AB PF525 strange behaviour

GaryS said:

It looks to me like that the drive is overloaded
Extend both the Accel and Decel time will help
there may be a parameter in the drive to limit the motor current during the acceleration time. this will automatically extend the accel time install as breaking resister will help with the overvoltage fault.
Up sizing the vfd will help with both

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What happens if a start command is sent during the decel time?

alexbeatle said:

These are my motors - VEM3546

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PLC Pie Guy said:

It is inverter rated. ...

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Just a side note... not related to the original issue I don't think.


NO it is not "inverter rated". Read it again, it says "Inverter READY". Not the same thing, it's tricksy marketing in my opinion and my experience. I have had a LOT of trouble with those low cost "inverter ready" motors on VFDs; massive failures in the field within months of installing them, all due to first-turn insulation damage. In the first one it was blamed on the installer having cut off the shield grounds on one end (inexperienced with shielded power cables), but I put a scope on them and never saw a spike over 1400V. Yet they lost 40 out of 80 motors within the first 3 months, more later. Baldor eventually admitted they were "bad motors" and replaced them. On the second project for the same contractor, they were fastidious about the installation and followed all installation guidelines, still lost dozens of those same motors, again eventually Baldor admitted they were bad and replaced them with actual "Inverter Duty" motors. Just yesterday another consulting engineer called me to ask if I would get engaged in a lawsuit on yet another similar installation, same motors, same problems (different VFDs but designed and installed correctly).

Unfortunately there is no official definition of what Inverter Duty actually means, although MOST people use NEMA MG-1 Part 31 as a reference. Those "inverter ready" motors do NOT follow those design recommendations, in fact there is nothing from Baldor explaining just what that means.

As to your question of what happens if you restart the VFD while it is in Decel
the VFD will just accelerate from where it is up the set point. The same as if you hit the stop command while the VFD is in acieration.
VFD's are smarter than you think but you do need to give them the correct information to work with.
One thing just make sure that the motor FLA in VFD in the same as the Motor FLA.
I have seen to many that think they can push the limits by setting the VFD amps to a higher value then the motor, bad things happen then.

GaryS said:

As to your question of what happens if you restart the VFD while it is in Decel
the VFD will just accelerate from where it is up the set point. The same as if you hit the stop command while the VFD is in acieration.
VFD's are smarter than you think but you do need to give them the correct information to work with.
One thing just make sure that the motor FLA in VFD in the same as the Motor FLA.
I have seen to many that think they can push the limits by setting the VFD amps to a higher value then the motor, bad things happen then.

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The FLA is correct. See attached.
Looking more into it thinking of
-updating the current limiting. as it's currently set to 3.5, whilst the manual says 1.1*FLA for normal duty=1.65A
-changing all motors' stop mode to Ramp, CF and installing the brake resistors (throwing money at it)

What is the motor name plated FLA? that's what you go by
the VFD should be set at motor name plate * 1.5
if want to push it then motor name plate FLA * 1.8 this is the max
in no case should you exceed the VFD name plate FLA
a braking resistor will only help with an overhauling load (Regen)
if you at faulting on an under voltage while accelerating then the load is to much for the VFD - Motor combination. I knw that would be to throw money at it but sometimes that's the only fix. a longer acceleration time may get you past the problem if you can live with the longer time.
also if you don't need the speed increase the gear ratio (motor to conveyor) more reduction = more torque on the final load ( conveyor)

GaryS said:

What is the motor name plated FLA? that's what you go by

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As per VEM3546 the FLA is 1.5A@460V

GaryS said:

the VFD should be set at motor name plate * 1.5
if want to push it then motor name plate FLA * 1.8 this is the max
in no case should you exceed the VFD name plate FLA

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Are you talking about current limiting setting - A484?

GaryS said:

a braking resistor will only help with an overhauling load (Regen)
if you at faulting on an under voltage while accelerating then the load is to much for the VFD - Motor combination. I knw that would be to throw money at it but sometimes that's the only fix. a longer acceleration time may get you past the problem if you can live with the longer time.
also if you don't need the speed increase the gear ratio (motor to conveyor) more reduction = more torque on the final load ( conveyor)

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Accel time = 5s. Seems like long already

1.5 * 1.5 = 2.25 that's the VFD calls for but it the load is continuous you will overheat the motor even more so at slower speeds. Remember lower motor speed means less air over the motor more heat.

GaryS said:

1.5 * 1.5 = 2.25 that's the VFD calls for but it the load is continuous you will overheat the motor even more so at slower speeds. Remember lower motor speed means less air over the motor more heat.

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Why should the A34 Motor NP FLA = 2.25 when the nameplate reads 1.5@460V?

I don't know where you are the FLA of 2.25 from the link you show clearly shows FLA of 1.25 @ 460V. That would be correct for 1hp motor 2.25 would be almost a 2hp motor
the VFD manual says for the FLA = Motor LFLA * 1.5 that = 2.25
Most VFD's have you enter only the motor name plate FLA
If you are having overload problems adjusting the settings in VFD will not solve your problems. you need to upgrade the drive system

GaryS said:

What is the motor name plated FLA? that's what you go by
the VFD should be set at motor name plate * 1.5
if want to push it then motor name plate FLA * 1.8 this is the max
in no case should you exceed the VFD name plate FLA ...

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I think this may have caused some confusion with the OL setting. Current Limit in a VFD is not the same as Over Load.

MOTOR OVERLOAD protection should be set at the motor FLA.

Current Limit can be set higher. But the VFD has its own limits and in a PF525, it is 150% of the VFD rating for 60 seconds, 180% for 3 seconds. The mention of 110% for 60 seconds for "Normal Duty" only applies to drives that are sized as such, and that is only done at 25 and 30HP drives (@ 480V). In the PF525, when you program a Current Limit setting, the drive will override your Accel setting to keep the current down, so you have to be aware of that.

There is an internal "Hardware Current trip" that is hard coded to protect the transistors at 180% in no more than 3 seconds, or 300% instantaneously, that is NOT programmable. You CAN set the motor OL to be 200%, but don't expect it to deliver that for more than about 1 second.

In addition there is Stall fault and a thermal limit to the VFD, so if you attempt to hang out in Current Limit for too long, you will trip it on Stall Fault or overheat the drive and trip it on Over Temperature, then have to wait for it to cool down. Doing this repeatedly is one way to kill a VFD as well.

jraef said:

I think this may have caused some confusion with the OL setting. Current Limit in a VFD is not the same as Over Load.

MOTOR OVERLOAD protection should be set at the motor FLA.

Current Limit can be set higher. But the VFD has its own limits and in a PF525, it is 150% of the VFD rating for 60 seconds, 180% for 3 seconds. The mention of 110% for 60 seconds for "Normal Duty" only applies to drives that are sized as such, and that is only done at 25 and 30HP drives (@ 480V). In the PF525, when you program a Current Limit setting, the drive will override your Accel setting to keep the current down, so you have to be aware of that.

There is an internal "Hardware Current trip" that is hard coded to protect the transistors at 180% in no more than 3 seconds, or 300% instantaneously, that is NOT programmable. You CAN set the motor OL to be 200%, but don't expect it to deliver that for more than about 1 second.

In addition there is Stall fault and a thermal limit to the VFD, so if you attempt to hang out in Current Limit for too long, you will trip it on Stall Fault or overheat the drive and trip it on Over Temperature, then have to wait for it to cool down. Doing this repeatedly is one way to kill a VFD as well.

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Setup the A484 Current Limit 1 =2.2A, but got a F5 - 3.41A, 822V, Fault Freq = 0Hz.
Does it mean that the current 3.41A is coming from somewhere else?

Any chance the program could be stopping the drive and restarting it very quickly after due to a bug or just by chance? Like a scan or so later, or anytime before the motor has completely stopped? I've seen this happen before, usually causes the overvoltage fault due to regen. Enabling flying start doesn't always solve it, but setting stop mode to ramp or just fixing the programming issue does.

F005 is a fault code "Overvoltage"
"Monitor the AC line for high line voltage or transient conditions. Bus overvoltage can also be caused by motor regeneration. Extend the decel time
or install dynamic brake option."

If you are reading 3.41A at the time of the fault then your drive system is way undersized for the load. You can try to deal with it with a Breaking Resistor depending on the breaking duty cycle it may not solve the problem
that is over 200% of the rated load you can only do that about 1% of the time before the resister or drive burn up.
It looks to me like you have exceeded the load limit of your conveyor is an upgrade. I would go at lest to a 3 HP VFD and motor and still install the break resister to dump the regen load.
it's not cheap but it will solve the problem.
Good Luck

Hi there,


Just a couple things that I noticed in your fault history outside of the voltage thing.



>F04 always happens when you power down the drive, so this is likely why you see that fault in the list.


>as for the network faults, one question I have; are you using shielded comms cables and power cables? That can make a huge difference if you are experiencing comms faults in the drive.


>Flying start is really only intended for fan type applications where the motor may be spinning backwards, at the time the start command is given.


>A static autotuning of the drive would do a lot of benefits in motor performance.


>Decel time and Stop mode (as previously stated) are different things, if the drive is commanded to slow down, then decel time comes into play, but yes, if you are in ramp to stop mode, then decel time also plays into this as well.


>If you are going to adjust accel/decel times, I suggest adding a couple seconds, as too quick an accel time at start, or decel at stop can send a lot of energy through the drive to either get it going or try to stop it. Think of the energy it takes for your car to accelerate suddenly version gradually, and on the reverse side, think of how much energy has to go into stopping suddenly, versus a gradual stopping.


Hope some of this helps.

Drives_Guy_NS said:

Hi there,


Just a couple things that I noticed in your fault history outside of the voltage thing.



>F04 always happens when you power down the drive, so this is likely why you see that fault in the list.


>as for the network faults, one question I have; are you using shielded comms cables and power cables? That can make a huge difference if you are experiencing comms faults in the drive.

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Cables aren't shielded. I'd prefer they would be. But all of the VFD's are inside the MCP and the Ethernet are running only there - min 10cm away from the VFD power\motor cables.

Drives_Guy_NS said:

>Flying start is really only intended for fan type applications where the motor may be spinning backwards, at the time the start command is given.

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Noted. Disabled since not the application and hasn't helped to solve anyways.

Drives_Guy_NS said:

>A static autotuning of the drive would do a lot of benefits in motor performance.

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Will perform. Fro the Manual it only sets the A496 value. Is it safe to say that I can do it on one motor and set the same value for all of the others, since all motors are the same?

Drives_Guy_NS said:

>Decel time and Stop mode (as previously stated) are different things, if the drive is commanded to slow down, then decel time comes into play, but yes, if you are in ramp to stop mode, then decel time also plays into this as well.

>If you are going to adjust accel/decel times, I suggest adding a couple seconds, as too quick an accel time at start, or decel at stop can send a lot of energy through the drive to either get it going or try to stop it. Think of the energy it takes for your car to accelerate suddenly version gradually, and on the reverse side, think of how much energy has to go into stopping suddenly, versus a gradual stopping.

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Changed the StopMode=Ramp,CF with the decel 2-4s. Will observe.