Makita EG301A Instructions For Use Manual page 33

CHECKING CARBON BRUSH
Brush Maintenance Essentials (Effective Length)
The brush is the area which touches the slip ring, and its surface must be kept
smooth.
If it is not smooth then carbon and other substances will adhere between the brush
and slip ring.
This must be buffed with sandpaper or the like because it is hazardous.
The usable length of the brush is 5~11mm, so if the brush is 5mm long or less
replace it with a new one.
This is done because if the length of the
brush gets any shorter, its contact
pressure with the slip ring will decrease,
resulting in a drop in generator efficiency
and the output voltage.
Check the brush every 500 hours to
confirm its length.
In addition, check the brush length if the
generator malfunctions, such as when it is
not generating power or its voltage is low.
Length when new
Effective brush length
28
10~11mm
5 mm