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DC Motor
Hi Guys
Can any one suggest what are the various methods of performing bench test for a 20 Kw(25HP) DC electrical variable speed motor. Thank you Regards smitha |
"smitha4u" wrote in message oups.com... Hi Guys Can any one suggest what are the various methods of performing bench test for a 20 Kw(25HP) DC electrical variable speed motor. 1) hope the motor powers from some multiple of 6 or 12 volts. 2) lacking the above, build one MAN of a DC supply. 3) take it to a good motor shop It would cost you more than it's worth to figure out if the torque, speed, and stall current are within spec, if you had to build or buy the equipment. LLoyd |
its 12 V
thanks |
I believe i can bulid in my school lab.
Aprreciate if you can expalin it in detail Thanks Rgards smitha |
On 9 Aug 2005 06:22:06 -0700, "smitha4u"
wrote: Hi Guys Can any one suggest what are the various methods of performing bench test for a 20 Kw(25HP) DC electrical variable speed motor. Thank you Regards smitha Assuming that such a motor has a wound field rather than permanent magnet: 1) estimate rated field current by seeing what current results in a steadystate temperature rise of about 20C with armature not excited. 2) With that field current applied, energize the armature with rated voltage. Measure no-load speed and stall torque. (do the later test quickly!) Measure armature current while stalled. These tests are sufficient to determine the constants for the DC motor equations describing speed and torque as fns of armature voltage, armature current and field current. |
sorry
it rated for 250-360 volts any steps for the test regards smitha |
On Tue, 09 Aug 2005 12:06:45 -0500, Don Foreman
wrote: On 9 Aug 2005 06:22:06 -0700, "smitha4u" wrote: Hi Guys Can any one suggest what are the various methods of performing bench test for a 20 Kw(25HP) DC electrical variable speed motor. Thank you Regards smitha Assuming that such a motor has a wound field rather than permanent magnet: 1) estimate rated field current by seeing what current results in a steadystate temperature rise of about 20C with armature not excited. 2) With that field current applied, energize the armature with rated voltage. Measure no-load speed and stall torque. (do the later test quickly!) Measure armature current while stalled. These tests are sufficient to determine the constants for the DC motor equations describing speed and torque as fns of armature voltage, armature current and field current. A bit difficult to second guess the field rating and this is a problem because it has such a major effect on motor performance. Field dissipation of 5% of rated power or 20 deg C rise is a good starting point but a this assumption may be well removed from the manufacturers intended rating. I would have expected a motor of this size to carry more nameplate information. At rated voltage, the stalled armature current of a motor of this size is little short of spectacular! I think it would be safer to settle for a measurement of stalled torque per amp at close to rated full load amps together with a measurement of back EMF per thousand RPM Proper evaluation of a motor of this size needs pretty substantial ancilliary equipment and a good understanding of it's operation and limitations. For anything more than a rough test to see if it's a dud motor it's not a task to be taken lightly. The light hearted uncertainty on whether it's a 12 volt or 360 volt machine doesn't engender a lot of confidence! Jim |
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"smitha4u" wrote in message oups.com... I believe i can bulid in my school lab. Aprreciate if you can expalin it in detail Thanks Rgards smitha This is not a job to be undertaken by someone who has to ask such basic questions in a METALworking group. It is proper engineering job for an experienced consulting engineer with experience in this type of indstallation. -- John G Wot's Your Real Problem? |
Ignoramus6689 writes:
If you have a suitably rated rectifier, and a good electrical subpanel, you can rectify your 220V AC. That will deliver more than 300 volts. Best not to listen to casual advisors with machinery of this size. |
"smitha4u" wrote in message oups.com... Hi Guys Can any one suggest what are the various methods of performing bench test for a 20 Kw(25HP) DC electrical variable speed motor. Thank you Regards smitha Not sure what you mean by bench testing. Do you want to determine the characteristics or just see if it runs? Don explained some of the methods for determining motor constants. Depending on your use, and since it's a big motor, you may also want to measure friction and the armature inertia Other parameters would be armature resistance and inductance to complete the full set of parameters. Then you can model the DC motor... |
Ignoramus6689 writes:
That will deliver more than 300 volts. his motor is rated for 360 volts max, so I am not sure why you use this number to make an objection. I thought he said it was rated for 250 volts. Looking back I see he said "it [sic] rated for 250-360 volts". So, who knows. The OP does not project competence for this kind of tinkering. |
"Ignoramus6689" wrote in message ... it needs 80 amps at 250 V DC to run at rated load. Probably much less without load, except at startup. If you have a suitably rated rectifier, and a good electrical subpanel, you can rectify your 220V AC. If your motor is a permanent magnet design, it can function as a generator. You can try spinning the shaft with anything and measuring voltage across leads. If it spins and produces voltage, it is probably good. There are much better experts than me, so let's see what they say. i Drives for DC motors of this size typically use a 3 phase SCR bridge, but motor-generator sets (Ward Leonard system) were quite popular years ago... |
"Rick" wrote in message oups.com... wrote: On Tue, 09 Aug 2005 12:06:45 -0500, Don Foreman wrote: On 9 Aug 2005 06:22:06 -0700, "smitha4u" wrote: Hi Guys Can any one suggest what are the various methods of performing bench test for a 20 Kw(25HP) DC electrical variable speed motor. Thank you Regards smitha Assuming that such a motor has a wound field rather than permanent magnet: 1) estimate rated field current by seeing what current results in a steadystate temperature rise of about 20C with armature not excited. 2) With that field current applied, energize the armature with rated voltage. Measure no-load speed and stall torque. (do the later test quickly!) Measure armature current while stalled. These tests are sufficient to determine the constants for the DC motor equations describing speed and torque as fns of armature voltage, armature current and field current. A bit difficult to second guess the field rating and this is a problem because it has such a major effect on motor performance. Field dissipation of 5% of rated power or 20 deg C rise is a good starting point but a this assumption may be well removed from the manufacturers intended rating. I would have expected a motor of this size to carry more nameplate information. At rated voltage, the stalled armature current of a motor of this size is little short of spectacular! I think it would be safer to settle for a measurement of stalled torque per amp at close to rated full load amps together with a measurement of back EMF per thousand RPM Or if he has a dynamometer, hold speed constant and record a change in torque vs a change in armature current. For the EMF constant spin the motor with field current applied and measure the generated open circuit voltage at the armature terminals. He should post all of the information on the namplate as a start. Of course, he could calculate counter emf at various points too, by running the motor (if he knew the armature resistance) by measuring armature current and applied voltage As you say, a lot depends on the equipment available... Proper evaluation of a motor of this size needs pretty substantial ancilliary equipment and a good understanding of it's operation and limitations. For anything more than a rough test to see if it's a dud motor it's not a task to be taken lightly. The light hearted uncertainty on whether it's a 12 volt or 360 volt machine doesn't engender a lot of confidence! Jim |
On Wed, 10 Aug 2005 10:34:51 +1000, "John G"
wrote: "smitha4u" wrote in message roups.com... I believe i can bulid in my school lab. Aprreciate if you can expalin it in detail Thanks Rgards smitha This is not a job to be undertaken by someone who has to ask such basic questions in a METALworking group. It is proper engineering job for an experienced consulting engineer with experience in this type of indstallation. How do you suppose engineers become trained to do such consulting? That's why schools have labs. I'm glad there are still students working with real machines in a real laboratory rather than with 'puter sims. You can't simulate the experience of a 50 HP DC motor drawing a gazillion amps of armature current at stall, or if the field comes loose. Ya gotta see it in person, after duly noting the motor bits still embedded in the bricks from previous oopsies. Unscheduled experiment: how fast can a twit lab TA dive under a bench? Open field on big DC motor running with rated armature voltage, time the twit when he hears it accelerating rapidly toward kaboom. (Do close the field pretty quick. Forget about killing armature current at that point; opening the switch results in a big green arc) The show is well worth the ensuing loud lecture endured with simulated contrite humility. Your grade may partly depend on the quality of your simulation.... |
"Don Foreman" wrote in message ... On Wed, 10 Aug 2005 10:34:51 +1000, "John G" wrote: "smitha4u" wrote in message groups.com... I believe i can bulid in my school lab. Aprreciate if you can expalin it in detail Thanks Rgards smitha This is not a job to be undertaken by someone who has to ask such basic questions in a METALworking group. It is proper engineering job for an experienced consulting engineer with experience in this type of indstallation. How do you suppose engineers become trained to do such consulting? That's why schools have labs. I'm glad there are still students working with real machines in a real laboratory rather than with 'puter sims. You can't simulate the experience of a 50 HP DC motor drawing a gazillion amps of armature current at stall, or if the field comes loose. Ya gotta see it in person, after duly noting the motor bits still embedded in the bricks from previous oopsies. Unscheduled experiment: how fast can a twit lab TA dive under a bench? Open field on big DC motor running with rated armature voltage, time the twit when he hears it accelerating rapidly toward kaboom. (Do close the field pretty quick. Forget about killing armature current at that point; opening the switch results in a big green arc) The show is well worth the ensuing loud lecture endured with simulated contrite humility. Your grade may partly depend on the quality of your simulation.... Yes students do need labs with big machines and yes they do leave an indelible impression . Many years ago I was in a lab group that shut down the whole Physics school of a large college 3 times doing an experiment with a big machine where a careless technician (not a student) had reversed the wiring of a Synchroscope. but the lab was designed and built by experienced engineers and so no-one was hurt. The OP in this thread is asking questions that are obviously beyond his current (sic) level of expertise and this is not the place to learn that sort of stuff. He will get bits and pieces of advice and never know till after the fire that he didn't ask all the relevant questions and so did not get all the answers. -- John G Wot's Your Real Problem? |
Hi
Thank you all I agree with after reading all the messages that i really did not think of all the measures and questions. Could some body educate me what more i need to know. before testing I think i need to prepare a test plan/procedure and what all will i calculate and how i will show my demonstration. If they agree my experience with dealing large machines is not sufficient atleast they would see my test plan and do the test with some expeerienced. Hope i get some help and appreciate all for the info provided. Regards smitha |
Heh, heh. A man after my own heart!!
I'm currently developing various lab exercises for ME students in machine design. Trying to do 'real' stuff in this day of computer simulations is a challenge. And getting across the message that flaws in your simulation have nasty effects in the real world is best done with things like 20hp motors and 10:1 gear boxes. Only issue is how to get it impressive but still safe for udergrads who's idea of a big power supply is a 300 watt ATX box for their computer. Don Foreman wrote: On Wed, 10 Aug 2005 10:34:51 +1000, "John G" wrote: "smitha4u" wrote in message groups.com... I believe i can bulid in my school lab. Aprreciate if you can expalin it in detail Thanks Rgards smitha This is not a job to be undertaken by someone who has to ask such basic questions in a METALworking group. It is proper engineering job for an experienced consulting engineer with experience in this type of indstallation. How do you suppose engineers become trained to do such consulting? That's why schools have labs. I'm glad there are still students working with real machines in a real laboratory rather than with 'puter sims. You can't simulate the experience of a 50 HP DC motor drawing a gazillion amps of armature current at stall, or if the field comes loose. Ya gotta see it in person, after duly noting the motor bits still embedded in the bricks from previous oopsies. Unscheduled experiment: how fast can a twit lab TA dive under a bench? Open field on big DC motor running with rated armature voltage, time the twit when he hears it accelerating rapidly toward kaboom. (Do close the field pretty quick. Forget about killing armature current at that point; opening the switch results in a big green arc) The show is well worth the ensuing loud lecture endured with simulated contrite humility. Your grade may partly depend on the quality of your simulation.... |
Smitha Would it be OK for me to ask what kind of school you are attending?? It is difficult to consider that there is a school that would present you with a 25 HP DC motor without first acquainting you with the the fundamentals. Perhaps English isnt your first language. When you ask this News Group to educate you, it seems that you have no instructions available from that school. I's suspecting this is a prank post. How about you supply a little more background on what you are doing and maybe where you are. Jerry "smitha4u" wrote in message ps.com... Hi Thank you all I agree with after reading all the messages that i really did not think of all the measures and questions. Could some body educate me what more i need to know. before testing I think i need to prepare a test plan/procedure and what all will i calculate and how i will show my demonstration. If they agree my experience with dealing large machines is not sufficient atleast they would see my test plan and do the test with some expeerienced. Hope i get some help and appreciate all for the info provided. Regards smitha |
"Don Foreman" wrote in message ... On Wed, 10 Aug 2005 10:34:51 +1000, "John G" wrote: "smitha4u" wrote in message roups.com... I believe i can bulid in my school lab. Aprreciate if you can expalin it in detail Thanks Rgards smitha This is not a job to be undertaken by someone who has to ask such basic questions in a METALworking group. It is proper engineering job for an experienced consulting engineer with experience in this type of indstallation. How do you suppose engineers become trained to do such consulting? That's why schools have labs. I'm glad there are still students working with real machines in a real laboratory rather than with 'puter sims. You can't simulate the experience of a 50 HP DC motor drawing a gazillion amps of armature current at stall, or if the field comes loose. Ya gotta see it in person, after duly noting the motor bits still embedded in the bricks from previous oopsies. Unscheduled experiment: how fast can a twit lab TA dive under a bench? Open field on big DC motor running with rated armature voltage, time the twit when he hears it accelerating rapidly toward kaboom. (Do close the field pretty quick. Forget about killing armature current at that point; opening the switch results in a big green arc) The show is well worth the ensuing loud lecture endured with simulated contrite humility. Your grade may partly depend on the quality of your simulation.... Have to agree-the only computer simulation I ever did was a second order system patch wired on a General Dynamics analog computer. Everything else was lab work... |
"smitha4u" wrote in message ps.com... Hi Thank you all I agree with after reading all the messages that i really did not think of all the measures and questions. Could some body educate me what more i need to know. before testing I think i need to prepare a test plan/procedure and what all will i calculate and how i will show my demonstration. If they agree my experience with dealing large machines is not sufficient atleast they would see my test plan and do the test with some expeerienced. Hope i get some help and appreciate all for the info provided. Regards smitha As you have seen from the replies, there's various ways to determine motor constants.You need to tell everyone what you DO know about DC motors first. Are you familiar with the basic DC motor equations? What are the capabilities of the lab-any equipment to measure large torques and currents? The electrical and mechanical input/output levels you will be dealing with can be lethal. If this is for a school lab project I'd suggest you consider a 12 volt permanent magnet motor from a car (engine cooling fan or blower motor) and determine the motor constants. |
I'd put something like 100V across the field winding and see what the output
is for the armature when turned at a speed near the rated speed. The thing that is nice about DC motors is that the can be used easily as DC generators, especially if the field is a magnet. The other thing about DC motors is that they will spin on much lower voltages (10^ os rated voltage is a good starting point for low speed operation) although the current will be the same approximate valuee as the full speed current. Currrent, of course, goes up with load from some value which may be 50% of the max current. -- Why do penguins walk so far to get to their nesting grounds? |
On Wed, 10 Aug 2005 06:03:56 GMT, Ignoramus6689
wrote: I am not sure what it is that they can learn with a 20 kW motor, that they cannot learn with a 1 HP motor. Respect and perspective. Ya can't get into much trouble with a 1 HP motor. Wiring a 24-volt doorbell is not sufficient preparation for working wtih 440V wiring, though the same theory applies to both. |
In all actuality this might be a drill press from Sears. You know "Maximum
Developed HP" crap they label everything with. Sears has really turned into a joke. Everyday I am on edge that they will go out of business and my hand tools will be about worthless. Should I just start buying the Chinese crap now? I actually took a glance at a drill press at Sears. Looked at the back to find the plate on the motor in an attempt to find the true HP. Conveniently the plate was missing, but the 4 rivet holes where there. Nothing more insulting. "smitha4u" wrote in message oups.com... Hi Guys Can any one suggest what are the various methods of performing bench test for a 20 Kw(25HP) DC electrical variable speed motor. Thank you Regards smitha |
Jerry Martes writes:
and maybe where you are. NNTP-Posting-Host: 12.2.142.7 resolves to: Caterpillar, Inc. CATERPILLAR-142-0 (NET-12-2-142-0-1) 12.2.142.0 - 12.2.142.255 |
On Wed, 10 Aug 2005 20:57:52 -0500, Richard J Kinch
wrote: Jerry Martes writes: and maybe where you are. NNTP-Posting-Host: 12.2.142.7 resolves to: Caterpillar, Inc. CATERPILLAR-142-0 (NET-12-2-142-0-1) 12.2.142.0 - 12.2.142.255 Bingo. Troll Gunner The two highest achievements of the human mind are the twin concepts of "loyalty" and "duty." Whenever these twin concepts fall into disrepute -- get out of there fast! You may possibly save yourself, but it is too late to save that society. It is doomed. " Lazarus Long |
"Ignoramus6689" wrote in message ... On Tue, 09 Aug 2005 23:17:22 -0500, Richard J Kinch wrote: Ignoramus6689 writes: That will deliver more than 300 volts. his motor is rated for 360 volts max, so I am not sure why you use this number to make an objection. I thought he said it was rated for 250 volts. Looking back I see he said "it [sic] rated for 250-360 volts". exactly. So, who knows. The OP does not project competence for this kind of tinkering. If I got a 20 kW DC motor (shudder), I would not try to run it. It it was a permanent magnet motor, I would try to spin it up and see if there is DC voltage generated by the motor. i I would start by making sure that sucker was very securely anchored to something fairly bit -- you set something like that on a "bench" or anywhere else for that matter and apply power it will do 2 things: 1) take off in a hurry in some direction from the torque and 2) either rip your wires out or just twist them together for lots of fireworks (and 25 Hp is capable of taking a small "bench" with it when it starts). mikey |
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