Shelf maintenance for VFDs ?

[Ken Roach]

This is a little OT, but I know there are some experts here on the forum with the relevant experience.

I have a project that expects a very long lifespan from PowerFlex 70 VFDs. To insure them against inevitable obsolescence, I would like to buy a few and have them available in our stock as replacements.

But I know that capacitors get cranky if left on the shelf for years. I don't do enough VFD repair to be capable of doing capacitor reformation on these little 1/2 HP drives.

I was thinking of basically automating my storage: I have a disused cabinet with an old MicroLogix and a 480V contactor. I could have the MicroLogix power those drives up once every few months, read their serial numbers and runtime hours, then send me an e-mail to remind me that they've done so.

If you did that, how often would you power up those drives ? Every 3 months ? 6 ? 12 ?

 

[keithsimpson]

If you speak to a Rockwell drive expert they will tell you how to setup a DC voltage to reform the capacitors. I asked about this in the past and that was the general answer but I cant remember the details.

 

[JesperMP]

This what Siemens says for their VFDs:

If a unit has been non-operational for more than one year, the DC link
capacitors have to be newly formed. If this is not carried out, the unit
can be damaged when the line voltage is powered up.
If the unit was started-up within one year after having been
manufactured, the DC link capacitors do not have to be re-formed. The
date of manufacture of the unit can be read from the serial number.

So every 12 months, or every 6 months to be on the safe side. And that would be when just powering the VFD up normally, without a special pre-charge device.

 

[tarik1978]

In page 3 of this document,you can find the reforming capacitors recommendations
Preventive Maintenance Checklist of Industrial
Control and Drive System Equipment
https://literature.rockwellautomation.com/idc/groups/literature/documents/td/drives-td001_-en-p.pdf

 

[d x l]

There was a Rockwell webinar around January 2021. I'm not sure if these can be looked up later on. The title was "AC Drive Best Practices."

This is what I wrote about reforming:
• Reforming capacitor guidelines/recommendations
○ <1 year stored as rated - no reforming required
○ 1 - 2 years: apply rated voltage as normal for 60 min w/o load
○ 2 - 3 years: connect DC power supply directly to DC terminals, ramp up voltage from 0-100% of DC bus voltage in steps of 25%, under no load. Dwell at 25, 50, 75% for 30 minutes each, dwell at 100% for 60 minutes.
○ >3 years: apply DC power supply as above but dwell at each step for 120 minutes
○ DC bus voltage: 325 VDC on 230V input drive, 680 VDC on 400/480V drive, 848 VDC on 600V drive

 

[LegacyLee]

You can also use a regular single-phase AC XFMR going up in 25% increments(different taps) connected to just two of the L terminals. The rectifier bridge doesn't care one bit about lower voltages or what "Lx" the voltage is coming from. It would care if it were a 230V vs 480V. Just take care on that matter.
No way I'm buying a 1000V adjustable DC power supply.

 

[d x l]

There was a Rockwell webinar around January 2021. I'm not sure if these can be looked up later on. The title was "AC Drive Best Practices."

I found the webinar, and "registered." It sent me a link to watch on demand. It should work for anyone with a Rockwell account - mine isn't linked to any software license (currently), just a free account!
https://www.rockwellautomation.com/en-au/company/events/webinars/best-practices-for-ac-drive-installations.html