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What
makes e-bikes
go?
How
Brushless
Motors work and
their
Benefits
Brushless
DC (BLDC)
systems combine
the positive
attributes of
AC and DC
systems. As a
result, their
usage in new
applications
continues to
grow.
Permanent
magnet (PM)
designs are the
most common
brush type DC
motors sold on
the market
today. They
employ
permanent
magnets on the
stator which in
turn react with
wound
electromagnets
on the rotor.
These DC motors
incorporate
carbon brushes
which slide
over and
transmit
electrical
power to the
commutator
which in turn
switches power
to the rotor
windings to
provide smooth
rotation.
Benefits of
this design
include a
linear
speed-torque
performance
which is easily
controlled, a
small motor
diameter,
predictable
torque
throughout a
wide speed
range, high
starting
torque, and
minimal
wiring.
Cut-away view
of a
conventional
permanent-magnet
DC motor
assembly
(left)
Cut-away view
of a brushless
DC motor
assembly
(right)
BLDC
motors also
address several
of the
pitfalls
of the DC Brush
motor, while
maintaining
the advantages
of permanent
magnet DC motor
performance.
BLDC motors are
similar to
permanent
magnet AC
synchronous
motors with a
magnetic rotor
and wound
stator
construction.
BLDC wound
stators can
rapidly
dissipate heat
to the housing
and environment
in contrast to
PM brush motors
which trap the
heat under a
non-conductive
air gap. This
results in
greater
efficiency and
power density
for the BLDC
design and
provides high
torque-to-inertia
ratios.
Some
common BLDC
advantages
include:
- Ability
to control
motors over
a wide range
of speeds
- Precise
speed
regulation
without
additional
cost
- Rapid
acceleration
and
deceleration
capability
- Starting
torque and
dynamic
response
equal to or
better than
conventional
DC drives
- Ability
to operate
several
brushless
drives from
a common DC
bus
- No
mechanical
wear or
conductive
brush dust
from brushes
Electronic
commutation in
brushless
drives
eliminates need
for brushes in
the motor, and
therefore all
associated
maintenance.
Brushless
drives use
hall-effect
sensors located
within the
motor to
determine the
rotor position
for proper
commutation and
determination
of which power
transistors to
turn ON to
obtain maximum
motor torque.
Since
commutation now
becomes
electrical,
only motor
bearings suffer
from mechanical
wear. BLDC
motors run at
higher speeds
than PM DC
motors because
the frictional
components of
mechanical
commutation do
not limit their
speed and
higher
efficiencies
can be achieved
at higher
speeds. BLDC
motors provide
more reliable
performance
since
environmental
issues such as
humidity or
elevation do
not play a part
in the now
non-existent
brushes, brush
film, voltage
drops, and
mechanical
wear. If
properly sized,
and properly
packaged, your
next BLDC motor
could handle
all your
electric
scooter needs
and last you a
lifetime.
Summary
Brushless
Motors
deliver...
-
Higher
speed
- Higher Torque
per size and
weight
- Higher
acceleration
due to lower
inertia
- No
RFI/EMI
- Lower
temperature
rise
Our
electric
bicycle
products all
use brushless
dc
motors.
36
Volt or 48 Volt
system?
Which is
better?
Assuming
that both units
are using the
same motor
capable of
attaining the
same travel
speed, it
becomes a
matter of
endurance of
the power
supply.
In a relatively
level area a
36V system is
sufficient to
provide both
the same speed
and nearly the
same travel
distance while
weighing less
than a 48V
system.
In
hilly areas,
however, the
batteries
discharge more
rapidly
dissipating the
stored
electrical
energy and
producing
heat. The
48V system is
more capable of
reaching the
top of climb
without
resorting to
pedal
assistance.
The higher
endurance of
the 48V system
also tends to
reduce the
added battery
weight
factor.
The recharge
time is
relatively the
same for both
systems.
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