Gene is right. The input surge from transformers and capacitors can be quite major. To get around that I build a couple of circuits to slow down the input surge and to also clamp over voltage from decelerating DC servos plus drain the caps of the 105VDC quickly so that it was safe to work on.
http://www.autoartisans.com/mill/drawings/MillCNCDrawings.html The above link is to my dirty laundry so to speak. Essentially I put a 47 Ohm 10W resistor in series with the primary winding on power up. How long it's there is based on the PIC controller that also runs the high voltage clamp and drain circuit. John Dammeyer > -----Original Message----- > From: Gene Heskett [mailto:ghesk...@shentel.net] > Sent: July-28-21 3:24 PM > To: emc-users@lists.sourceforge.net > Subject: Re: [Emc-users] Lathe Spindle Drive Questions > > On Wednesday 28 July 2021 15:25:01 Chris Albertson wrote: > > > Do you really need to worry about inrush tripping the breaker? > > 1) If the DC supply is the old linear type, it will have a very large > > filter capacitor and supply peak loads without a large AC draw. The > > trick is to turn on the supply and then the motor a second later. > > Now, imagine that supply consists of 4 toroid transformers each capable > of developing the nominally 63 volts plus and minus, for a 1 kw analog > audio amp. and the filter caps are 6 in each supply of 9200 uf at 65 > volts, and each transformer is treated as a single supply. wired two in > parallel and two tall for a combined voltage of around 126 volts and > 220800 uf. Plug that into a 30 amp breaker and flip the switch. > clunkiest switch you ever heard because that 30 amp breaker went down > like a shotgun on the first half cycle of power, essentially > simultaneous with the click of the switch. So I hit the junkbox and come > up with two 40 amp SSR's and a 50 ohm 200 watt resistor, added a couple > time delays controlled by hal and driven by the F2 state such that the > 50 ohm is in series with the supply line for the first 4 seconds and is > shorted after that. Now it runs fine on a 15 amp breaker, but will trip > it if I ignore the motors chirping because the pwm-servo is set to about > 17 amps but it takes several seconds, so I settled for a 20 amp in that > slot. > > And for Ralph's problem with the Washington inspectors, I suspect they > are reading the rules wrong, here they don't care about the load, the > only thing they checked outside of the box was the ground wiring to the > rods. > > And for lack of any other pressing duties, helped me bore 2 holes thru > about 8" of green concrete the required 6 feet apart to make it meet > code. After he ok'd hooking up the drop so we had power to run the > hammerdrill. > > Cheers Chris, 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 _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
