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Discussion Starter · #1 ·
I have a problem with 2 vfd's in same cabinet faulting out around the same time. The fault code is F5, which indicates A/C line problem or possibly regeneration problem. This happens very intermittently, roughly 2 random times a month, and always seems to trip both. The motors are part of a conveyor system, each being on a different conveyor. The motors also go through a gear box, which may take regeneration out of equation(?). Naturally it points to an obvious line voltage problem, but I for some reason find it hard to imagine, because there are 3 different control cabinets and all coming from same source/service, which makes me think if there was a spike or surge that all cabinets would be affected. Also each motor has a line reactor. Also, there is a PLC in the cabinet and would imagine that it would of also been affected from a spike(?). Would a loss of one incoming phase cause an F5 fault? Please help?
 

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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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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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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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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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Discussion Starter · #7 ·
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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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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Discussion Starter · #9 ·
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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Discussion Starter · #10 ·
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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Discussion Starter · #11 ·
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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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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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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Discussion Starter · #14 ·
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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Discussion Starter · #15 ·
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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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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Discussion Starter · #17 ·
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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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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Discussion Starter · #19 ·
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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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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