Is it possible to monitor and estimate where a brushed DC motor is in it's life cycle by monitoring how much power it's consuming? For instances would a worn DC motor draw more amps toward the end of it's life than it would in the beginning of it's use? I'm trying to figure out ways to electronically sense when a motor may be approaching the end of it's life.
-RG
ryangrg:
Is it possible to monitor and estimate where a brushed DC motor is in it's life cycle by monitoring how much power it's consuming? For instances would a worn DC motor draw more amps toward the end of it's life than it would in the beginning of it's use? I'm trying to figure out ways to electronically sense when a motor may be approaching the end of it's life.-RG
If your motor has replaceable brushes, then the brushes have no relation to the life of the motor. I once had a 100 year old brushed motor that ran just fine, but developed an internal short to the cast housing.
Talk to a motor repair shop. They will tell you the motor current goes down as the brushes age because the area in contact with the armature is reduced. Another way the current is reduced is the bare copper of the armature will become glazed over with dirt and carbon from brush wear and arcing.
The old tired motor can be refurbished by turning the armature on a lathe to clean up the copper and make it as smooth as when new. Wit new brushes and holders, the motor is as good as new.
But to give you a specific answer, the current will go down with age and this is why the motor looses torque.
Paul
Paul_KD7HB:
But to give you a specific answer, the current will go down with age and this is why the motor looses torque.Paul
That would mean it gets more efficient... Current depends on torque, may increase if the bearings are
seizing, will be higher at start up from cold due to more friction, but won't tell you anything about the
brush wear. Typical motor's no-load current drops 10's of percent during the first few minutes of operation
as the bearings and brushes warm up.
Full load current is much larger than this though.
If the permanent magnets change with age, losing magnetism, then the motor will want to run faster
for a given voltage, causing the load and friction torques to increase and again the current will increase.
As the armature windings heat up their resistance increases, reducing the motors speed a little, and
thus this can also reduce the current. (If a motor is being pushed to the limit, the resistance is a more
significant factor as more volts are dropped across it).
As the permanent magnets warm up their field strength may change significantly, depending on the type
of magnetic material - this could speed up or slow down the motor and affect the current.
So basically current can be affected by many things, including aging of some of the motor components,
but also temperature and supply voltage too.