DC Mentor II 6M7.5

[mluqman]

Mentor II Alarm Fb Trip

Hi, I have problem on our mentor ii when it comes to speed 150rpm above (Speed command at CNC Lathe) intermittently got alarm Fb Trip, Maybe anybody could help me with advice what to do. FYI, the motor use encoder for detect the speed/rpm.

 

[GaryS]

As few things that I see in this
Is the motor running in the expended speed range 850-2600 RPM ?
This is also called field weakening
You stated that the field current is 700ma that way to low for that motor. I would expect it to be no lower than 3.4 amps. The motor name plate states 17.6 / 3.4 that would be 17.6 amps from 0 to 850 RPM and them field weakening would kick in from 850 to 2600 RPM at the 2600 RPM the field current should be 3.5 amps.
As side note when the motor is operating below base speed (850) it’s operating in variable torque mode
And when it’s operating in the extender speed range (850- 2600) it operating in constant HP mode.
If as you say the field current is holding study at 700ma then there is definitely something wrong someplace the field supply it should not go that low.
Measure the motor RPM’s while it running, if the field is really 700ms then I would expect the motor to be running at well over 4000 RPM’s that would be dangerous for the motor and any personnel in the area. I have seen DC motors running over 3600 RPM arc flash over the commutator and burn up just from the high rpm’s. Also with speed’s over 4000 RPM the motor can blow up from the centrifugal force. I would expect the motor to be ok at 4000 RPM but over 3600 RPM would be considered dangerous. Now I don’t mean to scare anybody but I don’t want see anybody get hurt working on something they don’t fully understand.
Motor speed on a wound field motor is controlled by 2 things the load on the armature and the field current If there is no load on the motor and no field or too low a field current the motor would continue to accelerate until it blows up sending pieces all over and it happens quick.
I have seen the results of both of these.
You need to look at all of that carefully.

Another thing that I see is that you have an 1024 PPR encoder. I would have to assume that it is there to provide a more precise speed regulation but if the encoder signal failed or was not providing the full signal back how would the drive react. Unless there are precautions set up in the drive It could just keep trying to increase the motor speed to get the speed feedback (Encoder) to equal the set point. The way the drive can do that is to increase the armature voltage to the drive limit and keep lowering the field current to the drive field minimum. I would think there would be a limit as to the lowest current it can supply. And it may be the 700 ma you are seeing, but in this case it clearly too low to safely operate this motor Remember the lowest field for safe operation is 3.4 `amps below that would be considered unsafe
There are other things to look at as well but this is a place to start
This is a problem that should be addressed, identified and fixed quickly

 

[drbitboy]

Necro-thread alert. FYI: the 700ma case was almost a decade ago; the post yesterday was a new thread.

 

[jdbrandt]

Dear team,

Ihave faced the same matter in one of my MENTOR 1 DC drive. it shows 118 error (Field loss) Checked the motor and the field current as well.
i could not find anything unusaul that may drive to this error. Since my drive is old about 15 years i though that this might be an error inside the drive.
What i did was removed the field loss tripping ( #187 put to 1) from the drive and after that my DC motor is working properly.
Also i got this error while i am trying to run my motor on inch function,means in very slow speed.

What i need to know is will this may cause any harm to my DC motor? At the time i dont have any spare drive for replace in my factory. Please advice me asap guys.

Running a shunt-wound DC motor with no field current is not the recommended mode.
The posters seem poised to disable the field loss circuitry.
If having a field were NOT important, why would there be an alarm for it.
An education in shunt-wound DC motors is called for here.

 

[Gene Bond]

Hi, I have problem on our mentor ii when it comes to speed 150rpm above (Speed command at CNC Lathe) intermittently got alarm Fb Trip, Maybe anybody could help me with advice what to do. FYI, the motor use encoder for detect the speed/rpm.

A feedback trip is indicating that the encoder feedback is not seen reliably. Either the encoder, cable, power supply to the encoder, or drive is bad. Start troubleshooting all the connections, cable and encoder.

 

[mluqman]

As few things that I see in this
Is the motor running in the expended speed range 850-2600 RPM ?
This is also called field weakening
You stated that the field current is 700ma that way to low for that motor. I would expect it to be no lower than 3.4 amps. The motor name plate states 17.6 / 3.4 that would be 17.6 amps from 0 to 850 RPM and them field weakening would kick in from 850 to 2600 RPM at the 2600 RPM the field current should be 3.5 amps.
As side note when the motor is operating below base speed (850) it’s operating in variable torque mode
And when it’s operating in the extender speed range (850- 2600) it operating in constant HP mode.
If as you say the field current is holding study at 700ma then there is definitely something wrong someplace the field supply it should not go that low.
Measure the motor RPM’s while it running, if the field is really 700ms then I would expect the motor to be running at well over 4000 RPM’s that would be dangerous for the motor and any personnel in the area. I have seen DC motors running over 3600 RPM arc flash over the commutator and burn up just from the high rpm’s. Also with speed’s over 4000 RPM the motor can blow up from the centrifugal force. I would expect the motor to be ok at 4000 RPM but over 3600 RPM would be considered dangerous. Now I don’t mean to scare anybody but I don’t want see anybody get hurt working on something they don’t fully understand.
Motor speed on a wound field motor is controlled by 2 things the load on the armature and the field current If there is no load on the motor and no field or too low a field current the motor would continue to accelerate until it blows up sending pieces all over and it happens quick.
I have seen the results of both of these.
You need to look at all of that carefully.

Another thing that I see is that you have an 1024 PPR encoder. I would have to assume that it is there to provide a more precise speed regulation but if the encoder signal failed or was not providing the full signal back how would the drive react. Unless there are precautions set up in the drive It could just keep trying to increase the motor speed to get the speed feedback (Encoder) to equal the set point. The way the drive can do that is to increase the armature voltage to the drive limit and keep lowering the field current to the drive field minimum. I would think there would be a limit as to the lowest current it can supply. And it may be the 700 ma you are seeing, but in this case it clearly too low to safely operate this motor Remember the lowest field for safe operation is 3.4 `amps below that would be considered unsafe
There are other things to look at as well but this is a place to start
This is a problem that should be addressed, identified and fixed quickly

Thank you for replying my question, i will check the motor rpm and field amp