The capacitor is charged when the switch is closed. A huge current will flow into the capacitor until it is “full”. The usual solutions are to (1) use a slow-blow fuse that can withstand the surge current or place a low value power resister in series with the AC to limit maximum current. Inductors can do this better than resistors.
Also it might just be luck. When you switch high-current AC, it is best to switch on the zero crossing when there is zero volts. Unless there is a circuit to make that happen it is just luck what the volts are when the contacts close. Most poweerful AC powered heaters are switched usung a solid state relay and these are designed to switch on zero. Domestic water heaters and resistive building heat is all done this way. >> >> >> I do not understand why was everything fine in initial testing - I did >> turn machine on and off lots of times and capacitor was discharged >> (and recharged!!!) numerous times. I have swapped that fuse for >> identical unit from a machine that has yet to go through the retrofit >> process. And it is the same. >> >> So my question to electronics gurus - could capacitor be damaged or >> was it just a beginners luck that everything worked and do I need to >> introduce some inductor between rectifier bridge and capacitor to >> limit the startup current that charges capacitor? >> >> Viesturs >> > > Typically a NTC is used to limit the surge current, either in the AC line > or the DC between the bridge and the filter capacitor. Here is a NTC > manufacturers page on this usage: > > https://product.tdk.com/en/techlibrary/applicationnote/howto_ntc-limiter.html > > > >> >> _______________________________________________ >> Emc-users mailing list >> [email protected] <mailto:[email protected]> >> https://lists.sourceforge.net/lists/listinfo/emc-users >> > > Peter Wallace > Mesa Electronics > > > _______________________________________________ > Emc-users mailing list > [email protected] <mailto:[email protected]> > https://lists.sourceforge.net/lists/listinfo/emc-users _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
