PowerFlex 525 hangs in BOOT

A customer has a PF525, and it recently started acting strange.

If they power it down, then power back up, it just hangs with BOOT on the display.

He played around with it and found if he hits ESC, then cycles power again it Boots normally.

Any Idea?

Don't know what firmware, but these were early 2014 drives, and only one has this issue.

Don't you love technology!

Rockwell suggests pulling the Control Module and re-seating it.

If that doesn't work they recommend replacing it, but I would investigate more before doing that. Replacing it will probably solve the issue, but you will have no idea what the root cause was, and it could well come up again.

Stu....

KnowledgeBase article #601846

The power-up cycle of the 520 series is that the CPU goes through the Boot stage of the main CPU, then it waits for the DC Bus pre-charge cycle, then it checks the start-up application code and finally the network connections are established. The display will stay in "Boot" until the CPU gets a signal from the power module that the pre-charge cycle is done. If the connection between the control module and the power module is a little iffy, it might not get that signal back so it doesn't move on with the next two cycles.

The reason why the article says to replace it if reseating it doesn't fix the problem is because that most likely means the pre-charge circuit has been compromised. The pre-charge circuit is essentially the "soft start" of the DC bus caps. caps will pull current at the available fault current level to charge themselves up instantly if allowed to, and that may damage them or the diode bridge that feeds them. So all VFDs deal with this by using a way of limiting the initial charging current to the caps, called a "pre-charge" circuit. There are several ways to do it, but on small drives likethe 525, it's a series resistor used as a current limiter, then when the DC bus voltage is stable, a relay shorts across that resistor to take it out of the circuit. That usually gets damaged as the result of constantly cycling power to the drive on and off. That is not good for any VFD and should be avoided because it basically burns out the pre-charge resistor.

Another possibility for damaging it comse from excessive attempts and using that pre-charge resistor to dissipate regenerative energy off of the motor, i.e. trying to do dynamic braking without adding the braking resistor. The pre-charge resistor also functions as the bleed-off resistor for the DC bus caps, so if you try to dynamically brake a load without using separate DB resistor, the drive charges up the DC bus and attempts to bleed it off through that pre-charge resistor, which eventually burns it out. So take a look at what you are trying to accomplish with the drive and if someone has programmed it for dynamic braking, but has not added the braking resistor, that might have lead to the failure of the pre-charge.

Assuming of course that the re-seating of the control module wasn't the issue.