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| Metalworking (rec.crafts.metalworking) Discuss various aspects of working with metal, such as machining, welding, metal joining, screwing, casting, hardening/tempering, blacksmithing/forging, spinning and hammer work, sheet metal work. |
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#81
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On Sat, 28 Aug 2004 09:33:05 GMT, Gunner
wrote: But really..what the dickens are those caps good for? Ive got a number of them. 7 Farad, what voltage? If they're only 6 or 8 volt, they were probably meant for BIG computer power supply filtering/momentary UPS use, and are pretty much worthless for anything else. Feed them 13.8 volts, and you'll have a nice little bomb on your hands... If they're rated 16V to 20V, you have a small gold mine - but as you describe the ones you have they would be too small, the 1 Farad 16V they use is the size of a cleanser can, 3" diameter by 8" tall. Car Stereo "Boom Car" nuts (the AH's you can hear three blocks away with your windows rolled up tight - because they're driving with their windows down and wearing earplugs...) use the 1 Farad caps as power supply boosters right in front of the amplifier, it will act as a huge battery to supply the momentary burst of power for each "Boomp!", then it recharges as the alternator valiantly tries to keep up. Wanna get them back? Get a nice stereo in your car, 100 WPC minimum, which doesn't have to be expensive if you can settle for last year's closeout amps and speakers... And when they pull up next to you booming (c)rap at a long red light, drop your windows and crank some Jazz, Classical or Big Band right back at them. Let Doc Severinsen or Don Dorsey's Beethoven "Rage over a Lost Penny" drown 'em out. I get dirty looks, but they get the message. ;-) -- Bruce -- -- Bruce L. Bergman, Woodland Hills (Los Angeles) CA - Desktop Electrician for Westend Electric - CA726700 5737 Kanan Rd. #359, Agoura CA 91301 (818) 889-9545 Spamtrapped address: Remove the python and the invalid, and use a net. |
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#82
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On Sat, 28 Aug 2004 07:56:40 -0400, Steve Smith
wrote: Jerry, I have a hard time believing a bigger fan will get you very far. If this were true, motor manufacturers would do it, especially on Sears compressors. I'm sure extra air will get you somewhere, but before long the hot spot will move inside the windings, where your fan can't reach. Extra air (and lower than rated ambient temps) might get you 10-20% (just a guess), but not 50-100% continuous duty. Intermittent, sure. I have done this on my single-phase air compressor motor. I rigged up some flexible dryer vent to a good-sized squirrel-cage blower, blowing a good blast of air into one end of the motor. It made a big difference when I was using lots of air, as in DA sanding. Take a look at heatsink specs as from Wakefield, note the thermal resistance from sink to ambient of any heatsink as a fn of air velocity (or not). . Motors do have fans in them, but they don't produce enough pressure to get much airflow thru the limited spaces inside the motor. |
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On Fri, 27 Aug 2004 18:09:20 GMT, "Jerry Martes"
wrote: snip I have a little dyno with which I can measure the efects of changing idler size on a 3 phase motor's ability to deliver power. The improvement in "tool motor power delivering ability" is almost undetectable for NO idler or for an idler 1 1/2 times tool motor HP when the tool motor is loaded up to 2/3 of its name plate Max HP. It impressed me that the 3 HP 3 phase motor that I use produces 3 HP at 1725 RPM to the load even when fed from single phase without idler. It is probably obvious to those who have thought about it, that a heavily loaded (near full name plate HP) 3 phase motor does run alot smoother when it is fed thru a big-big idler. It might be concluded that 3 phase motors that arent loaded heavily for long periods can be run from single phase without an idler. But, a 3 phase motor will produce its full name plate HP even when fed single phase with no idler. Jerry snip All the 3 pjase motors I've tested will produce more than their name plate rated HP when fed good 3 phase. A 3 HP motor will deliver 5 HP to the load when fed good 3 phase. It does get exactly as much hotter as you'd guess so you'd want to put an external fan on it. Heating of the motor is the principal factor that limits the amount of power that an induction motor can safely deliver. That could be improved by external fans and aditional heat sinks. Since the motor conducts heat away from the windings thru its frame, the entire frame becomes a significant factor in determining the max power rating. The 2/3 name plate HP 'rule of thumb' for guessing at the max power available from a 3 phase motor, fed single phase, must be altered to allow the fact that the heat sink and fan is working as though it is a 3/3 HP motor. It might be interesting to note that many 3 phase motors that are used in Rec Craft applications are often commercial tool motors that will not be loaded to their original ratings so the need for producing 'good 3 phase' is often misunderstood. A tool motor can easily spun up with an idler much smaller than the tool motor's name plate HP, contrary to the implication that Big idlers are needed. Most tools that use 3 phase motors can be unloaded while being started, so even a switch and capacitor can spin up most 3 phase tools. As I noted above, the 3 phase motor will provide the load with very nearly the same HP when fed either single phase or 3 phase, when the motor is loaded to only 1/2 its name plate HP. At those "lightly loaded" conditions, I've been unable to descern the difference between the performance of the 3 phase motor fed either 3 phase or single phase. The instanteous loss of torque every 1/120th of a second exist in either a single phase motor or a 3 phase motor fed single phase. That "pulsing" doesnt become measurable when the motor is loaded to less than about 3/4 its rated HP. For loads under about 3/4 its name plate rated HP (2 1/4 HP for a 3 HP motor) a 3 phase motor fed single benefits little from the use of in idler. The pulsing is probably the first noticable result of having no idler (or small idler) when using single phase to drive a heavily loaded 3 phase motor. I plotted (with Excel) the HP vs RPM for the 3 HP 3 phase motor, fed single phase, with a 5 HP idler and with no idler. I'll send you a copy if you'd want to see it.. Jerry A pair of good posts. It really is refreshing to see some solid input on 3 phase phase conversions which is both soundly based and backed up by direct measurement. I hope it will dispel some of the myths on minimum sizes of idlers and the practical usefulness of precision "tuning". Jim |
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Don Foreman wrote: On Sat, 28 Aug 2004 07:56:40 -0400, Steve Smith wrote: Jerry, I have a hard time believing a bigger fan will get you very far. If this were true, motor manufacturers would do it, especially on Sears compressors. I'm sure extra air will get you somewhere, but before long the hot spot will move inside the windings, where your fan can't reach. Extra air (and lower than rated ambient temps) might get you 10-20% (just a guess), but not 50-100% continuous duty. Intermittent, sure. I have done this on my single-phase air compressor motor. I rigged up some flexible dryer vent to a good-sized squirrel-cage blower, blowing a good blast of air into one end of the motor. It made a big difference when I was using lots of air, as in DA sanding. Take a look at heatsink specs as from Wakefield, note the thermal resistance from sink to ambient of any heatsink as a fn of air velocity (or not). . Motors do have fans in them, but they don't produce enough pressure to get much airflow thru the limited spaces inside the motor. I bow to the voice of experience. I wasn't so much concerned with sink to ambient as I was with inside motor to sink, but as you say, it seems to work. Steve |
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#85
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In article ,
Old Nick wrote: On 26 Aug 2004 16:31:22 -0400, (DoN. Nichols) vaguely proposed a theory ......and in reply I say!: remove ns from my header address to reply via email Now you see, _this_ is where the idea of a normal old 1 PH motor or 2 driving an alternator start to kick in again....G?) So. I have a 20HP motor...3PH. If I ran it up to speed, using a pony, I can then expect 80 amps, until I get it tuned? I just don't HAVE 80 Amps. Hmm ... you could start out by adding a respectable capacitance (power factor correction) in parallel with the motor to reduce that current quite a bit so you could then tune the converter, and then tune the power factor correction capacitance for the optimum current draw. Note that the optimum will shift somewhat depending on load applied, so if you expect to have the idler running unloaded more than at a respectable load, you probably should tune the power factor correction capacitance for the no-load condition. Apparently running these things unbalanced is a lot messier than running them on the right no of phases. I'm not sure about that as far as the power factor correction bit is concerned. It is just that if you have the right number of phases available, you also typically have beefier breakers and wiring available to start with. Also -- I *think* (but I don't know for sure) that a fully loaded motor would have much less need for the power factor correction. Once tuned, what current would it use? How much more would it use than say, a 10HP 3PH as an idler, in and of itself (not under load). With both tuned, of course the 20 HP one would draw more current. However a tuned (and power factor corrected) 20 HP motor running as an unloaded idler probably will draw significantly less than an unloaded 10 HP one running as an idler with no tuning or power factor correction. You have a clamp-on ammeter don't you? Check what the 10 HP is currently drawing (I believe that you already have that one). I don't have anything that big to check, since I actually use VFDs, and lucked into my first one before ever building the planned rotary converter -- or even acquiring the motor to serve as the idler. Good Luck, DoN. -- Email: | Voice (all times): (703) 938-4564 (too) near Washington D.C. | http://www.d-and-d.com/dnichols/DoN.html --- Black Holes are where God is dividing by zero --- |
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On Sat, 28 Aug 2004 15:12:33 GMT, Bruce L. Bergman
vaguely proposed a theory .......and in reply I say!: remove ns from my header address to reply via email No! No! I said this once before and was reminded of the title. Sousa's "The Liberty Bell"...Monty Python's theme tune. I suppose the littel crapheads will not know the implications, but the tune is so bouncy and silly when simply heard, which is probably why Python chose it. And when they pull up next to you booming (c)rap at a long red light, drop your windows and crank some Jazz, Classical or Big Band right back at them. Let Doc Severinsen or Don Dorsey's Beethoven "Rage over a Lost Penny" drown 'em out. I get dirty looks, but they get the message. ;-) -- Bruce -- ************************************************** *** I have decided that I should not be offended by anybody's behaviour but my own......the theory's good, anyway. |
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On Sat, 28 Aug 2004 05:00:28 -0700, Larry Jaques
vaguely proposed a theory .......and in reply I say!: remove ns from my header address to reply via email On Sat, 28 Aug 2004 18:32:28 +0800, Old Nick calmly ranted: On 24 Aug 2004 19:25:25 GMT, (Charles A. Sherwood) vaguely proposed a theory ......and in reply I say!: remove ns from my header address to reply via email I figured that the big grinder would act like a rotary phase converter for the dust collector, but I don't see any current in the third leg with a clamp on ampmeter. So to penetration, lubricant, heat, flow, affected zones, I can now add "amount of current in the third leg". He's obviously never peed on a 'lectric fence. nnnnnhhhhhhgh! I have touched one a couple of times, and well..... No wonder metalwork is more fun than sex. G Ooh, you _are_ getting old, Nick. Maybe I peed on an electric fence once! G rrgh! Makes me me feel quite ummmm...well, there's a significant pucker factor there! errreghgr! Actually I was thinking of the guy who was here a while make (Mike I think?) whose SO was lambasting him about not keeping in touch, on this forum. With all these terms popping up, I always thought she had no hope. ************************************************** *** I have decided that I should not be offended by anybody's behaviour but my own......the theory's good, anyway. |
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On Sat, 28 Aug 2004 18:47:16 +0800, Old Nick wrote:
So. I have a 20HP motor...3PH. If I ran it up to speed, using a pony, I can then expect 80 amps, until I get it tuned? I just don't HAVE 80 Amps. Well, you don't *have* to tune it. Motor loads in general don't care much if the phase to phase voltage balance is spot on or not. But you *will* want to use power factor correction to get the reactive currents seen by your supply wiring and breaker panel down into a more comfortable region. Once tuned, what current would it use? How much more would it use than say, a 10HP 3PH as an idler, in and of itself (not under load). If I have some idea of that, then I can say well, I need so much dfor idle, and so much for the actual load. Ok, my tuned 20 HP idler consumes less than 400 watts no load. In other words, the *real* current drawn by it to keep it running is under 2 amps. With a fully loaded 7.5 HP load motor being driven by the rotary, total *real* current draw from the wall is just over 25 amps, so it runs nicely on a 30A motor rated breaker in the panel. Now without power factor correction, the imaginary current draw is about 60 amps, so total draw, real and imaginary, with a 7.5 HP load motor is around 67 amps. (You're dealing with vectors here, so real and imaginary currents have to vector sum rather than just using simple addition.) If you don't use power factor correction, you're going to need a breaker, and associated wiring, heavy enough to handle that 67 amp draw. So use power factor correction. The size of the power factor correction capacitor is a function of the idler motor impedance, which will vary from one idler motor to another depending on internal motor construction factors not under your control, how well the phases are balanced, which will vary depending on how much capacitance you use to balance the phases (good balance here will reduce power factor, and hence the needed size of the power factor correction capacitor), and the real load power, which will vary depending on the size and loading of the load motor(s) being driven (this has only a small effect when the idler motor is substantially larger than the load motor, so it can normally be ignored). In short, you have to experiment to find the right size power factor correction capacitor for your particular setup. Just keep adding capacitance across the 1 ph line while monitoring an amp clamp meter *on the breaker side of the line* until you see a minimum current value. (Currents on the motor side of the power factor correction capacitor won't decrease.) For a 20 HP idler, start with a value of about 200 uF, then adjust from there. Current will decrease as you increase capacitance until you reach a minimum current, then it will increase again as the load becomes capacitive rather than inductive. I like to pick a power factor capacitor value that stays just a little on the inductive side of minimum. That avoids large voltage excursions on the load side with changes in load. (Load voltage regulation becomes touchy right at mimimum.) You'll need a box full of capacitors to make this adjustment. You can often get an assortment of used run capacitors from the back yard of an industrial air conditioning place for the asking, or for a nominal charge. These capacitors don't normally wear out (oil filled), unlike start capacitors (which you shouldn't use), so good used ones are fine. The A/C places generally use new capacitors when they do a motor replacement, and bill the customer, so they wind up with a bunch of good used ones laying around. Since disposing of them requires that they be treated as hazardous waste, they're usually glad to give them to you. Gary |
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In article ,
Old Nick wrote: On 28 Aug 2004 08:00:46 -0700, (Dan Caster) vaguely proposed a theory ......and in reply I say!: [ ... ] Ok. Again here I come up against the feeling that both the RPC and this device need "tuning" to a specific _driven_ device. in other words they drastically alter their characteristics as you alter their loads? Otherwise you get inefficiencies or imbalances.... Sorry to pound this, but I do feel that everybody says it's simple, and it's not that tough, I can see. But I get the feeling that most of these devices are used for pretty steady-state use. It depends on just how picky you are. If you are going to mostly have the idler running unloaded, and just run the machines for short periods -- tune it for the unloaded state. If you are going to be running a machine most of the time, tune it for that specific machine -- running about half loaded. If you are going to be running one machine or the other most of the time, but about equal times, tune it for the average of the two. I think that you are thinking that if it is just a little off tune, it will draw humoungous amounts of extra current. It won't. It will draw just a bit extra. Most people who bother to tune probably tune it for unloaded. And the things which really matter for keeping the breaker from blowing too frequently, or the wires from overheating is the power factor correction. The tuning mostly helps things like fast starts with a heavy load (e.g. a gearhead lathe in high), or things like "plug" reversing. The normal reason for tuning before power factor correction is that the tuning caps do a little bit of power factor correction too. So, if you want *optimum* power factor correction, you apply that *after* you are done tuning. With your big 20 HP motor, you can probably do without *any* tuning, but you *will* need the power factor correction to keep from blowing your breakers. I don't have enough power to run a 20 HP load in the shop. The best outlet that I have at 220 VAC single phase is a 30 A one, which I calculate to be about 7-1/2 HP. But I *might* be able to spin a 20 HP motor with a pony motor and then connect it as a rotary converter idler, as long as I don't ask it to handle too many HP of load. But I almost certainly would need to do power factor correction, or the breaker would be tripping all the time. I might even use an alternate circuit to power the pony motor. I don't know what a good starting point for power factor correction on a 20 HP motor would be -- perhaps someone who is using one could chip in with that information. Mostly -- stop worrying and *do the job*. If you want tuning later, you can apply it later -- and possibly need to tweak the power factor correction. But your machines will be happy. Enjoy, DoN. -- Email: | Voice (all times): (703) 938-4564 (too) near Washington D.C. | http://www.d-and-d.com/dnichols/DoN.html --- Black Holes are where God is dividing by zero --- |
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I am with Don. You don't need to tune this anymore than any other
motor driving a generator. You do need to adjust the pulleys so the single phase motor is driving the three phase motor. Dan (DoN. Nichols) wrote in message - Ok. Again here I come up against the feeling that both the RPC and this device need "tuning" to a specific _driven_ device. in other words they drastically alter their characteristics as you alter their loads? Otherwise you get inefficiencies or imbalances.... Sorry to pound this, but I do feel that everybody says it's simple, and it's not that tough, I can see. But I get the feeling that most of these devices are used for pretty steady-state use. It depends on just how picky you are. uld chip in with that information. Mostly -- stop worrying and *do the job*. If you want tuning later, you can apply it later -- and possibly need to tweak the power factor correction. But your machines will be happy. Enjoy, DoN. |
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#93
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Old Nick wrote in message . ..
On 26 Aug 2004 20:06:25 -0700, (Dan Caster) vaguely proposed a theory ......and in reply I say!: remove ns from my header address to reply via email If you can't find cheap three phase motors, you probably are not looking in the right places. Try the scrap yards. I mean the yards that supply steel scrap to steel mills. Not salvage yards. Actually I just a 30" circular saw that I am going to drive from my tractor, and it has a 6hp 3PH motor attached, which I don;t need. I also remembered I have a 3PH motor in the other shed. However that one's 20 HP! and I believe they suck juice just to run. If you weren't so far away - you're in WA, right? - I'd give you a 3HP 3 phase motor to play with. I got quite a few over the years but I'm on the east coast. Nearly every tool I have is 3 phase. Frankly I think all this to-ing and fro-ing about faking 3 phase is fine & undoubtedly necessary for people living in the USA - their 110V power sucks and their tariff rates do too. Here in Australia - just go get 3 phase power put on and stop screwing about. I've had it put on to 3 separate places over the last 30 years without any dramas, just varying costs :-) I've got 3 phase 415V 90A per phase coming into my place and I can plug reverse a 7.5HP motor with only a momentary blink on the light circuit. It also means that I really, really don't need to worry about what size welder I want to run. Paying the power bill hasn't been an issue - so far. PDW |
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#95
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On Sun, 29 Aug 2004 07:32:47 +0800, Old Nick
wrote: On Sat, 28 Aug 2004 15:12:33 GMT, Bruce L. Bergman vaguely proposed a theory ......and in reply I say!: And when they pull up next to you booming (c)rap at a long red light, drop your windows and crank some Jazz, Classical or Big Band right back at them. Let Doc Severinsen or Don Dorsey's Beethoven "Rage over a Lost Penny" drown 'em out. I get dirty looks, but they get the message. ;-) No! No! I said this once before and was reminded of the title. Sousa's "The Liberty Bell"...Monty Python's theme tune. I suppose the littel crapheads will not know the implications, but the tune is so bouncy and silly when simply heard, which is probably why Python chose it. And I say No! No! right back, I can't use the Liberty Bell march. That's already my Cellphone Ringtone... ;-) (Not to say that working in a small business can sometimes seem like the Ministry of Silly Walks or anything, mind you...) Heck, I don't even know the implications to which you imply. Mind giving us the Cliff Notes version to enlighten the unwashed masses? -- Bruce -- |
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In article ,
Old Nick wrote: On 29 Aug 2004 01:26:22 -0400, (DoN. Nichols) vaguely proposed a theory ......and in reply I say!: remove ns from my header address to reply via email Will the RPC be anywhere near as effective and versatile, under limited power availability and in particular under varying load conditions? I have been told various answers to this. I reckon a motor gen will be maybe 70% efficient. With no personal experience with a modern motor generator (the closest are the dynamotors and 28 VDC to three-phase 400 Hz units used in WW-II aircraft) (And also a somewhat more modern "Georator" -- a motor-generator which takes 60 Hz input and produces 400 Hz output.) The Georator is made perhaps fifty miles from here, but as it does not do anything that *I* need, I've not visited them. They can be found by a web search -- but the shipping would kill you, I suspect. However, unless you have synchronous motors on both ends, you will need some difference in pulley size (an adjustable one) to tune the output frequency to match the input frequency (60 Hz in the US, 50 Hz in the UK, not sure which in Oz). Those pulleys and the belt are certainly going to contribute to poor efficiency. So -- unless you have a motor and a generator actually sharing a single shaft and set of bearings, I think that your efficiency will be far less than a typical rotary converter. So I get somewhere around 6.7KVA. I get the feeling that a mogen will alter its characterisitics under varying loads, but not as much as an RPC. Therefore the headroom is a lot less. That last bit sums up my problem. Sorry about the rant A heavily oversized rotary converter (something in excess of the 1.5X guideline) will probably not notice much of the smaller loads, so the tuning (if any) can be pretty much ignored. If you want to change the tuning with a single load at a time, you can add tuning capacitors at the load motor (which will effectively be in parallel with the those on the idler motor), so you are tuned for each single load condition. Personally, I would not bother to go this far. However, if you are running several small loads and one big one (say an air compressor), you might want to tune the air compressor load. But note that each additional load, once it is started, adds to the capability to start other loads, as the motor of the machine tool becomes an addition to the idler. OK. I have 40A, 240 Volt available. 9.5KVA. I have not built any RPCs. I realise I can do it on the cheap as I have (maybe) a lot of the gear I need already. So -- build one and try it. If it doesn't cost you much but time, why not see whether it serves your needs. I need a big motor, well-balanced and power factored. Bit of fiddling. OK. You need power factored. If the motor is big enough, compared to the loads, there is probably very little reason to tune the balance, other than to feel that you've done the best that you can. I have a rough (foggy with age and 25 years of little- to non-use) idea of starting currents and no-load synch currents of sync motors. I know what happens as you start to load them and they slip a bit and start using power. But the stopping point for me is that an idler basically MISuses a 3PH motor, and all the rules come under question immediately. So -- don't analyze it to death. Breadboard up a RPC using what you have and see how it works for *your* needs. If it does what you need, fabricate a housing for the components, so things are cleanly mounted and people are protected from exposure to the high voltage terminals. (Obviously, while it is breadboarded, you should be the only one near it, since you will know what not to touch. :-) I have googled, and looked at all the articles. The above is how far I have got. I have tried, and sorry if I am missing something. I know a motor-gen setup is heavy and expensive. I can live with that, because the cost of getting a bigger 33KV - 240V trannie on my line would be a heap. The next step is 20KVA, and probably $4000. "Trannie"? I presume that you mean "transformer", not "transmission" which is what I normally hear that short form used for? I know I can tweak the RPC. But after all the tweaking, the RPC _still_ appears to suit a certain load; No -- a *static* phase converter only works with a narrow range of load. A rotary phase converter can easily handle any load from 66% of the idler's rating on down to so tiny that you barely know that it is running. (E.G. you could run a 1/8 HP three-phase motor from a 7.5 HP inverter with no problems. Yes, it would cost you less to *run* a smaller rotary converter to do that particular task, but if you are also using it for other equipment, size it for the largest that you need to run -- or if you have a larger motor, go *beyond* the 1.5X starting point. It will draw a bit more current, even after power factor correction, but it will cost less than building two or three rotary converters -- each to run a different load. And remember that as you switch on extra machines on that RPC, they are contributing to the conversion job for the next machine you need to start -- until you get enough machines running that the total current trips your master breaker for the RPC. not given the cost, or the size of idler making it easier, but because if you tweak for no load, then use various loads, you get efficiency losses. Again, this is not a cost issue, so much as limited power supply and making that work. So I realise it takes a lot of power costs to _pay_ for the thousand dollars a motor gen will cost me to set up. Again -- *try* a RPC -- breadboarded just to convince you that it will work. Your major cost is likely to be the capacitors to tune the power factor (ignoring any balancing capacitors which are optional, after all). And elsewhere in this by now massive thread, you have a starting point for the power factor capacitor values. (Not from me, but from someone who is *running* a RPC of the same size. I think that I will now drop out of this thread, as I seem to be typing the same thing time after time. Come back with more questions after you *try* a RPC with the materials you have on hand. Talking about it any more is counterproductive. Good Luck, DoN. -- Email: | Voice (all times): (703) 938-4564 (too) near Washington D.C. | http://www.d-and-d.com/dnichols/DoN.html --- Black Holes are where God is dividing by zero --- |
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On Mon, 30 Aug 2004 10:58:19 +0800, Old Nick wrote:
I have a rough (foggy with age and 25 years of little- to non-use) idea of starting currents and no-load synch currents of sync motors. I know what happens as you start to load them and they slip a bit and start using power. But the stopping point for me is that an idler basically MISuses a 3PH motor, and all the rules come under question immediately. Thinking of it as a motor just confuses the issue. Think of it as a rotary *transformer*. That's the function it actually performs. Like any transformer, as long as it is big enough (at least 1.5x the hp rating of the largest single load), and is designed correctly, it does its job with very good efficiency. But after all the tweaking, the RPC _still_ appears to suit a certain load; not given the cost, or the size of idler making it easier, but because if you tweak for no load, then use various loads, you get efficiency losses. Again, this is not a cost issue, so much as limited power supply and making that work. So I realise it takes a lot of power costs to _pay_ for the thousand dollars a motor gen will cost me to set up. No! Tuning has very little effect on RPC efficiency. What tuning does is improve phase to phase *voltage balance*. As long as phase balance is reasonable (and reasonable can be a pretty rough approximation when you're only driving motor loads, which is why so many people are able to use RPCs with no tuning), efficiency will be good if the RPC had good efficiency *as a 3 ph motor*. The primary factors which determine RPC efficiency are the winding resistance (wire size), the magnetic path lengths, and the magnetic permeability. The people who designed the motor you use as a RPC determined those things. If it was a good motor, it'll be a good RPC. End of story. The main reason to tune a RPC is if you have sensitive loads, like control electronics, running off of it. Some (by no means all) electronic loads are picky about phase to phase voltage balance. An example of this sort of equipment would be a CNC machining center. Some, again not all, welders will bitch about poor phase to phase balance. In those cases, balancing the converter, or making sure the sensitive loads are fed by the stiff legs (L1-L2) will resolve the problem. Gary |
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On Mon, 30 Aug 2004 03:26:16 GMT, Bruce L. Bergman
vaguely proposed a theory .......and in reply I say!: remove ns from my header address to reply via email Basically that anybody playing those things would say "Monty Who?" Heck, I don't even know the implications to which you imply. Mind giving us the Cliff Notes version to enlighten the unwashed masses? -- Bruce -- ************************************************** *** I have decided that I should not be offended by anybody's behaviour but my own......the theory's good, anyway. |
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On Mon, 30 Aug 2004 02:54:22 -0400, Gary Coffman
vaguely proposed a theory .......and in reply I say!: remove ns from my header address to reply via email OKOK! G I accept the input. But there is that capital cost enticement. I am more interested in the resultant output. If I can't afford a motor-driven alternator than I can't. I need to check out figures before I will be happy. Wish me happy hunting. I mean it when I say thanks. ************************************************** *** I have decided that I should not be offended by anybody's behaviour but my own......the theory's good, anyway. |
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On Sat, 28 Aug 2004 16:21:41 -0400, Steve Smith
wrote: I bow to the voice of experience. I wasn't so much concerned with sink to ambient as I was with inside motor to sink, but as you say, it seems to work. Threephase motors are designed to run on threephase power. The designers include enough fan to cool the motor when run as it was designed to run. They work hard to optimize the design for cost, size, and efficiency when run under specified conditions. The fan is a source of inefficiency so they don't use any more fan than necessary. It has been said many times that 3phase motors must be derated when run on singlephase or unbalanced 3-phase power because of increased I^2R losses. But this is just heat. If we can deal with the heat with better cooling in our misapplications, then they can pull the load. We'll just have less efficiency as the price for our misapplication. The largest thermal gradient is probably in the insulation between the windings and the stator iron. If we can signficantly increase airflow over those windings then we can greatly improve the rate of heat removal, and therefore increase the power we can get from a motor operating under conditions different than it was designed for. Sorry if this violates any sacred beliefs, but it does work. |
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#103
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Well, Nick, the incremental cost for 3 phase should have been:
heavier poles, maybe. I had to go from 100mm round 6.5m steel poles to 125mm SHS 8m poles. If you had heavy timber poles, no difference. 2 extra wire runs. I had bundled aerial cable run in. To get the equivalent single phase supply - say 270A 240V - I shudder to think what the cable alone would have cost. a 3 phase transformer instead of single phase. Been there, done that here in Tas in the last year. It cost me $8K. Yes, you can buy a lotta single phase and 3 phase motors for the price difference, but all the screwing about in the world still won't deliver you true 3 phase, nor will you ever be able to pull more than (say) 90A off your single phase supply. Nor can you extend your power cabling anywhere near as simply & cheaply. I had the meter box put on the last pole and ran my consumer mains myself to my house, shed and to a future shed site by a dam. The cabling costs to run 20A 3 phase over any distance are a lot less than trying to run 60A single phase over the same distance, and I get to run 3 phase motors for water pumps etc. I ran a 63A 3 phase supply to a sub board in the house then pulled my single phase circuits off it. Ditto for shed and 20A down to the dam. It cost me upfront but life is a lot simpler long term - which was my point. You could just leave that 6 HP motor on the sawmill instead of screwing about using the tractor PTO for example, coz you're gonna find you need to use the tractor to move stuff at the same time as you need its PTO drive, I'll bet. Been there - I have a 36" dia circular sawmill modelled loosely after Rick Buxton's. I designed it for a PTO drive so I could move it about on my NSW farm. In the end it was easier to move logs to the saw using the tractor. Course, if you have 2 tractors....... PDW Umm....I am 3 Km from the nearest 3PH. :- It cost $8000 to get 1Ph put in just from next door. Frankly I think all this to-ing and fro-ing about faking 3 phase is fine & undoubtedly necessary for people living in the USA - their 110V power sucks and their tariff rates do too. Here in Australia - just go get 3 phase power put on and stop screwing about. I've had it put on to 3 separate places over the last 30 years without any dramas, just varying costs :-) I've got 3 phase 415V 90A per phase coming into my place and I can plug reverse a 7.5HP motor with only a momentary blink on the light circuit. It also means that I really, really don't need to worry about what size welder I want to run. ************************************************** *** I have decided that I should not be offended by anybody's behaviour but my own......the theory's good, anyway. |
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#104
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In article , Peter Wiley
says... Been there, done that here in Tas in the last year. It cost me $8K. Yes, you can buy a lotta single phase and 3 phase motors for the price difference, but all the screwing about in the world still won't deliver you true 3 phase, nor will you ever be able to pull more than (say) 90A off your single phase supply. Nor can you extend your power cabling anywhere near as simply & cheaply. I had the meter box put on the last pole and ran my consumer mains myself to my house, shed and to a future shed site by a dam. The cabling costs to run 20A 3 phase over any distance are a lot less than trying to run 60A single phase over the same distance, and I get to run 3 phase motors for water pumps etc. I ran a 63A 3 phase supply to a sub board in the house then pulled my single phase circuits off it. Ditto for shed and 20A down to the dam. Sounds nice - but I notice you did not mention anything about the peak demand meter. Jim -- ================================================== please reply to: JRR(zero) at pkmfgvm4 (dot) vnet (dot) ibm (dot) com ================================================== |
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A RPC does not need much tweaking and the very best tweaking does not
change much from no load to full load. So I disagree with you when you say if you tweak for no load, you get efficency losses at various loads. Dan Old Nick wrote in message But after all the tweaking, the RPC _still_ appears to suit a certain load; not given the cost, or the size of idler making it easier, but because if you tweak for no load, then use various loads, you get efficiency losses. Again, this is not a cost issue, so much as limited power supply and making that work. So I realise it takes a lot of power costs to _pay_ for the thousand dollars a motor gen will cost me to set up. ************************************************** *** I have decided that I should not be offended by anybody's behaviour but my own......the theory's good, anyway. |
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#107
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I missed the staff meeting but the minutes show Bruce L. Bergman
wrote back on Mon, 30 Aug 2004 03:26:16 GMT in rec.crafts.metalworking : On Sun, 29 Aug 2004 07:32:47 +0800, Old Nick wrote: On Sat, 28 Aug 2004 15:12:33 GMT, Bruce L. Bergman vaguely proposed a theory ......and in reply I say!: And when they pull up next to you booming (c)rap at a long red light, drop your windows and crank some Jazz, Classical or Big Band right back at them. Let Doc Severinsen or Don Dorsey's Beethoven "Rage over a Lost Penny" drown 'em out. I get dirty looks, but they get the message. ;-) No! No! I said this once before and was reminded of the title. Sousa's "The Liberty Bell"...Monty Python's theme tune. I suppose the littel crapheads will not know the implications, but the tune is so bouncy and silly when simply heard, which is probably why Python chose it. And I say No! No! right back, I can't use the Liberty Bell march. That's already my Cellphone Ringtone... ;-) Bach's Tacotta and Fugue in D. Atomic Bach! Heavy Metal Boroque! That or Glenn Miller's "in the mood" - lively, up beat, and punchy. "Music to win a war too." tschus pyotr -- pyotr filipivich. as an explaination for the decline in the US's tech edge, James Niccol wrote "It used to be that the USA was pretty good at producing stuff teenaged boys could lose a finger or two playing with." |
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SNIP
Greetings Nick, In your post you mentioned that building a rotary phase converter is illegal. Does this mean you can buy one and hook it up? Or is that illegal too. If so, why? And, could they tell? Would they need a search warrant? Sheesh, Eric |
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#110
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On Tue, 31 Aug 2004 05:37:09 GMT, pyotr filipivich
vaguely proposed a theory .......and in reply I say!: remove ns from my header address to reply via email Musically I agree with you. Both are far removed from the techo-based "brill" of whatever this week calls it that comes out of the (totally metal-fatiguing but audiophile-sickening) vibration of car panels. As a boombox deterrent, I disagree. Both are stirring, powerful pieces of music that excite the THING that gets excited. Bach's Tocatta ROCKS. BIG TIME. Ask the group "Sky". It was the only thing that a group of classically-trained musicians could sell to the rock masses. "In the Mood" always puzzled me, but that's its genius. Like "Bolero". It's a repetition of a simple theme, over and over, with subtle variations. Why is it magnifico? Sorry. The Liberty Bell may have adopted a ludicrous meaning for me. Blame Monty. I do feel it was well-chosen. :- I will try to get onside even more. I once had a neighbour who bought a new power system. It would appear the that system cost so much that they could afford on.y one middle-of-the-road-rock LP. After 50 repeats of that LP (this was back when most TV was new content, and our tolernace was low) I had had enough. I had built a pair of boxes that were about 20% efficient, over the audio band. Experimental. They were not horn loaded. they sounded reasonable. They were not all power, bu sounded mmmmmmmmm reasonable. Anyway. I set them up in the window nearest my neighbours, and played Beethoven's Pastoral at unbearable levels, and went out for the afternoon. It worked. So maybe you are right! Even the BEST and most PEACEFUL classical will **** the boomsters off! G My problem is, success may result in a beating! (recent victim of way OTT, insane, road rage) Bach's Tacotta and Fugue in D. Atomic Bach! Heavy Metal Boroque! That or Glenn Miller's "in the mood" - lively, up beat, and punchy. "Music to win a war too." tschus pyotr ************************************************** *** I have decided that I should not be offended by anybody's behaviour but my own......the theory's good, anyway. |
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On Tue, 31 Aug 2004 07:11:31 -0700, Eric R Snow
vaguely proposed a theory .......and in reply I say!: remove ns from my header address to reply via email SNIP Greetings Nick, In your post you mentioned that building a rotary phase converter is illegal. Does this mean you can buy one and hook it up? Or is that illegal too. If so, why? And, could they tell? Would they need a search warrant? Haha! _Building_ one is actually probably not illegal. I mis-worded! G But no, I could not hook it up, unless it had a plug to plug in, and a socket to take out. I cannot wire it in. I realise it _may_ be hard to tell who did what, if it's a bought one. But a home-built one one would be a little easier to spot, even if well done. If anyone in control was suspicious, they could ask me to prove installation by a electrician. Interesting about the search warrant. Firstly, if I had any work done by an electrician, he has to submit a "ticket" to say it's done. It can be inspected. He may also report what he sees, of course. A story. A little while back, I was in a situation where my bush-pig neighbour was stealing water from my dam (he set fire to the place while he was doing it), and repeatedly dumping his household rubbish on my property. I reported this to the police, who took no action, and the Council, who sent the Health inspector out, accompanied by police. He had more powers of entry and search than the police. They were there to provide muscle, and to arrest the guy if he tried to stop the inspector. So he and other statutory folk often have more power than police! ************************************************** *** I have decided that I should not be offended by anybody's behaviour but my own......the theory's good, anyway. |
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#112
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I really think you ought to put one together and see if it works for
you. Since your limit is power available, let me tell you of one I put together. It was for a fishing rod blank company that had a centerless sander. This was about twenty five years ago so I may remember somethings incorrectly. But I think the main motor on the sander was a 5 hp three phase motor. I used a 7.5 hp three phase motor and a two hp single phase motor with a belt drive between the two. I forget the size of the breaker, but it was just big enough after some fiddling. The pulleys were adjusted until the current drawn by the single phase motor was about 85 to 90 % of the name plate current. Some capacitors were connected between one of the hot legs to the leg not connected to facility power. As I remember the current drawn by the single phase motor decreased as caps were added and then started to go back up. So some caps were removed so current was a minimum. Then some caps were added across the power line for power factor correction. I never try to completely correct for power factor. If you plot current as you add pf caps, you will see the first one drops the current a good deal, the second one drops it less. The third one even less. And remember that power factor correction only decreases the imaginary current. The real current varies with the load. The imaginary current does not vary with load. But for your case where you are current limited, reducing the current when unloaded, will cut the heating of the breaker and wires when you are not loading the output. And helps keep the breaker from blowing. Anyway I played around with caps of a couple of hours, and the guy used it for over twenty years ( But only used the sander maybe every ten days, it was not 8 hours a day 5 days a week ). One thing to remember about RPC is that they are only generating the current and voltage for the third leg. So if you can get two thirds of the power out of a three phase motor running it on single phase power, you only need to generate one third of what a three phase generator would have to generate. Dan Old Nick wrote in message . .. Hehe! You can't "disagree" with somebody who has no idea what they are talking about! GG - the emphasis was on capital outlay. My limit is power available. - there was frequent qualification of claims about capacitors and tweaking and people who had wonderful success with a given load. Very little about this vs a nice expensive "sedate" 3PH generator setup, or true 3PH power. - SORRY. There was one about getting 3PH power on. At this stage, short of some sort of "community action" group, that's out of the question. - I am one of those wacko individualistic socialists....BUM! G I got the definite impression that even under varying loads, the efficiency was very high. You, Dan, are correct. So now I have apocryphal statements that these things are great, and "actual" figures from people trying to sell them to me GG. Bugger! However, I have to admit that if the claims for a well-tuned RPC are 50% out, the efficiency is still above a belt-driven motor-gen setup. I have to admit that some of my caution here is "free lunch" stuff.....sounds too good etc. |
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#113
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Actually the power factor correction does not change at all with load.
Changing the load only changes the real power and the power factor caps only change the imaginary current. The effects of power factor are much more obvious at no load, so do power factor correction at no load. If there is always going to be a good sized load, then power factor correction is a waste of time. If you measure the current to just a PF cap across the line, you will know the imaginary current that goes thru that cap. ( slightly off for puritans, but close onough for the real world ). Then measure the current of the motor with no load and no PF cap. Then put the PF cap across the input to the motor and measure the current. Now plot a triangle with the side proportional to the three currents you just measured. Now rotate that triangle so the imaginary current is vertical ( the current to just the power factor cap ). Now draw a line horizontal from the angle of the triangle that is away from the imaginary current line. And extend the imaginary current line down to the horizontal line. The length of the horizontal line is the real current. And by now it ought to be obvious to the most casual observer that it isn't worth correcting the power factor completely. Dan (DoN. Nichols) wrote in message ... Hmm ... you could start out by adding a respectable capacitance (power factor correction) in parallel with the motor to reduce that current quite a bit so you could then tune the converter, and then tune the power factor correction capacitance for the optimum current draw. Note that the optimum will shift somewhat depending on load applied, so if you expect to have the idler running unloaded more than at a respectable load, you probably should tune the power factor correction capacitance for the no-load condition. Apparently running these things unbalanced is a lot messier than running them on the right no of phases. I'm not sure about that as far as the power factor correction bit is concerned. It is just that if you have the right number of phases available, you also typically have beefier breakers and wiring available to start with. Also -- I *think* (but I don't know for sure) that a fully loaded motor would have much less need for the power factor correction. Good Luck, DoN. |
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jim rozen wrote in message ...
In article , Peter Wiley says... Been there, done that here in Tas in the last year. It cost me $8K. Yes, you can buy a lotta single phase and 3 phase motors for the price difference, but all the screwing about in the world still won't deliver you true 3 phase, nor will you ever be able to pull more than (say) 90A off your single phase supply. Nor can you extend your power cabling anywhere near as simply & cheaply. I had the meter box put on the last pole and ran my consumer mains myself to my house, shed and to a future shed site by a dam. The cabling costs to run 20A 3 phase over any distance are a lot less than trying to run 60A single phase over the same distance, and I get to run 3 phase motors for water pumps etc. I ran a 63A 3 phase supply to a sub board in the house then pulled my single phase circuits off it. Ditto for shed and 20A down to the dam. Sounds nice - but I notice you did not mention anything about the peak demand meter. That's because here, there is no such thing. I pay for the kW-hours I use and at normal domestic tariff. Period. In fact I also have a 240V off peak metered supply that I can use for water heating and other approved activities. Funnily enough my water heater is installed with a 20A plug rather than being hard wired. Precisely what I mean about you guys being screwed over on your power systems. First you have 110V meaning you need much heavier cable to get any decent amount of current and second your suppliers screw you over on the tariffs. We have neither problem so faking 3 phase is generally a waste of effort. PDW |
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In article , Peter Wiley
says... Sounds nice - but I notice you did not mention anything about the peak demand meter. That's because here, there is no such thing. Ah haaa. Here one begins to understand why there's such a proliferation of home-brew approaches to generating three phase power in the US - a peak demand meter is invariably installed with polyphase service around here, with the idea that the user is commercial by definition if they run three phase machinery. The cost can be staggering. Precisely what I mean about you guys being screwed over on your power systems. First you have 110V meaning you need much heavier cable to get any decent amount of current and second your suppliers screw you over on the tariffs. We have neither problem so faking 3 phase is generally a waste of effort. Well, the utilities are pretty consistent in their treatment - we all get stuffed equally, alike - for the most part. Jim -- ================================================== please reply to: JRR(zero) at pkmfgvm4 (dot) vnet (dot) ibm (dot) com ================================================== |
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On Wed, 01 Sep 2004 00:40:45 GMT, Old Nick
wrote: On Tue, 31 Aug 2004 07:11:31 -0700, Eric R Snow vaguely proposed a theory ......and in reply I say!: remove ns from my header address to reply via email SNIP Greetings Nick, In your post you mentioned that building a rotary phase converter is illegal. Does this mean you can buy one and hook it up? Or is that illegal too. If so, why? And, could they tell? Would they need a search warrant? Haha! _Building_ one is actually probably not illegal. I mis-worded! G But no, I could not hook it up, unless it had a plug to plug in, and a socket to take out. I cannot wire it in. I realise it _may_ be hard to tell who did what, if it's a bought one. But a home-built one one would be a little easier to spot, even if well done. If anyone in control was suspicious, they could ask me to prove installation by a electrician. Interesting about the search warrant. Firstly, if I had any work done by an electrician, he has to submit a "ticket" to say it's done. It can be inspected. He may also report what he sees, of course. A story. A little while back, I was in a situation where my bush-pig neighbour was stealing water from my dam (he set fire to the place while he was doing it), and repeatedly dumping his household rubbish on my property. I reported this to the police, who took no action, and the Council, who sent the Health inspector out, accompanied by police. He had more powers of entry and search than the police. They were there to provide muscle, and to arrest the guy if he tried to stop the inspector. So he and other statutory folk often have more power than police! ************************************************* **** I have decided that I should not be offended by anybody's behaviour but my own......the theory's good, anyway. So, if it can be plugged in, why not plug it in? I am probably missing something here but it seems to be the obvious solution. In my shop some of the machines are plugged in. The largest plugged in machine is only 5 HP but the outlets and plugs I'm using have the capacity to be used with my 10 HP 230 volt machines. Eric |
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#119
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On Wed, 01 Sep 2004 07:05:12 -0700, Eric R Snow
vaguely proposed a theory .......and in reply I say!: remove ns from my header address to reply via email There seems to be a misunderstanding here, to the point of discomfort. I am not deliberately being illogical. I actually regularly break this law, but some things get under the radar, others do not. Building an RPC is painting a target on my arse. The law says: - If I buy one, and it can be plugged in, I can plug it in. * Buying one is an expensive option. I have seen them here (Oz) for $2000 or so for any reasonable size. I _have_ to buy motor and all, as otherwise, if I add my own motor, and any wiring, I am building it.... - If I build one and wire OR _plug_ it in, it's illegal. * Not to build (as far as I know), but to plug in. I have a 12KVA 1PH generator sans motor sitting in my shop. Until I actually connect it, nobody can do anything except steal it (and welcome to try. It weighs a ton!G) - If I get caught, I am in the ****, and will be under the scope thereafter. * I could be caught by any inspection * I am not allowed to do _any_ electrical wiring in a shop. - Once I start adding illegal gear on the scale of an RPC, I am on a difficult path. I get tied in to having to do all future wiring illegally. A sparky comes and works and sees the gear etc. Once I place something as large and obvious as an RPC in a workshop, any sparky worth his spark will pick it up. He is probably duty bound to report it, and since it's money out of his pocket if stuff gets DIY'd, he will probably do so with great alacrity. - If I sell this place or for any other reason someone else uses any equipment that I have installed illegally, and they either don't like it or are hurt by it, I am in the **** in the first place, and _really_ in the **** in the second place. I use tractors without ROPS, PTO shafts without covers etc etc. But as I said, some stuff slips under the radar. For some reason electricity is a very hot topic. There is a powerful trade incentive there, for a start, and it has a very high horse from which to dictate terms in order to protect itself. The building trade here is much the same. Owner building is _very_ difficult to do here. Before you scream "nanny state" read a few of the posts about boat building in the US. We don't have anything _like_ half the rules about that here. shrug. So, if it can be plugged in, why not plug it in? I am probably missing something here but it seems to be the obvious solution. In my shop some of the machines are plugged in. The largest plugged in machine is only 5 HP but the outlets and plugs I'm using have the capacity to be used with my 10 HP 230 volt machines. Eric ************************************************** *** I have decided that I should not be offended by anybody's behaviour but my own......the theory's good, anyway. |
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On Thu, 02 Sep 2004 12:45:18 +0800, Old Nick
wrote: A lot to indicate that OZ. is run by the almighty shop steward. If this is the case, I feel for you, but from a great distance. Gerry :-)} London, Canada |
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