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  #1  
Old Thu 11 July 2013, 11:17
Richards
Just call me: Mike
 
South Jordan, UT
United States of America
Motor Voltage: Mike Richard versus Gerald_D Debate

This discussion extracted from another thread . . . . . . .

Did you catch the part that voltage is the force that "forces" current into the coils. Inductance is the resistance to that happening. The lower the inductance, the easier it is to force current into the cols.

Heat is generated as the product of voltage X current. The greater the voltage, at a given current, the greater the heat.

The goal is to get adequate performance without frying things. Some motor manufacturers allow an 80-degree 'C' rise in temperature with a 100-degree 'C' maximum. That is HOT. It's probably nearly hot enough to ignite vapors that might be leaking from a spray booth. Don't think that just because you or someone else has never had a fire that excessive heat caused by higher than recommended voltage can never happen. Look very closely at your fire insurance policy. Most policies will not pay if you exceed recommended current or recommended voltage. Who determines what those "recommended" currents or voltages are? The manufacturer of the motors and the stepper drivers are seen as the "experts" when insurance companies have to pay on a policy.

If you need slightly more torque than your current motor/driver/gearbox can give you, get a bigger motor and stay within the recommendations. Paying for four larger motors is much less expensive than paying for a burned up shop.

Last edited by Gerald D; Fri 12 July 2013 at 20:45.. Reason: added red intro statement
  #2  
Old Thu 11 July 2013, 14:20
Gerald D
Just call me: Gerald (retired)
 
Cape Town
South Africa
100C is 212F, the temperature of boiling water . . . . we drink that without worrying that it may start fires.

Choose your power supply voltage as high as will be allowed by the drives. Then, if you find that your motors are too hot to your liking, reduce the current setting on the drives.

If you take a very conservative route and choose a low voltage power supply, you permanently cripple your machine.

I would start worrying about motor heat if we have reports of guys having burnt their motors. The fact that burnt motors are extremely rare tells us that we are generally choosing voltages which are too low.

We have rebuilt our power supplies to give higher voltages than those suggested by the conservative Mariss formula and have not lost a motor due to heat.
  #3  
Old Thu 11 July 2013, 21:24
DocTanner
Just call me: Don Ross
 
Blue Ridge, Texas
United States of America
Wow, Same discussion for 6-7 years. Gerald is correct. No need to leave the power on the drawing board. <--- Literally
Not much around the steppers to burn. Most shop fires are started by dust collectors.

Have a nice day,
Don Ross
  #4  
Old Fri 12 July 2013, 08:26
Richards
Just call me: Mike
 
South Jordan, UT
United States of America
I thought that Gerald might respond, unfortunately he's given some advice that could hurt you, could expose himself to unlimited liability and could put this forum in jepordy. Mariss, at Gecko drive, warns everyone that the voltage calculated by his formula is the MAXIMUM voltage, not the suggested starting point for experimentation. The insurance industry would use Geckodrive as the "expert" before paying out damages.

If any of you have ever seen the result of an electrical fire, you've probably seen how the "impossible" happened. One component got too hot. It caused another to overheat. Before long things cascaded. Insulation melted. Bare metal carrying electricity touched bare metal. Sparks were created and the business burned.

Early in my career, I walked through Borge Anderson's burned out building. He had been using a 25W fish tank heater to keep photo chemicals warm. A 25W heater puts out 1/3 the heat of a typical stepper motor. The wiring was frayed. Something happened and his building burned to the ground causing nearly one-million dollars damage. He thought that the circuit breaker would keep the wiring from overheating, but he didn't realize that he needed to put a fuse rated for the size of the heater's wiring in the circuit.

Most shops have a light coating of sawdust covering everything. During a cut, the air can be filled with fine sawdust. If the insulation on the wiring at the junction between the motor's wires and the cable going to the controller melts, because that insulation touched a hot stepper motor, all bets are off.

What about the actual voltage going to the transformer? Right now, in my shop, the incoming voltage is 127VAC. This afternoon, when demand is high the voltage will droop to 105VAC and sometimes lower. The rating on the transformers I use assume a voltage of 115VAC. What happens to wattage when you raise the voltage 10% or 15%? If your temperature was 100-degrees C with incoming voltage of 105VAC, what will it be at 127VAC?

Building your own CNC machine puts you in control of everything. It's your choice whether you think so little of standards that you would risk everything. You only have to be burned once before you learn to respect heat.
  #5  
Old Fri 12 July 2013, 11:35
danilom
Just call me: Danilo #64
 
Novi Sad
Serbia
If you look at this motor datasheet

http://www.jat-gmbh.de/pdf_engl/mot/2_3_34S_e.pdf

it's one that I own, it was designed with an encoder and run as closed loop.
If you look at the characteristics curve diagram there are curves for three voltages

highest is 150 V !!! and the motor has a inductance from 1.2 to 4mH
  #6  
Old Fri 12 July 2013, 18:36
Richards
Just call me: Mike
 
South Jordan, UT
United States of America
I decided to run a test to solve, for me at least, whether Mariss at Geckodrive was actually telling us that maximum really meant maximum. That was not an easiy decision. I had been invited to contribute my expertise on this forum many years ago, so I had assumed that the methods that I used was acceptable and that the testing that I had done followed the methods and testing that people in the industry used. I also knew, from first-hand experience, having spent 2-1/2 years in Belgium and France, how difficult it is for someone to understand technical terms in a 2nd language. Many people who read this forum struggle with English. If they are like I was in Belgium and France, some of the basic concepts being presented are glossed over, such as the duty cycle published by the stepper motor manufacturer or the size of the heat sink required. Most people gloss over those specifications, thinking that they are not important. If they were not important, the manufacturer would not have included them in the specifications.

Here's the test that I ran. I used an Oriental Motor PK296A2B-SG3.6 stepper motor, which has the same electrical characteristics as the PK296A2A-SG7.2 commonly used here. I used a Geckodrive G203v stepper driver, which is also commonly used here. I used a Variac transformer in front of a 25VAC torodial transformer. The Variac allowed me to adjust the voltage going to the torodial transformer.

I loaded the motor with a resistive load, such that the motor could ramp up to speed using numbers that I had used for years on my Shopbot PRT-Alpha CNC machine. I increased the voltage so that the torodial transformer produced 45VDC. I ran a routine until the motor reached 105-degrees C, similar to what would happen on a warm summer afternoon while running 3-D cuts. I attached the motor to a 30-foot length of 7-strand, 22-guage conductor cable that did NOT have teflon insulation, immitating the wiring used in many parts of the world where the proper flexible cable is not available. The extension cable was soldered directly to the motor leads, again trying to mimic the conditions that would be found in many parts of the world where terminal blocks and crimped conductors were not readily available.

After one hour on the bench, I flexed the non-approved cable into a 2-inch radius, which is less than the radius that many use, but still greater than the radius specified for "proper" cable. The insulation, close to the solder joints, split, allowing two of the four conductors to be exposed on a length exceeding 1/2-inch. That alarmed me. Having bare wire exposed posed a safety threat.

As far as I can see, my test showed that Mariss was correct and that maximum really means maximum.

As to the comments that some data sheets allow high voltages to be used with stepper motors, I can agree with those manufacturers. A stepper-driver is not a constant voltage source, but is normally called a "chopper". To get the fast pulse needed for CNC operation, a momentary high-voltage pulse is given to the motor to force current into the coils. As soon as the coils approach their designed current, that voltage is reduced to a very low level to sustain the current during that step. There are many designs commonly used, but the principle is fairly common, i.e., use a high voltage source to force current into the coils and then modulate or chop the voltage so that the coil does not oversaturate. The design of a stepper driver and the methods used is beyond the ability of most builders. They rely on the expertise of the manufacturer. Many people on this forum use GeckoDrive stepper drivers. Mariss is the designer of those drives. He knows what voltages, what currents, and what heat his design produces. My tests showed that his calculations can be trusted.

........... removed un needed comment ......... (metalhead)

The saefty of people all over the world who may not have the vocabulary to understand every part of a stepper motor or a stepper drivers datasheet was important to me.

If you have questions or conserns, please contact me via private email at miker@xmission.com.
  #7  
Old Fri 12 July 2013, 21:11
Gerald D
Just call me: Gerald (retired)
 
Cape Town
South Africa
Mike, you have not built your own MechMate

When I started this forum, I did not invite you to contribute your "expertise". I felt obliged to humour you here because you appeared to have a group of supporters.

Earlier this year you got very upset when I put it to you that a new poster, who had just given you a glowing letter of support, posted it from your IP address. Those posts were deleted by the moderators and unfortunately most readers did not get a chance to understand the real Mike Richards.

Your "test" earlier today is so typical of the nonsense we have had to endure from you: it has no bearing to MechMates constructed according to the guidelines posted here! You used dodgy wiring and then conclude that you shouldn't use dodgy wiring, but you prove nothing regarding voltage.

Remember, we all agree that hot motors are not good. A hot motor is not instantly caused by the voltage alone. It develops slowly, it is easily detected and it can be controlled by reducing the current setting on the drive. Very simple and non-dramatic. You seem to think it is the end of the world?
  #8  
Old Sat 13 July 2013, 10:14
Richards
Just call me: Mike
 
South Jordan, UT
United States of America
Gerald,

If you want, I will post the email you sent to me asking me to post on your MechMate forum.

You say that a test is nonsense, but you ignore all of the posts on the forum where users have asked if they could use non-standard cabling because of the cost or the difficulty of obtaining the recommended "flexible" cable. I used wiring that I bought from Colemans, a company that supplies most of the wire in Salt Lake City. That wire did exactly what it was designed to do. At room temperature, with no bending, it will last forever. The sheathing is stamped with 60-degrees C. You are the one who said that 100-degrees C was the temperature of boiling water. At 105-degrees C, the insulation softened to the point of rupture, causing an unsafe condition. I used 105-degrees because that was the temperature generated by the stepper motor when the ingoing voltage was raised to 127VAC instead of 115VAC. My line voltage was 127VAC.

Motors get hot when their duty cycle exceeds 50%, the duty cycle specified by the manufacturer (Oriental Motor). In a typical process control situation, the duty cycle of a motor can easily be determined. Determining the duty cycle on a CNC machine is not possible. If the machine is used to cut cabinet parts, it would be difficult to exceed a 50% duty cycle. If the machine is used to cut 3-D parts, it could easily exceed 50% duty cycle. In addition a 3-D cut usually has very short moves, which are exactly the type of moves that cause a motor to heat.

When a motor is driven at the maximum recommended voltage or at a voltage lower than maximum, heating never becomes a problem.

How many users are going to stop a 3-D cut because the motors are hot? How many users are even aware that their motors are hot during a cut? How many users even have an infrared thermometer?

How many users would see posts about a PK296A2A-SG7.2 motor and a Gecko G203v being run at higher that maximum voltage and then conclude that their "other brand" motor and their "other brand" driver could also be used at 135% of maximum? That is the root of the problem. This forum is read by people who struggle with English. It is read by people who have no knowledge of electronics. It is read by people who don't know that just because a PK296A2A-SG7.2 motor driven by a G203v with high-temperature wiring can handle 135% of the maximum voltage, does not mean that their motor, their driver, and their wiring can handle that excess voltage.

You assume that those users will change the current limiting resistors on their stepper drivers. How can you make that assumption when they ignore maximum ratings already? You're assuming that they are knowledgable about current limiting resistors. You're assuming that they are knowledgable about the relationship of currents vs voltage. You're assuming a lot. What you shoud be assuming is that they have read posts that you have written where you have ridiculed maximum voltage, where you have ridiculed cautions about exceeding maximums, where you have ridiculed tests run that show what happens when maximums are exceeded. What you should assume is that users will blindly follow your "expertise" and that they will ignore the formula written by Mariss at Geckodrive. What you should assume is that they will use whatever materials they can buy and that those materials may not be the "recommended" materials. What you should assume is that if they follow your recommendations about excessive voltage with "regular" wiring, that they will have built a machine that WILL be a hazard if they use that machine to cut time consuming 3-D parts, where the motors exceed a 50% duty cycle, where the motors are not mounted on the recommend large aluminum heat sink.

What I am promoting is that accepting maximums will negate all of those "assumptions"; that keeping the voltage at or less than the maximum will not cause excessive heat (unless the coils on the motor "shorts" out); that keeping the voltage at or less than maximum will not cause the insulation on non-flexible wiring to melt; that keeping the voltage at or less than maximum will not give the impression that "maximum voltage" can safely be ignored.

Did you notice post #7 on this thread. That poster implied that voltages up to 150V could be used with motors that had an inductance of 1.2mH to 4mH. That poster did not relate that voltage to any stepper driver. Someone reading that post might assume that he could run a G203v at 80V (the maximum for that driver) with motors that had an inductance of 1.2mH to 4mH. Eighty volts would be 228% higher than maximum for a 1.2mH motor and 125% higher than maximum for a 4mH motor. That misunderstanding of motors, drivers and voltage would be disastrous.

You told everyone that you transfered this forum to Mike (Metalhead), yet you are now telling us who can and who cannot post. So, what is it? Do you still own this forum or does Mike (Metalhead). Do you control who posts or does Mike (Metalhead)? Mike (Metalhead) seems to trust my expertise. He sent me motors to test and seemed to value the effort that I expended to help him.

You have already received my offer which is that you delete ALL my posts if you think that my "expertise" has no value to MechMate builders. AFTER you have deleted ALL my posts, I'll stop posting and you can tell MechMate builders to use any voltage that you want and you can take full responsibility if they exceed maximum voltage.
  #9  
Old Sat 13 July 2013, 10:29
danilom
Just call me: Danilo #64
 
Novi Sad
Serbia
I respect the test and agree with it, some maximums must apply.
The motors I posted are used as said with a closed loop system servo like drive with much less heat produced than our standard stepper drives. Just wanted to point that there are high voltage stepper systems.

This reminds me of War of Currents, where Nikola Tesla and Edison fought about which electric current is safer, Edison claimed that the 220V alternating current is a killer, they even publicly electrocuted dogs to show this, but with time and safety measures and people realizing the dangers with alternating current learned to live with it.

Motor heating is dangerous, but so is the operating a cnc. If you don't respect it ... it can kill you, rip a finger or worse.
There should be a warning or something, that anyone who does not feel comfortable working with high voltages or eletronics hires an certified electrician to do the wiring. And do a temperature test of the system.
  #10  
Old Sat 13 July 2013, 11:22
Gerald D
Just call me: Gerald (retired)
 
Cape Town
South Africa
Mike, the stepper motors have leadwires about 8" long at minimum - the ends of those lead wires are not as hot as the motor. You are just throwing in another red herring.

The readers of this forum are free to follow whoever they want. I feel they need to know you give extremely conservative advice and any MechMate built to your guidelines will be a poorly performing machine with motors stalling and loosing steps when even a short burst of power is needed to get a cutter through a hard knot.

Mariss published his formula as a guideline with no concerns about fire safety. Since his formula does not recognise duty cycle, it must be for 100% duty, while our application has a much lower duty.

My challenge still stands; find some real life examples of MechMate motors starting fires, melting insulation, burning blisters, seizing bearings, loosing magnetism, whatever, caused by high heat. Until you actually find these examples, you are wasting our time.
  #11  
Old Sat 13 July 2013, 11:40
Richards
Just call me: Mike
 
South Jordan, UT
United States of America
Danilo,

Thank you for posting. I agree with you. I used Oriental Motor Alpha motors with their Alpha stepper drivers. They also used high voltage. I have some Oriental Motor Vexta UMD268-01 and UDP599H-NAA motor/drivers units on my shelf. They also work at high voltage. The driver/motor has the proper "chopper/modulation" timing for each step that makes high voltage possible. When used as directed, those Vexta motor/drivers and the Alpha motor/driver runs at reasonable temperatures, never reaching even 80-degrees C.

Geckodrive designed its G20x series of stepper drivers to work properly under certain conditions. When used as directed, everything works. When not used as directed, "strange" things can happen.

Your comment about operating a CNC being dangerous is perfectly true. We take every precaution when changing a cutter. We follow all guidelines when operating that machine. In other words, we don't take chances and we don't diregard "standards".

Those "standards" should apply to all aspects of building and operating any tool.

A certified electrician would not exceed maximum voltages. He would not risk the consequences. I don't think that anyone should do anything that a licensed and qualified electrician would not do.
  #12  
Old Sat 13 July 2013, 12:12
Richards
Just call me: Mike
 
South Jordan, UT
United States of America
Gerald, you posted while I was responding to Danilo. You're assuming that those wires do not touch the motor or the mounting bracket. That assumption can be false. Most of us put a "strain relief" on our wiring. That "strain relief" can be connected to the motor's mounting bracket. The mounting bracket can easily reach the motor's temperature.

You're also claiming that Mariss assumed 100% duty cycle. Nothing on his site claims that, but he has stated on his forum that few of his stepper drivers are used on CNC machines compared to the percent of drivers used in process control. You also know that running a 3-D file exceeds 50% duty. Anyone who runs that type of file knows how long a 3-D cut can take, sometimes many hours.

Your challenge is nonsense. If someone gets injured or his business burns down because of overheating motors, you will know and so will everyone in the CNC community. They will be able to trace the thinking and the advice that lead to that overheating.

Yes, I am conservative in my advice. I value safety over speed. If a MechMate performs poorly at the recommended voltages, that simply means that the motor/driver is too small for the application. A larger motor/driver/gearbox should be used to get the desired performance within the safety limits specified. No one needs to "hotrod" a stepper/driver to get that performance edge when off-the-shelf components that do what he needs to do are readily available.

Building a poorly performing or poorly built machine is up to the user. You know and I know that many use the parts and pieces that they can find in their country. They don't always build a machine to "spec". They don't have the expertise to know the consequences to using "sub-standard" parts and pieces. My advice is directed to "those" users.

You've built and modified many machines. You have the luxury of making modifications when you see that a modification will improve the design. Do all MechMate builders have that luxury? Do they have sufficient funds to change something? Or, do most MechMate builders live on a very tight budget where substitution of parts is out of the question? Personally, I think that most MechMate builders hope to build their machine at the lowest possible cost.

Yes, each builder is free to design and use any part and any component. I have nothing but admiration for your mechanical design. It gets the job done at a "price point" that most people find acceptable. I agree with almost everything that you've posted about electronics. Some of your suggestions have been ingenious. The only "picking point" is about maximum voltage. You see it as a performance issue. I see it as a safety issue.

You can call my tests anything that you want. I am not trying to "defame" you, but to show that my concerns are founded in reality and that serious problems can happen when people use parts, pieces and practices that are available to them, when those people, new to CNC building, assume that because one person used sub-standard wiring that they can too or that because one person used high voltages with a certain motor/driver that they can exceed maximum on their motor/driver.

Gerald, this does not need to be a feud. I'm not trying pick a fight with you and I'm not trying to "smear" you or your reputation. I have not mocked you or your posts. I have not tried to use "tricks" to trap you. I would appreciate it if you gave me the same consideration.
  #13  
Old Sat 13 July 2013, 12:34
Richards
Just call me: Mike
 
South Jordan, UT
United States of America
A comment on substituting motors.

Using an Oriental Motor PK296-F4.5A wired half-coil gives a holding torque of 300 oz*in. When that motor is used with Mike's (metalhead) belt drive, with a 4:1 ratio, that motor gives 1,200 oz*in of holding torque. When wired bipolar parallel with a 4:1 belt-drive, that motors gives 1,700 oz*in of holding torque.

The PK296A2A-SG7.2 geared motor is restricted to 700 oz*in because of the gearbox.

The PK296-F4.5A costs $139. I don't know how much Mike charges for the belt-drive. The PK296A2A-SG7.2 costs $257.

The PK296-F4.5A with Mike's belt-drive would outperform Oriental Motors SG geared motors and it would do that at 35VDC.

It's an option that people might want to consider. The total price is probably very comparable. Because the 4:1 gearing offers lower resolution than the 7.2:1 gearing of the SG7.2 motor, some users might be concerned; however, Oriental Motor opening tells us the SGxx motors can have some backlash. All of that must be taken nto consideration. The 4:1 belt-drive model, with a 1.25" pitch diameter pinion would give 0.0005" movement per step. The 7.2:1 unit with the same pinion and without backlash would give 0.0003" per step. I doubt that the 0.0002" difference would be repeatable, but it could be a consideration.
  #14  
Old Sat 13 July 2013, 19:21
bradm
Just call me: Brad #10
 
Somerville(MA)
United States of America
Can we hold down the personal attacks please? I see no evidence of a grudge on either side. I do want to note that it is quite clear that Mike (MetalHead) owns the forum, so questions about moderation or removing content should be addressed to him, and not Gerald.

From what I've seen so far, the question about MOTOR heating has NOT been addressed. There is a test (*) that indicates that running too much AMPERAGE through a 22 gauge wire leads to dangerous heating of the WIRE. That increase in amperage can be directly attributed to using a higher voltage in this type of circuit. It is certainly reasonable to have a discussion about what the wiring requirements should be for a given configuration.

I don't think it's clear whether or not "loading the motor with a resistive load" - presumably clamping the output shaft in a pad or the like - is a valid model for what a CNC machine load looks like. However, with over a hundred MechMates out there, surely there is someone who can give us some empirical evidence - who has 22 gauge wiring and has run some intensive 3d carving? Did your wires warm?

I'd try to test this myself, except that I have 18 gauge wiring. My MechMate under performed at 39 volts, so I wound a new secondary to get 48-49 volts. I have neither wiring nor motor heating problems, but I haven't done 3d carving.

I support both Mike and Gerald being able to express their positions, and to rebut each other every time this topic comes up so that both positions are clear. I'd really like to see more evidence using real world conditions on real MechMates rather than the perennial theory debates. The absence of reports of excessive motor or wiring heating is currently leaning Gerald's way.

(*) Let's note for the record that this is a single test by someone holding a specific position. Normally, we'd want to see the test results repeated and confirmed by another party, but I'm willing to accept this test report at face value for the condition that it measures. I am not willing to presume that it models a CNC machine accurately without further evidence.
  #15  
Old Sat 13 July 2013, 20:50
David Bryant
Just call me: David #99
 
Western Australia
Australia
Hi Guys

I am from Australia and would NEVER consider building anything permanent out of 60 degree C rated wire insulation! I use 105 degree as a usual wire temp rating.

Australian Electrical standards consider Extra Low Voltage to be under 50 V ac and under 120V dc. These are good limits to be under to reduce the risk to the builder / experimenter. Above these limits we are required by law to use an electrician.

If you are concerned with the temperature of your motors you can buy temperature Crayons or Non-reversible temperature labels to find out if you have a problem that needs addressing. The addressing might be to slow the operation or reduce the drives current. Hands are not good temperature gauges and some warmth in the motor is essential to get rid of the wasted energy in the motor.

The heat build up in the stepper is related to Copper Losses, Iron Losses and load.
Copper losses are related to the square of the current times the dc resistance of the motor winding. (But remember the current waveform is chopped and not simply related to the drivers supply voltage). This is why reducing the current control point often via a resistor attached to the driver, or DIP switch settings, greatly changes the temperature.
Iron losses are mostly related to the loss due to Hysteresis in the magnetic material in the core of the motor. Reduced frequency, so speed reduction, can help run the motors cooler, especially if half current is used when holding the position (half current gives a quarter of the copper losses). Reduced speed will not be as effective in reducing motor temps as the current is squared for the copper losses.
Reducing the load slows our primary reason for playing with the machine so would be a last resort.

I think the MM has been one of the best things I have ever built. It is elegant in its simplicity. It makes you think about all the choices to make. How will my stepper work? How fast can I get it to go? How fast do I need it to go?

All motor manufacturers do not all apply standard testing or data representations to their products. We need to continue the engineering for what we have built and are operating. So we can measure currents and Voltages and temperatures. Compare these to costs and production benefits and continue to improve our individual machines.



Most of all when the argument gets hotter than the motors I think It is time to head to the MM and Make something
  #16  
Old Sat 13 July 2013, 23:32
Richards
Just call me: Mike
 
South Jordan, UT
United States of America
I've wondered whether expecting people to respect maximum as true maximum is being too conservative, so I called the senior electrical engineer where one of my sons works as a junior electrial engineer and asked him a very simple question. I asked him if he would ever install a transformer into a machine that raised the voltage to 134% of maximum. He asked me who set the limit for "maximum". I told him that the designer of the stepper driver used a formula that used the inductance of the motor to determine what maximum was. I also told him that running a stepper motor at that voltage under a load suited for that motor would cause the temperature to raise to 70 or 80 degrees C and that running the motor under the same load at the elevated voltage would cause the temperature to raise to 100-degrees C or higher.

He went the to geckodrive web site, read the white paper and then read the FAQs. He said that as a licensed electrical engineer he would never under any condition use a voltage above that recommended by Mariss. He said that doing so would cause him to loose his license if a problem occurred. He futher said that a problem would occur, sooner or later, if the motor ran at 100-degrees C for any sustained length of time. Then, he asked how long it took for a motor to reach 100-degrees C. I told him that in my test, it took about an hour. He asked how many times a motor would be running for more than an hour without having time to cool down to room temperature. I told him that the length of time depended on the type of file being run. Cutting sheet goods took 10 to 30 minutes, but cutting 3-D files could easily take several hours. He asked whether a machine was dedicated to sheet goods only or whether a machine was expected to be used for all purposes. I told him that most shops had only one CNC router and that that single router would be used for all production. He stood by his answer. He said that no licensed electrical engineer in America would wire or encourage wiring anything above "maximum" when "maximum" was set by someone who was considered to be an expert in the field. He said that if "experts" disagreed on what "maximum" meant, that he and most other licensed electrical engineers used the more conservative "maximum" because of the cost of defending themselves in court, if a problem ever occurred with one of their designs.

Finally, I fowarded a copy of this thread to him and asked for his opinion. First he asked why anyone would use excessive voltage as a cure for the geared motor when he could use normal voltages with a motor attached to a belt-drive. I told him that some people wanted the convenience of not needing to buy or build a belt-drive. He said that convenience is never a valid answer when health and safety are concerned. When I pressed him for his opinion about the posts, he just laughed and said that he hoped anyone who publicly advised exceeding maximum values had either very good insurance or a very good lawyer.

The electrical standards in America are not the same as those required in other parts of the world, so I would recommend that you hire a licensed electrical engineer for an hour to two. It will be the best $500 that you ever spend, especially if you ever have to file an insurance claim caused by electrical components overheating. The very fact that CNC routers are used in all kinds of situations and under all kinds of loads should be a caution that cutting plywood is not the same as cutting 3-D and that duty-cycles and heatsink specs are prominently displayed on the Oriental Motor web site so that nobody can ever claim that they were not aware of the manufacturer's cautions about the proper use of Oriental Motor stepper motors.
  #17  
Old Sun 14 July 2013, 03:08
Gerald D
Just call me: Gerald (retired)
 
Cape Town
South Africa
I was wondering when you were going to bring a supporter into the discussion . . .you obviously realise that I doubt if he really exists. Is this the "Thomas" that posted on this forum from your computer before? I would appreciate to see photos of the test setup you had above, and of the resulting damage to the wires.

To repeat: My challenge still stands; find some real life examples of MechMate motors starting fires, melting insulation, burning blisters, seizing bearings, loosing magnetism, whatever, caused by high heat. Until you actually find these examples, you are wasting our time.

Some of the background here: http://finance.groups.yahoo.com/grou.../message/18796

Before Mariss published his formula, the conventional advice was to pick a voltage 20 to 25 times the Volt rating printed on the motor nameplate. It would seem that there is still a strong preference for 20 to 25 times rule, about 5 years after Geckodrive (Mariss) put out a rule based on inductance.

The only concern that the motor manufacturers have, is that one shouldn't run the motors over 85C. Anything published by drive manufacturers is only a suggestion, not a Commandment. We have seen that we can keep our motors well below 85C, for our application, and push the voltage up for extra performance.

In the older days, motors got hot while standing idle, doing nothing. In those days you could only control the motor temp with voltage. Times have changed and drives are smarter . . . .voltage is no longer the absolute factor influencing temperature.

PS. The "3D" cutting is another bit of red herring . . . the max load on a motor is decided by the operator, not by the voltage or profile. Take a deep cut at high speed with a blunt cutter for an extended period of time and you will get the hottest condition for a motor. This is typically achieved when re-surfacing the spoil board in a hurry. You can cool the motor by going shallower, slower.

Last edited by Gerald D; Thu 26 March 2015 at 11:21.. Reason: spelling
  #18  
Old Sun 14 July 2013, 06:37
MetalHead
Just call me: Mike
 
Columbiana AL
United States of America
Ok guys

I think in this world, people will disagree on a topic. I understand everyone seems to get worked up over this and I agree that after all of this time , I would think we could get to the "agree to disagree" stage.

I try to make sure everyone here has access to as much information possible about building a MechMate.

ANY industrial grade process is not without risks. If you push the edge , sometimes you will fail. That call (and responsibility) is totaly up to the builder.

No matter what view you take on this voltage issue, in the end it is YOU that has to decide how to build YOUR machine. You are the one that agrees, when you join this forum, that you accept the complete resposibility for YOUR machine and safety.

I have been away for a few days and will review and update this thread so it contains what I feel is real information related to this issue.

I picked up this forum so that this data could remain available to anyone who wanted to build a MechMate. I felt to loose such a vast set of data on such a great platform was not something I wanted to happen. I had the oportunity so I chose to keep this available to everyone around the world.

IF you are not happy with the content in this forum, LEAVE.
IF you do not like how the content of this forum presents itself, LEAVE

No content I feel that is needed to support this forum will be deleted.All content posted in this forum is there to help others around the world build a machine that they can use to do hobby or industrial grade work. We have some great minds that support this forum and I would greatly appreciate it if we can let our junior members get on with their builds.
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