Stator - Husqvarna DMS 240 Workshop Manual

120 V
B
230 V
A
B

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.
Preparing for inspection
Checking the stator condition requires minimal preparation:
– Remove the carbon brushes
– Remove the connection box
Measurement
The stator has two windings which are measured separately. Connect one test
lead to the carbon brush holder for this winding and the other to the stator
cable. Repeat for the other winding. 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 induction values. Unfasten the switch to access the
cable connections.
120 V: Disconnect the cable at switch A. Use a pointed test probe and insert it
into connection point B. Measure between the carbon brush holder A and B.
Measured values 120 V: Typical measurement values for a full stator are
around 2.9 mH and 0.1 ohms respectively for resistance measurement.
A disassembled stator that is measured without installed rotor gives about
A 0.5 mH.
230 V: Remove one cable lug from the switch and the other cable from the
terminal block. Measure between the carbon brush holder A and B.
Measured values 230 V: Typical measurement values for a intact stator
are around 9.5 mH and 0.4 ohms respectively for resistance measurement.
A disassembled stator that is measured without installed rotor gives about
1.8 mH.
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 bring down the inductance and resistance. If
the difference is greater than 30 % of the typical value, the stator is defective.
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 measurement readings will be affected.
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