PowerFlex error F7

DaveZR2 · Jun 6, 2016

We're getting the occassional F7 (Motor Overload). error on a PowerFlex 40 drive.

I checked the P033 setting and found that it was set for 9.3 amps. So, while the system was running I watched d003 (Output Current). It stayed between 9.8 amps and 10.8 amps the entire time that I watched it, and up until the F007 fault occurred (after about 8 minutes of run time).

This doesn't make sense to me, because according the manual: "The drive will fault on an F7 Motor Overload if the value of this parameter is exceeded by 150% for 60 seconds."

150% of 9.3 amps is 13.95amps, which I did not observe at any time while the system was running. So, to me, the fault should not be occurring at all. Any ideas?

ASF · Jun 6, 2016

There is an exponential (or at least closely approximating exponential) trip curve built into every device. At 150%, it will trip in 60 seconds. At 200%, probably around 20 seconds. At 300%, maybe 3-4 seconds. When you're only running at 105-110%, it will run for a good little while, but will still eventually trip.

I don't have the PF40 manuals handy, but if you look them up you'll probably find a chart that shows an 8-10 minute trip time at 105-110%

DaveZR2 · Jun 6, 2016

Interesting. Makes sense.

For the life of me I can't find the chart in any documentation online. If anyone happens to know where it might be I'd love to see it!

Thanks for the reply!

Cow · Jun 6, 2016

Is there a reason you're more concerned with how the drive handles the overload instead of finding out why the motor is overloaded in the first place?

jraef · Jun 6, 2016

Yeah, no kidding. It's as if you are questioning the number of seat cushions in the lifeboats of the Titanic.

Ken Roach · Jun 7, 2016

I am not an expert, but I'll contribute what I do know.

Remember that overload protection is generally meant to protect against overtemperature damage of the motor, so the drive tries to model the thermal behavior of a typical motor.

Check out the overload section of this technical data table:

http://www.ab.com/support/abdrives/powerflex40/specifications.html

It describes "intermittent overload" ability to handle 150% of full load amps for up to 60 seconds.

But it also describes "Electronic Motor Overload Protection", in which the drive tries to emulate a Class 10 motor overload relay of the classic thermal style.

Google "NEMA 10 overload curve" and you'll see the near-exponential curve that ASF described.

Because your drive is going consistently above the nominal current capacity of the drive (is it an 8A unit or a 12A unit ?), the drive is using that Class 10 curve to model the temperature of the motor and trips because it has calculated that the motor has become too hot over time.

willxfmr · Jun 7, 2016

Ken Roach said:
I am not an expert, but I'll contribute what I do know.

And he then proceeds to provide a detailed explanation complete with reference to supporting documentation.....

Not sure why, but that made me chuckle.

redbarron55 · Jun 7, 2016

Lie if you have to.
Tell the drive the FLA is higher than nameplate.
Not the best idea, but it will work until the motor burns up.
Of course many believe it is OK to run in the service factor range (I don't)
so if the motor is rated 115% service factor and the FLA is 9.3 X 115% = 10.695 and maybe you are OK, maybe not.

DaveZR2 · Jun 7, 2016

jraef said:
Yeah, no kidding. It's as if you are questioning the number of seat cushions in the lifeboats of the Titanic.

Thanks dude, real helpful.

DaveZR2 · Jun 7, 2016

Cow said:
Is there a reason you're more concerned with how the drive handles the overload instead of finding out why the motor is overloaded in the first place?

The drive isn't functioning the way it's described in the manual. The drive is what's telling me that the motor is overloaded so that's where I went first.

DaveZR2 · Jun 7, 2016

Ken Roach said:
I am not an expert, but I'll contribute what I do know.

Remember that overload protection is generally meant to protect against overtemperature damage of the motor, so the drive tries to model the thermal behavior of a typical motor.

Check out the overload section of this technical data table:

http://www.ab.com/support/abdrives/powerflex40/specifications.html

It describes "intermittent overload" ability to handle 150% of full load amps for up to 60 seconds.

But it also describes "Electronic Motor Overload Protection", in which the drive tries to emulate a Class 10 motor overload relay of the classic thermal style.

Google "NEMA 10 overload curve" and you'll see the near-exponential curve that ASF described.

Because your drive is going consistently above the nominal current capacity of the drive (is it an 8A unit or a 12A unit ?), the drive is using that Class 10 curve to model the temperature of the motor and trips because it has calculated that the motor has become too hot over time.

Perfect, exactly what I was looking for. Thanks for taking the time to respond. It's a 12A unit.

Dravik · Jun 7, 2016

It also derates that curve by default if you are running below 20hz, I don't remember the parameter for that offhand but you can change it(and should if your motor is rated to run below 20hz)

PowerFlex error F7

DaveZR2

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