How to Test a Screwdriver Engine with a Multimeter

A malfunction of the car generator belongs to the critical class, in which further operation of vehicles is not allowed. You can use a multimeter to perform a health check on the generator.

How to Test a Screwdriver Engine with a Multimeter

Signs of generator failure

Signs of abnormal operation of the car generator may include:

  • lack of indication "battery" on the dashboard during ignition on;
  • the glow of the "battery" bulb after starting the engine;
  • Periodic blinking of the signal indicator “battery” in the process of movement;
  • the smell of burning electrical wiring in the area of ​​the generator;
  • failure to start the engine after parking.

Lack of battery charge with a faulty generator leads to problems with starting the engine. dangerous is the malfunction associated with excess current and charge voltage of the car battery. Many motorists use starting the engine from a donor battery, and then disconnect the battery terminals to switch to charging their own battery. At this point, the vehicle’s electrical equipment is powered by a generator.

If the generator is faulty, the voltage in the on-board network can be more than 17 volts, which leads to the breakdown of protective zener diodes in the engine control unit. In this case, expensive repair of the engine control unit is required.

Causes and possible consequences of a malfunction

Failure of the generator is possible for the following reasons:

  • malfunction of the voltage regulator ("tablets", "chocolates" on the slang of motorists);
  • wear (destruction) of brushes;
  • short circuit of the exciting winding (rotor);
  • breakdown of diodes (located in a horseshoe);
  • wear of bearings and bushings.

A fault in the voltage regulator usually results in a lack of battery charge. In this case, the battery icon is lit on the dashboard. The engine continues to run until the battery is discharged to a voltage of approximately 8 to 9 volts.

In the daytime, the battery charge can last 30.50 kilometers, provided that the battery was well charged at the time of the malfunction.

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During the breakdown of the output stages of the voltage regulator, a malfunction may occur associated with an increase in the output voltage of the generator to 17–20 Volts. In this case, the battery is recharged. The result of overcharging is the process of boiling electrolyte. If under the hood there are signs of corrosion in the battery area, it is necessary to check the generator.

Breakdown of the diode bridge can occur in case of accidental polarity reversal of the battery (installation of terminals in the wrong polarity). Usually diodes break through in pairs in one shoulder. A faulty diode has a resistance close to zero. The stator winding of the generator in this case works in the short circuit mode, it heats up very much.

After a few minutes of operation of the engine, the windings overheat, under the hood of the car there is a smell of burned electrical wiring. To avoid ignition, the engine must be turned off and the generator checked.

Wear of the brushes leads to a gradual failure of the generator. First, during the movement, the charge indicator lamp on the dashboard starts to blink, then it starts to glow constantly. In many generator models, the brushes change in conjunction with the voltage regulator.

Closing the generator windings can lead to a significant change in the output parameters, overheating of the device.

Initial Inspection Sequence

Initial performance monitoring can be done without dismantling the generator. To do this, set the multimeter switch to the "constant voltage 20V" mode. Next, connect the black probe to the negative terminal of the battery, red to the positive terminal. After this, it is necessary to start the engine, let it enter stable idle mode. Multimeter readings ranging from 13.5 to 14.5 volts are considered normal.

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If the multimeter shows a value less than 12.8 volts, the charge process either does not go at all, or the charge current is extremely small. The generator is operating in an emergency mode. At voltages greater than 14.8 volts, the battery is being recharged. This can lead to boiling of the electrolyte, an increase in acid concentration, and destruction of the battery plates.

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To control the voltage at the generator output, it is necessary to turn on the car lamp in the open circuit from terminal 30 on the generator (the place of contact with the thick wire leading to the positive terminal of the battery or starter).

Next, connect the multimeter in the “= 20V” mode with a red probe to the contact 30 of the generator, black. to the cleaned contact on the engine or body. Start the engine. The readings on the multimeter should not be more than 15.5 volts when you press the accelerator pedal. Otherwise, further operation of the generator is dangerous for the electrical equipment of the car.

When checking, you should evaluate the degree of tension of the alternator belt. By a simplified technique, this can be done by pressing on the belt with your finger.

The amount of deflection should be in the range of 0.5. 1 centimeter. At the same time, check the degree of wear on the belt.
To determine the causes of abnormal operation of the generator, repair work requires the dismantling of the generator.

Checking the generator nodes

The test begins with the monitoring of the performance of the voltage regulator. To do this, the regulator is dismantled from the generator and a simple electrical circuit is created.

As an incandescent lamp, use any bulb in the passenger compartment. With a working voltage regulator 3, lamp 6 should not glow at full power. When connected in parallel with the lamp (brushes) of the multimeter, its readings should be from 5.0 to 10.0 volts. If the multimeter readings go beyond these limits, the regulator must be changed. The design of some models of generators provides for the possibility of replacing the regulator without dismantling the device.

Next, check the exciting winding of the generator for breakdown. For this, the multimeter is set in the resistance measurement mode to the limit of 200 kilo ohms. The probes are connected: black. to the collector lamella, red. to the metal part of the anchor. Resistance should be more than 100 kilohms or higher than the upper limit of measurements, as shown in the photograph.

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The resistance between the lamellas (rotor windings) is usually 0.5. 2 Ohms.

The stator test begins with the control of the windings for breakdown. For this, the red probe of the multimeter is connected to the metal part of the stator, black. in series to the windings.

Resistance should be above the upper limit of measurements. Then perform the measurement of resistances between the contacts of the windings. They should differ by no more than 5%. The measurement limit of the multimeter is set to 200 ohms.

If the winding has an electrical breakdown, short circuit or open circuit, it must be replaced. There are workshops that rewind stators and rotors.

To monitor the health of the diode bridge, the multimeter measurement mode translates the diode test. Then the diodes “ring” sequentially (their number on the horseshoe is usually 9) in the forward and reverse connection. In the forward direction (black probe to the cathode), the resistance is 550. 700 Ohms, when turned back on, it is greater than the maximum measurement limit.

With the breakdown of the diodes, the resistance in all directions will be practically zero. Such a diode should be changed. The difficulty of replacing the diode is that the diodes in the generators are not soldered, but are spot-welded to ensure reliable contact at different temperature conditions.

A car generator is an essential part of a car’s electrical equipment. At the first manifestation of signs of inoperability, it is necessary to check it with a multimeter.