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  #1  
Old Wed 02 January 2008, 11:58
Richards
Just call me: Mike
 
South Jordan, UT
United States of America
Wiring the PK296A2A-SG7.2 motors & power supply voltage selection

I written quite a bit about using Oriental Motors PK296A2A-SGxx motors wired half-coil. Recently, some users have posted parts lists showing high voltage power supplies that have too much voltage for half-coil connections. Because I hadn't run bipolar series tests for more than a year, I decided to re-wire my test setup and see how fast I could spin those motors.

Here's the electronic parts:

1 - AVEL Y236801 (25V + 25V) transformer
1 - PMDX-135-8020 power module
1 - PMDX-122 breakout board
4 - Gecko G202 stepper drivers
4 - PK296B2A-SG3.6 stepper motors

(Current set resistor is 20K to limit the motors to 2.1A)

Normally I use Gecko G203v stepper drivers, but that test setup is not easily modified. I have no reason to believe that the test results would have any substantial difference whether I used the G202 or the G203v.

The PK296B2A motors are the same as the PK296A2A motor except they have the shaft protruding from both the front and the back of the motor. At one time I was going to mount encoders on the motors, so I bought the dual shaft model. Performance-wise, the motors are identical.

Mariss's formula to determine maximum voltage (1000 X SQRT(0.006)) gives the maximum voltage for those motors to be 77VDC. I wired the transformer to give 70V.

In Mach 3, I configured the motors as if they were PK296A2A-SG7.2 (since that seems to be the most popular motor choice). Assuming the use of a 30-tooth spur gear, the steps per second was determined with the formula: 1/(30/20*3.14159/7.2/2000) = 3055.775 steps per inch. With the Mach 3 pulse generator set to 45,000 pulses per second, that allowed a top speed a little higher than 800 inches per minute, so I selected 800 inches per minute as the top speed. I picked an arbitrary ramp of 40, which may be too fast or two slow, depending on how heavy the gantry is on your machine.

To my complete surprise, the motors ran at top speed with no problem. They stayed almost at room temperature during a three hour test. The room temperature is 67 F. The motors range between 80 F and 88 F. The G202s are running at 85 F.

The test consisted of running the X and slaved A axis to 10 inches, the Y axis to 10 inches, the Z axis to 10 inches and then running all three axes together to 0.

When that test showed no problems of any kind, I re-coded the test to do the same thing, but I varied the speed from 100 ipm to 800 ipm in 100 ipm increments. All single-axis moves at all speeds sounded really good. Three-axis moves sounded somewhat rough, but that seems to be a characteristic of Mach 3.

So, bottom line, the PK296A2A-SGxx motor, seems to have excellent speed capability whether wired bipolar series at 70VDC and 2.1A or half-coil at 35VDC and 3A.
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  #2  
Old Wed 02 January 2008, 12:18
smreish
Just call me: Sean - #5, 28, 58 and others
 
Orlando, Florida
United States of America
Mike,
Thank you for your diligence and commitment to the MM forum. I truly appreciate the bench test and data backup on the bipolar wiring configuration.
Many Thanks,
Sean
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  #3  
Old Wed 02 January 2008, 14:41
sailfl
Just call me: Nils #12
 
Winter Park, FL
United States of America
Mike,

I agree with Sean. Thank you for taking the time to provide us with this technical information. I am learning and gaining from your expertise.

Nils
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  #4  
Old Wed 02 January 2008, 18:07
Doug_Ford
Just call me: Doug #3
 
Conway (Arkansas)
United States of America
Thanks a million Mike.

Over the weekend, I built a 35VDC PS to use instead of my 70VDC PS from Antek. Now, I'm not sure what I should do. Since you have both setups and you've determined that they both work well, what are you going to do? I respect your opinion tremendously so whatever you do, I'm going to do the same thing.
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  #5  
Old Wed 02 January 2008, 19:28
Richards
Just call me: Mike
 
South Jordan, UT
United States of America
Doug,
I still prefer the half-coil connections. That is just a personal preference. It hasn't proved to be better or worse, but it works for me.

I hope that all of you know that I have, at any one time, at least two and sometimes three or four 'test' systems. They are used just to test electronics. They are NOT used to run my machine. My machine uses Oriental Motor's Alpha stepper drivers and Alpha motors. There are several things that I don't like about those drivers and motors, but they work with my controller, so I leave them alone. When those motors die, I'll replace them with Oriental Motors PK series stepper motors and Gecko G203v stepper drivers, but until the Alpha motors die, they are going to be the motors that run my machine. Like they say, "If it ain't broke, don't fix it."
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  #6  
Old Wed 02 January 2008, 20:19
Roadkill_321
Just call me: John #7
 
Wiseton, Saskatchewan
Canada
Mike,

I'll say thanks too for test work you've done. It puts my mind at ease knowing that I'll not have to worry about not being able to operate my motors up to potential.

John
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  #7  
Old Wed 02 January 2008, 21:49
gmessler
Just call me: Greg #15
 
Chicago IL
United States of America
Hi Mike,

Any recommendations for those of us who bought the PK296A1A-SG7.2 motors?
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  #8  
Old Wed 02 January 2008, 22:43
cobra427mnsi
Just call me: Paul
 
Leamington, Ontario
Canada
Thanks Mike
Your input to this forum is invaluable. Your knowledge of electronics amazes an electronically challenged soul like myself. Thank you!
Could I ask a question? I have been reading and studying a lot of posts from people listing their power supply, bob, and motor choices. I have not seen a PMDX-135-8020 on anyone's list yet. What is it and what is its purpose? (ok that's 2 questions, sorry).


Thanks again
Paul
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  #9  
Old Thu 03 January 2008, 06:21
Richards
Just call me: Mike
 
South Jordan, UT
United States of America
Greg,
The PK296A1A-SGxx motors are a special case. Their high inductance (30.8 mH) when wired bipolar series, makes that type of wiring impractical when used with Gecko stepper drivers because it would require a power supply voltage of 175VDC. So with that motor, wire it half-coil and use a power supply of about 70VDC (50V to 80V would all work well).

Paul,
The PMDX-135-8020 is a power supply module. It includes everything that you need to make a power supply except the toroidal transformer. It costs about $120, so, by itself, it costs about the same as an entire power supply from Antek.

Everyone,
I ran some slow speed tests with the PK296B2A-SGxx motors yesterday after posting my preliminary results. At slow speeds, the motors started to get warm - about 120 F. That temperature is well within the motor's design, but it does show that a 70VDC power supply is near the upper limit. If I were going to install those motors on my machine, and if I were going to wire the motors bipolar series, I would start with a power supply that is nearer to 50VDC than to 70VDC.
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  #10  
Old Thu 03 January 2008, 06:48
Doug_Ford
Just call me: Doug #3
 
Conway (Arkansas)
United States of America
Thanks Mike. I think I'll setup this machine with my 35VDC system and save the 70VDC for the plasma cutting MM I hope to build in the future.
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  #11  
Old Thu 03 January 2008, 07:33
cobra427mnsi
Just call me: Paul
 
Leamington, Ontario
Canada
Thanks, Mike,for the reply. I understand .

I am planning on using the PMDX122, OM PK296A2A-SG7.2 and the Geko 203V controllers. Will the Antek PS-6N56R5R12 be ok for this setup. Would it be better to use the 5volt or the 12 volt to power the PMDX122? I think I read in one of your posts that the 5 volt output might be slightly less than 5 volts by the time it reaches the bob. Thank you for your input. You have no idea how much this helps us novices. I appreciate it.

Paul
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  #12  
Old Thu 03 January 2008, 08:35
Richards
Just call me: Mike
 
South Jordan, UT
United States of America
Paul,
The Antek PS-6N56R5R12 should work just fine if you wire the motors Bipolar Series. 56VDC is just about ideal for Bipolar Series wiring.

The PMDX-122 has several connection methods for the auxiliary power input. Connector J11, which uses a 'plug' type connector is the connection point that I use. J11 can receive EITHER AC voltage (6 to 9 volts) OR DC voltage (7 to 12 volts). I use a Triad brand 'wall-wart' transformer that has the proper plug to connect to J11. It is a 12VDC module.

Section 4.7 of the PMDX-122 manual give the specs for incoming power to the board. You can use two pins of J8 instead of J11. Section 3.2 of the manual gives very vague instructions for J8. I don't remember whether I've ever used J8 or if I've ever traced the circuits from J8 to J11 to see whether power that is applied to J8 is filters and rectified by the circuitry of J11.. You also have the option to use power from the USB connector to power the board. I can't remember that I've ever tried that option.
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  #13  
Old Thu 03 January 2008, 12:25
cobra427mnsi
Just call me: Paul
 
Leamington, Ontario
Canada
Thanks Mike
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  #14  
Old Thu 03 January 2008, 12:40
BernardR
Just call me: Bernard
 
Georgetown Texas
United States of America
Mike,

Where were you when I was doing my sevo's setup?
Thank you for an excellent set of tests, I will probably go with steppers when I get into the MM and I'm afraid I have zero experience there. One of the lessons I learned very hard, is that servos have zero torque at low speed and zero speed at max torque, i.e. the motor is stalled!!

On the question of motor feedback, it is trivial, though a little pricey, to fit a US Digital DIY encoder, the interesting part is how to process the signals once you get them back.

One of my objections to the 3 series of Gecko Servo controllers is that the feedback terminates in the Gecko, which is normally hidden in some convenient but unobservable location. Thus when for no explicable reason the Gecko trips, all you know is that it tripped, if you didn't feed a signal back to Mach 3, which was not but by now may be documented; Mach3 goes merrily on running the part!!! As far as I'm concerned it's a quasi feedback system with zero diagnostic capability.

A good source of power supply parts are dead UPSs, normally the battery dies and they go out buy a new one, even on large expensive units. My power supply is based on what was a 48 volt battery rated at 1kw, nearly broke my back carrying it. Cost me $25, the real neat part though was that it had all the surge suppression boards and if I looked for them the protection movs as well. 24 volt battery systems will give 34 VDC which may be a bit light, but I recently picked up 2 350 VAs and a 500 VA, all working for $10 each. Though the transformer voltages are too low to be practical in this case, the stuff is out there if you keep your eyes open and know what you're looking at.
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  #15  
Old Fri 04 January 2008, 04:19
DMS
Just call me: Sharma #9 India
 
Rajasthan
India
Thanks Mike,
Now I can stay firm on my decision of using PK292A2A 7.2 with 30 teeth pinion.
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  #16  
Old Sun 06 January 2008, 08:51
gmessler
Just call me: Greg #15
 
Chicago IL
United States of America
Thanks Mike!
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  #17  
Old Mon 09 June 2008, 23:50
Gerald D
Just call me: Gerald (retired)
 
Cape Town
South Africa
Quote:
Originally Posted by Richards View Post
I ran some slow speed tests with the PK296x2A-SGxx motors yesterday after posting my preliminary results. At slow speeds, the motors started to get warm - about 120 F. That temperature is well within the motor's design, but it does show that a 70VDC power supply is near the upper limit. If I were going to install those motors on my machine, and if I were going to wire the motors bipolar series, I would start with a power supply that is nearer to 50VDC than to 70VDC.
Now that a couple of guys are running PK296A2A-SG7.2 motors with G203 drives, I am interested in feedback regarding heat of the motors versus power supply voltage . . . . .

The higher the voltage, the more power output, which is more force at a given speed, or the ability to reach higher speeds with the same load before losing steps. We therefore want our power supplies to be as high a voltage as possible. (granted, that this high voltage may be wasted if doing a light job).

The upper limit on the power supply voltage, for the G203, is 80 Volts. However, at 80 Volts, the stepper motor will theoretically get too hot. But, what is happening in practice? Are you guys finding that your motors are getting too hot?

Too hot is over about 85o C [185F] on the outside of the motor casing - that is about a hot metal mug of soup or coffee.

Comments please.
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  #18  
Old Tue 10 June 2008, 00:00
Roadkill_321
Just call me: John #7
 
Wiseton, Saskatchewan
Canada
I'm running the Antek 56V power supply, wired Bipolar Series, with the PK296A2A-SG7.2 motors with G203 drives and the motors stay very cool. I have had the X axis motors slightly warm to the touch if the machine has to rapid on the X axis much, but otherwise they all stay very cool.

John
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  #19  
Old Tue 10 June 2008, 02:10
smreish
Just call me: Sean - #5, 28, 58 and others
 
Orlando, Florida
United States of America
ditto. About a warm cup of coffee all day. No issues. 56v ps. 7.2:1 steppers
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  #20  
Old Tue 10 June 2008, 05:32
Gerald D
Just call me: Gerald (retired)
 
Cape Town
South Africa
from http://www.cnczone.com/forums/showthread.php?t=52090:
Quote:
Q.) How hot is too hot for a step motor?

A.) The maximum heat for most steppers is around 100C (212F), but it is generally never good to have the motor heat go above 85C (185F).
While this coffee warmer has a plate surface temp of 96C [205F], it is holding a 1/3 cup of coffee at 50C [122F] here in my office where the ambient temp is 21C [70F].

I stuck the thermocouple probe against the outside of the ceramic mug (12mm [.5"] from the bottom) and that also reads 50C [122F]. This is a nice warm drinking temperature.

Have just made a fresh cup of coffee - by the time I had poured the milk (room temp) and walked to my office, it was 72C [162F] inside the ceramic mug, and about 60C [140F] outside, which mug I couldn't hold for more than 5 seconds. (Have not yet had a stepper anywhere near as hot - where I felt that I had to remove my hand)

Quote:
Originally Posted by Gerald D View Post
Too hot is over about 85o C [185F] on the outside of the motor casing - that is about a hot metal mug of soup or coffee.
The point of all of the above is that our concept of hot/cool/warm/too hot is extremely subjective. I want to build my next MM's to have the maximum power available for the day that I might need it. It is not easy to fiddle with the power supply voltages, so I am going to go as high as possible (75 to 80V), and if there is a heating problem (actually measured with a contact thermocouple) , then I will trim back on the current limit by changing the resistor on the Gecko. Anybody see anything wrong or dangerous in this logic?

This might seem like a casual approach..... I would be a lot more cautious if there were a significant number of reports from folk that had destroyed their motors with too high a voltage - these reports are mysteriously absent where everyone is nervous of raising the voltage? Let's not forget; an increase in voltage gives a direct increase in the available power output.
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  #21  
Old Tue 10 June 2008, 05:54
Greg J
Just call me: Greg #13
 
Hagerman, New Mexico
United States of America
I'm using the AnTek 70 V power supply with the PK296A1A-SG7.2 motors (wired unipolar, 1/2 coil) and G203 drives.

For the very little cutting I've done to date (sign making), I was amazed how warm the motors were. My temp. gun is broken and waiting on new one to arrive. When using Gerald's calibrated hand technique, I'd say it's in the temp. range of 60 C (140 F).

The ambient temp. is around 100 F (37.7 C)
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  #22  
Old Tue 10 June 2008, 06:21
Gerald D
Just call me: Gerald (retired)
 
Cape Town
South Africa
Greg, you are wired unipolar 1/2 coil, while John & Sean are wired bipolar, full coil. That makes a big difference. If memory serves me right, unipolar should be 1.4 times less voltage than bipolar? (You have about 1.4 times more than the bipolar wired guys, and you don't see smoke yet?) Since realised that Greg has the A1A motor
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  #23  
Old Tue 10 June 2008, 06:30
Greg J
Just call me: Greg #13
 
Hagerman, New Mexico
United States of America
No smoke. I thought with my setup, unipolar (1/2 coil) was the correct wiring.
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  #24  
Old Tue 10 June 2008, 06:35
Gerald D
Just call me: Gerald (retired)
 
Cape Town
South Africa
Greg, let's have a cup of coffee while more folk chip into this thread. I have gone very rusty on wirings and voltages and that's why I kicked this thread back into life today - I need to order 4 transformers tomorrow......

Good time to revisit the first posts of this thread. Remember, that was before Mariss came up with his inductance based formula for voltage.
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  #25  
Old Tue 10 June 2008, 06:43
Greg J
Just call me: Greg #13
 
Hagerman, New Mexico
United States of America
Agree.

Let me get a new temperature gun also. I want to make sure I'm reporting accurate data.
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  #26  
Old Tue 10 June 2008, 06:50
Gerald D
Just call me: Gerald (retired)
 
Cape Town
South Africa
Greg, methinks you are nearer to the right voltage while the other guys are too low


From Mariss's modern formula: Drive supply voltage = 32 * √mH Inductance on the A2A motor

Bipolar (Series) : 32 * √6 = 78 Volt
Unipolar (Half-coil) : 32 * √1.5 = 39 Volt
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  #27  
Old Tue 10 June 2008, 07:14
Greg J
Just call me: Greg #13
 
Hagerman, New Mexico
United States of America
Gerald,

I have the PK296A1A-SG7.2 motors.

Using 7.7 mH/phase and equating to 88.8 Volt capable.

Dang it, gotta run, day job is calling.
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  #28  
Old Tue 10 June 2008, 07:51
Gerald D
Just call me: Gerald (retired)
 
Cape Town
South Africa
Anyone running an A2A motor at unipolar (half-coil)?

I would want more torque at high speed, and that is why the unipolar half-coil configuration appeals to me:

001.gif
Original pic borrowed from here

Lines A and B represent "loads" we are putting on our motors by pushing a router bit through wood - the faster we push the bit, the more torque we need.

We don't know (without experimenting and measuring) if our router application is an A or B line. A could be for hard wood while B for softwood? Measuring could show us that both woods actually lie below B, in which case the unipolar/halfcoil is clearly the better connection. If both woods cause loads in the vicinity of A, then bipolar/series is the better connection.

However, with the 7.2 reduction gearboxes, I strongly suspect that we are running in the B region - the little motors now spin 7.2 times faster.

Mariss gave this formula a while back:
Motor's "corner" speed, where the motor transitions from
constant torque to inverse torque with speed, that is also the speed
the motor reaches its maximum available power output , is = (0.191 * Vs) / (L * Is)


Where:
Vs = supply voltage
L = winding inductance in Henries
Is = drive's set phase current in Amperes

for the PK296A2A-SG7.2 motor

Series winding: (0.191 * 78) / (0.006 * 2.1) = 1182 RPM. With 7.2 gearboxes and 30T pinions, that is a 770 inch per minute move speed

Half-coil winding: (0.191 * 39) / (0.0015 * 3.0) = 1655 RPM. With 7.2 gearboxes and 30T pinions, that is a 1083 inch per minute move speed

(In the above formulae, I used the voltages calculated by the 32sqrootinduct method)
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  #29  
Old Tue 10 June 2008, 11:46
Gerald D
Just call me: Gerald (retired)
 
Cape Town
South Africa
For those following my rambling in this thread today, I have gone back and made quite a few edits. Sorry about that.
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  #30  
Old Tue 10 June 2008, 12:12
Doug_Ford
Just call me: Doug #3
 
Conway (Arkansas)
United States of America
Gerald,

I'm running A2A motors wired half-coil. However, because of work, I haven't cut much. Are there some tests you would like me to run?
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