On Tue, 6 Sep 2011, Peter Blodow wrote: > Date: Tue, 06 Sep 2011 18:15:33 +0200 > From: Peter Blodow <p.blo...@dreki.de> > Reply-To: "Enhanced Machine Controller (EMC)" > <emc-users@lists.sourceforge.net> > To: "Enhanced Machine Controller (EMC)" <emc-users@lists.sourceforge.net> > Subject: Re: [Emc-users] Servo PSU > > Andy, > looks like a neatly made power box. Rectifying AC line power without > potential insulation, however, is unusual and bears some risks.
Basically nearly every servo drive/VFD above several hundred watts is done this way. > > - Be aware that both of your DC lines will have potential to ground, > none can be grounded. Yes very true > > - Be sure that every metallic enclosure that is powered by this device > will be properly connected to protective earth (PE) and none of the > motor's leads will be near earth! This is true in any case (V- == ground or not) > > - Be sure that the drives and motors have sufficient high voltage > protection to ground, check technical specs. > > - You can't connect the control circuitry, which will be ground > referenced in most cases (zero of the 5 V supply connected to the metal > parts and PE) without an optical or other insulator which makes things > more complicated than usual. This isolation is usually needed with drives of larger sizes even with grounded V- because of ground noise. > > - Think about the effects that plugging the mains plug 180 degrees > turned over could have, don't rely on wires having seemingly no > potential in one case! With bridge rectifiers neither DC bus line is close to ground > > - Be aware of the fact that ordinary switches, relay contacts, fuses > etc. can switch off much less DC voltage than in the AC case. A DC arc, > several inches long, will be stationary at as little as 110 volts DC in > some cases. And it creates a lot of heat... In the good old DC times we > used to have spring loaded, fast acting switches with wide gaps between > the contacts, remember? Absolutely, make is OK. Breaking DC current requires special DC rated contactors (with fast action, blowout coils etc) > > - Honestly: You must be a much braver man than I because I myself > wouldn't dare using that box knowing that I'm too much used to the way > of thinking that one leg will always have zero volts.... Have you > considered using a 1:1 transformer? Any 320V VBUS servo drive is dangerous, I dont think that having one side of the PS close to ground really makes it much safer. Safest would be a fully floating PS but that has its own issues... > > Good luck! > Peter > > > andy pugh schrieb: >> I have made a servo PSU. It simply rectifies mains voltage to give me 325V >> DC. >> https://picasaweb.google.com/lh/photo/HdNJXBD5wPqDUi9E8C46HQ?feat=directlink >> https://picasaweb.google.com/lh/photo/dTcU2i7GYh53xSrqjh--BQ?feat=directlink >> There is a bit of extra componentry in the box to discharge the caps >> on power-off and to switch in a resistor for soft start, but basically >> it is just a rectifier and some caps. >> >> I am a bit puzzled about the status of my -V. >> I guess that my 0V will be a few volts away from neutral, which is a >> few volts from earth. Should there be an explicit connection between >> my DC- and earth, machine 0V, mains neutral, none of the above? >> >> I think perhaps I should have a 1:1 transformer to float the DC, which >> would then allow such a connection. >> >> > > > ------------------------------------------------------------------------------ > Special Offer -- Download ArcSight Logger for FREE! > Finally, a world-class log management solution at an even better > price-free! And you'll get a free "Love Thy Logs" t-shirt when you > download Logger. Secure your free ArcSight Logger TODAY! > http://p.sf.net/sfu/arcsisghtdev2dev > _______________________________________________ > Emc-users mailing list > Emc-users@lists.sourceforge.net > https://lists.sourceforge.net/lists/listinfo/emc-users > Peter Wallace Mesa Electronics (\__/) (='.'=) This is Bunny. Copy and paste bunny into your (")_(") signature to help him gain world domination. ------------------------------------------------------------------------------ Special Offer -- Download ArcSight Logger for FREE! Finally, a world-class log management solution at an even better price-free! And you'll get a free "Love Thy Logs" t-shirt when you download Logger. Secure your free ArcSight Logger TODAY! http://p.sf.net/sfu/arcsisghtdev2dev _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
