Husqvarna DM220 Workshop Manual page 23

1
2
mH
STATOR
Functional test
Breaks in the stator winding are detected easily with the following functionality
check. In general, short-circuited windings can also be identified, particularly
if the short circuit eliminates current in several winding turns. If the short
circuit only eliminates a few turns, the measurement is unlikely to record this.
A fault like this has hardly any noticeable effect on the performance of the
motor either.
Resistance measurement – Ohm Ω
Resistance measurement provides an unequivocal answer as to whether the
stator winding is fractured. However, the method gives unclear indications for
short-circuited winding turns.
Inductance measurement – Henry (H)
The dimension is "Henry", abbreviated H (1H = 1000 mH). Inductance
measurement is best applied to both identify fractures in the stator winding or
short-circuited winding turns.
Preparations, illustration 1
Remove the inspection cover to the carbon brushes.
The stator winding is screwed at the circuit breaker and is connected with
the flat pin connector at the circuit board. The arrows show the positions.
Make an adapter as shown in the illustration and connect the stator cables.
Measuring cables - inductance measurement
Use short measuring cables and lay these close to each other: the easiest way is
to twist them. Cables run in a coiled way give incorrect readings.
Testing – inductance measurement, illustration 2
You do not need to remove the carbon brushes. Lift these up and lock with the
spring. Connect the test pins to the cables on the carbon brushes.
Measured values
Typical measured values for a complete stator is around 60 mH. Typical value
for resistance measurement is around 1.6 – 1.8 ohm.
If the stator winding is broken you get the value 0 mH. Resistance measure-
ment gives a maximum, or immeasurable ohm figure.
Short-circuited winding turns reduce the inductance value. If the value is less
than 45 mH the stator is unusable.
A disassembled stator that is measured without installed rotor gives about
9 mH. If the value is less than 6 mH the stator is defective.
Ω
IMPORTANT! When measuring the inductance, it is extremely important
that no large iron or steel objects are in the immediate vicinity. If the stator is
placed on a plate covered workbench the readings will be useless.
Dismantling
Remove the carbon brush
holders.
Remove both stator screws.
Pull the stator out of the motor
housing.
Dismantling
Separate the motor unit from the gear
housing as described in Chapter 4.
Remove the carbon brush holders.
Remove the two screws that hold the
stator in the motor housing.
Pull the stator out of the motor housing
by hand.
Reassembly
Note that the stator must be turned so
that the cable with the flat pin connector
comes on the motor housing's top side.
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