1) A break in one phase causes an increase in resistance in the circuit of the remaining phases, which leads to a decrease in generator power and undercharging of the battery. If 2 phases are broken, the entire stator winding is switched off and the generator will not work.
Checking for a break is carried out by alternately connecting a test lamp to the ends of 2 phases. If there is a break in one of the phases, the lamp will not light.
2) A short circuit of the stator winding to the core occurs when there is mechanical or thermal damage to the insulation. In this case, the power of the generator decreases and it overheats; the battery will be charged only at an increased rotor speed.
A short circuit is determined using a 220 V test lamp by connecting one winding terminal to the core and the other to any winding terminal.
3) An interturn short circuit in the stator winding occurs when overheating due to insulation destruction. In this case, a higher current will flow in the short-circuited turns, which leads to further overheating of the winding and its burnout. Because of this, the power of the generator is sharply reduced, especially when the load is turned on.
An interturn short circuit is diagnosed by measuring the winding phase resistance. The resistance of all phases must be the same (G250 R Ф = 0.12 Ohm).
Rice. 9. Scheme for checking the generator stator winding: a) short circuit to the housing; b) winding break; c) interturn short circuit.
4) Checking the stator on the machine is carried out by measuring the alternating voltage at the terminals of the winding phases up to the rectifier unit at a constant average crankshaft speed. An AC voltmeter is connected in turn to the heads of the mounting bolts of the BVP type rectifier block. If the voltage is not the same, then the windings are faulty.
Rectifier. Breakdown of the diodes of the rectifier unit occurs when overheating by high current, the generator voltage increases above normal, and mechanical damage. A broken diode of the “positive” or “negative” bus conducts current in both directions, as a result of which the power of the generator decreases, as well as the voltage it supplies to the on-board network. The battery will not be fully charged.
If a breakdown occurs simultaneously in both buses, this causes a short circuit in the phases of the stator winding and a short circuit in the battery. A high current will flow in the charging circuit, which will lead to burnout, i.e. open circuit in the diode. This is equivalent to a break in one phase of the stator, and when the engine is not running, the battery will discharge through the broken diode.
During normal operation of the generator, the range of voltage fluctuations in the on-board network usually does not exceed 1.0 - 1.2 V for gasoline engines and is even lower for diesel engines. If the diode is broken, then due to the loss of its rectifying properties, the range of voltage changes increases to 2.5 - 3.5V. The average voltage level does not change, however, large voltage fluctuations - “surges” - reduce the durability of the battery and other elements of the electrical system.
Rice. 10. Effect of diode breakdown on the generator voltage: a – serviceable condition; b – one diode of the generator is broken.
Diodes are checked for breakdown and breakage using a test lamp with a power of 1–3 W or an ohmmeter.
Before checking, the wires from the generator and RR are disconnected, then the “+” AB is connected through a lamp to the “+” terminal (“30” for VAZ) of the generator. If the lamp is on, then the diodes of direct and reverse polarity are broken.
Rice. 11. Scheme for checking the rectifier on the machine.
To check individual diodes connected to the bus, connect a wire from the “–” terminal of the battery to it, and alternately touch the terminals of the block with another wire connected to the “+” battery. The lamp will light up when the diode breaks down. If you change the polarity of the connection, then if the diode is working, the lamp will not light. If there is a break in the diode circuit, the lamp will not light in both cases.
Rice. 12. Scheme for checking the diodes of the “positive” bus of the generator.
Checking the diodes of the “negative” bus and at the same time shorting the stator winding with the core is determined according to the following diagram.
Rice. 13. Scheme for checking diodes and generator stator windings.
The control lamp will light up if the diode breaks down or the stator windings are shorted to the housing.
The serviceability of the rectifier diodes can be checked using an ohmmeter. The diode resistance for direct connection is R ≈ 200 Ohm, for reverse connection R ≈ 200 kOhm.
Generator rotor should not have noticeable axial and radial play (occurs when bearings wear out).
The contact rings should not have uneven wear across the width and deposits on the surface. If there are such defects, they are cleaned with fine sandpaper or turned on a lathe. After grooving, check the radial runout of the rings. If the runout is more than permissible (0.08 mm for the GAZ-24 engine), this will lead to rapid burning of the rings and wear of the brushes.
Generator pulley. The drive belt contacts the pulley with its side surfaces. If, when the pulley wears, contact occurs along the inner surface, then its area decreases.
Rice. 14. Diagram of contact between the pulley and the generator belt: a – normal contact; b – the pulley is worn out.
In this case, when the load in the chain increases (the headlights are turned on), the belt begins to slip and a characteristic whistle appears.
Drive belt. Testing of belts according to GOST 5813-93. After 500 hours of testing (equivalent to 140,000 km), the belt elongation should not exceed 2.5%.
Rewinding a generator, at first glance, may seem like a very complicated process, which even professionals do not always undertake. But it's not that difficult. If you have some experience and know at least a little about cars, then it’s quite possible to do this yourself at home. A few hours and the job will be done. The winding may fail due to an interturn short circuit or a short circuit on the unit body. This can happen due to overload during operation of the generator, delamination of the plates, shift of the winding to the housing, or if foreign liquid that is used in the car gets on the winding. The winding is laid in the cavities of a metal case in the form of a circle with high magnetic characteristics, and it is made of copper wire.
1. List of necessary tools
To rewind the generator, you don't need many tools. You will need a winding machine to wind the coils, which may also have a counter for the number of turns, copper wire of the required diameter, and a tamper to place the coils in the grooves. It would be useful to have a drilling machine, drying and burning furnace to dry the stator after coating it with varnish.
You also need a container where you will saturate the stator with varnish. You will also need a hammer, scissors, a pencil to write down the necessary information, a ruler to measure the length and width of the stator, and a set of screwdrivers and keys. These are the main tools. We will see later based on the situation.
2. Preparing the generator for winding
Before you start rewinding the generator, you need to check the winding. To do this, you need to remove and disassemble the electric motor. Remove the fan cover, fan and rotor. Then the rotor winding is checked. To do this, you will need an ohmmeter or multimeter. Using an ohmmeter, you need to measure the winding resistance by touching the rotor rings with the device.
If the resistance is within 1.8-5 Ohms, the rotor is working; if it is below the specified limits, there are short-circuited turns, and if the resistance is very high, this will mean that the winding circuit is broken. This can happen in places where the winding leads are soldered to the rings. If you see darkening and shedding of the winding, then this indicates its combustion. Also, after the generator has already been disassembled, you need to check the stator. It is checked separately.
Connect an ohmmeter to the stator winding terminals. If the stator winding is intact and not broken, then the device will show low resistance. By eye you can determine whether the winding insulation is burning or cracking. The stator where the winding is damaged must be replaced.
3. Draw a winding diagram
In a single-phase generator, the windings are connected to each other according to a linear principle. For example: the beginning of the first winding is the beginning of the second, the end of the second winding is the end of the third, the beginning of the third winding is the beginning of the fourth, and so on. In a three-phase generator, the connection occurs as follows: the beginning of the first winding is the end of the second, the beginning of the second is the end of the third, and so on, and the other two phases are similarly connected. Also, a three-phase generator can have star and delta connections. In a star connection, the voltage increases by 1.72 times relative to the phase voltage, and in a delta connection it is equal to the phase voltage.
4. Let's get started
The initial stage of the work will be disassembling the electric motor. Then we remove, if necessary, the winding data of the engine. After the winding has been removed, you need to clean the grooves where the old insulation was and blow out the stator. Then cut off the front part of the winding and remove the coils. After this, the stator should be completely cleaned and groove insulation should be placed in the grooves. At the same time, measure the length of the stator and add another 1 cm to it for the so-called “tie”. It is also necessary to determine the width of the groove insulation. To do this, we make a groove sleeve so that the insulation lies as tightly as possible in the groove and does not protrude beyond its limits, and then we make all the sleeve blanks for the groove insulation.
Draw them according to the template and cut them, then make a sleeve for the groove insulation. Then we remove the template for the coils. To wind the coils, you will need a wire of the required diameter. After the coils are wound, you can try to place them in the stator slots. It is still necessary to put insulation between the phase coils. It can be made from film-electrocardboard, which is an electrical insulating material; we cut it and put it between the coils, thereby separating the coils of different phases from each other.
Next, we tie the frontal part with nylon, cord or linen thread. Before impregnating the rewound stator, it is necessary to assemble the motor in order to check the resistance between the housing and the winding with a megger, and also measure the motor current; and then the engine is disassembled again and impregnated with varnish. After this, we hang the stator so that the excess varnish drips off. Then the finished stator is dried in an oven with natural ventilation at a temperature not lower than 120°C. Drying must be done for at least two hours. And only then the electric motor is assembled, and the stator winding is checked again with a megger.
The generator stopped charging (burnt out),
Why is this happening?
What to do if the generator burns out?
- Buy a new “original” generator. It stands like “a support from a cast iron bridge.” If you have additional equipment installed on your motorcycle, no one knows how long it will work.
- Buy a cheap "Chinese" one. There's actually roulette here. All the ones I met do not correspond to the parameters of the “native” generators. The wire wound on the generator stator is much thinner than the original one, which means the power is less.
- Rewind the motorcycle alternator. Wind the wire of the same section, preferably thicker, if the stator allows. The stator allows you to almost always, in extreme cases you can wind 1-3 fewer turns. You can calculate how many volts one turn produces. To do this, divide the charging voltage to 13.8 V. by the number of turns in the winding and you get an average of 0.07 volts for different generators. The generator has 6 coils. If we remove 1 turn each, then 1 x 6 x 0.07 = 0.42 volts, at idle 13.3 volts. - not critical. If you remove 3 turns, then 3 x 6 x 0.07 = 1.26 in., i.e. at idle 12.54 volts. - not enough, but you can raise the idle a little to 1000-1100 rpm. - usually this is enough. At idle speed, charging with all consumers turned on should be at least 12.8 V, which corresponds to a fully charged battery. In practice, 12.5 V is enough. (losses due to not the thickest motorcycle wiring wires). We lose charge at idle, but at the same time we get an eternal generator. It's up to you to decide whether to increase the cross-section of the wire or leave it as it was.
We rewind the motorcycle generator.
- We remove the generator and wash it.
- We unwind the generator. Don’t forget to count the number of turns on the stator coils, the direction of winding (you can take a photo of the process, the number of turns on each coil is usually the same).
- Checking the generator stator. An insulating layer is applied to it; if it is broken somewhere, we restore it (it is needed so that the wire does not touch the iron parts of the stator).
- We take the wire of the required section and rewind the motorcycle generator according to the scheme as we unwind it (the photo shows the most common winding scheme, there are others).
- We dilute EAF glue (epoxy glue) with solvent 1:1, fill in our stator with wound wire. The main thing is that everything spills and is fixed (to speed up the process, you can put it all in the oven at 60-80 degrees).
- We wait for complete hardening (usually 24 hours for EAF).
- We put it on the motorcycle.