Greetings all; Having destroyed one 40 amp SSR by turning on the switching psu;s for the two running the X&y motors and the builtin supply of the even bigger drive running the Z axis, already, I am now contemplating how to do a soft start to limit the initial in-rush of charging up those 3 power supplies.
And doing it in a lower powered version of how I am doing the huge analog supply that runs the spindle motor. There, I have two timers which are controlling two 40 amp SSR's with a 50 ohm 200 watt resistor, so it starts charging that supply with its thousands of u-f's by applying the power thru that big resistor, then the 2nd SSR comes on applying it directly 3 seconds later. This has worked flawlessly for about 4 years now. Now I have obtained two more used genuine crydom 40 amp 480 volt SSR's, and am considering doing the same thing in essence, only with a much smaller ohmage R to limit the in-rush this batch of switchers in a similar manner. But switchers, I have heard, need that initial bump to get started correctly. To that end I've also ordered a pair of 10 ohm 70 watt resistors, which if need be can be paralleled for 5 ohms in series with these supplies for the first 1/2 to 1 second. But I intend to use one of these in another analog supply, starting the spindle psu in The Little Monster too, putting all its heavy power under LCNC's control. But that is a different project. These switchers are, or s/b all fused to protect them in the event they don't start. So I don't expect a start failure to do more than blow the fuse. Has anyone else any experience with this, that can add gotcha's to watch for in such a current limited startup? 10 ohms in series with the power to protect the SSR's is the basic idea. 10 ohms would limit at 12.5 amps of in-rush, which seems reasonable. Thanks all. Cheers, Gene Heskett -- "There are four boxes to be used in defense of liberty: soap, ballot, jury, and ammo. Please use in that order." -Ed Howdershelt (Author) If we desire respect for the law, we must first make the law respectable. - Louis D. Brandeis Genes Web page <http://geneslinuxbox.net:6309/gene> _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
