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Testing BLDC motor's Phase Wiring - Hall Sensors and Wiring.

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    Testing BLDC motor's Phase Wiring - Hall Sensors and Wiring.

    Testing electrical components of a typical hub motor with a digital multi meter.

    First take a few minuets and look over the wiring going into the motor for cuts, scrapes, missing insulation and other wiring issues or poor connections that should be resolved first. Smell for evidence of overheating or burning that could have damaged the winding insulation, wires, or connections.

    Two major electrical systems need to be checked out in a typical BLDC hub motor that has hall sensors.

    1) The motor's 3 phase windings. (high voltage components-thicker wires)
    2) The motor's 3 hall sensors, (low voltage components-thinner wires) if present. If not, you will need a "sensor less" capable controller and skip these tests.

    Motor Winding Testing.
    • With the 3 phase wire leads (heavy gauge wires) disconnected from everything, and not moving or turning the motor. Test resistance (ohms)between two phases at a time, and comparing all three phase combination's resistances. All three readings should match. Note that this is just a general check with a Digital Multi Meter. As the resistance readings are very low to be real accurate. It's not so much an exact same matching reading, but if they all are comparable. Very easily can be much less than 1 ohm.
    • Then check resistance between each phase wire at a time and a metal part of the motor. It should read infinity or open circuit. Nothing shorted or any resistance reading to ground. If so, do not use the motor until repairs (if possible) are made.
    • Then tie two phase wires together in different combinations at a time for a total of three tests. At each combination, a similar magnetic resistance (also known a "cogging ') should be felt while trying to turn the wheel by hand. With no resistance present when all wires are separated.
    Note: If resistance to turning by hand is felt when the motor is connected to the controller, and NOT with the motor disconnected from the controller. This would indicate bad FETs, I.E problem with the controller. See an excellent tutorial on testing controller MOSFETS here... GRIN: Testing for Blown Mosfets
    Also on a geared hub motor, wheel will have to be turned in reverse to engage the motor.
    • And lastly, if your able to spin your motor with a drill or other set-up at the same constant speed for all testing. Spin the motor up and first check for hot spots in the windings. Then compare the AC voltage outputs of all three combinations of phase wires. They should all be close to the same.
    Note: A slight degradation of the winding insulation may not show up in a resistance test. So by putting some load, or voltage stress on the windings as in this last test. Will give a more accurate assessment of the health of the motor. By all means, use a LCR meter if available.

    Motor Hall Sensor Testing.

    Always check the wiring and connections first for any damage or poor connection.


    In a BLDC motor that has hall sensors. The hall sensors are used to determine the actual position of the rotor for accurate sensored type controller operation. Typically they are mounted on a PCB board, with the sensors close to and facing the motor's magnets. Or they can be mounted at the correct positions directly in or besides the motor's stators, facing the magnets. (see hall sensor picture below for sensing surface) Note: Depending on the motor's phase angle, and the separation between each sensor used by the manufacturer. It would not be unusual to have the center hall sensor face, facing the opposite direction as the other two. I.E. They all won't necessarily have to be facing the same direction. Label before removal.

    Each individual hall sensor has three wires going to it, as it requires a voltage input (typically 5vdc) , 0vdc, (batt negative, or ground), with the last wire being signal. This will bring the wiring harness for the hall sensors to a total of 5. Typically, RED=5vdc+ ,BLACK=0vdc, and each of the last three are the signal wires of their respective sensor, YELLOW, BLUE, and GREEN.

    Note: Some motors may include a 6th wire in this bundle. Typically white in color and often used to connect to an internal thermal sensor. It may also provide a signal for a speedometer input.
    Some motors may provide an extra set of hall sensor wiring and sensors.

    When effected by the motor's magnet's gauss, ether positive or negative passing by the sensor. It will switch the hall sensor output's signal voltage from HIGH (typically 5 or 3.3vdc as provided by the controller to the signal wire) to LOW or 0vdc. It does this by grounding (or not) the reference electronic signal voltage supplied by the controller. (much like how the electronic cruise or low brake signal wires are shorted to ground to trigger their actions.)

    This electronically recognized voltage switching, at the correct time, and in the correct order is used by the controller to determine when each of it's phase winding FETs are actuated. Causing the motor to move in the correct direction, at the desired speed or current.

    For replacement a well known and often used hall sensor used in BLDC motors to determine rotor position would be the Honeywell SS41 series.
    Here is the data sheet for the G model.

    1) Testing when connected to a working controller.

    See this tutorial...

    If you find a hall sensor's signal output stuck on 0vdc, check Note 1: seen below.

    2) Bench testing not using a controller.

    As a controller provides a reference signal voltage to the hall sensor's output terminal, typically 5vdc to 3.3vdc. This being the voltage used that is shown switching between the HIGH and LOW values during testing. (5 to 3.3vdc... and 0vdc) This voltage will have to be supplied and added to the circuit when testing the motor by itself. This is done by adding a 10K resistor connected between the 5vdc input voltage and the signal output of the hall sensor being tested. (see picture below) The external 5vdc source can be provided by a USB 5vdc type wall wort transformer, 3- 1.5vdc AA batteries in series, or USB type rechargeable cell phone back-up battery which I prefer. Current or amperage requirements are low. (<25mAs...)

    Note: Geared hub motors need to be turned in reverse, as the clutch will not move the motor components going forward. Direct drive will work in ether direction.

    See this tutorial...

    And this...

    Example of testing set-up...

    Note 1: If during the non-controller testing, all hall sensor operations check out correctly but your still having an issue. While disconnected from the motor, test for voltage at the controller's motor hall sensor input wires. You should read a steady electronic signal voltage provided by the controller of typically 5vdc to 3.3vdc to all 3 hall sensors. If this positive reference voltage is missing, check wiring to the PCB board, or replacement of the controller may be required.

    Bad Testing Results?

    If properly done initial testing indicates problems. The motor will have to be opened up to gain access to the internals. To further narrow down the cause of the problem between wiring, connections, or parts.

    Hall Sensor to Phase Wiring Configuration

    After the motor's wiring and components have been verified as good. The motor's phase wiring to hall sensor locations need to be correctly identified and wired for the correct controller output.

    If you have a controller with "learning wires" or "auto configuration" by all means put it to use. As the controller will magically configure itself. If not, use this chart to successfully pair the hall sensors to their respective phase windings...

    Take it easy on the throttle till better results are obtained! (see Testing Recommendation box in the chart.)

    Last edited by Tommycat; 05-21-2021, 06:42 AM.
    See my completed Magic Pie V5 rear hub motor E-Bike build HERE.

    Thanks for this comprehensive write up Tommycat