Dc Bus Capacitor Issues
Posted 06 November 2009 - 03:00 AM
The recommended procedure for dealing with a drive that's been out of service for a long time (2 years or more) is to soft power the drive with a Variac to "reform" the capacitor chemistry. Sometimes this is done by running the Variac through a 3 phase rectifier directly into the DC Bus to get around drive's SCR front end.
My question is: How effective is this procedure and does it totally "repair" the capacitors chemistry ?
Posted 10 November 2009 - 07:20 AM
Yes, electrolytic capacitors will often need to be reformed if they have not been charged up for a period of years.
The easiest way to reform the capacitors is to charge them via a large resistor to limit the current.
If you have a bridge rectifier that supplies DC of the right voltage through a resistor, you will find that the voltage will climb slowly to the full voltage. The unformed capacitors will limit the maximum voltage when fed by a resistor until they are formed.
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