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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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#41
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On Thu, 26 Aug 2004 00:57:04 -0400, Brian Lawson
wrote: Hey Gunner, I was going to use a 20HP motor too. I kicked it into gear with a pony motor, and it was drawing 80 plus amps. I've settled for a 7-1/2HP, which is still drawing 20 or so.- Gack!! Maybe Ill use a 10 hp. Ive got that 1501 Clausing with the 7.5 hp motor. Its a bit slow to start on my 5hp Star International RPC (old *******) and doesnt like starting in Low range. I can get by a bit by firing up the OD grinder at the same time, which acts as a slave, but its still under powered. Gunner Take care. Brian Lawson, Bothwell, Ontario. XXXXXXXXXXXXXXXXXXXX On Thu, 26 Aug 2004 03:52:18 GMT, Gunner wrote: On 25 Aug 2004 13:18:31 -0700, jim rozen wrote: You have to understand that most of the designs you see are highly optimized. Using an oversized idler motor that is started with a pony motor means you don't need any power factor correction, no balancing, and no starting circuitry. It gets built for free, runs forever, and never has to be thought about. Example is the patented "jim's stone age converter" seen he http://www.metalworking.com/DropBox/_2000_retired_files/Conv.jpg Got a wiring diagram? Ive got a 20hp 3600rpm Western Electric waiting to be turned into a RPC. Pony motors Ive got by the score. Gunner, who was given a Hardinge DV-59 today. Disassembled but complete....sigh Anyone need any Federal air gauges? Got about a dozen of them G Schaublin Lever action tailstock with built in collet holder in the nose of the ram? Scored today.... VBG) "In my humble opinion, the petty carping levied against Bush by the Democrats proves again, it is better to have your eye plucked out by an eagle than to be nibbled to death by ducks." - Norman Liebmann "In my humble opinion, the petty carping levied against Bush by the Democrats proves again, it is better to have your eye plucked out by an eagle than to be nibbled to death by ducks." - Norman Liebmann |
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In article , Gunner says...
http://www.metalworking.com/DropBox/_2000_retired_files/Conv.jpg Got a wiring diagram? Like the man said, we don't need no stinkin' diagrams.  You power two of the leads from your incoming 240 line via a fused knife switch, and take the 3~ off all three wires. And like he said, a dropout contactor is a nice idea. Jim -- ================================================== please reply to: JRR(zero) at pkmfgvm4 (dot) vnet (dot) ibm (dot) com ================================================== |
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#43
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In article , DoN. Nichols says...
Note, also, that this has *no* safety circuit to disconnect the idler when the power fails, so when it comes back on, the motor will sit there humming until it burns up, or trips the breaker. So *always* turn it off when you walk away. Well nobody would be dumb enough to leave the darn thing on all night. Ahem. Trouble is, this converter is really really quiet. I simply cannot hear it running inside the little root celler it sits in. The rubber stoppers do a great job of vibration isolation, and I think it's a pretty high quality motor to start with. I've got it powered off of a 15 amp breaker, through number 12 wire. The fuses in the knife switch are 10 amp, so it's on a pretty short leash. I've had momentary lapses of grey matter on occasion and threw the knife switch *before* spinning the idler up - and the result is that it grunts for about a second before one of the fuses pops. Still a drop-out contactor is now on my list-O-stuff to do. Until then I'll just be sure to turn the damn thing off before leaving the shop, religiously. Maybe a note on the cellar door, or a big red light in parallel with the drive. Ahem. Jim -- ================================================== please reply to: JRR(zero) at pkmfgvm4 (dot) vnet (dot) ibm (dot) com ================================================== |
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In article , Old Nick says...
I did some reading. I remember now what my reservation was. While you can throw plenty into the RPC, they are not good at allowing the driven motor to produce full power. This is news to me. Where did you read that? For a reasonably sized rotary converter (at least 50% larger than the driven motor) you can develop full hp on the driven motor. Jim -- ================================================== please reply to: JRR(zero) at pkmfgvm4 (dot) vnet (dot) ibm (dot) com ================================================== |
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#45
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On Thu, 26 Aug 2004 08:34:57 -0500, "Robert Swinney"
wrote: Gunner sez: "Got a wiring diagram? Ive got a 20hp 3600rpm Western Electric waiting to be turned into a RPC. Pony motors Ive got by the score." Wiring, schmiring, Gunner! Get after it, dude. I think it could be started with about 1400 microFarad of motor start caps, but that wouldn't be code, now would it? Bob Swinney Code smode. At work, I follow code to the letter, at home, I follow proper practices based on safety. Often times not to "code" I picked up about a half case of semi rectangular caps, about 2" thick, by 5" wide by about 8" tall. Only problem is..they are about 7fd. Not sure what they can be used for. But the price was right.."can you use those? Toss em on your truck" Gunner "Gunner" wrote in message .. . On 25 Aug 2004 13:18:31 -0700, jim rozen wrote: You have to understand that most of the designs you see are highly optimized. Using an oversized idler motor that is started with a pony motor means you don't need any power factor correction, no balancing, and no starting circuitry. It gets built for free, runs forever, and never has to be thought about. Example is the patented "jim's stone age converter" seen he http://www.metalworking.com/DropBox/_2000_retired_files/Conv.jpg Gunner, who was given a Hardinge DV-59 today. Disassembled but complete....sigh Anyone need any Federal air gauges? Got about a dozen of them G Schaublin Lever action tailstock with built in collet holder in the nose of the ram? Scored today.... VBG) "In my humble opinion, the petty carping levied against Bush by the Democrats proves again, it is better to have your eye plucked out by an eagle than to be nibbled to death by ducks." - Norman Liebmann "In my humble opinion, the petty carping levied against Bush by the Democrats proves again, it is better to have your eye plucked out by an eagle than to be nibbled to death by ducks." - Norman Liebmann |
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On 26 Aug 2004 09:10:49 -0700, jim rozen
wrote: In article , Gunner says... http://www.metalworking.com/DropBox/_2000_retired_files/Conv.jpg Got a wiring diagram? Like the man said, we don't need no stinkin' diagrams. You power two of the leads from your incoming 240 line via a fused knife switch, and take the 3~ off all three wires. And like he said, a dropout contactor is a nice idea. Jim Ill try just it. Ive got a nice 10hp in my motor pile. I assume that I have to spin it up to data plate rpm? Which is better, a 1725 or 3600 rpm motor? And what is a drop out contactor and how does it work? Gunner "In my humble opinion, the petty carping levied against Bush by the Democrats proves again, it is better to have your eye plucked out by an eagle than to be nibbled to death by ducks." - Norman Liebmann |
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On 26 Aug 2004 09:15:46 -0700, jim rozen
wrote: In article , DoN. Nichols says... Note, also, that this has *no* safety circuit to disconnect the idler when the power fails, so when it comes back on, the motor will sit there humming until it burns up, or trips the breaker. So *always* turn it off when you walk away. Well nobody would be dumb enough to leave the darn thing on all night. Ahem. Trouble is, this converter is really really quiet. I simply cannot hear it running inside the little root celler it sits in. The rubber stoppers do a great job of vibration isolation, and I think it's a pretty high quality motor to start with. I've got it powered off of a 15 amp breaker, through number 12 wire. The fuses in the knife switch are 10 amp, so it's on a pretty short leash. I've had momentary lapses of grey matter on occasion and threw the knife switch *before* spinning the idler up - and the result is that it grunts for about a second before one of the fuses pops. Still a drop-out contactor is now on my list-O-stuff to do. Until then I'll just be sure to turn the damn thing off before leaving the shop, religiously. Maybe a note on the cellar door, or a big red light in parallel with the drive. Ahem. Jim What you need to do Jim is connect the power also to an electromagnetic lock on the door. That way, as long as the RPC has power the door cannot be opened. Keeps people out too. You know, can't stop in the middle of a cut so you can't shut off the power. Come back later when I'm finished. Mebbe get you out of a chore or two. Then again, mebbe not... ERS |
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#48
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Jim sez:
"... or a big red light in parallel with the drive." Better yet a 110V, 7-1/2W night lamp wired across the manufactured phase. Yeah, I said, 110V night lamp because they are cheap, so don't forget the 2k Ohm, 10W, series dropping resistor. Mine is glued to the inside bottom of the 3-phase start-switch box. The night light is contained in a nice socket on the wall along side the start box, so it comes on with the RPC. Bob Swinney "jim rozen" wrote in message ... In article , DoN. Nichols says... Note, also, that this has *no* safety circuit to disconnect the idler when the power fails, so when it comes back on, the motor will sit there humming until it burns up, or trips the breaker. So *always* turn it off when you walk away. Well nobody would be dumb enough to leave the darn thing on all night. Ahem. Trouble is, this converter is really really quiet. I simply cannot hear it running inside the little root celler it sits in. The rubber stoppers do a great job of vibration isolation, and I think it's a pretty high quality motor to start with. I've got it powered off of a 15 amp breaker, through number 12 wire. The fuses in the knife switch are 10 amp, so it's on a pretty short leash. I've had momentary lapses of grey matter on occasion and threw the knife switch *before* spinning the idler up - and the result is that it grunts for about a second before one of the fuses pops. Still a drop-out contactor is now on my list-O-stuff to do. Until then I'll just be sure to turn the damn thing off before leaving the shop, religiously. Maybe a note on the cellar door, Ahem. Jim -- ================================================== please reply to: JRR(zero) at pkmfgvm4 (dot) vnet (dot) ibm (dot) com ================================================== |
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#49
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No prob, man! Hook 200 o' them little suckers in parallel.
Bob Swinney "Gunner" wrote in message ... On Thu, 26 Aug 2004 08:34:57 -0500, "Robert Swinney" wrote: Gunner sez: "Got a wiring diagram? Ive got a 20hp 3600rpm Western Electric waiting to be turned into a RPC. Pony motors Ive got by the score." Wiring, schmiring, Gunner! Get after it, dude. I think it could be started with about 1400 microFarad of motor start caps, but that wouldn't be code, now would it? Bob Swinney Code smode. At work, I follow code to the letter, at home, I follow proper practices based on safety. Often times not to "code" I picked up about a half case of semi rectangular caps, about 2" thick, by 5" wide by about 8" tall. Only problem is..they are about 7fd. Not sure what they can be used for. But the price was right.."can you use those? Toss em on your truck" Gunner "Gunner" wrote in message .. . On 25 Aug 2004 13:18:31 -0700, jim rozen wrote: You have to understand that most of the designs you see are highly optimized. Using an oversized idler motor that is started with a pony motor means you don't need any power factor correction, no balancing, and no starting circuitry. It gets built for free, runs forever, and never has to be thought about. Example is the patented "jim's stone age converter" seen he http://www.metalworking.com/DropBox/_2000_retired_files/Conv.jpg Gunner, who was given a Hardinge DV-59 today. Disassembled but complete....sigh Anyone need any Federal air gauges? Got about a dozen of them G Schaublin Lever action tailstock with built in collet holder in the nose of the ram? Scored today.... VBG) "In my humble opinion, the petty carping levied against Bush by the Democrats proves again, it is better to have your eye plucked out by an eagle than to be nibbled to death by ducks." - Norman Liebmann "In my humble opinion, the petty carping levied against Bush by the Democrats proves again, it is better to have your eye plucked out by an eagle than to be nibbled to death by ducks." - Norman Liebmann |
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#50
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Gunner sez:
" Ill try just it. Ive got a nice 10hp in my motor pile. I assume that I have to spin it up to data plate rpm? Which is better, a 1725 or 3600 rpm motor?" Immaterial, my good man! Pretty much, anyway. Some say the 1725 rpm machine is quieter. You don't have to spin it up to "name plate" speed -- just a good pull on the rope will do it, but have something set up so's you can switch on the power soon after spin up. In other words, don't walk across the pasture to the switch, or the spin will be all gone before you get there! Bob Swinney "Gunner" wrote in message ... On 26 Aug 2004 09:10:49 -0700, jim rozen wrote: In article , Gunner says... http://www.metalworking.com/DropBox/_2000_retired_files/Conv.jpg Got a wiring diagram? Like the man said, we don't need no stinkin' diagrams. You power two of the leads from your incoming 240 line via a fused knife switch, and take the 3~ off all three wires. And like he said, a dropout contactor is a nice idea. Jim Gunner "In my humble opinion, the petty carping levied against Bush by the Democrats proves again, it is better to have your eye plucked out by an eagle than to be nibbled to death by ducks." - Norman Liebmann |
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#51
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In article , Gunner says...
Ill try just it. Ive got a nice 10hp in my motor pile. I assume that I have to spin it up to data plate rpm? Which is better, a 1725 or 3600 rpm motor? And what is a drop out contactor and how does it work? Anecdotal evidence suggests the slower motor is better. I've never seen anyone do this with a motor that runs slower than 1725 though. I would steer away from the 3600. A drop-out contactor is simply a large three-pole relay that take the place of (or is in series with, for you belt-and-suspenders types) the knife switch. The coil to pull that relay in is operated with a start/stop pushbutton ciricuit - best is if the coil is 240 volt, so one end of the coil goes to one incoming line, then it goes to a normally closed pushbutton, and then to one of the outgoing (load side) terminals of the relay, on the other phase. The load is switched by two dedicated contacts, it's the third one that runs the coil itself. Then you put a normally closed pushbutton across that third contact set on the relay. So the drill is, load is off, coil is off. When you push the 'start' button (normally open one) it engerizes the relay briefly, and the contacts suck in. At that point you can take your hand off the button because the third set of contacts are now closed, and provide juice to energize the coil. Normally you turn the thing off by briefly interrupting current in the coil with the normally closed button. But if there's a power dip, the relay drops out - and will not suck back in until you hit the start button again. All the newer hardinge stuff is wired this way - try it. Start up the spindle, and leave the levers on 'run' while you unplug or otherwise disconnect the machine. When you plug it back in, the machine will not start until you hit the go button the electrical box. This is now an OSHA requirement for all moving machinery - the idea is that the spindle should not start unexpectedly after a power fail, if the machine is left on 'run.' I had to go and put contactors like that on all our shop equipment - grinder, drill press, etc. Though, now that the drill press is VFD driven, they have a "no restart" feature built in. And btw if you do implement this, be sure to *fuse* the contactor circuit appropriately. Most times the wiring is number 16 gage or so, and it should have a fuse rated for much less than the 20 amp branch circuit rating! Jim -- ================================================== please reply to: JRR(zero) at pkmfgvm4 (dot) vnet (dot) ibm (dot) com ================================================== |
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#52
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In article ,
Charles A. Sherwood wrote: Are the motors truly in parallel? As in; all three legs of one motor connected to all three legs of the other motor? If so, you should see some They are both on the same contactor and start at the same time. However they are connected together before the overload controls. One contactor suppling power to seperate "heaters" for each motor. The third wire of the static converter connects to the third wire of the motors through the heaters. Seems like the logical way to wire it (at least to me). I could connect the third legs together before the heaters, but I really don't think that would make any difference. I see no current in the third leg with a clamp on ampmeter after the motors have started. The voltage in the third leg is 208 and 224 with respect to the other two legs. I guess there is no current because the voltage is low. Where are you applying the clamp-on ammeter? If between the junction of the two motors' wires and the static converter, there *should* be no current once the motors are started. However, if you clamp around one or the other of the motors, you should see some current at least. (Mostly the amount would be based on the horsepower and the loading of the smaller motor.) Perhaps if both motors are equally lightly loaded, they are each generating about the same voltage for the third phase, and as a result, are generating very little current between them. Put a serious load on one motor or the other and see whether there is a visible upswing in the current. 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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#53
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In article ,
Gunner wrote: On Thu, 26 Aug 2004 00:57:04 -0400, Brian Lawson wrote: Hey Gunner, I was going to use a 20HP motor too. I kicked it into gear with a pony motor, and it was drawing 80 plus amps. I've settled for a 7-1/2HP, which is still drawing 20 or so.- Gack!! Maybe Ill use a 10 hp. If you take the time to tune the 20 HP converter for better balance, and once that is done, you start adding capacitance across the 240 feed from the wall, you will eventually reach a point at which the current is at a minimum, where more capacitance will increase the current again. Note that the extra current will not cost you anything (other than nuisance trips on the circuit breaker) -- *if* you are on a residential feed. If you were on a commercial feed, they could (and probably would) charge you based on the reactive current. But if you were on a commercial feed, you probably would also have three-phase power available and not need to make a rotary phase converter. 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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#54
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On Thu, 26 Aug 2004 12:27:16 -0500, "Robert Swinney"
calmly ranted: No prob, man! Hook 200 o' them little suckers in parallel. "Gunner" wrote in message Only problem is..they are about 7fd. Not sure what they can be used SEVEN FARAD, not microfarad, Bob. To test, don't you hook 'em up across a wall outlet then check with the leads on either side of your tongue? If it zaps, it's good? (Kids: don't try this at home.) - Inside every older person is a younger person wondering WTF happened. --- http://diversify.com Website Application Programming |
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#55
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On 26 Aug 2004 09:22:39 -0700, jim rozen
vaguely proposed a theory .......and in reply I say!: remove ns from my header address to reply via email In article , Old Nick says... I did some reading. I remember now what my reservation was. While you can throw plenty into the RPC, they are not good at allowing the driven motor to produce full power. This is news to me. Where did you read that? For a reasonably sized rotary converter (at least 50% larger than the driven motor) you can develop full hp on the driven motor. D'OH. Now I have to find it again! G I do take your and Don's point that the big muvva idea and some tuning sound OK. It would appear that I was getting muxed ip with the static converter. http://www.metalwebnews.com/howto/ph-conv/ph-conv.html "The static converter is basically only a start circuit that once the motor starts, disengages and lets the motor run on single phase power. The disadvantage of this method is that the motor winding currents will be very unbalanced and the motor will not be able to run above about two-thirds its rated horsepower. The rotary converter provides current in all 3 phases and although not perfect, will allow a motor to provide all or nearly all its rated horsepower. If the motor has a service factor of 1.15 to 1.25 then you should be able to use full rated horsepower. The service factor can be found on the motor nameplate and is usually abbreviated S.F. " http://www.deselectric.com/ "Either a static converter or rotary phase converter can make it possible to run a three phase motor on single phase power. The Static Phase Converter does not actually generate three phase but only starts an electric motor and then allows the motor to operate on only two of the three windings in the motor. This being the case, the motor then is running at 2/3 of its rated Hp. A Rotary Phase Converter does provide full rated three phase power to operate equipment without this loss of Hp. Rotary Converters are always the best way to go, if you size them correctly for the application." Apart from that, I can remember discussions here about it. ************************************************** *** 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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#57
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On 25 Aug 2004 13:18:31 -0700, jim rozen
vaguely proposed a theory .......and in reply I say!: remove ns from my header address to reply via email I have to admit that http://www.deselectric.com/rotarypanels 's prices are quite surprising, if you use a free or very cheap 3PH motor that you supply. As far as I can tell they design to suit your motor, and the price for a panel is it. ************************************************** *** 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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#58
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Errr, welll, yesss - I saw that they were 7 farad. I just wanted to see if
gunner would bring down the grid. Bob Swinney "Larry Jaques" wrote in message ... On Thu, 26 Aug 2004 12:27:16 -0500, "Robert Swinney" calmly ranted: No prob, man! Hook 200 o' them little suckers in parallel. "Gunner" wrote in message Only problem is..they are about 7fd. Not sure what they can be used SEVEN FARAD, not microfarad, Bob. To test, don't you hook 'em up across a wall outlet then check with the leads on either side of your tongue? If it zaps, it's good? (Kids: don't try this at home.) - Inside every older person is a younger person wondering WTF happened. --- http://diversify.com Website Application Programming |
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#59
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In article , Old Nick says...
I do take your and Don's point that the big muvva idea and some tuning sound OK. It would appear that I was getting muxed ip with the static converter. I sort of suspected that. The thing is, most of the techies here (and that is not a derogatory term) love to do stuff the *right* way, the best way. And they have the design princples down to an iota for rotary converters like that. The deal is though, if you simply oversize the idler motor a lot, you don't need to do any tuning or power factor correction at all, if you are only running a couple of 1 hp or so machines in your shop. In my case it's a five hp idler that runs small machines, and there's no tuning or fancyness involved. Sure you can run the same machines on a two hp idler motor, but once again, the 5 or or so hp motors seem to be easier to come by for free, at least around here. Jim -- ================================================== please reply to: JRR(zero) at pkmfgvm4 (dot) vnet (dot) ibm (dot) com ================================================== |
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On Thu, 26 Aug 2004 19:13:59 -0500, "Robert Swinney"
calmly ranted: Errr, welll, yesss - I saw that they were 7 farad. I just wanted to see if gunner would bring down the grid. Grid? Oh, you must mean ex-Governor Davis's fine, triple-priced CA electrical grid. Gotcha. No, he'll just have to saw off some of the cap height so they measure up, er, down. - Inside every older person is a younger person wondering WTF happened. --- http://diversify.com Website Application Programming |
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In article ,
Old Nick wrote: On 26 Aug 2004 00:17:46 -0400, (DoN. Nichols) vaguely proposed a theory ......and in reply I say!: remove ns from my header address to reply via email This is a problem with a "static" phase converter, but for a reasonably sized rotary converter -- especially one which has been tuned and balanced by tweaking capacitance on the windings -- you should be able to get full power out of the driven motor. [ ... ] I am probably thinking of the fact that the rotary part of the converter needs a driver that is at least 1.5 times the power of the driven gear, because of the trouble with the fact that it running as if started by a static...on two legs only. This -- I agree with. But the driven equipment should run very close to full power unless the balance of the rotary converter is really bad. :-) (And going seriously oversized on the idler motor size will eliminate a lot of that, too. 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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In article ,
Old Nick wrote: On 25 Aug 2004 13:18:31 -0700, jim rozen vaguely proposed a theory ......and in reply I say!: remove ns from my header address to reply via email I have to admit that http://www.deselectric.com/rotarypanels 's prices are quite surprising, if you use a free or very cheap 3PH motor that you supply. The prices are not bad for what appears to be in a converter based on the (rather too small) image on the front page. There are enough capacitors in there so they appear to be tuning the converter -- at least for a typical example of the motor which you specify. I'm sure that by careful scrounging you could beat that price, but it saves a lot of time and scrounging, and it looks as though it is quite well done. (Except that I'm not clear how the capacitors are mounted in the housing. The two banks at the bottom seem to be clamped in with bars across each layer of caps. But I can't see enough to be sure how they are doing it with the ones up top -- at least some of which are probably the starting caps. Looking at the terminals on that horizontal bar across the middle, I suspect that this is one of the larger of their products -- for a 20 HP or larger idler motor. As far as I can tell they design to suit your motor, and the price for a panel is it. As long as you can find a suitable motor locally, that would be it. (I'm not sure what their shipping costs would be, but since it appears to be a steel housing, they might be significant -- especially for you. (Unless they are located in OZ. I didn't think to check that while I was there.) 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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#63
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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. As far as looking at a motor generator, have you considered using a three phase induction generator? Dan Old Nick wrote in message Seriously, I did, and have experienced a lot of the same pricing troubles and problems with the RPC idea that you have and so I still want to keep looking at the motor-gen idea. I have looked for surplus motors to build a phase converter but frankly I have not found the oasis where they are available for cheap. The shipping costs are usually the killer. ************************************************** *** 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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#64
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"jim rozen" wrote in message ... In article , Old Nick says... I do take your and Don's point that the big muvva idea and some tuning sound OK. It would appear that I was getting muxed ip with the static converter. I sort of suspected that. The thing is, most of the techies here (and that is not a derogatory term) love to do stuff the *right* way, the best way. And they have the design princples down to an iota for rotary converters like that. The deal is though, if you simply oversize the idler motor a lot, you don't need to do any tuning or power factor correction at all, if you are only running a couple of 1 hp or so machines in your shop. In my case it's a five hp idler that runs small machines, and there's no tuning or fancyness involved. Sure you can run the same machines on a two hp idler motor, but once again, the 5 or or so hp motors seem to be easier to come by for free, at least around here. Jim Jim 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 |
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On Fri, 27 Aug 2004 03:44:47 GMT, "Jerry Martes" wrote:
It might be concluded that 3 phase motors that arent loaded heavily for long periods can be run from single phase without an idler. Right, though they can't start on 1 ph. You need either a rotary converter, a static converter, or a pony motor to start the 3 ph motor. It also won't run smoothly on 1 ph power because torque will go through zero twice a cycle. But, a 3 phase motor will produce its full name plate HP even when fed single phase with no idler. It may, for a short period, but it will be drawing current in excess of its ratings on the driven phase. A 3 ph motor driven by 3 ph power has its current divided 3 ways. In other words, its windings are sized to each handle 1/3rd of its rated power. If you try to draw full nameplate HP from it while it is driven by 1 ph power, the driven windings will be overloaded. That's why there's a rule of thumb that a rotary converter needs to be sized 1.5 times the HP of the load motor, so the driven windings of the rotary converter aren't overloaded when delivering full 3 ph power to the load motor. Example, 1 HP load motor should be driven by a 1.5 HP rotary converter, 0.5 + 0.5 + 0.5 = 1.5, so that the current drawn by the load motor, 1/3 + 1/3 + 1/3 = 1 is the same as the maximum permissable 0.5 + 0.5 = 1 of the two driven windings of the rotary. Of course the rotary does the *transformation* from 0.5 + 0.5 to 1/3 + 1/3 + 1/3 by its rotary transformer action. But the key concept is that power in must equal power out no matter how it is transformed, and the currents must not overload any windings in the process. Gary |
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In article P6yXc.1002$yP4.369@trnddc08, Jerry Martes says...
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. This is an unexpected, yet fascinating result. It may be that the hp ratings on some motors is fairly conservatve ("anti-sears power rating...") which could account for some of this. I wonder if the same 3 hp motor would actually do 4, if it were run on utility 3~? Jim -- ================================================== please reply to: JRR(zero) at pkmfgvm4 (dot) vnet (dot) ibm (dot) com ================================================== |
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Right Gary! You explained it very well: "It may, for a short period, but
it will be drawing current in excess of its ratings on the the driven phase" -- and further, when you said, "If you try to draw full nameplate HP from it while it is driven by 1 ph power, the driven windings will be overloaded." This apparent ability to produce full power on "2/3 of a motor" is a function of the motor's service factor. Surely a motor driven to full name plate output on 2/3's of windings will draw excessive input current, eventually overheating to failure.. Bob Swinney "Gary Coffman" wrote in message ... On Fri, 27 Aug 2004 03:44:47 GMT, "Jerry Martes" wrote: It might be concluded that 3 phase motors that arent loaded heavily for long periods can be run from single phase without an idler. Right, though they can't start on 1 ph. You need either a rotary converter, a static converter, or a pony motor to start the 3 ph motor. It also won't run smoothly on 1 ph power because torque will go through zero twice a cycle. But, a 3 phase motor will produce its full name plate HP even when fed single phase with no idler. It may, for a short period, but it will be drawing current in excess of its ratings on the driven phase. A 3 ph motor driven by 3 ph power has its current divided 3 ways. In other words, its windings are sized to each handle 1/3rd of its rated power. That's why there's a rule of thumb that a rotary converter needs to be sized 1.5 times the HP of the load motor, so the driven windings of the rotary converter aren't overloaded when delivering full 3 ph power to the load motor. Example, 1 HP load motor should be driven by a 1.5 HP rotary converter, 0.5 + 0.5 + 0.5 = 1.5, so that the current drawn by the load motor, 1/3 + 1/3 + 1/3 = 1 is the same as the maximum permissable 0.5 + 0.5 = 1 of the two driven windings of the rotary. Of course the rotary does the *transformation* from 0.5 + 0.5 to 1/3 + 1/3 + 1/3 by its rotary transformer action. But the key concept is that power in must equal power out no matter how it is transformed, and the currents must not overload any windings in the process. Gary |
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"jim rozen" wrote in message ... In article P6yXc.1002$yP4.369@trnddc08, Jerry Martes says... 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. This is an unexpected, yet fascinating result. It may be that the hp ratings on some motors is fairly conservatve ("anti-sears power rating...") which could account for some of this. I wonder if the same 3 hp motor would actually do 4, if it were run on utility 3~? Jim Jim 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 |
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On Thu, 26 Aug 2004 19:13:59 -0500, "Robert Swinney"
wrote: Errr, welll, yesss - I saw that they were 7 farad. I just wanted to see if gunner would bring down the grid. As three generators at Hoover Dam stall and half of CA goes dark... StevenUrkel "Did I do that??" /StevenUrkel ;-) -- 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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On Sat, 28 Aug 2004 04:14:37 GMT, Bruce L. Bergman
wrote: On Thu, 26 Aug 2004 19:13:59 -0500, "Robert Swinney" wrote: Errr, welll, yesss - I saw that they were 7 farad. I just wanted to see if gunner would bring down the grid. As three generators at Hoover Dam stall and half of CA goes dark... StevenUrkel "Did I do that??" /StevenUrkel ;-) G But really..what the dickens are those caps good for? Ive got a number of them. Gunner No 220-pound thug can threaten the well-being or dignity of a 110-pound woman who has two pounds of iron to even things out. Is that evil? Is that wrong? People who object to weapons aren't abolishing violence, they're begging for the rule of brute force, when the biggest, strongest animals among men were always automatically "right". Guns end that, and social democracy is a hollow farce without an armed populace to make it work. - L. Neil Smith |
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Gunner wrote: But really..what the dickens are those caps good for? Ive got a number of them. Gunner The obvious reply--put them on Ebay. Steve |
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Jerry Martes wrote: 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. 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. 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. I agree. I've started an unloaded 20HP motor using a 7.5HP rotary converter. My gear head mill, on the other hand (significant starting torque needed) was a 1HP motor and needed a 3HP idler in my rpc. 2HP wouldn't start it in the high speeds. Steve |
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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. No wonder metalwork is more fun than sex. G Ooh, you _are_ getting old, Nick. ---=====--- After all else fails, read the instructions. ---=====--- Website Design and Update http://www.diversify.com |
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You don't have to chase it up. I will tell you about induction
generators. They are just that same three phase motor that you would use for a RPC , but with that big single phase motor driving it and one leg of the three phase motor connected to the single phase power. When you do this it is easiest (in my opinion ) to use a belt drive with one of the pulleys being one that can be varied in size. And you adjust the drive so that the single phase motor is trying to drive the three phase motor a little faster than synchronous speed. In doing that you are putting in mechonical energy into the three phase motor and it comes out as electrical three phase power. When ( and if ) you do this measure the input current of the three phase motor and adjust the variable pulley so that the input current is close to the rated input current while driving whatever it is you want to drive with the three phase power . This needs no special start up circuits and no protection circuits in case you lose the single phase power and it comes back up. It can be further tuned with caps to reduce the imaginary current and therefore the size of wire and circuit breaker on the single phase power. In my opinion this is the best way to get three phase power that is the same frequency as the single phase power. If you want variable frequency to control the speed of a motor, use a VFD. Induction generators will work driven by a gasolene engine and not connected to the single phase line but that is a bit trickier. They will also work with a single phase motor and a gasolene engine. Again trickier ( needs the correct amount of caps across the line and maybe some DC voltage to get it started. Dan Old Nick wrote in message As far as looking at a motor generator, have you considered using a three phase induction generator? eerrr..no? G I will chase it up. This will probably start a whole new _chain_ of back and forths. I think I saw some before about these. Dan Old Nick wrote in message |
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