On Thursday 26 December 2019 01:49:40 andrew beck wrote: > Hey guys. > > I have a bit of a story here and some questions.. I Have been seeing > the emails coming through and there looks like there is a massive pool > of knowledge here in the user list and the forum. So here it goes > hopefully someone can help me. > > I have a Big 6.5 ton VMC that I have been retrofitting with new > chinese servo drives and motors. 3 months ago I wired it up and after > a bit of mucking around I got the X and y axis moving fine. (I am > just using step and direction with a mesa 5i25-7i76 combo for now) > Then I connected up the Z axis motor and powered the 24v to the brake > with a cheap powersupply from aliexpress. > > I was trouble shooting the limit switches and moving the wires while > the machine was live when there was a big bang and the limit switch > arced across into the steel cabinet. It absolutely freaked me out and > I haven't been back to the mill since lol. > > Once I recovered myself I realised that I have blown the Z axis servo > drive up. What I think has happened is the powersupply was a floating > powersuppply(I actually knew that but didn't realise what that would > mean.) That meant that the brake actually had a lot more than 24 > volts in it relative to machine earth(like 200v I am guessing, it was > a big bang!) > > Anyway I think somehow the power backfed via the Z axis servo down the > 24 volt brake line and into the servo drive and made the magic smoke > come out. > > They are about $400 usd so I wasn't to happy about that. > > But the good news is I told my supplier about it and he said they > would repair it for free. they decided it was truely toast when they > had a look, so they just gave me a new drive. which was pretty cool. > > And after all that I am just getting into connecting this thing up > again and I don't want to blow anything up. > > I will send a diagram later and some photos but for now I have these > questions. > > > 1. how do I ground the 24 volt switching powersupplies.
Single point bolt, star ground. - rail of all. With only one ohmic connection to the buildings static ground at that bolt.Get > 2. Should I isolate the 24volt switching > powersupplies from machine > ground? bearing in mind that one of the powersupplies is for logic > power and one is just the the servo motor brake. > 3. The old wiring had a isolating transformer to make 240 V single > phase for the switch powersupplies. They didn't use a neutral back to > the shed main board. Will a neutral help me here? A neutral is std practice here. No clue, where you are. Recommended by grandpa Gene. But keep the neutral separately wired from static ground to prevent ground loops. According to the NEC here, the only place they should be common is at the service entrance ground rod connection. Do not connect it to your single point ground as that will create a huge ground loop just waiting for a nearby lightning strike. > 4. My biggest unknown is not knowing all the best safe practices > when working with large voltages. (my brother is a apprentice > electrician which helps but I would appreciate some tips of what not > to do and what to do as a checklist or something. > If he's an apprentice, he should have a copy of whatever serves as the NEC in your region. > Regards > > Andrew > > _______________________________________________ > Emc-users mailing list > Emc-users@lists.sourceforge.net > https://lists.sourceforge.net/lists/listinfo/emc-users 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
