
control button.

By means of a diode bridge the transformer is connected to the network, and to the bridge, while the thyristor of the electronic relay must be connected. The transformer is designed to power the control branch of the thyristor circuit.

The spotter works as follows:

when the S3 button is pressed, the capacitor C1 is discharged, and the resistor R1 and the thyristor V9 are turned on for a while;
then alternating voltage is applied to the primary transformer winding using D232 diodes;
there is a procedure for welding parts and an electrode;
when the capacitor C1 is discharged, the thyristor closes, and the winding of the power transformer is de-energized;
in this state of affairs, the welding process comes to an end, and the capacitor C1 continues to be charged from the transformer T1 for subsequent work.

Remember that the diode bridge and thyristor can be replaced by triacs. Homemade spotters must be carefully thought out from a constructive point of view. It should work correctly regardless of size and investment.

Iron for a spotter needs to be allocated in a volume of 35 to 40 square centimeters. Overheating does not happen on the thyristor, they are only in the sections that are located after the cable. Also the rod made of ferrous metal is very hot with a diameter of 16 mm. It is desirable that it be made of brass.

As for the cable for the spotter, you need to choose with a cross-sectional area of the order of 70 square millimeters, and for the mass and the hammer, its lengths of 1.7 and 2.1 m, respectively, will be sufficient. You will also need to provide for pulse control on the TCh-40 thyristor.

First, the secondary transformer winding is wound using a 6.5 x 4 copper bar in the third winding. It can also be replaced with an aluminum one. Then two more must be added to the secondary winding. The final version of the apparatus consists of an aluminum transformer winding of 250 square millimeters, which is equal to 5 windings of six turns.

Pay close attention to the appearance of the hammer, which is the electrode. Most often the handle is made on the basis of a glue gun, and the work cable has an insulating layer and a commutation wire. Also remember that when heated, the thermal insulation layer begins to shrink.

A home-made or factory spotter, which has an industrial purpose, has a number of such important functions:

joining parts by welding repair washers using a spotter;
spot welding using a metal electrode, which pulls the metal of the panel;
the ability to heat metal parts with a carbon electrode and then cool them. Thanks to this function of the welding machine, it is possible to carry out the upsetting of metals;
design features of the spotter make it very simple and convenient in terms of operation;
the presence of two welding modes in the spotter. The first is a permanent switch-on mode using a carbon electrode, and the second - with a short-term switch-on, which is time-controlled. It is used with a metal electrode and is often used for welding washers;
presence in the spotter forced cooling system and thermostat to turn off the welding machine when overheating and automatically turn it on at the desired temperature for welding.

Main technical characteristics of the device:

220 volts - required supply voltage for normal operation of the spotter;
56-60 Hz - required frequency of the alternating current network;
10 kW - maximum allowable power;
1300 A - maximum possible operating current;
about 8-9 V - voltage for the secondary winding of the welding machine;
0-1.2 seconds - time setting limit;
two working welding modes - timer for precision welding and continuous mode for normal welding and tempering;
15 percent - productivity in spot welding of metal parts, taking into account the maximum output power;
75 percent - performance with coal brew, taking into account the maximum power output;
from 100 kg and more - traction condition for the needle;
100 kg and more - traction condition for the washer;
380 by 290 by 840 mm - length, width and height of the product;
32 kg - weight of the structure.

There is a recognized technology for working with a spotter, which was determined by the body repairmen. It is relevant when repairing hard-to-reach deformed body parts on a car. Often this scheme of work is applied in relation to deformed car doors, fenders and other parts of the vehicle. It is relevant wherever the forces are directed to the outer side of the working surface and where the deformed section of the structure is located.

Spot welding is performed using an incoming current, and then the local surface is leveled with a stop or an inertial hammer. Thanks to such manipulations, the damaged part of the car will be pulled out to its original position rather quickly.

Then the deformed and leveled surface is sanded. This must be done so that the points are far from the weld and the working surface is smooth. Do not forget about the mandatory grounding for the chassis, the negative terminal must also be disconnected from the battery.

Welding technology with a spotter is as follows:

thoroughly clean the deformed area on the car part until the metal surface is visible;
attach a grounding contact to the prepared surface;
weld the fasteners;
capture these elements with the help of special devices and tools that will be needed to melt metals;
we pull out the deformed section of the surface of the metal structure;
the welded element can be easily removed with your own hands using rotational movements;
clean the surface of the part that was repaired and prepare this area for putty.

To work with a spotter, regardless of whether it is home-made or factory-made, you need to have welding skills. Also you must follow the rules for using this device and follow the rules for welding. All this will allow you to repair the deformed part of the car quickly and successfully.

The spotter will become indispensable when performing all kinds of repair work on a car body that requires pinpoint concentration. And as you can see, this device can be assembled with your own hands.

Video (click to play).