An alternator, which consists of a stator and a rotor, powers the engine by transforming mechanical energy into electricity, but it also charges the battery. Therefore, if anything goes wrong with a stator or a rotor, your vehicle will experience problems, even when the battery is fine.
Although a rotor is robust, a stator is relatively more prone to failures as it contains stator coils and wiring. Hence, testing a stator with a good multimeter is an integral step in troubleshooting problems with alternators.
The following steps will guide you on how to check a stator using a digital multimeter.
How to Check a Stator using a Multimeter?
If you are experiencing issues related to car or motorcycle charging, then it is time to take out your digital multimeter.
To begin with, set up your digital multimeter to Ohms. Moreover, when you touch the meter leads together, it should show 0Ω on the screen. After prepping the digital multimeter, check the battery using the meter leads. If the digital multimeter shows voltage around 12.6 Volts, it means your battery is good, and the problem exists most probably with the stator coil or stator wire. (1)
There are three ways to test stators:
1. Static Stator Test
A static test is recommended when you experience problems with your car or motorcycle charging. Moreover, this is the only test you can perform when your vehicle is not starting. You can either take out the stator from the vehicle’s engine, or you can test it in the engine itself. But before checking the resistance values and inspecting any shorting of the stator wires, make sure that the engine is off. (2)
The following steps are performed in the static test of a stator:
(a) Switch Off the Engine
To test stators in a static mode the engine should be turned off. As said earlier, if the vehicle is not starting at all, then the static stator test is the only way of testing stators.
(b) Set Up your Multimeter
Set your multimeter to DC. Insert the black lead of your multimeter in the black-colored COM slot, which stands for ‘Common’. The red lead will go in the red slot, which has ‘V’ and ‘Ω’ symbols. Please make sure that the red lead is not inserted in the Ampere slot. It should only be in the Volts/Resistance slot.
Now, to check the continuity, rotate the knob of the digital multimeter and set it to the Audio Symbol, as you will be looking to hear a beep sound to see if everything is fine with the circuit or not. If you have never used a multimeter before, go and check out its service manual before operating it.
(c) Perform the Static Test
To check the continuity, insert both the multimeter’s probes into the sockets of the stator. If you hear a beep sound, it means that the circuit is fine.
If you have a three-phase stator, then you need to perform this test three times by inserting the multimeter probes in phase 1 and phase 2, then phase 2 and phase 3 and then phase 3 and phase 1. If the stator is fine, you should hear the beep sound on all occasions.
The next step is to test for any short circuit inside the stator. Simply take out one lead from the stator socket and touch the stator coil or the ground, or the chassis of the vehicle. If there is no beep, it means there is no shorting in the stator.
Now, to check the resistance values, set the knob of the digital multimeter to the Ω symbol. Insert the multimeter probes into the sockets of the stator. The reading should be between 0.2Ω to 0.5Ω. If reading is not within this range, or if the reading is infinity, it is a clear indication that the stator is faulty.
We advise you to read the service manual of your vehicle to know the safe readings.
2. Dynamic Stator Test
The dynamic stator test is performed directly on the vehicle and by keeping the multimeter in AC mode. This tests the rotor, which contains magnets and spins around the stator. The following steps are followed to perform the stator test in dynamic mode:
(a) Switch Off the Ignition
Following the same procedure as the static test, insert the multimeter probes in the stator sockets. If the stator has three phases, you need to perform this test three times by inserting probes into the sockets of phase 1 and phase 2, phase 2 and phase 3, and phase 3 and phase 1. You should not get any reading while doing this test, with the ignition switched off.
(b) Switch on the Ignition
Start the engine by switching on the ignition and repeat the above step between each pair of phases. The multimeter should show a reading of around 25V.
If for any pair of phases, the reading is extremely low, say around 4-5V, it means there is a problem with one of the phases, and it is time to change the stator.
(c) Revv the Engine
Revv the engine and increase the RPMs to around 3000 and perform the testing again. This time the multimeter should show a reading of around 60V, and this will increase along with RPM. If the reading is below 60V, it means that the problem lies with the rotor.
(d) Test the Regulator Rectifier
The regulator maintains the voltage generated by the stator under the safe limit. Connect the stator of your vehicle to the regulator and set the digital multimeter to check amperes on the lowest scale. Turn on the ignition as well as all the electricals and disconnect the negative cable of the battery.
Connect the probes of the digital multimeter in series, and in between the negative post of the battery and the negative terminal. If all previous tests are fine, but during this test, the multimeter shows a reading below 4 Amperes, then the regulator rectifier is faulty.
3. Visual Inspection
Static and Dynamic are two ways for testing stators. But, If you see obvious signs of damage to the stator, for example, if it looks burnt, then it is a clear indication of a faulty stator. And for this, you don’t need a multimeter.
Before you go, you may want to check other learning guides below. Until our next article!
- How to test a capacitor with a multimeter
- Cen-Tech 7 function digital multimeter review
- Astroai digital multimeter TRMS-6000 review
(1) Ohms – https://www.britannica.com/science/ohm
(2) vehicle’s engine – https://auto.howstuffworks.com/engine.htm