MechMate CNC Router Forum

Go Back   MechMate CNC Router Forum > After Building the Beast - Operating , Troubleshooting and Maintenance > Troubleshooting
Register Options Profile Last 1 | 3 | 7 Days Search Today's Posts Mark Forums Read

Reply
 
Thread Tools
  #31  
Old Thu 08 November 2007, 05:17
Richards
Just call me: Mike
 
South Jordan, UT
United States of America
Hi guys,

Sorry, but I slept in until 4:45 a.m. this morning. It looks like you've found the problem. I just checked two of my PK296B2A-SG3.6 motors. With the power off, the gear shaft, without a spur gear, is hard to turn, but I can turn it. With a 20-tooth or a 30-tooth spur gear, it should be fairly easy to turn.

You also said that one coil measured 5 ohms and the other coil measured 1 ohm. The Oriental Motol web site shows that the full coil resistance of the PK296A1A-SGxx motor is 4.4 ohms and the half-coil resistance is 2.2 ohms. With the motor disconnected from the G202, the half-coil resistance between the Black and the Yellow wire should be the same as the resistance between the Yellow and the Green wire. The half-coil resistance between the Red and the White wire should be the same as the resistance between the White and the Blue wire. And the full-coil resistance between the Black and the Green wires should be the same as the resistance between the Red and the Blue wires. Some meters cannot accurately measure such low resistance, so, if the readings don't look right, if possible, try another brand of meter. Also, be very certain that the motors are wired properly. If they are wired full-coil (Bipolar Series), then you should be using the Black and Green wires for the A coil. You should be using the Red and the Blue wires for the B coil. If you are wiring the motors half-coil, then you should be using the Yellow wire and either the Black or the Green wire for the A coil. You should be using the White wire and either the Red or the Blue wire for the B coil. (From your description, I'm wondering if you had one coil on the motors wired Bipolar Series (full-coil) and the other coil wired half-coil?)
Reply With Quote
  #32  
Old Thu 08 November 2007, 05:47
Daya
Just call me: Fabrica
 
Kandy
Sri Lanka
Mike thanks for your input. I will check all these and give you the results by tomorrow morning.
Reply With Quote
  #33  
Old Thu 15 November 2007, 04:45
Daya
Just call me: Fabrica
 
Kandy
Sri Lanka
Finally made the decision to dismantle the motors. Found four windings burnt (all coil B windings). Got a motor winder to re wind.

He brought the re wound motor today. Did check on the resistance of the coild before connecting. The original windings of Coil A was 5 ohms and on coil B which was re wound was 4.6 ohms. When questioned about the difference he said that he did exactly the same number of turns (50) on each coil. The size of the wire had been 50 swg. He says that their maybe a material difference in the winding wires which he used and what was originally used in the motor.

Connected the wires and did some jogging. While starting and stopping the motor gives a rattling noise. Once it picks up speed the motor runs smooth.

Guys please advice me on what I should do. Shall I get the winder to re wind Coil A as well so that both coils will have a resistance of 4.6 Ohms each or should i increase the number of turns so it finally gives a reading of 5 ohms.

Last edited by Daya; Thu 15 November 2007 at 04:45.. Reason: spellings
Reply With Quote
  #34  
Old Thu 15 November 2007, 04:58
Gerald D
Just call me: Gerald (retired)
 
Cape Town
South Africa
Daya, you are the very first person I hear of that is attempting to rewind the stepper motor. I don't know if anyone of us are qualified to advise you, but we are surely very interested in the results!

You could try to adjust the potentiometer on the Gecko for that motor?

If you can get that motor to run properly again, I think that is a total bonus. As an outsider, I am concerned what caused the damage and how do other guys stop the same thing happening to them. . . . .
- Why could the motor not be turned by hand?
- Do you not have "half coils" that still worked? Maybe you could have avoided the rewinding?
Reply With Quote
  #35  
Old Thu 15 November 2007, 05:39
Richards
Just call me: Mike
 
South Jordan, UT
United States of America
This is something that I know nothing about. However, I think that having the windings on the A coil match the windings on the B coil would be necessary. To me the bigger problem would be magnetism. As far as I understand, stepper motors are magnetized after they are assembled, which is the reason that taking them apart can lead to problems. In other words, I have no idea whether the rattling noise is caused by bearings, winding differences, magnetism problems, or a combination of all three.
Reply With Quote
  #36  
Old Thu 15 November 2007, 06:08
Daya
Just call me: Fabrica
 
Kandy
Sri Lanka
Ok Mike Just one question. Can I get both coils to have a resistance of 4.6 ohms. What difference would it make when the coil resistance is 4.6 ohms and 5.0 ohms. Will they have a effect on the accuracy and the torque.


Four motors are gone. I have no option but to keep on trying things.
Reply With Quote
  #37  
Old Thu 15 November 2007, 06:13
Daya
Just call me: Fabrica
 
Kandy
Sri Lanka
Mike, According to our knowledge the reason for the four motors to get burnt had been due to current being present in the earth wire. How do we provide protection to the control box in order to stop the same thing happening again.
Reply With Quote
  #38  
Old Thu 15 November 2007, 08:48
Gerald D
Just call me: Gerald (retired)
 
Cape Town
South Africa
Daya, on the latest drawings there is a note to include GFI (Ground Fault Interrupt) protection. In Sri Lanka it might be called RCD (residual current), or Earth Leakage, protection. http://en.wikipedia.org/wiki/Residual-current_device

This device is added to whole building, or to the outlet where the MechMate is plugged in - not added to the MM control box.
Reply With Quote
  #39  
Old Thu 15 November 2007, 09:35
Richards
Just call me: Mike
 
South Jordan, UT
United States of America
Daya,

Gerald's suggestion to use a GFI is very important. The GFI will protect you and your equipment if current starts to flow through the Earth Ground.

The difference between 5 ohms and 4.6 ohms is about 8%. As far as I know that is too much difference between coils. I just measured three different motors, a PK299-02A, a PK299-F4.5 and a PK296B2A-SG3.6. The greatest difference between the A coil and the B coil on any motor was 0.1 ohm. My old Fluke 77 meter wasn't designed to read low resistance at high accuracy, so the readings may not be exact; however, the readings basically show that the coils are matched.

The voltage being present in the earth conductor is a very serious problem. There are only two common ways to have that happen:

(1). Ground loop. A ground loop can be caused by connecting each end of an earth ground to different ground points. By definition, all ground points MUST be connected to the same point. Here in the USA, we have to connect all earth grounds on a machine to a common ground bolt on the machine. The common ground bolt is connected to the common earth ground in the electrical panel by a bare copper wire. If various machines are grounded, the only common point of connection between all of the machines is the common earth ground in the electrical panel. In other words, all earth grounds radiate from the earth ground in the electrical panel like points on a star.

(2). Disconnecting the NEUTRAL conductor while the HOT or LINE conductor is still connected (turned on). Here in the USA, only the HOT or LINE conductor is switched. The NEUTRAL conductor is hard wired so that it cannot be switched. If the NEUTRAL is switched, it MUST be switched using a multi-pole switch so that the NEUTRAL is switched at the same time as the HOT or LINE conductor.

Of course, when we talk about Earth Ground, Neutral, and HOT or LINE conductors, we're talking about AC voltage. Every DC power supply also has a GROUND conductor and a HOT or PLUS conductor. Because the DC GROUND is the point from which all DC voltages are measured, it is considered to be 0-Volts. Many engineers consider it safe to connect all DC GROUND conductors together. Many engineers also consider it safe to connect all DC GROUNDs and AC Earth GROUND together. You must verify that only the DC HOT or PLUS conductor is switched. Whenever possible, I float the DC GROUND. What that means is that there is NO connection between the DC circuits and the AC circuits except through the transformer. I also opto-isolate different DC voltages. That means that if I'm running a 12VDC or a 24VDC circuit (proximity switches, for example), the only way the 12V or 24V circuit communicates with the 5V computer circuit is through the infared light of the opto-isolator. Sometimes I have to connect all of the GROUNDs together to make a circuit work. That is the case when I've added electronics to my Shopbot control box. I don't like to do that, because serious damage can occur if the ground line is switched and the HOT or PLUS line is not switched.

EDITED: I have edited this post to emphasize that ONLY the DC HOT or PLUS signal line is to be switched. DO NOT SWITCH THE DC GROUND line.

Last edited by Richards; Thu 15 November 2007 at 09:45..
Reply With Quote
  #40  
Old Thu 15 November 2007, 09:52
Gerald D
Just call me: Gerald (retired)
 
Cape Town
South Africa
Mike, wouldn't it be more important that the coil inductances matched, rather than the resistances? And it can't be any fun to match inductances . . . . the best he could do is to match wire size, quality and number of turns I suppose?
Reply With Quote
  #41  
Old Thu 15 November 2007, 10:23
Daya
Just call me: Fabrica
 
Kandy
Sri Lanka
Dear Mike and Gerald.

Mike first of all let me thank you for going the extra yard to explaining to me the intricacies involved with the power supplies.

Gerald I do thank you as well. I feel all my five motors are dead and gone. I read some articles on the net which proved to me that once a coil is damaged in a stepper they are not repairable. The magnetic power in the permenent magnets get's disturbed no sooner you dismantle the motor which I have done. They are are not reversible unless you have very sophisticated equipment.
Reply With Quote
  #42  
Old Thu 15 November 2007, 10:48
Richards
Just call me: Mike
 
South Jordan, UT
United States of America
Gerald,
Yes, Inductance is the important measurement. And, just as you pointed out, winding matching coils by counting turns and using wire from the same spool is about the only way that most of us would have to insure matching inductance between coils. Measuring resistance is an easy way to see if something has gone terribly wrong; but, because of all the other factors involved around inductance, measuring resistance is not the best way to verify that two coils will match when they are powered up.

Daya,
I'm really sorry to hear that the motors were destroyed. I hope that you can find the cause of the problem before you install the new motors.
Reply With Quote
  #43  
Old Thu 15 November 2007, 11:07
Gerald D
Just call me: Gerald (retired)
 
Cape Town
South Africa
Daya, it is indeed tragic to hear that your motors are gone. I asked at the geckodrive forum if anyone has hints on what might have caused it. Mariss has already replied: http://finance.groups.yahoo.com/grou.../message/13830 and he suggests a check that you must do on your drives to see if they are really okay.
Reply With Quote
  #44  
Old Thu 15 November 2007, 18:54
Daya
Just call me: Fabrica
 
Kandy
Sri Lanka
Thanks Gerald I will follow your link and do the needfull.
Reply With Quote
  #45  
Old Fri 16 November 2007, 08:57
Gerald D
Just call me: Gerald (retired)
 
Cape Town
South Africa
For the others keenly following this thread and wondering if their motors might also get damaged in this way, I think I need to put minds at rest, but at the same time give the "heads up" on the danger of mains electricity.

Daya has agreed (in an offline note) that his ground system could not have been connected during his unfortunate incident. It cannot be stressed too many times that a solid ground system be connected at all times. I have maybe erred in always talking of grounding in the sense of avoiding interference, and seldom in the sense of safety. To me it was always so "obvious" that one grounds all metal parts so that fault currents flow straight to ground instead of via humans or other expensive components like motors or drives, etc. (Same as for lightning conductors - blowing 5 motors simultaneously was cause by the equivalent of a "lightning bolt"). If Daya's ground system was connected, the motors would not have had to carry the fault current.

What caused the fault current? Daya is still looking for that. It could have been a wire at one of his 230V limit switches that came loose or chafed through, or a faulty portable tool or extension lead was used at the table, or a welder touched the table by mistake, etc. etc. If a solid ground was in place, the damage would have been limited to a tripped circuit breaker or a blown fuse.

A GFI (or RCD) device would have given earlier warning of a disconnected ground system - still a highly recommended safety device.
Reply With Quote
  #46  
Old Mon 21 April 2008, 01:05
Glenn D
Just call me: Glenn
 
Baton Rouge, La.
United States of America
Gerald After reading a number of your treads I think I will do as you suggested I will start with the control box. I have no idea what size stepper motor to start with ? I plan to cut MDF/plywood and sign material . I would like five stepper motors 2 on x, 1 on y, 1 on z and 1 on indexer. What do you suggest is a good place to start. Also what is two phase I am formulary with single an three phase, but not two phase Thank you glenn
Reply With Quote
Reply

Register Options Profile Last 1 | 3 | 7 Days Search Today's Posts Mark Forums Read

Thread Tools

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump


All times are GMT -6. The time now is 04:25.


Powered by vBulletin® Version 3.8.3
Copyright ©2000 - 2024, Jelsoft Enterprises Ltd.