SECTION 2 -BRUSH DESIGN, MANUFACTURE AND APPLICATION
Question 2:12 Are There Any Warning Devices To Indicate Short Brushes?
Apart from visual indication lines or marks on the brush itself, some brush holders have a built in indicator that protrude from the top of the holder and provide a quick and easy indication of brush length.
There are some type of brush holders which have contacts built into the holder which can be combined with external circuitry to indicate individual brushes or rows of brushes which require attention. The contacts can be incorporated into the protective control system and be sued to raise an alarm or shut the machine down.
Detectors can also be embedded within each brush which, combined with appropriate external circuitry, can positively indicate brushes of critical length.
Remember that adequate short circuit protection must be used where these indicating circuits are directly connected to the brush holders as armature voltages and high prospective fault currents are present.
Smaller power tools and small two brush machines can have lift-off devices fitted into the brush which consist of a spring loaded pin which releases when the brush wears to the predetermined position.
This lifts the brush off the commutator, and causes an open circuit. This is a very effective form of protection as the machine stops and won't restart until the brushes are replaced and it all happens before the commutator is damaged.
These can only be applied in two brush machines because parallel brushes would not be expected to wear so evenly that they would life off simultaneously. This would result in overload of those brushes still in contact and possibly also damage to the machine.
SECTION 3 - BRUSH THEORY AND CHARACTERISTICS
Question 3:1 What is "Commutation"?
The information has been drawn from experience of Morganite Taiwan Limited Application Specialists combined with a wide range of published information from major carbon supplier and motor manufacture. However, the material can not be downloaded, copied or used without written permission.
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