It may happen that the wound coil does not contain short-circuited turns, and in the process of operation there is a doubt about its serviceability. How to make sure? Do not disassemble the same transformer to check the coil again. In such cases, another device will help, which allows you to check assembled transformers, chokes and other inductors.
The device is assembled on two transistors and is a low-frequency generator. The occurrence of oscillations occurs as a result of positive feedback between cascades. The depth of feedback depends on whether there are short-circuited turns in the coil being tested, or they are absent. In the presence of closed coils, the generation breaks down. In addition, the circuit has negative feedback, which is regulated by potentiometer R5. It allows you to select the desired mode of operation of the generator when testing coils with different inductances.
To control the voltage of the generator in the circuit there is a voltmeter alternating current. It consists of a milliammeter and two rectifier diodes. AC voltage is applied through capacitor C5. This capacitor also serves as a limiter, allowing you to set a certain deviation of the milliammeter needle. Here it is desirable to use a milliammeter with a low deviation current (1 mA, 0.5 mA) so that the measuring circuit does not affect the operation of the generator.
As rectifier diodes, diodes of the type D1, D2 with any letter index. When the generator is running, select the capacitance of the capacitor C5 so that the milliammeter needle deviates to the middle of the scale. If this fails, put a resistor in series with the milliammeter and select its resistance according to the required arrow deviation.
Transistors take type MP39-MP42 (P13-P15) with an average gain (40-50). Resistors can be of any type with a power of 0.12 W. Buttons, switch, terminals, you can also take any.
The device is powered by a Krona battery or any other source with a voltage of 7-9 V.
Use a suitable sized wooden, metal or plastic box to assemble the instrument. On the front panel, fix the control knobs and milliammeter, and on top of the terminals for connecting the coils under test.
How to use the device? Turn on the VK toggle switch. The arrow of the milliammeter should deviate approximately to the middle of the scale. Connect the terminals of the tested coil to the terminals "Lx" and press the Kn1 button. Between the base of the transistor T1 and the power plus, the capacitor C1 will be connected, which with the capacitor C2 will form a voltage divider, which sharply reduces the connection between the stages. If there are no short-circuited turns in the winding under test, then the milliammeter readings may increase or decrease slightly. In the presence of even one short-circuited coil, the oscillations of the generator break down, and the needle returns to zero.
The position of the slider of the variable resistor R5 depends on the inductance of the tested coil. If this is, for example, the winding of a power transformer or a rectifier choke, which have a large inductance, the engine should be in the far right position according to the diagram. With a decrease in the inductance of the tested coil, the amplitude of the oscillations of the generator decreases, and with very small inductances, generation may not occur at all. Therefore, with a decrease in inductance, the variable resistor slider must be moved to the left according to the circuit. This allows you to reduce the depth of negative feedback and thereby increase the voltage between the emitter and collector of transistor T1
When testing coils of very low inductance - the circuit of receivers with ferrite cores, the inductance of which is from 3 to 15 mH, it is additionally necessary to increase the depth of positive feedback. To do this, just press the button Kn2. The device can test coils with inductance from 3 mH to 10 H.
Attention!
If you cannot find a 1.2 kΩ variable resistor, assemble the circuit section near R5 according to the following scheme:
100Ω R5 1kΩ 100Ω To R3 (---[___]----[___]----[___]---) to R7 | To R6
The variable resistor must be single-turn and non-inductive, such as SP0, SP3, SP4 (or a foreign equivalent). The main thing is that the track should be graphite, not wire.
100 Ω resistors should be soldered to the R5 terminals, then put on them with cambric or heat shrink tubing.
Transistors are suitable for any of the series: MP39B, MP40 (A / B), MP41, MP41B, MP42, MP42B (or analogues). If you change the layout of the board, you can install transistors KT361 (except KT361A), KT209D or any other low power P-N-P with Ku=40…50.
Printed circuit board: 
(download in Sprint-Layout 5 format)
The scheme is taken from the brochure "The first steps of a radio amateur - issue 4/1971", spread printed circuit board- Alexander Tauenis.
ATTENTION! 05/13/2013 updated board layout, a new version available at the same link. In addition to the original version for transistors MP39-42, the .lay file also includes versions with transistors KT361 (conventional mounting) and KT361 (surface mounting, size 0805). The SMD version includes 1kΩ resistors, so you can use a regular 1kΩ variable resistor R5 without any 1960s twists and turns.
Probably, many people noticed, when checking the integrity of the windings of electric motors, transformers, chokes using a tester, that if you break the inductor-tester circuit, and then immediately accidentally touch the coil terminals, you can feel a slight electric shock. You can not attach any importance to this effect, you can think that the EMF of the self-induction of the coil is probably manifested, or you can think about it: is it possible to somehow benefit from this?
It turned out that it is possible, because. The self-induced emf of an inductor is a very specific voltage surge, the amplitude of which depends on the supply voltage of the circuit being broken, on the inductance of the coil and on its quality factor. During experimental verification, it turned out that if a neon lamp of the type TN-0.2, TN-0.3, etc., is connected in parallel with the coil under test, then when the circuit is broken, the power source-EMF coil of self-induction of the coil causes flashes of the neon lamp, which are the brighter , the higher the supply voltage of the circuit under test, the inductance of the coil and its quality factor.
This condition is met by network windings power transformers, just high-voltage transformer windings, inductor windings with significant inductance, electric motor windings, i.e. it is precisely those units of electrical equipment that are most susceptible to failure due to electrical overloads, leading to overheating of the windings, insulation failure between the turns of the winding and the appearance of short-circuited turns. K.z. turns may also appear due to mechanical damage to the windings. But in any case, when they appear, the inductor (winding) sharply reduces its quality factor, its resistance to industrial frequency currents decreases and it will heat up above the permissible value, i.e. it will become unsuitable for further use.
It turned out that if we assemble the test circuit shown in the figure, then serviceable inductors when the power circuit is broken (pressing the button) give bright flashes of a neon light bulb. And if there are short-circuited turns in the inductor, then there are no flashes at all, or they are very weak. It is this effect that is useful, because it allows you to identify unusable electrical products that are subject to culling or repair.
It is obvious that windings wound with a thick wire and having a small number of turns, i.e. small inductance, it will not be possible to check this method - even serviceable coils will not flash a neon light bulb. This must be taken into account in order not to draw erroneous conclusions. But for inductors having an ohmic resistance to direct current of the order of tens to hundreds of ohms or more, this scheme detection of short-circuited turns is very convenient. Connector X1 can be of any type and is designed to connect a DC voltage source. The value of the supply voltage is not critical and can be in the range of 3 - 24 V, i.e. You can use any batteries or accumulators you have on hand. Toggle switch S1 serves to turn off the device during long breaks in operation. Lamp HL1 can be of any type for a voltage not lower than Epit. It is needed to control the supply voltage to the circuit (to prevent erroneous conclusions about the unsuitability of the tested coil). It is useful to have a known good coil of the same type next to the tested coils for comparative testing. Button S2 can be of any type and serves to break the power circuit when checking the coil. Resistor R1 Tr. (Other) serves to limit the current flowing through the neon bulb HL2. Х2, ХЗ - pins of the LU4 type with clips of the type<крокодил>, which, with flexible conductors soldered to them, are connected directly to the terminals of the inductor being tested.
Assembled without errors, the device does not need to be configured. It can be placed in any small-sized case. I want to draw the attention of novice radio amateurs that this method checks of inductors for the absence or presence of short-circuited turns should in no case be used to test radio-frequency coils, because tuning cores may be demagnetized or even conductors of the coils may burn out.
The circuit of the interturn tester and its operation are quite simple and accessible for assembly even by novice electronics engineers. Thanks to this device, it is possible to test almost any transformers, generators, chokes and inductors with a nominal value from 200 μH to 2 H. The indicator is able to determine not only the integrity of the winding under study, but also perfectly detects an interturn circuit, and in addition, it can be used to check p-n junctions for silicon semiconductor diodes.
Electric motors often fail, and the main reason for this is the turn-to-turn short circuit. It accounts for about 40% of all engine breakdowns. What causes a short circuit between the turns? There are several reasons for this.
The main reason is the excessive load on the electric motor, which is higher than the established norm. The stator windings heat up, destroy the insulation, and a short circuit occurs between the turns of the windings. Incorrectly operating the electric machine, the worker creates an excessive load on the electric motor.
The normal load can be found in the passport for the equipment, or on the motor plate. Excessive load may occur due to a breakdown of the mechanical part of the electric motor. Rolling bearings can be the cause. They can jam from wear or lack of lubrication, as a result of which the armature coil turns will close.
The closure of the turns also occurs during the repair or manufacture of the engine, as a result of marriage, if the engine was manufactured or repaired in an unsuitable workshop. It is necessary to store and operate the electric motor according to certain rules, otherwise moisture can penetrate into the motor, the windings will become damp, as a result, a turn circuit will occur.
With a coil circuit, the electric motor does not work properly and for a short time. If the turn-to-turn short circuit is not detected in time, then soon you will have to buy a new electric motor or a completely new electric machine, for example, an electric drill.
When the turns of the motor winding are closed, the excitation current increases, the winding overheats, destroys the insulation, and other turns of the winding close. Due to the increase in current, it can cause the failure of the voltage regulator. The coil circuit is found out by comparing the winding resistance with the norm according to the technical conditions. If it has decreased, the winding must be rewound, replaced.
Closing turns is easy to determine, there are several methods for this. While the motor is running, pay attention to uneven heating of the stator. If one part of it is hotter than the engine housing, then it is necessary to stop work and conduct an accurate diagnosis of the motor.
There are devices for diagnosing the closure of turns, you can check it with current clamps. It is necessary to measure the load of each phase in turn. With a difference in loads on the phases, you need to think about the presence of an interturn circuit. You can confuse the turn circuit with the phase imbalance of the power supply. To avoid misdiagnosis, the incoming supply voltage must be measured.
The windings are checked with a multimeter by dialing. We check each winding with the device separately, compare the results. If only 2-3 turns are closed, then the difference will be imperceptible, the closure will not be detected. Using a megohmmeter, you can ring the electric motor, revealing the presence of a short to the case. We connect one contact of the device to the motor housing, the second to the terminals of each winding.
If there is no confidence in the serviceability of the engine, then it is necessary to disassemble the motor. When parsing, you need to inspect the windings of the rotor, stator, you will probably see the place of the circuit.
The most accurate method for checking the short circuit between winding turns is to check with a step-down transformer on three phases with a ball bearing. We connect three phases from a low-voltage transformer to the stator of the electric motor in disassembled form. We throw the bearing ball into the stator. The ball runs in a circle - this is normal, but if it is magnetized to one place, then there is a short circuit in this place.
Instead of a ball, you can use a plate from the transformer core. It is also carried out inside the stator. In the place where the turns are closed, it will rattle, and where there is no short circuit, it will simply be attracted to the iron. During such checks, one should not forget about the grounding of the motor case, the transformer must be low-voltage. Experiments with a plate and a ball at 380 volts are prohibited, it is life-threatening.
Let's make a choke with our own hands to check the interturn circuit in the motor winding. We need a U-shaped transformer iron. It can be taken, for example, from the old vibration pump "Brook", "Kid". We disassemble its lower part, heat it well. There are coils filled with epoxy resin.
We heat up the epoxy and knock out the coils with the core. With the help of emery or grinder, we cut off the sponges of the core.
These coils are wound just on a U-shaped transformer iron.
No corners required. It is necessary to make a place in which a small and a large anchor can easily fall.
When processing, it must be taken into account that the iron is puff. You can not process it so that the stone lifts it. It is necessary to process in such a direction that the layers lie to each other so that there are no burrs. After processing, remove all chamfers and burrs, as you will have to work with enameled wire, it is undesirable to scratch it.
Now we need to make two coils for this core, which we will place on both sides. We measure the thickness and width of the core in the widest places, along the rivets. We take a thick cardboard, mark it according to the size of the core. We take into account the size of the groove in the core between the coils. We draw the non-sharp edge of the scissors along the fold points, so that it is more convenient to bend the cardboard. Cut out the blank for the coil frame. Fold along the fold lines. It turns out the frame of the coil.
Now we make four covers for each side of the coils. We get two cardboard frames for coils.
We calculate the number of turns of the coils according to the formula for transformers.
13200 divided by the cross section of the core in cm 2. The cross section of our core:
3.6 cm x 2.1 cm \u003d 7.56 cm 2.
13200: 7.56 = 1746 turns on two coils. This number is optional, a deviation of 10% in both directions will not play any role. Rounding in big side, 1800: 2 = 900 turns to be wound on each coil. We have a 0.16mm wire that will work fine for our coils. You can wrap it any way you like. 900 turns can also be wound by hand. If you make a mistake by 20-30 turns, then there will be nothing terrible. Better roll more. Before winding with an awl, we make holes along the edges of the frame to output the wire of the coils.
We put on a heat-shrinkable cambric at the end of the wire. We insert the end of the wire into the hole, bend it, and start winding the coil.
The filling turned out to be small, so you can wind the wire thicker. At the second end, solder the wiring with cambric and insert it into the hole. Do not wind the coil until the test has been carried out.
Both coils are wound. We put them on the core so that the wires go down and are on one side. The coils are wound in exactly the same way, the direction of the turns is in the same direction, the ends are brought out the same way. Now you need to connect one end from one coil and one to the other, and apply 220 volts to the remaining two ends. The main thing is not to get confused and connect the correct wires. To understand the connection order, you need to mentally unbend our U-shaped core into one line so that the turns in the coils are located in one direction, moving from one coil to the second. We connect the two beginnings of the coils. Apply voltage to both ends.
Compare the choke factory and homemade.
We check the factory throttle with a metal plate for vibration of the place of the coil circuits of the motor armature and mark them with a marker. Now we do the same on our homemade throttle. The results were identical. Our new throttle works fine.
We remove our coils from the core, fix the windings with electrical tape. We also isolate the solder with tape. We put the finished coils on the core, solder 220 V power to the ends of the wires. The choke is ready for operation.
To check the armature, we use a special device, which is a transformer with a cut core. When we put an armature in this gap, its winding starts to work as a secondary winding of a transformer. In this case, if there is an interturn short circuit on the armature, the metal plate, which will be located on top of the armature, will vibrate or be magnetized to the armature body due to local oversaturation with iron.
We turn on the device. For clarity, we specifically closed two lamellas on the collector to show how the diagnostics are performed. We place the plate on the anchor and immediately see the result. Our record became magnetized and began to vibrate. We turn the anchor, the turns are displaced, and the plate stops vibrating.
Now let's remove the lamella closure for verification. We repeat the check and see that the armature winding is working, the plate does not vibrate in any places.
This method is suitable for those who are not engaged in professional repair of power tools. For accurate diagnosis of an interturn circuit, a bracket with a coil is required.
With a multimeter, you can only find out a break in the armature coil. It is better to use an analog tester for this purpose. Between each two lamellas we measure the resistance.
The resistance should be the same everywhere. There are cases when the windings did not burn out, the collector is normal. Then the closure of the turns is determined only using a device with a bracket from the transformer. Now we set the multimeter to 200 kOhm, we close one probe to ground, and with the other we touch each collector lamella, provided that there is no break in the coils.
If the anchor does not ring to ground, then it is serviceable, or there may be an inter-turn short circuit.
Transformers have a common fault - the circuit of the turns between themselves. It is not always possible to detect this defect with a multimeter. You need to carefully inspect the transformer. The winding wire has lacquer insulation; when it breaks down, there is a resistance between the turns of the winding, which is not equal to zero. It also leads to the heating of the winding.
When examining the transformer, it should not have burning, charred paper, swelling of the filling, blackening. If you know the type and brand of the transformer, you can find out what the resistance of the windings should be. The multimeter is switched to resistance mode. Compare the measured resistance with reference data. If the difference is more than 50%, then the windings are faulty. If the resistance data could not be found in the reference book, then the number of turns, the type and cross section of the wire are probably known, you can calculate the resistance using the formulas.
To check with a low voltage output, we connect a voltage of 220 V to the primary winding. If there is smoke, smell, then immediately turn it off, the winding is faulty. If there are no such signs, then we measure the voltage with a tester on the secondary winding. If the voltage is underestimated by 20%, there is a risk of failure of the secondary winding.
If there is a second serviceable transformer, then by comparing the resistances, the health of the windings is determined. To check in more detail, use an oscilloscope and a generator.
Often a faulty motor has an inter-turn short circuit. First, check the stator winding for resistance. This is an unreliable method, since the multimeter cannot always accurately show the measurement result. It also depends on the technology of rewinding the engine, on the old age of the iron.
Clamps can also measure resistance and current. Sometimes they check by the sound of a running motor, provided that the bearings are in good condition, lubricated, the drive gearbox is working. They also check the interturn circuit with an oscilloscope, but they are more expensive, not everyone has this device.
Externally inspect the engine. There should be no traces of oil, smudges, smell. The current measured in phases must be the same. good tester check windings for resistance. With a difference in measurements of more than 10%, there is a possibility of closing the turns of the windings.
Write comments, additions to the article, maybe I missed something. Take a look at , I will be glad if you find something else useful on mine.
"Admitting our mistakes, we find a source of strength"
I decided to make a device for checking anchors for short-circuited turns and so on. Useful if you decide to renovate commutator motor and check if it is wound correctly. A very useful thing and was once produced in the USSR. But now you won't find it by day with fire.
We will not go into complex formulas, I will try to explain in a moment what I did. I will divide the article into 2 parts. "Part one. Magnetic core. "Part two. Electricity". Then I will explain why 2 parts.
Part one. Magnetic core.
Firstly, we need a magnetic circuit, or, in other words, a stator from a vacuum cleaner motor. Then we need to cut a part in one side of it at an angle of 90 degrees, where the anchor itself will lie down for verification. You can use a grinder, a saw, a spoon - whichever is more convenient for you.
Next, we need to create a platform for winding the coil. Many write that you need to take an electric cardboard, some other tone, but I don’t have it and it’s not planned in the next 50 kilometers in a circle, there is nowhere to buy it. And so an alternative is needed. Remember, when motorcycle and car engines are being repaired and there is no gasket - it used to be cut out from the “Case No.” folder. So we will do just that, but you need to keep in mind - the folder is rough, the cover of the notebook will do for us. I had a similar magnetic circuit and there was an electric cardboard, but a little narrower than necessary. But after all, it is enough for us to measure the thickness and approximately pick it up. If only there was a layer between the wire and the stator itself.
P.S. The device on the stator of the vacuum cleaner, inspired by the motives of the topic on one forum. Original . Thanks to the author for pushing me in the right direction.
We measure the thickness:
Electric cardboard from a different engine, but in which the windings once fit.
and notebook cover
Now cut out:
And we wind it in one layer on the magnetic circuit, fastening the whole thing with adhesive tape:
Then we need cheeks so that the wire rests on the sides and we get a full-fledged coil. We cut them out of plywood, having previously calculated the dimensions.
And we choose the excess with a chisel. You can clean it up a little with sandpaper.
Do not forget to take into account the angle of the stator and adjust it with the same emery - a small angle on the cheeks themselves
It is desirable that the cheeks themselves become tight on the magnetic circuit.
If not, we take a notebook and cut off a piece of sheet according to the size of the cheeks and wind it with gluing. Until the wall becomes more or less tight.
We insert the cheeks and glue with glue. I got almost half a pack of PVAK. Glued and filled it about a dozen times. Everything was ready the next morning.
That's all for the magnetic circuit.
Let's start. We need wire. I found a wire that was once wound from a kinescope from an old TV set. the resistance immediately seemed to me not sufficient - only 13 ohms, with a diameter of 0.4 with a wire length, as I later calculated 93m. 1 mm square copper wire withstands 3.2 -3.5 amperes. With us, if it survives half, it will already be happiness, this should be enough for us. I thought so.
(According to the calculations (number of turns = 50 / S * 220v) on this site, I calculated the required number of turns, it turned out to be 660. But I didn’t like that this applies to all wire thicknesses! How so?? The site seems to be good, but in the calculations I doubted. and I misunderstood something.)
But then, vague doubts began to overcome me. Although I am not an electrician, but still, as is known from Ohm's law (here I \u003d U \ R) - if we apply 220 Volts to a conductor with a wire resistance of 13 Ohms, then a current of about 16 A will flow through it. Our wire can withstand where is 1.25A. In short, she just puffs and vanishes through the window. I thought and thought, writing off the rest to the miraculous magnetic saturation of the core and the inductance (energy storage) of the coil itself, which I know little about, but decided to wind. In the end, the attempt is not torture. And any attempt, even a failed one, is a lesson for those who want to learn.
I've been running for about 4-5 hours. Turn to turn, diligently. Less and less faith in success. It turned out about 800 turns.
When finished, went to bed and left for the morning.
Checked today. I put the tester and ammeter in the right modes to take readings.
20 volts - about 1 ampere
50 Volts - 2 Amps
And taking a risk, realizing that he was right yesterday, he applied a hundred volts:
100 Volts - 4.5 Amps.
So what kind of 220 are we talking about? It will definitely “weather”, this wire.
Have you forgotten how much it should have been? Not more than 1.25A, and here 4.5A only at 100 Volts. The experiment was crowned with smoke from under the electrical tape, melting of the wire and a complete failure. But it's better than sitting and looking out the window with a drunken mug, thumping soundly.
Now for the Parts. Part "Magnitoprovod" - fully suitable for implementation. But as for the "Electricity" part - I think the mistake here was that you need to increase the resistance - in other words, take as much wire as to withstand 220 volts.
There is already a suitable donor, some kind of old choke from a TV with a resistance of 240 ohms, a wire diameter of 0.08 mm. I think it will last. Or maybe not. So to be continued.
Collected today and checked. Works.
R not less than 20 kOhm... on the board 10 kOhm. R2, R5, R6 at 470 ohms.
R1 10ohm
R2, R5, R6 820 ohms ... less is possible, but then R is needed with more resistance.
R3 47 kOhm
R4 365 Ohm
R7 10k
C1 - C3 30 nF
C4 0.5nF
L1 5 ohm 360 turns with 0.13 wire insulated
L2 10 ohm 460 turns with 0.09 mm wire insulated
Wound on 5 mm spools. I wound it by 10 mm and with a larger section and more coils. there were no smaller ones at hand.
The distance between the centers of the coils is 27 mm (important).
VD1 any diode
VD2 LED. Or 2 different or 2 color.
VT1 - VT5 any low-frequency transistor (in this case kt361). It is better to use not those on the board, but modern analogues.
S1 switch.
Power supply 3V.
The generator frequency should be 34.5 kHz .... there was nothing to check ... because. the oscilloscope was written off and dismantled, there is no personal money.
r.s. on the diagram, with a green marker, he marked what he drew on the printed circuit board.
the rosin was not washed off. this is a test instrument.
in the future I plan to do the same on a transistor assembly or common logic.
I drew the board in SL 6.0.
