Hello all. We have 10 identical br

[bill1055]

Hello all. We have 10 identical brake motors in our shop for bearing change and clean ups. All the windings are factory, all surge test good etc. When we run test motors here, we use a soft start system. The system starts at 200v the ramps to 480v in aprox 10 seconds. When we did our final run test, seven of the motors started smooth and ran "normal" as the voltage ramped up, nothing unusual. The other three motors struggled, ran like they were fighting the soft start. When full voltage was reached, it took off, running normal. These units are run on VFDs for the customers application. The three units, when they took off had same no load current as the other units. The three units start fine full voltage. Just wondering, what could be the reason for the three units strange opeation?

 

[theode]

Brakes may need adjusting.If set too tight a slightly higher voltage will be needed to operate.Different rates of wear and tear.
Although most operate at the 200 volt start up,the other three need the higher voltage to get away.

 

[jraef]

I suggest separating the brake circuit from the motor winding power. If you are using VFDs, it needs to be that way no matter what.


"You measure the size of the accomplishment by the obstacles you had to overcome to reach your goals" -- Booker T. Washington

 

[lukin1977]

brake on those 3 motors aren´t fully releasing

 

[waross]

You have provided no information as to the design of the brakes.
Some more than one type of electric brake experiences an increased air gap as the friction material wears. Some are adjustable, some aren't adjustable.
As the air gap icreases the minimum voltage needed to release the brake increases. At full voltage, most designs will still release properly despite maximum wear.
However, if you are applying soft start voltage to the motor, it is probable that the brakes with the most wear do not release fully until near the end of the starting ramp.
Try arranging the wiring motors so that full voltage is applied to the brake while the Soft Start ramps up the motor voltage.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[bill1055]

The brakes are powered by a separate supply, we release the brake, check the adjustment, air gap and all before we run the motors.

 

[waross]

You may want to check the voltage at the brake coil as the motor starts.
Possibly the three brakes were wired incorrectly.
If the brakes may be released manually, try a start with the brakes released.


Bill
--------------------
"Why not the best?"
Jimmy Carter