Any vehicle has attachments. These are the nodes and mechanisms without which his work is not possible. Attachments include starter, power steering pump, air conditioning compressor, intake and exhaust manifold, clutch. But also the automobile generator is included in this list. It is he who allows you to maintain a stable voltage in the on-board network. Few people know the device of an automobile generator and its principle of operation. But this information will be useful for each driver. Well, let's look at how this hinged element is arranged and operates.
Characteristic
A generator is an electric motor that converts mechanical energy into current.
This element is used to power electrical equipment with an internal combustion engine running, as well as to charge a car’s battery. All modern cars use a car alternator.
Where is
Often this mechanism is located in front of the engine. It works from the crankshaft by means of a belt (brook or gear type). Typically, automakers place the generator at the highest point relative to the engine. However, there are models where the mechanism is mounted almost in the area of the ICE crankcase. Why is it important to position the mechanism at the highest point? The fact is that the car generator is very afraid of water. The ingress of even a small amount of moisture can damage it. Therefore, manufacturers are trying to exclude the possibility of penetration of water and other liquids onto the surface of this mechanism. The higher this element is located, the safer it is for it.
Device
The generator design includes:
- Stator winding.
- Front cover.
- Field winding.
- Brush assembly.
- Back cover.
- Slip rings.
- Pole halves.
- Rectifier block.
- Drive pulley.
- Impeller fan.
Also note that this node may have a different layout:
The differences are in the structure of the fan, rectifier unit and drive pulley. Otherwise, the device and the operation of the automobile generator are identical. Both the traditional and the compact mechanism consist of a rotor, a rectifier unit, a brush assembly, a voltage regulator and a stator. What are all these components for, we will consider further.
Rotor
This mechanism serves to create a magnetic field in the generator. An excitation winding is provided on the rotor shaft. The latter is placed in special pole plates, each of which has six protrusions. In addition, a contact ring is located on the shaft. It serves to power the field winding. Typically, rings are made of copper (less commonly brass). The excitation winding leads are soldered to these elements.
Also on the rotor shaft is one or two fan impellers. They provide cooling of the winding during operation of the generator. The rotating rotor mechanism consists of two maintenance-free ball bearings.
Stator
Its function is to create alternating current. The automobile generator is necessarily equipped with this element. The stator is structurally combined with the winding and core. The latter is a set of several plates. In 36 grooves of the winding there are three more windings, which form a three-phase connection. Manufacturers use two types of winding stacking:
The connection itself is carried out by different technologies:
- The triangle pattern. In this case, the ends of the windings are connected in series.
- The "star" scheme. Here the ends of the winding are connected at a single point.
Housing
It contains most of the components of the generator. The case consists of two covers: back and front. The first is on the side of the slip rings, the second is on the side of the drive pulley.
Between themselves, these parts are pulled together by long bolts. The covers themselves are made of non-magnetic aluminum alloy. The case also provides ventilation windows and mounting legs in the amount of two pieces.
Brushes and rectifier unit
The brush assembly serves to transfer current from the field winding to the contact rings. How does this node work? It consists of two graphite brushes with springs. The whole structure is combined with a voltage regulator of a car generator.
Now about the rectifier block. It is necessary to convert the sinusoidal voltage into direct current on-board network. This block consists of plates. They serve as a heat sink, and diodes are mounted on them. In total, there are six semiconductor diodes in the block. For each phase, there are two such elements. One is connected to the positive, and the second to the negative terminal of the car generator. Usually, the connection is carried out by soldering or welding at installation sites.
Voltage regulator
We continue to study the device of a car generator. In the design of the mechanism there is always a voltage regulator (on the slang of motorists - “chocolate”). This item may have:
- Hybrid compound. In this case, all the radioelements and electric drives are used in the circuit with microelectronic thick-film elements.
- Integral. Here, all the elements of the regulator, with the exception of the output stage, are performed by thin-film microelectronic technology.
The main task of the “chocolate bar” is to stabilize the voltage, which can vary with a change in the number of revolutions of the crankshaft and the total load of the onboard network.
This correction is carried out automatically due to the effect on the field current. The controller changes the duration and frequency of the current pulses. Modern generators have regulators with thermal compensation. Thus, the lower the temperature of the battery, the more voltage is supplied to its charge.
Generator drive
On all vehicles, this equipment is driven from the crankshaft by a belt. The latter can be wedge or polycline type. The scope of the first is significantly limited by the diameter of the driven pulley. The rotor speed during engine operation is usually two or three times higher than the crankshaft speed.
Often a V-ribbed belt is used on cars. It is more versatile, because with a small diameter of the driven pulley, the belt allows for a greater gear ratio. The tension of the drive element is adjusted using a special roller.
The principle of operation of a car generator
How does this equipment work? The principle of its operation is as follows. When the key is turned, current from the battery is supplied to the field winding through the brush assembly and rings. A magnetic field is induced in the winding. When the engine rotates, the generator rotor also works. The magnetic field of the latter penetrates the stator winding. The terminals form an alternating voltage. At a certain speed, the generator begins to self-excite. Thus, the winding is powered from the generator itself.
The rectifier unit begins to convert this voltage to direct current. With a change in the load on the engine, the so-called. Chocolate bar. The regulator adjusts the frequency of inclusion of the generator winding. As the number of revolutions increases, the on-time decreases. Conversely, when the load drops, the frequency increases.
Brushless generator
On some cars, a brushless mechanism is installed. In its design, it has a rotor with pressed plates made of transformer iron. A winding is placed on the stator. And the electromotive force is formed by correcting the magnetic conductivity of the gap between the stator and the rotor.
Car Generator Features
The main parameters of this mechanism include:
- Rated current. Such is considered the peak recoil current at a speed of six thousand revolutions per minute.
- Rated voltage. Depending on the type of car electrical system, this parameter is 12 or 24 V. Most cars and SUVs use a 12-volt circuit.
- Power. A car generator can be either 60- or 120-amp. It all depends on the type of machine and the size of the engine itself. If we talk about most cars, they often use an 80-amp generator.
Diagnostics
Can I check the condition of the car generator with my own hands? Experts say that you can diagnose an element in a garage using a conventional multimeter. But before that, you need to check the connection of the car generator, and also make sure that all the connections are working. Open the hood of the car and find the drive belt. It should be stretched with such force that it will bend 1-1.5 centimeters in depth from pressing the thumb. If we talk about the exact values, this deflection is measured with a force of 10 kgf.
At the first stage, the voltage regulator is checked. To do this, put the multimeter in voltmeter mode. We warm the engine at medium speed with the headlights on for ten minutes. Next, we measure the voltage at the output of the generator mass and at its plus. The nominal indicator is from 13.5 to 14.6 V. If the figure is less or more, then the regulator does not cope with its task, and it needs to be replaced.
Next, we proceed to the diagnosis of the diode bridge. We turn on the device in AC measurement mode. We connect the probes to the clamp "30" and to the mass of the generator. The voltage should be no more than 0.5 V. Otherwise, the diode bridge does not work correctly. To check the breakdown for ground, turn off the generator and remove the generator cord, which is suitable for the positive 30th terminal. Next, connect the multimeter with the probes to the disconnected generator drive and terminal. The discharge current must not exceed 0.5 mA. If it is larger, a breakdown of the insulation of the winding or the diodes themselves has occurred.
Check the return current
Please note: the recoil current is measured using a probe, which is an addition to the multimeter. This element is a kind of clamp, with which the wires are covered, and the current strength is measured. So how do we check the generator? To do this, we cover the probe with the wire going to the clamp on the 30th terminal. Starts the engine and keep it at high speeds. Turn on the light, stove and other electrical appliances. Next, we alternately measure each consumer individually. The measurement should not exceed the sum of the readings of each consumer. The maximum discrepancy is 5 amperes down.
It will not be superfluous to check the excitation current of the generator. To do this, start the engine and let it run for five minutes at high speeds. Next, we place a measuring probe around the wire with terminal 67. The readings will be equal to the strength of the excitation current. On a working generator, this indicator is about three to seven amperes.
To check the field winding, it is necessary to dismantle the "chocolate bar" and the brush holder. We put the device into ohmmeter mode and apply probes to the slip rings. The resistance level should be between five and ten ohms. Then we connect one probe to the stator. We hold the second one on any of the slip rings. The device must show infinitely high resistance. If this is not so, then the winding closes to ground.
Conclusion
So, we found out what a car generator is and how to check it. As you can see, diagnostics can be done with your own hands. However, to understand this issue, you need to at least have a superficial knowledge of the device and the algorithm of the element.