Hey Gene thanks for the reply.
I think I follow most of what you said there. And my neutral and ground will only be tied back at the shed main electrical box definitely. I think the main problem I have is how the 24 volt powersupplies should be wired and connected to frame ground. I have sent some links in my reply to Andy and have a drawing on there. If you have a look I would appreciate the thoughts. Regards Andrew On Fri, Dec 27, 2019 at 1:08 AM Gene Heskett <ghesk...@shentel.net> wrote: > 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 > _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
