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  #1  
Old Fri 26 February 2010, 21:05
Gerald D
Just call me: Gerald (retired)
 
Cape Town
South Africa
A show of hands - MM builders who have found their motors running hot?

Very much has been written on the heating of motors, but I think that too much is made of it. Could we have a show of hands from MM builders who have found their motors running hot?
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  #2  
Old Fri 26 February 2010, 21:31
KenC
Just call me: Ken
 
Klang
Malaysia
Gerald, I suggest we be more specific about this.
What temperature are we talking about.
My MM is not tunning yet, but during kitchentable project, the temp of the motor goes upto 50~55C. the heat build up particularly obvious during holding position. 64V, Coil inductance ~3.8mH 86HS9801. current limit at 3A. Room temp 29~32C.
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  #3  
Old Fri 26 February 2010, 22:58
Gerald D
Just call me: Gerald (retired)
 
Cape Town
South Africa
Ken, I just want to get a general feeling whether motor heating is worth all the attention.

(You have DSP Based Microstepping Driver DM558's which may cause most heat at standstill - the modern gecko's have no heating issues at standstill - topic for another thread)

Last edited by Gerald D; Fri 26 February 2010 at 22:59.. Reason: merged 2 posts
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  #4  
Old Fri 26 February 2010, 23:56
hennie
Just call me: Hennie #23
 
Roodepoort JHB
South Africa
I had heating problems but I changed the current set resistors and had no need to put ice packs on the motors again to cool off.She runs just fine now.
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  #5  
Old Sat 27 February 2010, 00:14
Claudiu
Just call me: Claus #43
 
Arad
Romania
I`ve set up my current resistors to 4 A, after heavy cutting several hours and the machine running on y and x motor temp raises to about 60 - 70 dgrees celsius. I will measure today again and post exact results.
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  #6  
Old Sat 27 February 2010, 05:13
javeria
Just call me: Irfan #33
 
Bangalore
India
my motors as always run hot - maybe due to the max voltages they are working on - never misses a beat though

hot - "I cannot touch the motor contineously for one minute."
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  #7  
Old Sat 27 February 2010, 06:57
riesvantwisk
Just call me: Ries #46
 
Quito
Ecuador
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@Garald, I didn't notice heat problems yet, but going to bring a kitchen temp meter (don't tell my wife.. ) sometimes I do feel it by hand they get pretty hot, but nothing to worry about, for me at least.. like Irfan, "I cannot touch the motor contineously for one minute." but a little less than that I think..

Quote:
Originally Posted by KenC View Post
. the heat build up particularly obvious during holding position.
Ken, this is very interesting, because my motors cool down when they are waiting, and this is because the Gecko drive reduces the current through the motors to a recirculating current, just a idle current which is much lower then the set current. Can you check the specs of your drivers if they can do the same?

Gecko 203V, stepper 34hs 9801, 4Amp, 59Vdc

Ries

Last edited by riesvantwisk; Sat 27 February 2010 at 07:01.. Reason: Added motor specs
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  #8  
Old Sat 27 February 2010, 07:07
KenC
Just call me: Ken
 
Klang
Malaysia
My driver do have the reduce power feature, but I disable it just to see what is the highest temperature. I consider 50C is normal, I used an IR temp probe to measure the temp so the numbers should be accurate enough. At this temperature, the motor feels warm & I can grip on the motor longer then a few minutes, uncomfortable but won't burn my skin.
BTW, the temp hovers about 4~5C lower when they are running without load.
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  #9  
Old Sat 27 February 2010, 07:37
Richards
Just call me: Mike
 
South Jordan, UT
United States of America
Here's some data:

34-size motors / single stack
PK296B2A-SG3.6 / G203v / 35VDC / 1.5mH / 3A / 750 RPM = 50C
PK296-F4.5A / G203v / 35VDC / 1.5mH / 4.5A / 900 RPM = 65C
PK296-F4.5A / G203v / 35VDC / 1.5mH /6A / 900 RPM = 80C (bipolar parallel)

34-size motors / double stack
PK299-F4.5A / G203v / 50VDC / 2.5mH / 4.5A / 900 RPM = 65C
PK299-F4.5A / G203v / 50VDC / 2.5mH / 6A / 900 RPM = 80C (bipolar parallel)
PK299-02AA / G203v / 75VDC / 6mH / 3A / 900 RPM = 75C
PK299-02AA / G540 / 48VDC / 6mH / 3A / 900 RPM = 56C

23-size motor / triple stack
PK268-02AA / G540 / 48VDC / 3.6mH / 2A / 900 RPM = 57C

Note that the lowest temperatures came from running motors at reduced voltage or reduced current. The PK296B2A-SG3.6 was reduced current, 3A instead of 4.5A and slightly reduced voltage, 35VDC instead of 39VDC and at 750 RPM instead of 900 RPM. The PK299-02AA with the G540 was run at reduced voltage, 48VDC instead of 75VDC. The PK268-02AA was run at reduced voltage, 48VDC instead of 60VDC.

A G-code program was written that continuously exercised an axis, moving it 50-inches in one direction and then moving it 50-inches in the other direction. The program exercised the motors until they had temperature stabilized, which was at least 30 minutes. The motors were run without load.
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  #10  
Old Sat 27 February 2010, 10:18
Kobus_Joubert
Just call me: Kobus #6
 
Riversdale Western Cape
South Africa
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When I cut 3d stuff and the motors are really up and down, left and right they get pretty hot...cannot keep my hand on them...still thinking of reducin the resistors some time soon.
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  #11  
Old Sat 27 February 2010, 14:07
sprayhead
Just call me: Francis
 
sydney
Australia
Hot!!
mmmm,
I mean...
coooool


NICE DATA!!

Last edited by sprayhead; Sat 27 February 2010 at 14:19..
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  #12  
Old Sat 27 February 2010, 20:22
Gerald D
Just call me: Gerald (retired)
 
Cape Town
South Africa
With respect Mike (and Francis), the question for this thread is "Could we have a show of hands from MM builders who have found their motors running hot?"
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  #13  
Old Sat 27 February 2010, 20:28
rnixon
Just call me: Rick #45
 
Vic
Australia
Funny you should ask - surfacing the spoilboard on Friday and found the x axis motors running hot - too hot to hold on to. Stopped the program half way through and finished on Sat
Running standard setup with OM motors 7.2, G203V
regards, Rick
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  #14  
Old Sun 28 February 2010, 04:07
MetalHead
Just call me: Mike
 
Columbiana AL
United States of America
Gerald,

Changed the title (Had to shorten it a little)

Rick,

What motors are you running and what voltage output is your power supply?

How deep were your surfacing cuts?

Mike
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  #15  
Old Sun 28 February 2010, 04:33
Gerald D
Just call me: Gerald (retired)
 
Cape Town
South Africa
Okay Mike. Rick is running the "OM motors 7.2" (presumably PK296A2A), and in addition to your questions on voltage and depth of cut, we would need to know the motor coil wiring and the measured resistance of the current limit resistors.

But, so far I am not hearing a big problem on motor heating at all. I cannot deduce that Mariss's voltage formula is incorrect, and that he should have used a factor 24 instead of 32.
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  #16  
Old Sun 28 February 2010, 05:28
shaper
Just call me: Jed
 
Perth, WA
Australia
Gerald

I'm running the MK34hs9801 at 50V current limited to 3.5A (this is about 75% of the value from Mariss's formula) I'm limited to this by my driver and have at this stage only done bench runs, while the motor doesn't get so hot as to be concerned I can see that I may not be comfortable running it at higher voltage as there are time when it gets hot enough to be uncomfortable to touch for more than a few seconds.

Edit: just realised that the measured voltage from the supply is a little higher than that due to my supply voltage normally running a bit higher than spec, actual voltage as about 53v same thoughts as above apply though.

Last edited by shaper; Sun 28 February 2010 at 05:31..
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  #17  
Old Sun 28 February 2010, 05:34
liaoh75
Just call me: David
 
Taibao
Taiwan
In the summer (average 32 degrees C in the shop), my "standard PK296A2A SG 7.2s" (35V power supply) run at about 60 degrees C and a little above that and pretty much stays there on long cut jobs (over 2 hours) 3mm Spiral 0-flute cutting 16mm Acrylic lettering. The X and Y axis get hot enough where I can't keep my hands on it for more than about 3 seconds. The Z-axis is quite a bit cooler.

In the winter here (about 13-20 degrees C), the motors seem to be cooler.

Being concerned, I asked a few local stepper vendors about steppers in general and was told that this temperature was normal for the application I described to them. These conversations took place a while back so I can't remember exact details, but I was told not to be alarmed so I didn't pursue this further.

Does O.M. put out thermal data about this motor by any chance? I've read about this issue in other threads comparing the heat to a hot mug of coffee. Has anything changed? I thought this issue was put to bed a while back.
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  #18  
Old Sun 28 February 2010, 09:04
Richards
Just call me: Mike
 
South Jordan, UT
United States of America
Gerald,

I apologize if I'm overstepping. To me, Ohm's law doesn't take into consideration the make or model of a machine. The law is universal. Heat (Watts) is Voltage X Amps. In a stepper motor, Amps increase with speed and/or load. The formula from Mariss uses 85C as the goal. That is hot. A quality built stepper motor with class-B insulation can withstand that temperature and still give a year or two of service. That same motor, if run at 60C or lower will last probably last three times as long. When electronics cost about $2,000 or more, knowing that reducing voltage or reducing Amps could extend the life of the stepper motors by a factor of 3X, isn't that worth something?

Those that use the PK296A2A-SG7.2 motor and run it at 3A and 40V will probably never see high temperatures. That motor's Amp rating is underrated by the factory by 1.5A, so it will never develop enough heat to cause a problem. However, those that assume that they can push every motor at full current and full voltage, just because of the temperatures of the PK296A2A motor, need to know why that motor runs cooler and why their motor will run hotter.

Sorry, if I'm offending, but my whole goal is to take the mystery out of the electronics and to add sufficient data so that those who have never built a controller will know what happens when they push any parameter. When people are looking for a way to save a few dollars on stepper motors, stepper drivers and power supplies, it would be a shame if they burned things up because they didn't understand how hot things get when parameters are exceeded.
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  #19  
Old Sun 28 February 2010, 10:30
MetalHead
Just call me: Mike
 
Columbiana AL
United States of America
I don't think you are. It is a good question to ask to see how the derated (Or not) motors are running.

The rule of ohm's law gives us the ability to work inside a window, but being the tinkerers we all are we tend to "flirt" with the lines a bit sometimes to see how we can push the limits.

Some will subscribe that derating is something that the manufacturer has already built into the product and futher derating may in fact be more than is needed.

I am sure the derating calculation the Gecko platform uses makes sure you are safe inside the operating window of those products.

But again some folks like to live on the edge.

So please keep giving the information you have because it helps us all !!

Mike
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  #20  
Old Sun 28 February 2010, 11:29
Gerald D
Just call me: Gerald (retired)
 
Cape Town
South Africa
Mike, you are not overstepping - I am the one being argumentative!

What is missing out of all that gets written about stepper motors, is the duty cycle of the application. Sure, we can think of cutting conditions, and tests, that will make the motors run hotter than for other conditions. And if we run under those conditions for 60 minutes in an hour, then we will get hot motors. (3D carving, with one axis running back and forth for hours is the extreme case). However, I believe that it is the minority of MM owners who do big 3D carvings.

Quote:
Originally Posted by Richards View Post
. . . 85C as the goal. That is hot. A quality built stepper motor with class-B insulation can withstand that temperature and still give a year or two of service. That same motor, if run at 60C or lower will last probably last three times as long. . . . .
I would be interested to see where those numbers come from? The MM'ers who have considered their motors running on the hot side may not know what 60C (or 85C) feels like. Holding 60C in your hand makes you go ouch! in under 5 seconds. My guess is that most of the posters above are seeing temps around 50C.

I would agree that 85C is getting hot for a motor that has to run 24/7 at that temp, but there is nothing wrong with going that high for an hour a week (while surfacing the top, for example).

The car analogies can be used here; most of the day we can get by with a 4 cylinder, but we wouldn't dream of buying a 6-cylinder and then permanently disconnecting 2 of them. We want all 6 cylinders to be available for the odd overtaking.
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  #21  
Old Sun 28 February 2010, 11:35
Richards
Just call me: Mike
 
South Jordan, UT
United States of America
Mike,
Thanks. I surely don't want to offend anyone.

There is some historical information that might help us understand why some have never had to worry about stepper motors getting hot. The MechMate is a highly modified and greatly improved machine when compared to its ancient ancestor, the pre-PRT Shopbot. The Shopbot used a variety of stepper motors, but none of those motors were optimized. In fact, all of the motors were extremely under-utilized. Some machines had the equivalent of the Oriental Motor PK299-01AA motor (no gearbox, direct drive). That motor was often shipped by Shopbot with the motor's center leads clipped, which meant that the motor could only be wired bipolar series. With 56mH inductance, using an 80VDC gecko could only supply 33% of the 300 volts it would have taken to run that motor at maximum power. Even if the motor had its center taps unclipped, at 14mH, it would still require 119VDC for maximum efficiency, which is 150% of the Geckos rated voltage.

The other popular motor was equivalent to the PK296A1A-SG3.6 motor. That motor also had it's center tap wires removed, so it could only be used bipolar series. That would have required a maximum voltage of 177VDC, which is 220% higher than a Gecko can handle. That is why that motor never runs hot.

The next popular motor, which was not at all related to Shopbot, was the PK296A2A-SG7.2. That is still the most popular motor for the MechMate (as far as I've read). But, that motor also has a quirk. Oriental Motor derated it from 4.5A to 3A, probably because of its gearbox. Because it only draws 66% of the current that it was designed to be able to draw, it runs substantially cooler than other motors.

Now we get to the point in history when things get interesting. Builders living mostly outside the United States found that their local suppliers of Oriental Motor stepper motors were charging much, much to much money for that motor. Those builders started looking around for alternatives. What many of those builders didn't realize is that if they used Mariss' formula, that they would have motors that could easily hit 80C. That's the heat 'problem' that concerns me. 80C is within the temperature range of a good stepper motor. It's too hot to touch, but the motor can handle it for the motor's entire expected life. But at lower temperatures, the expected life is much longer.

I don't want anyone to think that I disagree with Gerald or Mariss. Stepper motors are expected to run hot if they're working hard. In the United States, where the price is very reasonable, they're considered to be expendable, just like light bulbs. If they're doing their job and making money for the operator, the cost to replace them is a small budget item.

My only desire is that those who are using untested motors have enough background information to know why a motor runs hot and how to lower that temperature and still get adequate torque and adequate speed from the motor.
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