On Thursday, May 24, 2012 10:23:34 AM John Thornton did opine: > Just to update the results of last nights test run of the cobbled up > generator setup. While we had a devil of a time trying to make the > diesel motor that we coupled up to the generator stay at 1800 rpm it > stayed close enough for me to rapid my Z axis up and down at 295 IPM > with the spindle turning 2k for about 5 minutes with no complaints from > the Simodrive 611 despite the voltage varying wildly as motor powering > the generator surged up and down. > > So now I have two options as I see it and option B is preferred due to > the noise of running a diesel generator. > > 1) buy a 3 phase generator to run the shop. > No.
> B) figure out how to make my phase converter put out a proper 3 phase. You might be able to tune it eventually, but then it is still a load sensitive lashup. A true electric motor, driving a 3 phase alternator, is not load sensitive other than when overloaded. You will likely be down to about 56-57 hz at full load using one of those, but you will have accurate phase angles between the phase lines at all times. This is I believe, the important point being somewhat ignored when all I see are line to line voltages being discussed, and IIRC you posted links to some waveforms, none of which looked terribly clean to me. But the one thing your scope, a tek IIRC, couldn't do was display all 3 phases at the same time, the problem being that this scope has a 3rd wire ground. It cannot do that safely unless that 3rd wire ground is re-wired so that its ground is effectively the center, neutral wire of the 4 that make up the 3 phase wiring. Given that that would place the scopes case a considerable voltage above true earthen ground, that 'considerable' having the potential of being lethal, and it could overstress any noise bypassing filters in the scope, with failures there being rather impressive, the only real way to drive the scope's power would be from a full isolation transformer. But that, while safe for the scope, still leaves it potentially lethal to touch unless you yourself are well isolated from ground. But that is the only way to actually get to see the phasing relationships that are apparently AFU with the existing lashup. Looking at one phase at a time doesn't give ANY phasing info unless the scope can be triggered from its powerline, some can be. By doing that, then taking 3 pictures and overlaying them, or a triple exposure would likely be usable. > If anyone has any ideas on option B I'm all ears. I have a small line > reactor (rated at 3hp) that I can put on the phase converter output and > see what that does. I see claims of true 3 phase power from rotary phase > converters when searching for rotary phase converter and cnc so there > must be a way cause these claims don't seem to be coming from small time > shysters. For those methods that depend on capacitative and inductive reactance to shift the phases, the load range where it all just works, is relatively narrow. I favor the motor/alternator kit as the 2nd best solution. It is relatively insensitive to the load, maintaining the phase relationships at any load. If that generator set is for sale, and the coupling between it and the Diesel is easily unhooked, it can then be driven with a suitably sized single phase electric motor, while leaving the Diesel available should a prolonged power outage occur. [...] > >>>>>>> I think the idea of making a single-phase DC bus supply and > >>>>>>> losing the phase convertor had a lot of positives. So do I, but the knowledge to do that isn't hanging on yonder plum tree. The problem is that the average techie doesn't deal with high power stuff, and the average journeyman electrician deals with 3 phase only in terms of wire sizes, with no clue about the phase vectors that make it work. I have seen that first hand by a childhood friend who had been carrying a J card for 30 years. They might think to reverse 2 wires if the motor runs backwards but I wouldn't make a wager I couldn't afford to lose on that detail. My experience with tv broadcast puts me in the middle, but tv transmitters, being hungry beasts, are generally 3 phase from the gitgo, so the power folks gladly bring all 3 phases up the hill for a 50k-500k/hour customer and we don't have to deal with problems like this. Even if some custom logic has to be fudged up to make it work, the DC buss is at the end of the day, the cheapest, most cost effective way to do it. Probably by at least a 2/1 margin. That is why I said the motor-alternator is the 2nd best solution. It looks better when there are local laws about power factor correction since a DC supply of this size will probably be subject to such rules. Research time. Do it right, and once. 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> When I was little, I went into a pet shop and they asked how big I'd get. -- Rodney Dangerfield ------------------------------------------------------------------------------ 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
