# Power Flex 40 fault



## MDShunk

Undocumented in the PF40 manual, but I have also seen F5's (DC bus overvoltage) in cases where the cable between the drive and the motor was long. A load reactor fixes that. Even if the situation worked for a long time, and it just started happening, the addition of the load reactor cures it.

I have also seen cable or conductors that meg bad (pinholes) that will cause F5, and motors that have water infiltration cause an F5.

I have actually never seen an F5 because of an overhauling load or AC line conditions, as Rockwell suggests. 

In every case that I've observed an F5, it was never while the motor was idle or while the motor was running. It was always on startup. That's what makes me look for things that will "suck up a lot of power" on startup and make the DC bus spike to try to keep up. 

Oh.... I've seen parameters spontaneously get "changed". Either by poltergeists or by unknowing service people. The "cure" is to get a HIM module and cable, do a "HIM copycat" of a good drive that does similar duty, and copy that into the problem drive. It's a fool's errand sometimes to weed through all the parameters and try to decode what might be wrong. The HIM copycat makes that easy.


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## JRaef

What MDShunk is describing has to do with excess cable capacitance. The cable acts like a capacitor and the charging current to feed that cap, when you first turn it on, is too fast for the drive and it either falsely trips on short circuit or, if it has a slightly slower rate-of-rise, becomes a high ripple dip on the DC bus. Thats why the load reactor fixes it, the reactor adds an inductive time constant to the circuit that slows down the rate-of-rise time. Doing this intermittantly often is the result of water in the conduit, where the water acts as the electrolyte. But if the conduit is dry or there is not enough water in it, you don't have the problem. 

Excess DC bus ripple causes this too, which can be caused by an incoming phase loss or severe imbalance, sometimes by failing capacitors when the drive is old or was bought off of FleaBay and was unpowered for years. But if it's failing caps, it usually doesn't go away like that, it's more consistent. You might have a loose connection somewhere which, under vibration, creates a high resistance connection on an incoming phase.


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## MDShunk

I know you said this only happens a couple times a month, but for completeness sake I'll say check the drive's line side fuses. This is NOT your problem, but it may be someone else's problem searching the threads one day. These drives can be powered with single phase, and if the fuse that's blown is on the phase that is not required when powering the drive on single phase, the drive will often still be lit up and appear to be functional.

On a related note, when a "disposable" drive like a PF 4 or 40 blows a line side fuse, there's a very high chance that the drive has catastrophically failed and that's what took out the fuse. I cringe when I find a drive fuse blown, because that normally means I'm replacing a drive too.


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## JRaef

MDShunk said:


> I know you said this only happens a couple times a month, but for completeness sake I'll say check the drive's line side fuses. This is NOT your problem, but it may be someone else's problem searching the threads one day. These drives can be powered with single phase, and if the fuse that's blown is on the phase that is not required when powering the drive on single phase, the drive will often still be lit up and appear to be functional.
> 
> On a related note, when a "disposable" drive like a PF 4 or 40 blows a line side fuse, there's a very high chance that the drive has catastrophically failed and that's what took out the fuse. I cringe when I find a drive fuse blown, because that normally means I'm replacing a drive too.


Good point. The PF4 family uses a single set of caps in series, as opposed to caps in parallel, which means they need a 65% de-rate for a single phase supply. If the load is normally very light, ie 35% of full, you may run fine on a blown fuse, but the DC bus ripple gets too high when load increases.


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## GEORGE D

Thanks guys, awesome info, are the fuses easy to get to?


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## GEORGE D

Also, any ideas why they're faulting at same time? They share the same input power but I believe have different conduits to vfd's, but surely do share same panduit on output.


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## JRaef

GEORGE D said:


> Thanks guys, awesome info, are the fuses easy to get to?


The fuses would not be inside of the drive, they would be somewhere up stream. if the faults are common to two drives and happen at the same time, then it points to a problem with a common feed to the drives.


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## GEORGE D

Is there any chance that when an e-stop kills the power to the drive, then instantly reset, it could cause this type of fault? In other words, is there any situation on the control side that could cause/confuse the drive, possibly throw it off, that could cause this issue? I havent been back to site to check everything on the line side but still dont believe the problem is there.


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## GEORGE D

One other question I have is why when in 'coast' mode there is no regeneration? Is it because there isnt already dc voltage on the bus at that time, so no overvoltage occurs, because from what I understand there is generation as long as that motor is spinning, so in a situation where the motor was coasting at a high speed, wouldnt that have an affect on the dc bus if the vfd were activated/called upon?


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## GEORGE D

Nevermind that last part, I just read one of Jraef's old posts about the 2 conditions necessary to generate voltage with an AC motor. Good info btw, I guess thats why DC motors are used for certain generators, the permanent magnets.


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## JRaef

GEORGE D said:


> Is there any chance that when an e-stop kills the power to the drive, then instantly reset, it could cause this type of fault? In other words, is there any situation on the control side that could cause/confuse the drive, possibly throw it off, that could cause this issue? I havent been back to site to check everything on the line side but still dont believe the problem is there.


The only thing close that I have run into has to do with powering drives from portable generators. Sometimes when people use them, they get lazy at the end of the day and kill the fuel switch on the generator without opening the breaker. That means that the voltage AND frequency eventually collapse together, and that can screw up a LOT of electronics, not just VFDs. At really low frequencies, Switched Mode Power Supplies (which can be used to describe a VFD) can get really squirrelly and start pulsating the output, which gets through the filtering and can, in my observation, cause bits to flip on or off randomly. Some drives get their internal control power by tapping off the DC bus with a DC-DC power supply, some have an SMPS tapped off the AC terminals. Either way, the control power gets affected by the loss of frequency and voltage comng in. 

I haven't seen it with AB drives, but I have with many others so I'm sure it's possible. I have had older Toshiba drives end up with an unrecoverable fault due to this, had to replace them under warranty and although Tosh was good about providing replacements, I still had to go out in the field at my expense to fix it. That was how I discovered the cause, I watched an operator kill the fuel and witnessed all of my brand spanking new Tosh drives fault again!

_(I never told Toshiba, I have to admit...)_


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## MDShunk

If your e-stop arrangement actually kills the line side feed to the drive, that's not really a recommended idea in the first place. The "old" way was to break the enable signal, but now we use a DriveGuard module on the PF drive and break it's contacts. That module is pretty cheap. Just summarily dumping power to the drive is a, well... dumb idea. I know it's done every day, all across the globe, but it's still dumb.


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## GEORGE D

Thanks for advice guys, I believe I found the problem. It appears to have been a loose common wire that went to the disconnect auxiliary contacts for plc inputs. I was able to mimic the fault codes and HMI alarm report by purposely loosening the terminal screw. I REALLY hope this issue is finally put to rest, it's been ongoing for several months now. Btw, I had an analyser attached to the DC bus which recorded 790 at time of fault, I assume it was close enough to trigger fault being that 810 is drive's faulting point.


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## GEORGE D

Ok, nevermind, the damn things went out again last night. Checked logger and there was no spike on incoming power at that time. The dc bus did capture 815 at max on separate logger. Guys, I need some serious help here! I went out at 9 last night and got in at 6 this morn. I even changed input card on plc, in case that it's that somehow. Something tells me it's a software issue, because it seems to happen around the same time every time. It's happening while the motors are running. Thoughts?


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## MDShunk

Both drives still faulting out? 

Do both of these cables or sets of conductors leave in the same conduit? If so, have you megged them to each other? 

Are these VFD cable or THHN? If it's THHN, my mind is starting to lead me to similar issues I've had over the past years and it makes me want to suggest you prophylactically replace the THHN if that's not unreasonable. 

I know you said these motors are connected to gearboxes, and that regen can't really happen (I assume because the gear ratio is sufficient), but how is the motor and gearbox coupled? Is there a possibility that you have a rolled shaft key, loose set screw, or loose/worn coupling that lets that driven load "slip" when heavily loaded by the goons on night shift, quickly and intermittently causing the no-load DC bus spike?


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## GEORGE D

MDShunk said:


> Both drives still faulting out?
> 
> Do both of these cables or sets of conductors leave in the same conduit? If so, have you megged them to each other?
> 
> Are these VFD cable or THHN? If it's THHN, my mind is starting to lead me to similar issues I've had over the past years and it makes me want to suggest you prophylactically replace the THHN if that's not unreasonable.
> 
> I know you said these motors are connected to gearboxes, and that regen can't really happen (I assume because the gear ratio is sufficient), but how is the motor and gearbox coupled? Is there a possibility that you have a rolled shaft key, loose set screw, or loose/worn coupling that lets that driven load "slip" when heavily loaded by the goons on night shift, quickly and intermittently causing the no-load DC bus spike?


Well I know one of the motor&gearboxes have been replaced and actually upsized as well as the vfd. At that time it was determined by others that the motor bearings were bad, causing fault. I believe the other gearbox on other conveyor was also replaced. You make a great point about the mechanical possibility of causing fault, but want to say that unless the guys really f'd up on installing these motors. What are your thoughts about it possibly being a software issue? It happens every night around the same time, roughly a few hours into operation.


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## MDShunk

GEORGE D said:


> Well I know one of the motor&gearboxes have been replaced and actually upsized as well as the vfd. At that time it was determined by others that the motor bearings were bad, causing fault. I believe the other gearbox on other conveyor was also replaced. You make a great point about the mechanical possibility of causing fault, but want to say that unless the guys really f'd up on installing these motors. What are your thoughts about it possibly being a software issue? It happens every night around the same time, roughly a few hours into operation.


It's easy enough to flash the firmware in the drive. Give it a shot. Nothing to be lost by trying. 

You might also be suggesting that the PLC is dropping out the enable bit or run forward bit for a split second. If that's suspected, run a "trend" on that bit in the logic and go back and look if that happens. Also, if you enable flying restart, even if you drop out for a split second, the drive will handle it okay.


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## GEORGE D

MDShunk said:


> It's easy enough to flash the firmware in the drive. Give it a shot. Nothing to be lost by trying.
> 
> You might also be suggesting that the PLC is dropping out the enable bit or run forward bit for a split second. If that's suspected, run a "trend" on that bit in the logic and go back and look if that happens. Also, if you enable flying restart, even if you drop out for a split second, the drive will handle it okay.


How do you flash the firmware? I'm gonna look into the flying restart, that could definitely be a viable solution.Thanks


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## MDShunk

I could be talking out of my ass. I'm not sure if 40's are flashable, more I think about it. I've done plenty of 70's and 700's. If they are, it's just a little thing you download from Rockwell and connect by your favorite connection method.


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## JRaef

The PF40s (or all of the 4 class) are NOT field flashable.

I like the Flying Restart idea. Parameter A096, [Enable] will turn it on.

Another possibility is something else that turns on (or off) at the time that this happens, which has PFC capacitors with it or in some other way causes a large surge or spike. The caps may be interacting with the DC bus caps in these two drives and causing a DC bus ripple that the drive doesn't like. As to why that would not happen on other drives, it may be a proximity issue. There may be enough added impedance in the longer distances to other drives compared to this one. Had a similar thing happen with an air compressor once; kept getting weird unexplained trips that seemed random, then once when I was there watching it happen, I noticed the sound of the compressor from the other room around the corner. Disconnected the PFC caps and the problem went away.


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## GEORGE D

JRaef said:


> The PF40s (or all of the 4 class) are NOT field flashable.
> 
> I like the Flying Restart idea. Parameter A096, [Enable] will turn it on.
> 
> Another possibility is something else that turns on (or off) at the time that this happens, which has PFC capacitors with it or in some other way causes a large surge or spike. The caps may be interacting with the DC bus caps in these two drives and causing a DC bus ripple that the drive doesn't like. As to why that would not happen on other drives, it may be a proximity issue. There may be enough added impedance in the longer distances to other drives compared to this one. Had a similar thing happen with an air compressor once; kept getting weird unexplained trips that seemed random, then once when I was there watching it happen, I noticed the sound of the compressor from the other room around the corner. Disconnected the PFC caps and the problem went away.


If your referring to power factor caps this place doesn't have any. I'm going to meg the motor wires again. Btw, I'm on site right now so any one please feel free to chime in with suggestions.


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## JRaef

GEORGE D said:


> If your referring to power factor caps this place doesn't have any. I'm going to meg the motor wires again. Btw, I'm on site right now so any one please feel free to chime in with suggestions.


Geez, that's a late night for you...

I would still look for something that comes on at the same time these drives trip out. I doubt it would not be anything on the load side, because the load sides are not common to each other (hopefully!).

Did you get a chance to check out the Flying Restart option?


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## JRaef

Something else just occurred to me. Maybe it IS a High Voltage fault, but all of the OTHER drives have been set to Auto-Restart and these two have not!

A092 is the Auto Restart Attempts, A093 is Auto Restart Time Delay. Check the other drives to see if they have values other than zero in these. If so, then set A092 to something other than a 0, and ALSO set the Time delay to some reasonable value. Another mistake is that people set A092 for let's say 9 restart attempts, then they set the Time Delay for 0.1 second, so it does all 9 in less than a second!


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## GEORGE D

JRaef said:


> Something else just occurred to me. Maybe it IS a High Voltage fault, but all of the OTHER drives have been set to Auto-Restart and these two have not!
> 
> A092 is the Auto Restart Attempts, A093 is Auto Restart Time Delay. Check the other drives to see if they have values other than zero in these. If so, then set A092 to something other than a 0, and ALSO set the Time delay to some reasonable value. Another mistake is that people set A092 for let's say 9 restart attempts, then they set the Time Delay for 0.1 second, so it does all 9 in less than a second!


Unfortunately these are the only ones with keypads, all the others are the ones without,P40p's, so no hope there. Generally this system requires someone to reset overload/fault at cabinet to restart. Couldn't that present a safety issue?


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## MDShunk

GEORGE D said:


> Unfortunately these are the only ones with keypads, all the others are the ones without,P40p's, so no hope there. Generally this system requires someone to reset overload/fault at cabinet to restart. Couldn't that present a safety issue?


Go online with the drive with 5000, drive tools, or drive executive. You can also steal a HIM off any other 4 or 40 and plug into the DS1 port.


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## JRaef

If you don't have any of those software packages, you can now download Connected Components Workbench for free, it programs all AB drives (and Micro PLCs). You would need a cable though.


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## GEORGE D

Okay it was a very long night, got home at 3:30, I did figure some more information out but no solution. What I did see on the fault alarm screen is that one drive would fault out by itself and then shortly after both drives with fault out, then the other solo, then both, some sort of pattern. Also, the fault code in the drives went from 5 to 4 to 5, basically changing back and forth with every fault. Does this point to or mean anything?


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## GEORGE D

The 2 suspects are P46 and P78.

(images deleted at OP's request)


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## MDShunk

GEORGE D said:


> Okay it was a very long night, got home at 3:30, I did figure some more information out but no solution. What I did see on the fault alarm screen is that one drive would fault out by itself and then shortly after both drives with fault out, then the other solo, then both, some sort of pattern. Also, the fault code in the drives went from 5 to 4 to 5, basically changing back and forth with every fault. Does this point to or mean anything?


From DC bus undervoltage to DC bus overvoltage? Wow, man.

We sure yet that the line side of the drives has a clean bill of health, or no? I was thinking you said you had a power quality analyzer on the line side and everything was cool. 

Whereabouts are you? I got some airline points to use. I almost want to see this. Never really had a little wee drive like the junky PF40 kick my ass. At least not over the internet.


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## GEORGE D

The jobs in Greenville, SC, Im willing to pay...


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## sparkywannabee

George, these drives look pretty easy to change out, Don't you have a spare on the shelf you can swap one out with, see if it makes a difference, since you've tried all else. Maybe swap it with one of the other drives that works fine. Maybe both drives have gone bad to where they can't handle the slightest ripple or spike like the other good drives can. Strange stuff happens man, good luck, feel for you, I been there.


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## Jlarson

So the faults only happen on the night shift?


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## sparkywannabee

Did you mention what HP these drives are? If these drives have some amps flowing thru them and you are in a dusty environment, might be getting too hot in that cabinet, by the time you get called and open it, its cooled down. Cooling fans on drives, cabinet, filters etc could be the issue. Whenever i've had the ambient get too much around a drive, i never see overtemp, just some strange fault i've never seen before. I think thats because the electronics on the PCB's start to get goofy.


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## JRaef

GEORGE D said:


> Okay it was a very long night, got home at 3:30, I did figure some more information out but no solution. What I did see on the fault alarm screen is that one drive would fault out by itself and then shortly after both drives with fault out, then the other solo, then both, some sort of pattern. Also, the fault code in the drives went from 5 to 4 to 5, basically changing back and forth with every fault. Does this point to or mean anything?


Going back and forth between high DC bus (F05) and low DC bus (F04) is exactly what I would expect from something squirrely going on with the line voltage. I'd be looking for either a loose connection, high resistance contact on a breaker, bad fuse clip, failing conductor insulation, something that is intermittently dropping voltage on one phase significantly, but not continuously, and ahead of BOTH of these drives. A large motor starting at those times could do it too, especially if there was some nascent problem with that motor that has yet to cause a failure there. A big HVAC chiller or compressor coming on maybe?



GEORGE D said:


> The 2 suspects are P46 and P78.


There are no parameters numbered as P46 and P78 on that drive. Typo?


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## GEORGE D

JRaef said:


> Going back and forth between high DC bus (F05) and low DC bus (F04) is exactly what I would expect from something squirrely going on with the line voltage. I'd be looking for either a loose connection, high resistance contact on a breaker, bad fuse clip, failing conductor insulation, something that is intermittently dropping voltage on one phase significantly, but not continuously, and ahead of BOTH of these drives. A large motor starting at those times could do it too, especially if there was some nascent problem with that motor that has yet to cause a failure there. A big HVAC chiller or compressor coming on maybe? There are no parameters numbered as P46 and P78 on that drive. Typo?


Oh sorry J, the P46 and 78 were referring to the names of the conveyors involved, showing on the HMI display fault screen. The A/C lines are good, tested fine with Fluke 1750 and 43B during actual fault, never exceeded 485 volts. The last things we did was change a few parameters such as disabling reverse (just because/in-case), swapped some more I/O cards, and most importantly the VFD acceleration time, which was set for 1.0 second, we bumped it up to 3. We also found out from an operator that the fault seems to be happening on start-up. These conveyors are constantly stopped & started through the night and heavily loaded at times. What are your thoughts on the 1.0 accel time? If for some reason that shouldn't be a problem, then would a torque boost adjustment be necessary, or possibly an oversized drive?


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## varmit

One second ramp times seem way too short. If the conveyors are heavily loaded, probably somewhat overloaded, the drive could be trying to start in current limit. If the load (the conveyors) did not accelerate in this one second ramp time, the buss voltage probably would dip below the trip point. Also, if the conveyors are loaded with enough mass to cause a regen on stopping due to overshooting the stop ramp time, this could cause the over voltage fault.

Sometimes in high load starting, it is beneficial to set minimum drive output at more than zero, say 15 to 20 HZ to increase starting torque. I would try setting the start ramp at about 10 seconds. 

If you can not use "coast to stop", the desired stop ramp may be a trial and error exercise to determine setting that will stop the conveyor without causing enough regen to give a buss over voltage and not have too long a ramp to where the motor stalls before the stop ramp is completed.

There is a practical limit on the number of starts per hour on a motor. Larger motor = less starts per hour.


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