The purpose of a motor in a car is to convert electrical voltage and current into mechanical energy. If you are facing any motor-related problem such as poor connections, fully or partially shorted coils, incorrect coil connections and imbalance between phases, you should run a motor winding resistance test on your vehicle. Motor winding resistance test determines motor problems with car battery performance that other tests fail to perceive.
Here is a guide on motor winding – how it works and how to check the winding resistance of a 3-phases electric motor.
3-phase induction motor winding resistance
To understand the concept of motor winding resistance, you must see how the motor works. An electrical motor contains a wire wrapped around a cylindrical shaft. This wrapped wire forms the windings. An electric current passes through the wire and induces a magnetic field inside the coil of the wire. This magnetic field is responsible for the rotation of a metal bar inside the coil. This movement in turn powers the motor.
The motor operates correctly when the coil wire has a specific, predetermined resistance. The manufacturer gives this particular resistance value. Only at this resistance, the right amount of current is allowed to pass through the coil. To ensure the motor operates to its best potential, you must know how to measure motor winding resistance regularly.
How to conduct the motor winding resistance test
Checking the motor winding resistance is a straightforward process. You need a digital multimeter to do that. Follow the steps given below:
Step 1: Switch on the digital multimeter.
Step 2: Set the multimeter to resistance. Look for the capital Greek letter, Omega to locate the resistance setting. Omega is the symbol of the unit of resistance, ohm.
Step 3: Touch the positive (red) lead of the multimeter to the positive end of the winding wire on the motor.
Step 4: Now touch the negative (black) multimeter lead to the negative terminal of the wire windings on the motor. Once you do that, a reading will appear on the screen of the multimeter. This reading is the resistance in ohms.
Reading the resistance
Once you have read the multimeter, check the readings against the 3-phase motor winding resistance chart provided by the manufacturer. You can do that with a motor winding resistance calculator online too. Also, use the temperature factors if they apply as resistance is affected by the temperature. Compare the winding resistance test readings between the three phases.
The typical deviation for the three average winding readings should be between 1 to 3%. In case there are vast differences between the three readings, there could be a problem with the motor.
The readings vary depending on the motor type and manufacturing. Typically, however, lower resistance readings are preferred. The readings must not exceed 5 ohms. However, if your multimeter reads zero, it is an indication of incorrect testing.
Removing the leads after the motor winding resistance test
Once the test is complete, the multimeter screen shows the ‘DISCHARGING’ message. Do not touch the leads before this message, as the magnetic field will still have current. When the discharging message disappears from the screen, remove the leads first from the motor and then from the multimeter.
In addition to checking motor winding resistance, check car alternators and automobile arcing for optimum vehicle performance.
FAQS
What is the winding resistance of a motor?
Winding resistance measurements identify different faults in motors and transformers. These include short-circuits, broken strands, loose connections and faulty tap changer mechanisms. These measurements recognise problems in motors that other tests may not find.
How many ohms should a motor read?
A good motor must read under 0.5 ohms. Any value higher than 0.5 ohms means trouble with the motor.
What is the minimum insulation resistance of a motor?
Insulation resistance must be about 1 megohm for every 1,000 volts of operating voltage. The minimum value should be 1 megohm for this. For instance, a motor rated at 2,400 volts must have an insulation resistance of at least 2.4 megohms.
How do you test a motor with a multimeter?
Test between every winding terminal using a multimeter set to low resistance (200 ohms). If any of these gives a reading, then your car motor is bad. Refrain from using it.
This is how you check motor winding resistance of a car. Follow this test to avoid costly motor issues in the future. While rewinding the motor is one way to deal with the motor problems, if your car motor is beyond repair, you will have to replace it. However, if your car needs a few other repairs and the cost is piling up, you can buy a used car instead without breaking the budget.
Stay tuned to the UAE’s top blog for more information on car parts and repair.
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