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Old September 18th, 2023, 03:36 AM   #1
Ken Roach
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Shelf maintenance for VFDs ?

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 ?
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Old September 18th, 2023, 04:40 AM   #2
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It really depends what type of capacitor is used, but I'd have thought 12 months should be fine. Although if you're going to the effort of automating it you might as well have it fire up monthly. A place I used to work had an electrician wire up and test all spare drives on a monthly basis after they once had a replacement fail and cause production issues.

This is actually a pretty big issue with the original Xbox. The system clock was maintained by a capacitor and now that a lot of the consoles aren't used a lot, they've been known to leak and cause damage to the motherboard.
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Old September 18th, 2023, 02:25 PM   #3
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The VFD's with this spec listed that I have seen have all said 12 months to stop the capacitors from degrading.

Plus I think some said to build the incoming power, not just apply 240 or 480, but start at 100V and build slowly to line voltage over 12 to 24 hours

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Old September 18th, 2023, 02:30 PM   #4
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Ken. For some reason your post was created twice.

If you are going through the steps of automating it, you may as well just have them power up for an hour or so every two or three months.

Every few months will keep the capacitor smoke happy, but is not so often that you are going to realistically wear out the precharge circuits.
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Old September 18th, 2023, 03:21 PM   #5
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I think a ramp up is a better option in any case. I have some stock that I only pull when I need one, I'll take a half a day and charge them up incrementally over several hours.

Bear in mind that since they will only need minimal current so you can get away with a 120Vx480V XFMR with a series resistor for inrush protection and they will charge up just fine.
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