Mark Pictor wrote: > I knew there would be inrush current to the capacitors, but I > didn't realize that the transformer, in and of itself, would have > an inrush current. Guess that shows how much I know! > Yup. It varies with the transformer design, and if you end up using a 240 V primary winding on 120 V, the "inrush" will be very small. What is going on is that the transformer integrates volts times time, and the iron in the core is designed to just handle the rated conditions, where the magnetic field builds in one half cycle, and is cancelled out in the next half-cycle.
But, when you close the switch, the power line phase at that moment could be anything. If it happens to be right at the voltage zero crossing, then it gets a complete half cycle of the same polarity starting from zero magnetic field, and that saturates the core. The transformer will make a huge buzz for a half second, and the current will be enormous. > I was planning to use one or more motor run capacitors to limit > inrush current - use a relay in parallel with the cap, and close > the relay a few seconds after applying power. > This will kill your relay. Shorting a capacitor bank charged to 168 V peak will cause a minor explosion, and the L-C circuit will never settle. You need to use a low-value resistor, not capacitor, for this purpose. > Now that Jon brought it up, I think I will visit the local junkyard > instead. Depends entirely on the junkyard, of course, but almost any instance where old machinery is torn out of a plant, they get these transformers. Jon ------------------------------------------------------------------------- This SF.net email is sponsored by: Splunk Inc. Still grepping through log files to find problems? Stop. Now Search log events and configuration files using AJAX and a browser. Download your FREE copy of Splunk now >> http://get.splunk.com/ _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
