[ausev] experience no commutation

[JohnFM]

I assume your referencing this sentence? "I was just pointing out
induction AC motors are better suited for high speed
operation (over 2500 rpm) than a brushed DC motor and experience no
commutation,...".

Commutators are a inherent part of brushed DC motors commonly found in
EVs, not AC. Brian's link to Wikipedia on Brushed DC motors gives good
info on what the Commutator does. They require precision of many
parts, which can give problems under variable loads and are prone to
wear.
http://en.wikipedia.org/wiki/Brushed_DC_electric_motor

"When the armature becomes horizontally aligned, the commutator
reverses the direction of current through the coil, reversing the
magnetic field. The process then repeats" ...and turns the shaft

In regards to the RPM, The typical AC induction motor does not have
internal losses comparable to Brushed DC, it has no brushes (nor does
a pricey brushless DC). As you increase RPM in one of these motors,
you won't experience nearly the same friction losses found in a
brushed DC. This greatly limits the maximum rpm of a brushed DC motor.
Many of you know "terminal velocity" in regards to a free falling
object? This friction would causes a "terminal speed" of a motor.
That's why I stated that AC is better suited for higher RPM.

Regarding the noise you hear, Imperfect contact on these brushes can
cause electronic noise and other imperfections. Higher RPMs could
cause this. The sound you hear could be the spring trying to engage
more brushes or improve contact points.

Hope that helps



On Fri, Dec 19, 2008 at 9:05 AM, Jim Watson <osious at gmail.com> wrote:
> What does it mean to say that AC motors experience no commutation over 2500
> rpm? Is a commutator a device that kicks in over a certain rpm in order to
> produce higher rpms. I have heard in some motors, when they are
> accelerating, a click, and the motor keeps accelerating until it tops out at
> design voltage or speed. I have also taken some motors apart that have this
> thing on the armature that looks like it is the culprit that makes that
> click sound. It has a spring that holds it off the contact points until the
> armature is spinning fast enough to make it engage that is when you hear the
> click. What is this for? It sounds a bit like the train motor config to me
> only way simpler. By the way the explanation of the train engine was
> EXTREMELY fascinating. I have always wondered how the hell that worked. Some
> day maybe we can make an 18 wheeler,.... (when batteries catch up)
>
> Jim
>
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