Likely component fault on Powerflex 4 VFD?
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    Default Likely component fault on Powerflex 4 VFD?

    I have an Allen-Bradley Powerflex 4 VFD sitting on my desk that failed earlier in the week. Every time I'd try to start the motor, it would come up with fault F005, which is an over-voltage fault. The other two VFD in the same cabinet that run from the same power feed displayed the same buss voltage, 330-340 vdc. This one was made in December of 2005. It doesn't get heavy use, but it does sit powered up pretty much all the time.

    Does this sound like a main filter cap fault that is allowing excess ripple on the DC buss, or is it not something I could probably actually fix? I've already purchased a replacement drive, so if I can fix this it would just be for my own use at home. Replacing the caps wouldn't be a problem for me, but I don't want to waste my time or money if that probably isn't it. A quick visual inspection doesn't show any obvious problems, no burn marks, no bulged or leaky caps. All Nichicon parts too, not offbrand junk.

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    Hard to say, unless one is very familiar with that unit.

    I checked the manual to see if that is actually an excess ripple voltage fault, but that would be F003, not F005. So cap failure is not as likely a cause.

    The cause may be a fault in the voltage measuring circuit. If you dug around in the unit you might find a bad connection or other fairly simple fault on the power board that is presenting an incorrect high voltage input to the controls.

    Some of the units have an integrated power module that includes some of that circuitry, and is not repairable.

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    Most likely the little internal relay that is used to short out the pre-charge resistor is welded closed, so the resistor is not there to perform it's current limiting function when you power up the drive and the inrush drawn by the capacitors charging themselves up causes a ringing effect on the bus voltage that triggers the fault. You could try to take the drive apart and see if you can de-solder the relay, find a replacement, solder it back in etc. etc., might take you 3-4 hours if you are an average Joe bench technician, not counting the time to find the exact relay. So then the problem is, even after fixing that, you may find that just the few times you energized it trying to figure out what's happening has now damaged the capacitors and the drive is junk anyway.

    How that relay often gets fried / welded is that something "chattered" the voltage coming into the VFD, i.e. you turned line power off and back on rapidly and/or repeatedly.

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    Have not seen that version of the problem, but it is possible.

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    Quote Originally Posted by JST View Post

    The cause may be a fault in the voltage measuring circuit. If you dug around in the unit you might find a bad connection or other fairly simple fault on the power board that is presenting an incorrect high voltage input to the controls.
    I was using the internal display functions to read the buss voltage. I had not actually poked a meter in there. Would the display voltage likely be read by different components than what would set the fault code? I can also confirm the buss voltage with a meter to see if the internal matches.


    Quote Originally Posted by Jraef View Post
    Most likely the little internal relay that is used to short out the pre-charge resistor is welded closed,

    I can meter that out easy enough. Very possible its trash anyway but poking a meter in there to verify welded contacts won't cost anything. I'm not planning to spend any real time or money on this, just was hoping it might be something cheap and simple to fix.

    Thanks for the input, I'll give it a look and possibly deposit it in the circular file if thats where it belongs. This is the fourth drive unit to fail on me, and all of them have had the same fault. All around 10 years old too.

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    I'd suspect the same components do both, but that does not guarantee it will show up. Does the display not show a voltage that SHOULD be an overvoltage? If it shows 340V, then something else is fouled up, or else the two functions do NOT share parts..

    The one reason not to necessarily suspect the ringing problem is that it occurs when you start the motor, which is long after you power up the drive. The precharge relay should have operated way before that, and connection to the mains would also have happened long before. So that even if the relay was "welded shut", by the time you start the motor the drive should be just the same condition as if it were all perfectly correct.

    Dies the motor do anything before the error shows up? maybe jerk a little, or the like?

    Does the fault come up instantly or is there a couple seconds of delay?

    The drive may not check the status until asked to run. If it latched an overvolt status from back at turn-on, that would explain it, but usually the controls do not come on for a couple seconds after power is on the DC bus, as the power supply has to start up, and the micro controllers have to start up and verify communication from the interface to the actual power board. Untiil the micro is "on" and ready, it is generally not looking for voltage or doing anything other than booting up.

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    Display ran between 330 and 340, I presume because of line fluctuation. Over-voltage according to the manual is 405 volts, equivalent to 150 vac input. Power line voltage here runs right about 118 vac. This is a little 1hp single phase to 208 3 phase inverter, driving a 1/2 hp motor in a stretch wrap machine.

    Motor does absolutely nothing, it won't even try to budge. Hit the go button and the fault is instant. I did try resetting to factory defaults just in case it was some program issue, and that makes no difference. I can reset the fault and it will stay clear as long as the drive is not being commanded to do anything.

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    Well, then unless you see something obvious when looking inside, some obviously bad part, I don't know.

    I have seen cases where a condition sets several faults, and the one that actually appears o the display is just the first one in line, so it really may not be the true basic problem.

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    i know a long time has passed.the fault is in the dc power generation card below the control card of drive. imbalance in low voltages dc required to operate the drive

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    I know the fix for the f05 fault if you want to message me.

    Quote Originally Posted by gadget73 View Post
    I have an Allen-Bradley Powerflex 4 VFD sitting on my desk that failed earlier in the week. Every time I'd try to start the motor, it would come up with fault F005, which is an over-voltage fault. The other two VFD in the same cabinet that run from the same power feed displayed the same buss voltage, 330-340 vdc. This one was made in December of 2005. It doesn't get heavy use, but it does sit powered up pretty much all the time.

    Does this sound like a main filter cap fault that is allowing excess ripple on the DC buss, or is it not something I could probably actually fix? I've already purchased a replacement drive, so if I can fix this it would just be for my own use at home. Replacing the caps wouldn't be a problem for me, but I don't want to waste my time or money if that probably isn't it. A quick visual inspection doesn't show any obvious problems, no burn marks, no bulged or leaky caps. All Nichicon parts too, not offbrand junk.

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    Quote Originally Posted by isaacone View Post
    I know the fix for the f05 fault if you want to message me.
    I would like the fix for this fault. I have a powerflex4 that as soon as the start button is pressed for the motor, the drive will fault out with F05 - DC bus overvoltage. The motor is not attempting to start. I have swapped out motors, cables, and verified incoming voltage. I do have a replacement drive on order, but I would like to know the fix for this issue as I have never seen this occur.

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    Do you know how to access the Allen Bradley KnowledgeBase? If so, read article #62242, it is a list of most of the possible causes of this fault. In your case you have already eliminated the vast majority of them. of what's left, it's likely one of the following:


    Incoming Voltage is too high
    Noise on the incoming line (relays contactors brake coils welders)
    Voltage transients on the line, possible from power factor correction caps
    Ground fault such as a motor phase shorted to motor ground on a ungrounded (floating ground) or high resistive ground system
    Bus Capacitors may be degrading
    Bus Regulation is set for Adjust Voltage
    7th IGBT (brake chopper transistor) is damaged
    DC Bus pump up Boost Converter Phenomenon of DC Bus Voltage See Technote 864938 - DC Bus Pump Up - Boost Converter Phenomenon

    That last item, called the "Boost Converter Phenomenon" it a complex one, but essentially is the result of an interaction between your VFD and the line source impedance. One possible fix for that is to lower your Carrier Frequency (called the PWM frequency in the PF4). It's found in parameter A091 and the factory default is 4kHz. Check to see if someone raised that to a high value. Carrier (PWM) Frequency is the rate at which the transistors actually fire. Because it is the high speed switching of the transistors that causes the motor to "whine", people often raise that frequency to raise the pitch of the whine sound to be above that of normal human hearing, i.e. above 10kHz. The PF4 is capable of up to 16kHz and someone may have raised it. But that has negative consequences, one of which might be this Boost Converter Phenomenon. If it's set high, put it back down to 4kHz and see if that cures it. If not, it's likely something else. Of the list issues above, failing capacitors or a failing braking transistor are the most probable.


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