DC Motor brush life
DC Motor brush life
(OP)
Why do some dc motor manufacturers say you shouldn't run a motor at a voltage lower that rated? These are small motors, less that 2" in diameter.
Example:
12 volt motor at 6 volts.
They state that they need to install different brushes.
Example:
12 volt motor at 6 volts.
They state that they need to install different brushes.





RE: DC Motor brush life
There is formulas for brush grades and adjustments to meet your applications as suggested from the manufacture.
Kind Regards
motorhead
RE: DC Motor brush life
RE: DC Motor brush life
Carbon brush manufacturers add metals such as copper to reduce the resistance and volt drop in these applications. You can sometimes see this on the brush face.
RE: DC Motor brush life
RE: DC Motor brush life
RE: DC Motor brush life
Just out of curiousity, where did you come up with the notion that :
"Suggestion: If the motor terminal voltage decreases,
the motor current through the brushes increases,
since HP is a constant."
Didn't see anything in Clyde's original post that stated any facts to support your statement.... Nothing about application or operation that would lead one to conclude that the motor was being operated at constant HP.
Hmmmmmm.
RE: DC Motor brush life
For example, for operation at 5A/cm2:
A typical electrographitic brush (i.e. no additives) will have a total contact drop for both brushes added of approx 2V.
A typical soft graphite will have a total drop of around 1.5V.
A metal-graphite grade may have a total drop of 0.5V or less.
- hence the metal-graphite grade is preferred.
Note these are CONTACT drops i.e. the voltage between the brush contact surface and the commutator, this doesn't include any voltage drop along the brush due to the bulk resistance of the material.
RE: DC Motor brush life
http://www.reliance.com/mtr/cmdcbrmn.htm
DC Motor Brush Life
http://www.reliance.com/prodserv/motgen/c7090/
RE: DC Motor brush life
JB:
Just out of curiousity, where did you come up with the notion that :
"Suggestion: If the motor terminal voltage decreases,
the motor current through the brushes increases,
since HP is a constant."
///Motor load is often considered with a constant shaft load (HP). Since HP~Watts=ExI, then the only way to preserve the relationship for E decreasing is by I increasing.\\\
Didn't see anything in Clyde's original post that stated any facts to support your statement.... Nothing about application or operation that would lead one to conclude that the motor was being operated at constant HP.
///This is a very common and tacitly implied assumption. The electrical software imputers would be very puzzled by the level of this kind of comment.\\\
Hmmmmmm.
///Shape up a little bit.\\\
RE: DC Motor brush life
So as not to obfuscate the Clyde38's original post any further.... (discussion of constant HP operation of dc shunt machines has nothing to do with his original post)
I have replied to your comments in a new thread:
DC Motors : Constant HP vs Constant Torque
Thread237-77879