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Husqvarna K7000 Workshop Manual page 19

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Short-circuit testing
Measure between 1–4, 2–4 and 3–4
Testing stator windings
Measure between 1-2, 2-3 and 3-1
Resistance measurement approx. 2 Ohm
Inductance measurement approx. 10–12 mH
Insulation testing
Measure between 1-4, 2-4 and 3-4
Rotor testing
Measure between 1-2, 2-3 and 3-1
Normal value: 73 volts rms at 1,000 rpm
Minimum value: 65 volts rms at 1,000 rpm
Dismantle the cutting machine so that the motor's connectors are
accessible. The motor does not need to be removed from the
Short-circuit testing
Check first to make sure that the motor does not have shorted
windings to earth (motor material). This is easy to do using a
multimeter on the contact X1. Set the multimeter in position for
connection testing with a buzzer. A shorted motor gives a closed
circuit between the earth cable (4) and one of the phases (1, 2, 3).
If no fault is indicated, the test must be extended to include
insulation testing as indicated below.
Resistance and induction measurement
The following test shows whether the motor has shorted winding
turns. A small number of shorted winding turns means that the
motor loses power but can work for a short time. Fully shorted
windings mean that the motor will not start.
The check is carried out with resistance measurement in Ω
(Ohm), and inductance measurement in mH (milliHenry). An
intact motor gives values of approx. 2 Ohm or 10–12 mH.
Measure between 1–2, 2–3 and 3–1. If the deviation is more than
20 % lower, the motor must be regarded as defective.
Note: Measurement instruments may give incorrect readings.
Therefore, place greater emphasis on the relative values between the
windings than on the absolute readings.
Insulation testing
The insulation test is a test which indicates where there is inade -
quate insulation between the motor's windings and earthing.
Insulation measurement takes place in the same way as the
initial check between the earth cable (4) and phases 1, 2 and 3.
The insulation tester is set for a 1,000-volt voltage. The test must
show maximum resistance for the result to be approved.
Rotor magnets
The rotor in the motor has permanent magnets with high magnetic
energy, known as neodymium magnets. As with all permanent
magnets, high temperature, blows, vibration and powerful external
fields "wear out" the magnetic force. The service life of the machine
is probably not limited by the rotor. A defective rotor will reduce
motor output.
Neodymium is an earth metal, and the magnetic strength varies
slightly from magnet to magnet at the time of manufacture. It is
therefore impossible to set a precise limit as to when the rotor is
considered to be consumed. If the phase voltage in the test below
exceeds 65 volts, the rotor must be considered usable.
The rotor magnets are tested as follows:
Remove the belt pulley from the motor and replace the screw with
a long screw from which the head has been cut off. Connect a
screwdriver to the screw.
Connect test cables between two phases and set the multimeter
to read alternating current. Rotate the motor to 1,000 revolutions
per minute, and check this with a tachometer. The typical normal
value is 73 volts at 1,000 revolutions per minute.
Repeat the test for all three phases: these must all give the same
value, otherwise there is a fault in the stator windings.

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