There's a legend among powerchair users that motor brushes are a week link, requiring maintenance,
a component to closely watch. But, how valid is the concern, and how common are issues with motor brushes,
What is a Motor Brush?
A motor brush, as complex as some might imagine, is simply
the component that helps control current flow to the electromagnet of an electric motor - that is, a
small block via which current travels. Technically, the stationary brushes press against the spinning
contacts of the commutator, flipping the direction that the electrons are flowing at just the right moment
to create the motor's motion. In everyday terms, imagine a spinning globe, with a chalkboard eraser
on each side, controlling current, gently touching the surface as the globe spins - this is how a brush
works in relation to commutator contacts within a motor.
How do Motor Brushes Wear?|
As with erasers against a globe, placing a fixed object against a spinning
object creates wear - and motor brushes do wear. In practical use, however, brushes are a remarkably
dense carbon material, by far among the toughest materials within a motor, so wear is exceptionally controlled.
What's more, brushes are held against the contacts of the commentator by a spring, which optimizes pressure
against the brush as it wears over its life, so long-term reliability and consistency is intrinsic to
Now, "wear" is a very subjective term when related to motor brushes. In fact, "wear"
often improves a motor's performance in strategic ways. Going back to the spinning globe and erasers,
the rectangular erasers against the spinning globe do not ideally conform to the globe. However, imagine
holding the erasers on the spinning globe long enough that the erasers wore to conform to the globe's
surface - then contact is optimized. In this way, initial brush wear - or, break-in - is used by some
motor manufacturers to optimize motors in the production process - that is, new motors are run for several
hours to "set" the brushes. Further, most well-used powerchairs run quieter in the more-commonly traveled
forward direction than in reverse because the brushes wear optimally in the most traveled direction (in
a quiet setting, try driving your powerchair forward, then reverse, over some distance - the change in
pitch that you'll likely hear is the orientation of brush wear).
Do Powerchair Motor Brushes
Need Servicing and Replacement?
Quality motors in the powerchair industry contain brushes rated for
5,000 hours of use. To put such a lifespan in perspective, a very active, full-time powerchair user
may have a maximum of 2.5 hours of literal motor run time each day. The practical lifespan of a power
chair's motor brushes, then, is over five years - and, for less-active users, brush lifespan equates
even longer. In this way most brushes serve the user for the entire life of the powerchair.
Do You Know When a Brush Needs Replacing?
As some owner's manuals state, it is possible to inspect
motor brushes by unscrewing the retention caps on the motor, and removing the brushes. Visually, a brush
that needs replacement will show a dramatically uneven face, with discoloration in one spot, and, more
likely, chipping on an edge.
It's important to note, however, that it's usually not ideal to
remove and reinstall brushes on a powerchair without good reason. If one or more brushes need replacement
- which is extraordinarily rare on most quality powerchairs - the symptoms in operation are unmistakable,
including loss of power and the inability to drive in a straight line. Sure, after five years or so,
certainly brushes may need replacing, but inspecting and replacing them within the initial three or four
years of use is usually unnecessary if operation remains without fault. (And, again, a properly set
brushes are optimal, so removing them without good cause may alter the chair's performance or increase
the sound level.)
Should I Worry About Motor Brushes?
Powerchairs are complex products, with
components that certainly have modes of failure - from flat tires to batteries that won't hold a charge,
and so on. Yet, in the world of powerchairs, motor brushes are among the most reliable durable, simple
parts of a motor, designed to last the life of most powerchairs, warranting virtually no service, with
an extremely low likelihood of an outright failure - that is, most users never have to service or replace
a motor brush.
As the pop-culture saying goes, we may each have 99 problems, but motor brushes
likely ain't one.
Published 11/05, Copyright 2005, WheelchairJunkie.com