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Valid for AKD, S300, S400, S600, S700

Capacitors integrated in servo amplifiers may be uncharged to absolute zero level, if servo amplifiers are stored for longer than a year without being connected to mains voltage. If rated voltage is supplied to such a capacitor, then an extremely high charging current (depending on the charge characteristics curve) may flow for some time, which could overheat and destroy the capacitor or the PCB. Even load cycles during this phase  result in high current peaks due to recharging processes.

The capacitors must be reformed therefore after long storage phases. The servo amplifier must be connected with single phase (to L1/L2 terminals) and low voltage (therefore low charging current) for about 30 minutes. We recommend to use the lowest admitted rated mains supply voltage for the servo amplifier.

The safer, recommended procedure is the use of a variable transformer. If available, use a variable transformer to apply voltage in 50 Volt increments for at least 20 minutes at each step until rated voltage is reached, then hold the final (rated) voltage for at least 1 hour. In a separate operation, with all other electrical connections (including mains power) removed, apply 24VDC in the correct polarity across +24V and GND for approximately 30 minutes.

If storage times of over a year are anticipated, the above capacitor re-forming processes may be avoided by simultaneously powering the servo amplifier with 24VDC auxiliary power and full rated mains voltage for at least an hour at intervals of less than a year.  


Federico Pontisso SMI's picture
Federico Pontis...
Being old and new drives, we have several in stock ready for any replacements. The importance of "forming" the drive is fundamental to replace them on machines with decades of life; not knowing this procedure could cause damage and, above all, loss of customer confidence. This article is very important and should be published with more prominence.