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  #61  
Old Sat 14 June 2008, 08:35
Gerald D
Just call me: Gerald (retired)
 
Cape Town
South Africa
Spent all morning running a PK296A2A-SG7.2 motor, with thermocouple attached, at 25mm [1"] per minute equivalent router speed, with no load attached, at increasing voltages until the temperature stabilised.

At 39V power supply, the case rose 23C [41F] above the ambient temp.
At 45V, the temp increase was 27C [49F]

And finally, with a 50V power supply (which is about 30% higher than recommended by the Mariss induction-based formula) the temp settled at 31C [56F] above the room temp. On a hot 40C [104F] day, the motor should be at 71C [160F] . . . . . . . too hot to hold, but still well below the most conservative allowable temp for a stepper.

At this stage of testing, it seems this motor (wired unipolar) will be okay on a 50V supply . . . . will test at other speeds as well . . . . . it is a long weekend here. . . . .
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  #62  
Old Mon 16 June 2008, 12:11
Gerald D
Just call me: Gerald (retired)
 
Cape Town
South Africa
Tested the bare motor at an equivalent router speed of 320 inch per minute. It got a LOT hotter. When the temp reached 50C [90F] above ambient, I trimmed the power supply voltage back to hold the temp steady at that point. The temp steadied (at 50C [90F] above ambient) when the power was reduced down to 36 Volts.

This is all very confusing as the conventional wisdom is that a motor gets the hottest at very low speeds. Maybe the G203 and G201/2 behave differently to each other - the conventional wisdom comes from the G201/202 days. Need to repeat this test with a G202 . . . . .

This result is worrying, because 320 inch per minute could be a common speed for a lot of work.
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  #63  
Old Mon 16 June 2008, 13:16
smreish
Just call me: Sean - #5, 28, 58 and others
 
Orlando, Florida
United States of America
Gerald,
I have been running my table today since 6am (7 hrs straight) average speed of 200ipm and motors are just warm to hot.....Not to hot to hold, but like a fresh cup of coffee.
FYI. I don't have any measuring devices here for a real measurement.
Shop temperature is 89F....and climbing to 96F later on.

Sean
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  #64  
Old Tue 17 June 2008, 00:03
Gerald D
Just call me: Gerald (retired)
 
Cape Town
South Africa
Sean, your motors are wired bipolar(series), the voltage calc says they are capable of 78V and you are supplying them 56V, so they should definitely run on the cool side. In my unipolar(half-coil) case, the calc says 39V, and I am experimenting with voltages between 36 and 50V.

Will do more testing tonight, particularly with a G202 drive that has served us so well.
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  #65  
Old Mon 23 June 2008, 09:24
skypoke
Just call me: Chuck
 
Port Aransas
United States of America
I've got the a2a motors, which I intend to wire bipolar. I'm thinking of getting a dual output toroid xfmr which will give me either 25 or 50 volt output depending on how it's wired. So...70V dc would be the likely output which, if I understand this correctly, is a little on the high side for when motors are operated at low speeds. Here's the Q....

What if I feed the toroid with a variac? Would I maintain required isolation?

Chuck
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  #66  
Old Mon 23 June 2008, 10:47
Gerald D
Just call me: Gerald (retired)
 
Cape Town
South Africa
Chuck, I think you will be okay, but I am not a licensed electrician.
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  #67  
Old Tue 24 June 2008, 08:23
Richards
Just call me: Mike
 
South Jordan, UT
United States of America
If the Variac feeds the toroidal transformer, the circuit will work. I do exactly that when I'm testing various motors. NEVER use a variac in place of a transformer. Also, make sure that the variac only affects the toroidal transformer and not any other auxiliary power supplies.

Seventy volts is a little high for an A2A wired bipolar series, but within the permissible range (77 VDC is the computed maximum voltage).
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  #68  
Old Wed 25 June 2008, 09:49
skypoke
Just call me: Chuck
 
Port Aransas
United States of America
Thanks Mike and Gerald,

I'll start off with the variac and see what my optimal voltage is. Using the variac on a permanent basis is not that appealing.

Could I trim the output dc voltage, either with series diodes or using half a bridge rect.? Possibly a circuit that could be selected as needed?

Chuck
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  #69  
Old Wed 25 June 2008, 10:16
Gerald D
Just call me: Gerald (retired)
 
Cape Town
South Africa
Chuck, I am about to run a machine for a couple of months with a variac before its toroid (Our hottest month is February). I don't think it is dangerous if one respects the output as mains supply with a distinct live/hot and neutral, and there is a RCD breaker feeding it.

Trimming the DC voltage side is unheard of in my book, but then my book on this is very thin.
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  #70  
Old Thu 07 August 2008, 18:04
JAK
Just call me: Jason
 
Victoria
Australia
Hi all,

I’m having trouble deciding/working the power supply needed.
Could someone be kind enough to check my calculations?

Motor: PK296A2-SG7.2
Connection: Unipolar
Current: 3 amps
Inductance: 3.5 mH /Phase

For Volts:
32 x SQRT 3.5 = 60VDC
Therefore need a toroidal transformer
60/1.4 = 42.857 VAC

So use either
40VAC x 1.4 = 56VDC or 45VAC x 1.4 = 63VDC

Motor amps
= 4 off x 3 amps = 12 amps
= 0.67 x 12 = 8.04 Amps

For VA
8.04 x 56 = 450.24 watts, or 8.04 x 63 = 506.52 watts

Plan to go with the 56VDC option
thus looking at using a toroidal of 45 + 45V, 11.1A in parallel, 500VA

Cheers,

Last edited by JAK; Thu 07 August 2008 at 18:14..
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  #71  
Old Thu 07 August 2008, 21:06
Gerald D
Just call me: Gerald (retired)
 
Cape Town
South Africa
The voltage appears to be too high - check the inductance rating of the motor
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  #72  
Old Thu 07 August 2008, 21:14
domino11
Just call me: Heath
 
Cornwall, Ontario
Canada
Quote:
Originally Posted by Gerald D View Post

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
I think this is where the problem is. Where did you get the 3.5mH figure?

Gerald,
Sorry you posted while I was writing.
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  #73  
Old Thu 07 August 2008, 22:19
JAK
Just call me: Jason
 
Victoria
Australia
This is where i get lost.

if you look in the

"2000-2001 ORIENTAL MOTOR GENERAL CATALOG" page B-281

for a PK296A2A-SG7.2 motor it lists a current of 3A and a inductance of 3.5mH.

would attach the pdf if i knew how

going to emial oriental, but redo the calcs to 39 volts
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  #74  
Old Thu 07 August 2008, 23:00
Richards
Just call me: Mike
 
South Jordan, UT
United States of America
I agree with Gerald and Heath. When I went to http://www.orientalmotor.com and entered PK296A2A-SG7.2 for the motor and then clicked on "More Specifications", the inductance for that motor, Unipolar, is 1.5mH per phase.

The formula 32 * SQRT(1.5) = 39.14V. Keep in mind that 39.14V is the MAXIMUM voltage. I would use 35V or less with that motor. A 25VAC transformer would give about 25V X 1.4 = 35VDC.

Figuring the VA of the transformer is 3A X 4 X 66% = ~ 8A and 8A X 25VAC = 200VA (but I would use at least 250VA or even 500VA - the prices are nearly the same).

If I were building the power supply, I would use a 25 + 25 toroidal transformer rated at 500VA to get about 35VDC. If possible, I would use a 20 + 20 volt toroidal transformer to get about 28VDC so that the motors wouldn't get so hot. (I have used an 18 + 18 transformer @ 250VA with great success with 4 each PK296B2A-SG3.6 motors.)
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  #75  
Old Thu 07 August 2008, 23:35
JAK
Just call me: Jason
 
Victoria
Australia
thanks Mike,

Have you ever looked at using a switch mode type?

cheers,
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  #76  
Old Thu 07 August 2008, 23:50
Richards
Just call me: Mike
 
South Jordan, UT
United States of America
Jason,

A switching power supply is normally used in applications that require constant current at a fixed voltage. Stepper motors require varying current and can handle a range of voltages, so a switching power supply is not optimum for stepper motors. In fact, if you use a switching power supply, you should still use a large 10,000 uF (or larger) capacitor to help the power supply deal with the changing current requirements.

(Gerald will probably get a kick out of this, since, I basically defended the switching power supplies several years ago on the Shopbot forum. He had more experience than I and his wisdom proved to be correct.)
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  #77  
Old Fri 08 August 2008, 00:22
Gerald D
Just call me: Gerald (retired)
 
Cape Town
South Africa
Jason, you are indeed correct, that is what the 2000-2001 catalogue states for that motor.
http://www.orientalmotor.com/product..._B267-B288.PDF <---obsolete, don't save

However, the current catalogue has it at 1.5mH and our experience is that this is the figure to be used for the motors currently being sold.

Here are Oriental's current catalogues:
http://www.orientalmotor.com/products/CatalogPdfs.htm

The 2000-2001 version is in the Archive section.
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  #78  
Old Fri 08 August 2008, 00:29
Gerald D
Just call me: Gerald (retired)
 
Cape Town
South Africa
Quote:
Originally Posted by Richards View Post
. . . Gerald will probably get a kick out of this, since, I basically defended the switching power supplies several years ago on the Shopbot forum. . .
I defended the unregulated transformer/rectifier/capacitor because I could understand it and because I had just blown the ShopBot-supplied switch-mode because it became clogged with sawdust. It was a short experience and obstinacy that told me this stupid thing with the 3 components is going to work better out here than that thing with a million components and a teeny cooling fan
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  #79  
Old Fri 08 August 2008, 08:30
domino11
Just call me: Heath
 
Cornwall, Ontario
Canada
Sometimes the simplest solution to a problem is the best one. In my line of work, we only use switch mode power supplies where high efficiency is needed or space or weight is at a premium. I am also with Gerald on the linear supplies for a cnc table.
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  #80  
Old Thu 22 January 2009, 03:15
germanr52
Just call me: Germn
 
Mrida
Venezuela
Hi everybody!

In first place, this forum is pretty usefull and kind. I've been reading this forum for over a year learning about cnc routers. And it is time to build my first router!

I have a million questions to be done, and I will start by asking about my choice of Avel Y236801 500VA 25V +25 V Toroidal Transformer and PMDX-135. I tend towards the half-coil configuration and PK296A2A-SG7.2 motors.

Gerald and Mike thank you on behalf of humanity for his brilliant creation and wealth of knowledge.

My greatest respect,

Germn
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  #81  
Old Thu 22 January 2009, 06:18
Richards
Just call me: Mike
 
South Jordan, UT
United States of America
The Avel Y236801 500VA 25V + 25V toroidal transformer and the PMDX-135 power supply unit are exactly what I use on my test bench. Currently it is driving four PK296B2A-SG3.6 motors, which are electrically identical to the PK296A2A-SG7.2 motors that you specified. I have the transformer wired parallel to give about 35VDC and the motors are connected half-coil.

I've used those same components since I first started my motor testing project, about three years ago. So far, the only failure that I've had was the D1 diode on the PMDX-122 break-out-board. I tacked on a standard 1N4004 diode to replace the surface mount diode, and everything works perfectly. For the amount of abuse that I've put the components through, that speaks very highly for PMDX, Avel and Oriental Motor.
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  #82  
Old Thu 22 January 2009, 12:46
Gerald D
Just call me: Gerald (retired)
 
Cape Town
South Africa
My personal choice of Avel transformer would be the Y236751 (330VA 30 + 30 V). From experience I know that 300VA is more than enough and that 30V AC does not make the motors too hot. Mike's choice is more conservative - his will last longer.
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  #83  
Old Thu 15 October 2009, 14:35
Travish
Just call me: Travis #75
 
Wa
United States of America
power supply choice

Almost there I think. Im looking for some advice choosing between two power supplies from Antek.

The two Im looking at are-

PS-6N56R5R12 (56 VOLT 600WATT)
&
PS-6N53R5R12 (53 VOLT 600WATT)

Motor using is OM PK296A2A-SG7.2 QTY of 5 (1 for future indexer)
Bipolar wiring is 6mH per phase.

So 32 x SQRT(6) = 78.38 Max volts
78.38v x .67% = 52.5146 volts

VA is 2.1A X 5 X .67% = 7.035A X 78.38VAC = 551.4033VA

If this is right should I go with the 53 or the 56 volt power supply

Thanks for your help.
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  #84  
Old Thu 15 October 2009, 15:04
domino11
Just call me: Heath
 
Cornwall, Ontario
Canada
Travis,
You calculated your VA reqirement at the MAX voltage, not the 52 volts you have calculated.
So, VA=2.1Ax5x.67x53V= 372.9 Watts (or VA)
Does Antek have a 350W or 400W supply in the 53V variant?
What about making your own?
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  #85  
Old Thu 15 October 2009, 15:13
Travish
Just call me: Travis #75
 
Wa
United States of America
Thanks Heath!

Thanks for the correction on the VA size.
Yes, Antek makes a PS-4N53R5R12 which is a 53VDC 400W Power Supply,

http://www.antekinc.com/details.php?p=360

I would be perfectly fine with a premade one if it will fit my needs. But I will keep it in mind. I still may cut the plate and stack it like another member here has done.
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  #86  
Old Thu 15 October 2009, 16:20
Travish
Just call me: Travis #75
 
Wa
United States of America
My lack in experience has me puzzled why Sean and a few others are using a 56 Volt power supply then, if all I need is a 53 volt. Maybe at the time Antek didn’t offer them when some of you did your builds. Anyone object going with a 53 volt 400 watt?
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  #87  
Old Thu 15 October 2009, 18:53
domino11
Just call me: Heath
 
Cornwall, Ontario
Canada
Travis,
Some people push their car engines a little faster to get more performance too. 53 or 56 is so close it will not matte to the motor. Also do not forget that these are unregulated power supplies, and the voltage will fluctuate with the incoming line conditions. So expect to see some variance day to day and under different loading conditions.
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  #88  
Old Thu 15 October 2009, 19:25
Travish
Just call me: Travis #75
 
Wa
United States of America
Thanks for your support Heath and quick response. You are great help. I will place my order then, and start gathering components for my build.

Cheers,
Travis
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  #89  
Old Thu 15 October 2009, 22:04
MAC2009
Just call me: MAC
 
West ST Paul, MN
United States of America
What size is the Z steper

The lazer kit I have has a Z mounting plate for NEMA 23. You are all talking about NEMA 34s for all the steppers. If I use a NEMA 23 at the Z would I not need two power supplys?
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  #90  
Old Fri 16 October 2009, 06:28
Richards
Just call me: Mike
 
South Jordan, UT
United States of America
Travis,

There is an mistake in the way that you figured the voltage.

The maximum voltage is calculated by the formula: 32 X SQRT( Inductance). So, 32 X SQRT( 6mH ) = 78.4 VDC.

The current (Amps) required is determined by adding together the current requirements of all motors. The PK296A2A-SG7.2 motor, when wired bipolar series, i.e. 6mH, can draw about 2.1A per motor, so 5 X 2.1A = 10.5A total for all five motors. The 67% multiplier was used with the old-style round stepper motors. With the new-style square motors, many of us don't de-rate the current requirement.

So, for those motors wired bipolar series, I would use a 70VDC 10A power supply (700VA). The Antek PS-8N70 would be a close match.

For better speed, I would wire the motors half-coil. When wired half-coil, each motor's inductance is 1.5mH, so the maximum voltage would be 32 X SQRT( 1.5mH ) = 39.2 V and the motors could pull up to 3A, so 5 X 3A = 15A. For that configuration, I would use a 35VDC 15A power supply (approx. 500VA). The Antek 5N35 would be a close match for that wiring configuration.
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