On Monday, May 28, 2012 12:20:24 PM Kirk Wallace did opine: > On Mon, 2012-05-28 at 08:43 +0100, Dave Caroline wrote: > > I think most people looking at idler rotary converters dont actually > > scope the phases > > I only came across one site stating the obvious > > > > given the basic diagram of > > > > 120 ac to motor P1 and output phase L1 > > neutral--nc > > 120 ac to motor P3 and output phase L3 > > Capacitor P1 to P2 and to output phase L2 > > > > will notice the 180 deg phase of the two 120 lines are connected > > directly to L1 and L3 so that is at 180 degrees not the 120 it should > > be. So L2 is some where in between L1,L3 but if it was 120 degrees > > from L1 then it would be 60 from L3 > > the voltage imbalance would be silly so it is adjusted to be 90 form > > L1 and it just about works > > ... snip > > I made this argument a couple of years ago and I was eventually > persuaded that I was mistaken. In trying to understand why, I made this > diagram. > > http://wallacecompany.com/machine_shop/EMC2/three_phase_converter-1b.png > > This may change if the Neutral is used and taken into account, but this > is my current understanding of how the most popular rotary converters > work. I think a key point is that a Phase is not just one wire, it is > the signal created by two wires. That is why two 120 VAC sources, say L1 > and L2, no matter what their relation to Neutral is, produces a single > phase. For a converter, the other two phases are not L2 and L3, but > L1-L3 and L2-L3.
Correct. But to make 3 phases from one requires that the center, neutral "N" connection of the 3 phase motor idling like this, cannot be connected to the system neutral as it will be self pulled toward the L3 point by many tens of volts if it was to be measured to the neutral/ground. Now IF, note caps, Johns kit could be totally isolated from ground, then connected as a 4 wire wye load, using the N terminal as neutral, it should also work. Unfortunately this will put the frame ground of the whole kit a potentially lethal voltage away from a real ground, and all power to that machine, even for light bulbs, will have to come from the bastardized (that as kind as I can be) power of this wye hookup. A drop cord to a wall plug could lead to some very interesting fireworks. So we isolate it, at some cost yet to be determined, and everything is then safe & should be happy as a clam. By now, I'd be losing interest in the Siemans label, and would be checking the Yaskawa catalogs for a suitable single phase replacements. Cheers, Gene -- "There are four boxes to be used in defense of liberty: soap, ballot, jury, and ammo. Please use in that order." -Ed Howdershelt (Author) My web page: <http://coyoteden.dyndns-free.com:85/gene> I can't die until the government finds a safe place to bury my liver. -- Phil Harris ------------------------------------------------------------------------------ Live Security Virtual Conference Exclusive live event will cover all the ways today's security and threat landscape has changed and how IT managers can respond. Discussions will include endpoint security, mobile security and the latest in malware threats. http://www.accelacomm.com/jaw/sfrnl04242012/114/50122263/ _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
