# Cool Powerflex 40 F004 fault solution.



## MDShunk

Powerflex drives are certainly popular with machine builders, but there's a little issue with them when the machine's OEM wires the estops and operator interlocks/guard switches/remote lockouts in a certain way. 

Before the Allen Bradley "safe off relay" (a device that interrupts the DC bus output), it was traditional for machine OEM's to break the main power coming into a PowerFlex drive with a contactor. When an estop is pressed, a guard door is opened, a remote operator lockout station is turned off (like a trapped key interlock or key operated interlock), the power is dropped out to all the drives. This was very traditional once upon a time, and remains fairly typical even today. 

The main issue caused by this safety scheme is that the drive takes time to "drain" to fully power off. About 30 seconds for a 5hp drive. Shorter time for smaller drives, longer time for large drives. What's the issue? Well, if the operator got in the machine to do a quick adjustment or clear a jam, and it takes shorter than 30 seconds to fix, when he or she restores control power and the contactors pull back in to reenergize the drive, the drive will show an F004 (F4) fault. Why? If the drive's power is dropped out, the drive begins powering down. If the drive is reenergized before it fully powers down, it thinks it was a power blip. The F4 fault means "undervoltage". This requires the operator to power off the control circuit (by means of his or her local interlock/key switch/estop or whatever), wait the full amount of time for the drive to fully power down, then restore control power and restart the machine. It's incredibly frustrating for a machine operator.

There's a couple of fixes for this. First, you could wire a "fault reset" into an input terminal. In my experience, very few machine OEM's bothered to wire fault resets into the drives from the original build. While this could be done as a retrofit solution, there's an easier solution.

There's a parameter, A092, called "auto reset tries". It seems scary, auto resetting faults, and it's not something to be taken lightly. BUT.... there's a cool feature to auto reset. If you set parameter A092, auto restart tries, to for instance "1" (it's zero from factory), it will auto-restart most all faults once. BUT.... I don't want to auto reset all faults. That could be dangerous or destructive sometimes. The very next parameter A093 is called "auto restart delay". It's a parameter that delays between auto restart attempts. It's .1 second from the factory. It has another cool feature.... if you set parameter A093, auto restart delay to "0" it will only auto reset undervoltage and overvoltage faults. Pretty neat eh?

So, in summary, if you set parameter A092, "auto restart tries" to "1" and parameter A093, auto restart delay to "0"- when the operator shuts down the safety circuit (which powers down the drives) to do something quick, the drive will power right back up on restart without faulting out on F004, "undervoltage fault" no matter if the drive was off long enough to fully power down or not. 

I just figured this out the other day, and it's already saving downtime and frustration on machines from many different manufacturers where PowerFlex drives are installed.


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## pudge565

That is awesome to know!


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## varmit

If you are stuck with this installation scenario from the OEM ( probably since changing it could bring out the liability buzzards) your change would serve the purpose to avoid faults. The real down side to the original installation is the constant powering up and down of the VFD. This can considerably shorten a VFDs life span. 

If these are mostly smaller drives, it might be worth putting a plan together to, over a period of time, upgrade them to newer VFDs with the integral safety circuit.


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## MDShunk

varmit said:


> If you are stuck with this installation scenario from the OEM ( probably since changing it could bring out the liability buzzards) your change would serve the purpose to avoid faults. The real down side to the original installation is the constant powering up and down of the VFD. This can considerably shorten a VFDs life span.
> 
> If these are mostly smaller drives, it might be worth putting a plan together to, over a period of time, upgrade them to newer VFDs with the integral safety circuit.


Oh, the safe off relay can be added easily enough to the existing drives. I just don't care to if I can change a parameter. I fix stuff. Reliability is someone else's baby to rock. Getting more life out of any PowerFlex drive that starts with a "4" is like religious waxing of a Yugo. The juice ain't worth the squeeze.


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## ElectroBuff

It is a practice I've seen before. I had worked with drives which would "auto" reset 10 times (no kidding...). However, you should really consider re-working this mess to be monitored by a PLC (potentially already there?) which would monitor the status of your drives and reset when needed.

That being said, as others mentioned, cutting off power to the drive is really not the way to go for an E-Stop circuit. You could always upgrade to PowerFlex 525's that have dual safety monitoring channels and get rid of all the other hardware to shut them off...


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