Some designs fill the capacitor through a small resistor, then turn on a relay once the voltage is up. Drive operation needs to be inhibited during the fill process.
> On Aug 6, 2024, at 4:21 PM, Chris Albertson <albertson.ch...@gmail.com> wrote: > > 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 >>> Emc-users@lists.sourceforge.net <mailto:Emc-users@lists.sourceforge.net> >>> https://lists.sourceforge.net/lists/listinfo/emc-users >>> >> >> Peter Wallace >> Mesa Electronics >> >> >> _______________________________________________ >> Emc-users mailing list >> Emc-users@lists.sourceforge.net <mailto:Emc-users@lists.sourceforge.net> >> https://lists.sourceforge.net/lists/listinfo/emc-users > > > _______________________________________________ > Emc-users mailing list > Emc-users@lists.sourceforge.net > https://lists.sourceforge.net/lists/listinfo/emc-users _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
