My research shows that a suitable single phase motor to drive a generator does not exist above 7.5 hp and even at that level your talking >1k. I assume it would take more than 7.5hp to drive a generator capable of running a machine that size. So I really don't see this as an option at this point.
Heck I couldn't even figure out how to get 2 traces to show up much less try for 3 on the scope. I even tried to join the teck forum but they must have thought I was a spammer or they don't moderate it any more John On 5/24/2012 10:24 AM, gene heskett wrote: > 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 ------------------------------------------------------------------------------ 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. 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