How to check the operation of a car generator. Basic malfunctions and maintenance of generators

The correctness and stability of the operation of all vehicle electronics depends on the serviceability of the generator, because it powers all devices after the engine starts. Therefore, it is important to maintain the generator in “combat” condition, which means servicing it correctly. Periodically checking the generator with a multimeter will identify possible malfunctions of the device and increase its service life. More details on how to check a car generator with a multimeter (with and without removing the device) will be discussed in this article.

Multimeter - what is it

A multimeter is a measuring device used to measure resistance, current or voltage. Also, using such a device you can check the wiring for breaks. Each of these measurements involves the use of separate measuring instruments, such as a voltmeter, ammeter or ohmmeter. Therefore, a multimeter is considered a universal tool (mulmeter = voltmeter + ammeter + ohmmeter). In practice, analog and digital multimeters are used.

What is a multimeter

Analog

This multimeter is equipped with a special hand, like on a watch, by the movement of which the measurements are read. The analog multimeter is also equipped with a measuring scale with resistance, current and voltage values. The device is inexpensive, so it is very popular. The disadvantages of an analog multimeter include measurement errors (this mainly applies to products made in China).

Analog multimeter

Digital

Unlike an analog multimeter, a digital multimeter has an LCD or LED screen that displays data. These devices are easier to use and also have high accuracy, which cannot be said about cheaper analogues.

Digital multimeter

Note! Some types of digital multimeters can work in conjunction with a computer, transferring data obtained as a result of measurements to it.

Video - How to use a multimeter

What exactly is the problem?

If your car won't start, the problem is most likely with one of two elements of the charging system: the battery or the alternator. If you come to a car dealership, they may offer you a new expensive battery without conducting any tests. Don't make this mistake! A faulty alternator can ruin a perfectly good battery, putting you even further away from solving the problem. However, no need to worry. Diagnosing car electrical problems is so simple that anyone can do it. To do this, you need to perform the following tests. For tests, you will need a multimeter, which can be purchased at any auto parts store.

Possible generator breakdowns

All generator malfunctions can be divided into two types - mechanical and electrical. Mechanical breakdowns can be identified by visual inspection of the device (cracks in the housing, wear of the tension roller or belt, delamination, etc.). To identify electrical faults, special tools are needed.

Common generator problems

Table. Damage to the electrical part of the generator.

Some faults are difficult to notice, so drivers come to the service center with a generator that is no longer working and a “tired” battery. Therefore, it is important to periodically diagnose the generator using a multimeter.

How to test a generator with a multimeter

What components and parts are checked using a multimeter?

This operation involves diagnosing the electrical part, and checking the following parts:

• 
  Voltage measurements are taken at the generator output;

• the rotor excitation winding is checked for open circuit or short circuit to the housing;
• checking the stator windings for breakdown and open circuit;
• carry out fault detection of the diode bridge, capacitor;
• faults in the voltage regulator and brushes are detected;

Performing each of the listed operations requires special knowledge and skill to carry out measurements, so each test should be considered in more detail.

Checking the generator without removing it

Step 1: Set the parking brake and raise the hood.

Lift the hood

Step 2 . Connect the multimeter to the battery terminals (do not mix up the “+” and “-” terminals). Place the device itself on the battery, as in the photo. When the car is not running, the battery charge should be about 12.5-12.6 V.

Connect the multimeter to the battery

Step 3: Start the engine.

Start the vehicle

Step 4: Monitor your metrics. 1-2 seconds after startup, the voltage should increase to 14.3-14.4 V.

Monitor your multimeter readings

Step 5. Give maximum load to the generator. To do this, you need to turn on all the car's consumers: lights, heater, heated windows and mirrors.

Turn on the light

Turn on the stove

Turn on the heated seats

Step 6. Monitor the battery voltage. If the indicators have changed slightly (14.1-14.2 V), then this indicates normal operation of the generator. If the voltage drops significantly when the devices are turned on (to 13-13.5 V), then diagnostics of the generator is needed.

Monitor the voltage coming from the generator

What kind of charging should go to the battery from the generator?

It is traditionally believed that 13.5-14.5V should be supplied by the generator to the battery and this is absolutely enough to replenish the battery costs.

It is worth considering that using a battery with a higher power in a car than the manufacturer recommends also requires the installation of a more productive generating device.

It is necessary to take into account the load that the generator must withstand - it is calculated based on the maximum indicators of all electrical appliances and car systems.

Do not forget that the charging current from the energy-generating device will allow you to start the car in the cold season. In order to avoid problems with starting the car, we recommend purchasing generating equipment, the charge current of which will be approximately 10% of the capacity of the power source. That is, a battery of 100 A/h requires a generator that can produce 10A. Please note that for many cars, 100 amp equipment will operate at its maximum capacity, because the power consumption of the automotive system is in the region of 80 amps. Therefore, the choice of a source generating energy must take into account both the battery capacity and network consumption.

Check with removal

No preparations or preparatory steps are required for testing. You just need to remove the generator itself and prepare a multimeter. A full check of the device consists of diagnostics of the relay regulator, diode bridge, stator and rotor windings. Let's consider the procedure for checking each of these elements separately.

Checking the generator with a multimeter and removing

Checking the relay regulator

Step 1. Remove the relay regulator and prepare a multimeter.

Remove the relay regulator

Step 2. Prepare a light bulb with two wires (as in the photo).

Connect a light bulb with two wires

Step 3. Connect the wires from the light bulb to the brushes ( See Replacing generator brushes ) of the relay regulator.

Connect the wires to the brushes

Step 4. Now you need to connect an regulated power supply to the “+” and “-” relays.

You need to connect the power supply to the plus and minus

Step 5. Connect the negative of the power supply to the negative of the relay. Secure the wire using a metal crocodile clip.

Connect the minus of the power supply to the relay

Step 6. Connect the second terminal of the power supply in the same way.

Now connect the plus

Step 7. The finished design should look like this.

This is what the design looks like

Step 8. Now connect the multimeter to the terminals of the relay regulator. Everything is the same: “minus” to “minus”.

Connect the negative of the multimeter to the relay regulator

Step 9. Connect “Plus” to “Plus”.

Connect the positive terminal of the multimeter

Step 10: Turn on the power supply to supply voltage to the relay. The multimeter shows 3.8 V after switching on.

Turn on the power supply

Step 11. Gradually increase the voltage, look at the light bulb and the meter readings. The brightness of the light bulb gradually increases.

Slowly increase the voltage on the power supply

Step 12. At around 14 V, the light should go out suddenly. If this happens, then the relay regulator is working properly. Otherwise, replacement of this element is required. At this point, testing the relay-regulator under load can be considered complete.

When the voltage increases to 14 V, the lamp should go out

Checking the diode bridge

Step 1. To work, prepare a multimeter with a ringing function and a diode bridge, which must be removed from the generator in advance.

Prepare the diode bridge and multimeter

Step 2: Check the first diode. It has positive polarity. The resistance of a working diode when tested in one direction should be from 400 to 700 Ohms.

Check the first diode with positive polarity

Step 3. In the other direction the resistance should be infinity. If this is the case, then the diode is fully operational.

Test the diode in the other direction

Step 4. Test the second negative diode in the same way.

Check the second negative diode

On a note! The resistance of the diodes can vary within certain limits and depend on the ambient temperature. When heated, the resistance decreases, and when cooled, it increases.

Step 5. Using this diagram, check all the remaining diodes. A burnt-out diode will have a resistance of infinity.

Repeat the procedure for the remaining diodes

Step 6. Small diodes are tested in the same way as large ones. The resistance of these diodes will be slightly lower than that of larger ones. A slight difference in the resistance of these diodes is considered normal. This completes the check of the generator diode bridge.

Check the small diodes on the bridge in the same way

Stator check

Step 1. Prepare the generator winding for testing. It is advisable to do this in a well-lit place.

Prepare the stator for diagnostics

Step 2. Take a multimeter and set it to test.

Set the ringing mode on the multimeter

Step 3. The winding has three outputs and they should all “ring” with each other.

The winding outputs should be directed upwards for convenience

Step 4. Connect the first terminal of the multimeter to one output, and touch the second terminal to the other two outputs in turn.

Connect the multimeter terminal to the winding output

Step 5. Check the stator for any holes in the metal. To do this, press the multimeter terminal to the edge of the winding, and the second one to the second edge.

Check the stator for metal damage

Step 6. Connect the second probe in turn to the winding outputs. If there are no signals, then the winding is intact.

Connect the terminal to the winding outputs one by one

Rotor check

Step 1. Prepare the generator rotor for further diagnostics.

Prepare the rotor for diagnostics

Step 2. Take a multimeter and set it to dial mode. The black probe should be in its original place, and the red one should be for measuring voltage.

Set the dialing mode on the multimeter

Step 3. Check the device for serviceability by connecting the black and red probes.

Connect the probes of the device to check its functionality

Step 4. Attach one feeler gauge to one rotor ring and the other to the other. In this way you can check for a break.

Attach the probes to the rotor rings

Step 5. Check the rotor for breakdown. To do this, one probe must be pressed against the ring, and the second against the body. If there is no breakdown, then the multimeter shows infinity.

Check the rotor for breakdowns

Step 6. Set the multimeter to resistance measurement mode in the 200 ohm range.

Set the resistance measurement mode on the multimeter

Step 7. Place one feeler gauge on one rotor ring, and the second on the other (as done previously). If the winding is intact, then the resistance should be around 3 ohms.

Reattach the probes to the rotor rings

How many amperes does a car alternator produce per battery?

The current strength required by the electrical system of each car is individual and depends on the number of electricity consumers and their values. And also the charge current must be sufficient to charge the power source.

It is worth noting that ampere readings appear only when there is a load in the vehicle’s electrical system and, accordingly, the battery is discharged. After starting the car engine, the charging current is about 6-10 amperes and drops over time, because the battery is charging, taking on the main energy consumption. If you turn on additional equipment - headlights, radio or heated mirrors, you can see an increase in the charging current values.

When purchasing a generator, pay attention to its technical characteristics, which the manufacturer indicates on the case - that’s where you will find information about the maximum current that will flow to the battery.

In the table below you can see the approximate current values ​​​​that the generator shows at different loads.

Table 1. How many amperes the generator produces under load.

Additional recommendations

Before starting the test, you need to familiarize yourself with the type of generator set, because the relay regulator can support different values ​​depending on the car model. We are talking about the range from 13.6 to 14.2 V. All these subtleties need to be learned before starting the test, because the final result may depend on them.

Checking the car generator

Otherwise, the process of checking the generator is simple, so even without experience, the driver can do it on his own. Of course, you need to start by checking the generator without removing it. Only by its results can you determine whether the device needs to be dismantled or not. Also, during the test, you can identify other faults related to the generator or other electrical devices of the car.

Generator diagnostics will help prevent serious malfunctions

How to check the generator voltage regulator with a multimeter

In order to ensure the normal operation of light bulbs, power windows, windshield wipers and other electrical equipment, as well as charging the battery, you need to maintain a DC value of 13.5-14.5 volts. If this figure is less, the battery will not charge, and if it exceeds this level, the on-board electrical appliances will fail. High voltage also causes some damage to the battery, shortening its service life due to overcharging.

Therefore, to convert the current generated by the generator, there is a special device - a relay-voltage regulator. With its help, the on-board network is provided with a current that maintains the required parameters, regardless of the crankshaft speed. Situations often arise when it becomes necessary to check the generator voltage with a multimeter.

Modern relays are electronic, and their design is non-separable. If they fail, they cannot be adjusted or repaired, but require complete replacement. This is considered the only drawback of these devices, since otherwise the relays have a lot of advantages: compactness, durability, high accuracy of current parameters.

When can the voltage regulator be considered faulty?

1. The headlights change brightness depending on engine speed.
2. There is an insufficient charge of the battery or, conversely, its overcharging, accompanied by boiling off of the electrolyte.
3. There may be a burning smell inside the car. Failure of the regulator can occur due to moisture, various mechanical damage, short circuit and other non-standard short-term electrical influences.
4. Sometimes the regulator is initially of poor quality if it is a dubious product from unknown manufacturers.