When a household device based on an electric motor fails its “heart”, t. е. the electric motor, a well-known problem arises. what to do: try to repair the failed motor, replace it with the same new one or, if there is another more or less suitable motor on the farm, try to adapt it instead of the regular one? But a new electric motor is likely to cost a lot of money (service companies specializing in the sale of such parts will ask so much that it will be cheaper to buy a new device). Not everyone can repair the electric motor at home (of course, a lot depends on what exactly is broken in it). When this problem faced the author of the article, he chose the third way, replacing the failed “native” motors in broken lawnmowers with those that were at hand. And it turned out pretty good.
Two Bosch lawnmowers I bought at different times have fallen apart in the household. Rotak 32 and Rotak 34. The difference between them is the working width or the length of the blade. 320 and 340 mm. The second mower has a more powerful motor than the first one. But both machines have the same “illness”: the electric motor of both machines was damaged because of the unreliability of the plastic base of the rotor bearings. In the first one the upper bearing bracket broke to pieces and the rotor got jammed. The second one had the bottom bearing base melted from the heat of the motor. The rotor settled, its windings frayed and an internal short circuit occurred. After a little deliberation it was decided to replace the motors, especially as it turned out that there was.
On the shelves in the garage there was a three-phase asynchronous electric motor of suitable size with three inputs for connecting to the 220 V. On the nameplate it was possible to read only the speed of its shaft. 2870 rpm.
The first connection of the electric motor according to the capacitor scheme with a random capacitor at the rated voltage of 600 V made it possible to measure the current in the phase wire. It turned out to be 1.15 A. According to the empirical formula C = 4800I/U (where C. Capacitor capacity in microfarads;
I. current in amperes; U. I have calculated the capacitor capacity to run the motor in the AC 220V network:
To reliably start the motor under load, it is necessary to add an additional capacitor in parallel to the working capacitor with a capacity twice as large. That is, in this case, a capacitor with a capacity of 75 µF is needed at start-up. After starting the motor, the capacitor with a capacity of 50 uF must be deactivated by a special switch or an automatic control circuit. As the lawnmower works in the intermittent load mode (every time accelerating after a bump), and not to complicate the circuit, the author has applied a capacitor of average capacity (50 uF to 450 V), connected permanently.
The motor was simple to mount into the housing of the Rotak 32. Using a piece of hacksaw blade in the housing cut out the excess plastic laps of the previous motor mount and with observance of alignment of the factory installation of the blade and the shaft mounted asynchronous motor instead of the regular one with a belt drive. Two additional studs for mounting a new motor are installed. That is the end of the installation.
Exactly in the center of the shaft of the electric motor drilled a hole and cut an internal thread for the bolt fixing the brand-name blade. M8’s 25mm deep. If you use an old blade, it is desirable to balance it by cutting off the surplus metal with an “angle grinder”. this helps to preserve the rotor bearings for a long service life.
When installing the blade, remember that it also works as a fan to eject the cuttings, i.e. е. is installed on the shaft only with a certain side and must rotate in the right direction. The direction of the blade can be changed by interchanging the motor wires going to the capacitor C1 and the mains phase wire (it has a switch SA1).
The new motor and the capacitor (imported from Last One) are successfully placed in the old housing. The lawnmower looks the same, but has been made more reliable. The asynchronous motor has a soft start, it does not overheat when completely stopped, for example on a knot. The improved lawnmower is much quieter and cuts grass up to 20 cm high reliably.
For the “resuscitation” of the second lawnmower, a universal collector motor (UCD, Fig. 2) from an imported washing machine, at which a thunderstorm burned out all control electronics. Such motors are called universal because they can operate both on AC and DC voltages from 90 to 220 V.
Judging by messages on various electrical forums, self-made frightens by a large (from 6 to 10) number of wires coming out of such engine on the junction block. Let’s try to understand what they are designed for. First of all, we visually determine the tachogenerator wires. Let me remind readers that the tachogenerator. is an electric machine that converts the angular speed of the motor shaft into an electric voltage in proportion to it. At the tachogenerator output it depends linearly on the shaft speed. The tachogenerator is mounted on the VFD shaft on the opposite side of the pulley and has separate connections. So, we have identified two pins. Some RBM models have a hall sensor with three pins instead of a tachogenerator.
Next find the two leads from the rotor. This is also not difficult to do, since they are connected to the brush assemblies. Separate outputs from the motor stator and rotor to the control board in washing machines are necessary to organize the reversal of the direction of rotation by means of a relay.
It remains to find the stator winding leads. There can be three, four, or five outputs. immediately make sure (with an ohmmeter) that there are no short circuits in the stator winding to ground. A motor with this defect can not be operated without rewinding.
The odd number of leads of the stator winding shows that there is a lead from the middle of the winding (sometimes it is used in the motor control system for fast acceleration during the spinning of the laundry).
If there are four wires coming out of the stator. are two halves of its winding. They must be connected in series at once, i.e. е. Connect the terminal of the beginning of one half to the terminal of the other half (they are clearly distinguishable, so this operation will not cause difficulties). These leads in some models of washing machines are used to connect the motor heat shield on the control board.
How to test the electric motor multimeter
To identify faults in the electric motor at home for lack of expensive professional equipment nothing remains but to ring the motor with a multimeter. With its help you can determine most failures, and you do not have to involve a specialist. So, what you need to do?
Before carrying out the diagnostics, you should:
- De-energize the machine. If the resistance measurement is carried out in a circuit connected to the mains, the device will fail.
- Calibrate the machine, that is, set the arrow to the zero position (the probes must be closed).
- Inspect the engine to find out if it is flooded, if there is a smell of burning insulation or broken parts, etc.д.
Asynchronous, collector, single-phase and three-phase motors are tested according to the same technique, a small difference in design does not play a special role, but there are nuances that must be taken into account.
Stages of work
The most frequent faults can be divided into two types:
Let’s start by looking at how to wire a 3-phase motor with a multimeter. It has three coils connected in a “delta” or “star” circuit. The reliability of the contacts, the quality of the insulation and the correct winding influence its performance.
- First, check the short-circuit to the body (keep in mind, the value will turn out to be approximate, as more sensitive instruments are required for accurate readings).
- Set the measurement values on the multimeter to maximum.
- Connect the probes to one another to make sure that the settings are correct and the meter is in good working order.
- Connect one of the probes to the motor housing, if there is contact, connect the second probe to the housing and watch for readings.
- If there are no faults, alternately touch the lead of each of the three phases with the probe.
- If the insulation is good, the test should show sufficiently high resistance (several hundred or thousands of megohms).
It is necessary to remember that when measuring the insulation resistance with a multimeter the readings will be higher than admissible, because the EMF of the device does not exceed 9 volts. The motor, on the other hand, works at 220 or 380v. According to Ohm’s law the resistance value depends on the voltage, so discount the difference.
Repair of asynchronous motors
The most common are two- and three-phase asynchronous power units. The procedure of their diagnostics is not exactly the same, so we should dwell on it in more detail.
There are two types of faults in electrical units, regardless of their complexity: the presence of contact in the wrong place or its absence.
A three-phase alternating current motor has three coils that can be connected in a delta or star shape. There are three factors that determine the efficiency of this power unit:
Ground faults are usually checked with a megohmmeter, but if you don’t have one you can get by with a regular tester and set the maximum resistance value on it to megohms. There is no talk about high accuracy of measurement in this case, but it is possible to get approximate data.
Before you measure the resistance, make sure that the motor is not connected to the mains, or the multimeter will be useless. Then calibrate it by setting the needle to zero (the probes must be closed). Check the serviceability of the tester and the correctness of the settings by briefly touching one probe with the other each time before measuring the resistance value.
Put one of the probes on the case of the electric motor and check that there is contact. After that take a reading by touching the engine with the second probe. If the readings are within normal limits, connect the second probe to the output of each phase, one at a time. A high resistance value (500-1000 ohms or more) indicates good insulation.
How to check the insulation of the windings is shown in this
Then check that all three windings are intact. This can be checked by probing the ends that go into the motor terminal box. If a winding breakage is detected, the diagnosis should be stopped until the fault is corrected.
The next point to check is to determine if the windings are shorted. Quite often it can be seen by visual inspection, but if outwardly the windings look normal, then the fact of short circuit can be established by the unequal consumption of electric current.
Two-phase electric motor
The diagnosis of this type of power unit is slightly different from the above procedure. When checking a motor with two windings fed from a normal supply mains supply, the windings must be tested with an ohmmeter. The resistance value of the working winding should be 50% less than that of the starting winding.
The resistance to the housing must be measured and should be very high, as in the previous case. A low resistance value indicates the need to rewind the stator. Of course, to obtain accurate data, such measurements are better to be carried out with a megohmmeter, but such a possibility in the home is rarely available.
Checking the collector motors
Having understood the diagnostics of asynchronous motors, let’s move on to the question of how to test the electric motor with a multimeter, if the power unit belongs to the collector type, and what are the features of such checks.
To properly check the performance of these motors with a multimeter, you need to act in the following order:
- Turn on the ohm tester and measure the resistance of the collector lamellae in pairs. Normally these readings should not be different.
- Measure the resistance value by placing one probe of the meter on the armature body and the other on the collector. This value should be very high, tending toward infinity.
- Check the stator for winding continuity.
- Measure resistance by placing one probe on the stator housing and the other on the leads. The higher the reading, the better.
It is not possible to check the motor with a multimeter for inter-turn short circuits. Use a special tool to test the armature.
A detailed check of a power tool motor is shown in this
Regardless of the operating conditions, owners of lawn mowers sooner or later have to deal with the fact that they do not turn on at all or do not work in normal mode.
Timely recognition and effective troubleshooting is the key to achieving the longest possible working life of your machine. The “symptoms” of the most common breakdowns include:
- Unusual sounds in the deck area;
- strongly perceptible vibration when switching on the blade
- whistling during operation of the lawnmower;
- Significant deterioration of mowing quality.
In addition, in situations with gasoline mowers, it is not uncommon to encounter the fact that the device does not start well or does not gain momentum. The list of causes of such malfunctions is quite wide.
At the same time their timely detection and availability of certain knowledge allows you to repair the device by your own forces with minimal costs.
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Causes of faults
In the first case, the housing, handles, blades and wheels for lawnmowers need to be replaced. When the blades lock, the machine stops mechanically. Such defect is caused by trying to mow hard or tall grass. Repair of lawnmower consists in emptying cylinder of stuck grass and turning it in the other direction.
To keep the machine in good working order, it is recommended to sharpen the blades with a file (angle of 30°). Otherwise an abrasive tape is used. The gap must be between the 2 blades touching the strip. The machine switches cyclically (every 15 seconds). If the knives are sharp, then the strip is removed and the gap is adjusted.
Cylindrical lawnmower makes jerky and uncontrollable movements if the blades are incorrectly positioned. The normal cutting gap should be thinner than a sheet of paper. If this is not the case, the play must be readjusted. It is advisable to study the instruction manual beforehand, unplug the machine from the socket. If the connection is loose, the hissing sounds. The machine vibrates and rattles. Repair of the lawnmower means adjusting the bolt connections.
If the belt is broken or stretched, then it must be replaced. This requires the loosening of screws. Then the pulley is moved, the belt is removed. A new piece is put on the small pulley and then on the large pulley. The gear is returned to its original position. The next step is to check the tension of the new belt. The deflection should not exceed 4 mm.
Malfunction of electric models
Causes of sudden disconnection of the electric lawnmower are due to cord breakage or lack of current. In the first case it is recommended to check the cable for breaks. To replace the power cord, it is necessary to pull the plug out of the socket, open and remove the switch cover.
Before unscrewing the cable clamp strip? Remember the connection diagram of the switch. To disconnect the cord, use a hexagon (diameter 1 mm). The clamp is released and the conductors are removed. A multimeter is used to check the cable for breaks. If necessary, a new cord is installed. The reverse sequence is followed.
In the second case, it is advisable to connect another appliance to the mains. Electric machines may not work if the fuse in the plug is damaged. To do the repair work, you will need to disassemble the plug. To do this, use a screwdriver and a tester.
Motor malfunctions occur when the lawnmower overheats:
In the first case, it is recommended to wait a few minutes for the motor to cool down. In the second case, it will be necessary to remove the jammed object. The efficiency of the cooling system depends on the condition of the air filter. Dirty device does not pass air well, which contributes to the disconnection of the machine. Experts advise cleaning and changing the filter once every 3 months (if the lawnmower is constantly used). If the electric motor breaks down, there is a corresponding smell and noise. In this case it is necessary to replace the drive unit.
The design of the gasoline lawnmower, unlike its electric counterpart, is more complicated. In some cases, the unit is not repairable. If the engine does not start or immediately stops, then it is recommended to check the ignition. This requires removing the spark plug. Dry candle indicates problems in the feeding system, and wet. on the carburetor. In such cases, repair work is carried out by professionals.
If there is black fouling on the spark plug, then it is replaced. This does not take into account the cause of the lawnmower failure (carburetor adjustment, poor fuel quality). The fuel hose is often clogged in gasoline models. If the gasoline does not leak, then the saloon is cleaned with a needle, and the fuel filter is replaced with a new equivalent.
If the lawnmower does not mow the grass, then check the blades. If necessary they are replaced with new cutting elements or ground on an emery. In the second case, the use of protective goggles and thick gloves is recommended. Mower blades can be sharpened with special devices included in the set.
If the blades are blocked by long grass, then it is recommended to disengage the mower. Use a wooden stick to twist the cylinder (the other way around) until it rotates freely. If the mower does not work due to a faulty switch, then it is recommended to check and replace it with a working analogue.
If there is no voltage in the socket, check the switchboard. Some devices are equipped with a thermal protection. When the system works, check ventilation grilles for contamination. Use a soft brush to clean them.
The most common breakdowns
All machinery fails sooner or later. It is important to know how you can repair mowers, because not all cases need to go to a service center.
Mower does not cut the grass
In most cases blunt or severely damaged knives are the cause. For best results, simply change the knife every year. Choose the right knife for your model. When the blade is blunt, it can be resharpened using an electric grinder or file. Be sure to wear safety glasses and gloves when sharpening. The angle of sharpening on both sides is approximately 30 degrees.
Simple sharpening devices are available in stores. Before installing them, unplug the mower and adjust the cylinder positions so that the maximum cutting gap is highlighted.
In cylindrical mowers, the clearance between the blade and cylinder must be less than the thickness of the paper. Some of the most modern models have built-in regulators with notches. Otherwise you need to use wrenches and screwdrivers to make necessary adjustments. Keep an even gap across the entire length of the cylinder. To check the adjustment, insert a sheet of paper between the cylinder and blade while slowly rotating the drum by hand. Gradually adjust on both sides until the paper starts to cut cleanly at each point of the fixed blade.
The mower is difficult to move
- When the mower has difficulty moving across the lawn, you may be trying to remove too much grass and will need to adjust the mowing level. If the rollers or wheels are jammed, inspect them to make sure there are no grass clippings or debris. They most likely need to be removed and cleaned.
- If the air intake is obstructed, the mower‘s air cushion will have less lifting power and become difficult to move. Lack of air causes the engine to overheat. Turn off the power and remove any grass residue from the air intake grilles.
The machine does not turn on at all
Long, wet grass can easily block the blades. Remove the plug from the power supply and use a wooden object to rotate the cylinder away from the blade until the movement is free. Do not use this technique on petrol mowers.
The belt that makes cylinder lawnmowers work wears out over time, stretches and can tear. Remove the belt cover and check if a tear has occurred or if the belt just slipped. Loosen the mounting screws and slide the small drive pulley up to the large cylinder pulley. Put the new belt on the small pulley and turn the big pulley slowly, putting the belt on gradually. Pull the pulley to the side to tension the belt, then tighten the screws.
Before installing the cover, be sure to check the tension of the belt. the degree of deflection should not exceed 4 mm (the figure may vary slightly depending on the model, for details see the user manual).
Tearing in the cord
Every time you use it, you unroll, move, and roll the cord. This can cause internal wires to break. In many models, the cord is connected to the screw terminals, which allows you to quickly check and replace it. If double-insulated, connect a two-core cord.
Other models use clamping pins to make replacement easier. Disconnect the power supply, remove the plastic cover. When unscrewing the clamping plate, observe the connection of the cord to the switch to observe the polarity of the connection (color of the wires).
To disconnect the cord, insert a hex wrench into each of the holes where the conductors are placed. to release the clamp and the conductor. Check where the gap is formed.
If necessary, connect a new cord: twist together all the individual wires of each strand, then insert the twisted ends into the appropriate terminals. Pull lightly to check the connection. Then reinstall the clamping bar, cord bushing, and switch cover.
When the lawnmower does not start
Depending on the size of the lawn and the growth of grass on it the owners choose the best performance equipment. It comes in several types:
An average-priced mower can withstand about four seasons in the climatic conditions of St. Petersburg, Moscow or similar regions. expensive or less operated garden helpers can withstand 5-6 seasons in the field.
Also, the restoration of lawn mowers with their own hands will be needed in the event that the conditions of winter storage were improper. For example, no cleaning of the working surfaces after use or lack of inter-seasonal preventive maintenance. As a result, a variety of problems appear:
- Frequent sharpening of the mower blades is required;
- the lawn mower simply will not start;
- the engine starts but the lawnmower cuts out after a short period of time;
- malfunctions occur in the carburetor, which not only needs to be disassembled, but also cleaned and repaired;
- Repair the lawnmower with their own hands is required when there is a significant decrease in power during operation.
There is no need to go to an expensive service center. Many problems can be solved cost-effectively and can be repaired by yourself.
The cutting elements must be cleaned after each use of the tool. Regular oil changes and maintenance to reduce the risk of breakdowns to a minimum.