Brush Replacement - Baldor MN605 Installation And Operating Manual

Brush Replacement

Do not change brush grades or suppliers without first contacting Baldor for technical assistance.
Brush life will vary greatly due to motor load conditions and the operating environment. The brush pigtail leads
should be checked for secure connection to the brush support stud. Brushes should be replaced when their
pigtails touch the top of the brush holder.
When replacing brushes, proper seating is important!
1. Wrap a strip of coarse grit (60) sandpaper, rough side out, around the commutator and under the brush
holder. (Do not use metal oxide based sandpaper or emery cloth that contains electrically conductive
materials).
2. Slide the new brush into the holder and snap the spring clip in place.
3. Rotate the armature slowly in the direction of normal motor rotation.
4. Remove the brush and inspect the face. The brush should be seated over 90% of the face area and
completely seated from leading to trailing edge.
Brushes should move freely in their holders. If brushes stick, it is usually due to built up dirt and oil.
Brushes should be inspected on occasion to see that they are long enough to press firmly against the
commutator. Brush springs should have equal tension. Only brushes of the same size, grade and shape as those
originally supplied should be used.
All motors have their brushes set on neutral before leaving Baldor's factory. After replacing the brush holder,
realign it to the factory neutral mark.
When replacing a turned-down commutator in the motor with a new commutator, the brush holder assembly must
be adjusted. Keep 1/16" clearance between the bottom of the brush holder and commutator. The brush holder
assembly is designed with a nut/bolt guide assembly for ease in positioning of the brush-box.
During periodic inspections, check that electrical connections are tight and properly insulated.
Brush Springs
Brush springs should be inspected for proper tension during brush replacement. If the spring shows a loss in
tension, it should be replaced. Routine replacement of brush springs is recommended with every third set of
brushes.
Poor Brush Life
Poor brush life may be caused by overloading, brushes operating at higher than their rated speed, or very light
electrical loads. These can be corrected by using a brush with greater current-carrying capacity for overloads.
Friction-reducing treatments reduce wear on high speed applications. Where light loading is the cause, the
answer may be to remove some brushes from the motor (with multiple brushes per pole).
Another is to install brushes with a higher content of graphite that can handle the lower current and still
film properly. Poor brush life is generally not related to the "softness" or "hardness" of the brush.
Do not change brush grades or the number of brushes per pole. Doing so may void the warranty and
make the motor unsafe to operate. Contact your local Baldor district office or an authorized Baldor
service center for technical assistance.
Brush Chatter or Bounce
Brush chatter or bouncing can be caused by vibration from an external source. This may be a bad gearbox
coupling or condition, or insecure mounting of the motor. Stronger carbon grades are available that provide more
capacity for the brush to resist vibration. It is always best to fix the cause of the problem.
Brush Sparking
Excessive sparking of brushes may be due to electrical causes such as an overload or a very unstable DC power
supply. Mechanical causes include a flat spot on the commutator or external vibration.
Changing to a better brush grade, or a split-brush design may be required.
Carbon Brushes For Special Operating Conditions
Sometimes, there are problems if motor operation requires a different design or grade of carbon brush than what
was installed when the motor was built. These special operating conditions include long periods of operation with
loads that are significantly greater or less than rated load capacity. Also, operation in in the presence of certain
chemicals, or extreme temperature and humidity can degrade brush performance.
Generally, poor brush life or commutator wear can occur if one or more of the above conditions exist. The brush
used doesn't match the operating conditions.
Baldor offers optional brush grades for the above conditions and has replacement brushes available to retrofit
motors. Contact your local Baldor District Office or an Authorized Baldor Service Center for technical assistance.
Do not change brush grades or the number of brushes per pole. Doing so may void the warranty and make
the motor unsafe. Contact your local Baldor district office or an authorized Baldor service center for technical
assistance.
Authorized Service
Baldor catalog 505 (and the Baldor CD−ROM) lists service shops authorized to service Baldor DC motors.
Contact your local Baldor District Office for more information.
MN605 3-3