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Thread: VFD Maintenance
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18th Oct 2017, 03:35 PM #1Member: Blue and white apron brigade
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VFD Maintenance
I found this in the Powtran VFD manual and looks like useful info for folks with VFD in storage or on machine which have not been used for a while.
Bottom line looks like ,that for VFDs that have not been run for between 1 and 2 years, the VFD needs to be left on for an hour or so before use under load.
Beyond 2 years I'm not quite sire what " adjustable power" really means. It's the only section in the Manual that reads like "Chinglese" The rest I've read of the manual is very good.
Caprecharge.jpg
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18th Oct 2017, 06:01 PM #2Senior Member
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18th Oct 2017, 06:25 PM #3Member: Blue and white apron brigade
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18th Oct 2017, 08:10 PM #4
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18th Oct 2017, 08:48 PM #5Member: Blue and white apron brigade
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I did a bit of reading and this is one of the clearer explanations.
The dielectric oxide layer is the thin high resistance layer that separates the two charge holding plates inside a cap.
The dielectric oxide-insulating layer is created during manufacture. However, it will deteriorate in the absence of a sufficient rejuvenating voltage, and eventually the capacitor will fail if voltage is not applied. Maintaining the integrity of the dielectric requires the steady application of power. When voltage is applied, the oxide layer is rebuilt. The oxide layer thickness is the crucial factor to determine the voltage rating of the capacitor. Otherwise, the oxide layer will break down under voltage and cause a spectacular failure.By applying voltage to the capacitor on a regular basis, the oxide layer is “reformed”, and the integrity of the insulating characteristic is ensured. In EMA’s experience, the maximum time between power ups should be no longer than 1 year, provided the equipment is kept in a dry location at roughly 70 degrees F. Large temperature swings require less time between power ups.
The procedure to “reform” the capacitors in electronic equipment is to apply rated voltage for a period of at least 1 hour. Realizing after the unit is de-energized, a chemical reaction is still occurring for up to 24 hours, thereby rebuilding the oxide layer during this “resting” period. Should more than 12 months pass between power ups, great caution should be exercised.
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20th Oct 2017, 11:23 PM #6Senior Member
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Something I can almost remember from my electronic engineering days!
Yes, this relates to 'reforming' the dielectric.
Reducing the input voltage means the leakage current is limited to a point which won't cause damage, while the reforming happens.
The manual isn't the clearest in that part, for sure!
This issue occurs with any gear with electrolytic caps.
-russ
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