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  #31  
Old Wed 10 October 2007, 23:16
Gerald D
Just call me: Gerald (retired)
 
Cape Town
South Africa
Dave, if you thought that was confusing, try this . . . . . . . .

Quote:
Originally Posted by driller View Post
. . . . . . Look at the motor voltage, it should be between 1 volt and 12 volts, multiply by 20 to find the maximum voltage for that motor . . . .
A lot of motor manufacturers do not give a motor voltage. As Mariss recently suggested, the inductance of the square body style of stepper motor can be used to calculate optimum voltage . . .

Either take:

- the square root of the inductance in Henry (H) times 1000, or
- the square root of the inductance in milliHenry (mH) times 31.6

Have a look at this PK296-A2A Oriental Motor (Vexta) that is the first choice for the MechMate today:


Following the old 20X motor voltage approach would have given us 20X 2v = 40V.
Using the new square root of the inductance in milliHenry (mH) times 31.6 we get sqrt(6) x 31.6 = 77V

And that is apparently why the folk with Vexta motors discovered that more volts gives them more performance without overheating - their 20X calculated voltages were just too low to begin with in some models/configurations.

Looking at the Motionking 9801 motor:


. . . . the nominal motor voltage would have been 4A X 0.98ohm = 4 Volt and the power supply voltage calculated at 20 x 4 = 80 Volt.
Using the new square root of the inductance in milliHenry (mH) times 31.6 we get sqrt(4.1) x 31.6 = 64V
So the newer formula gives a much lower voltage in this case. (The old formula could have given you a hot motor)

Mariss suggests the difference lies in the packing density of the coils. Apparently the more expensive ("higher quality") motors have tighter, more closely wound, coils.
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  #32  
Old Thu 11 October 2007, 06:23
Richards
Just call me: Mike
 
South Jordan, UT
United States of America
The Motionking 9801 motor is an 8-lead motor, so connecting it using Parallel wiring would probably be most efficient. The current rating for Parallel would be 4A * 1.4 = 5.6A. The Inductance would still be 4.1mH. The maximum voltage would be SQRT(4.1) * 31.6 = 63.98VDC. So, if four motors were installed, the power supply that I would use would have a minimum current rating of: 4 motors * 5.6 A * 0.66 efficiency factor = about 15A. The maximum voltage that I would use would be: SQRT(4.1) * 31.6 * 90% = about 57 V. So, just to be on the safe side, I would use a 40VAC toroidal 800VA transformer. After rectification, that would give me about 56VDC. That would allow the motors to pull maximum current and reach near maximum speed at a little less than maximum temperature.

EDITED: Gerald, you posted while I was typing. The PK296A2A-SGxx motor is the single shaft motor. The B2A is the dual shaft version. Both the A2A and the B2A are rated at 6mH Bipolar and 1.5mH Unipolar (half-coil). I use the PK296B2A-SG3.6 motors wired half-coil with power supplies ranging from 26VDC to 35VDC with excellent results. For half-coil connections with a Gecko G202 or G203, I use the Black wire and the Yellow wire for the A coil and the Red wire and the White wire for the B coil. i.e. Term #3 = Black wire, Term #4 = Yellow wire, Term #5 = Red wire, and Term #6 = White wire.
  #33  
Old Thu 11 October 2007, 07:00
Gerald D
Just call me: Gerald (retired)
 
Cape Town
South Africa
Ouch, that is the second time the two model numbers made me think they were different electrically! Of course they are the same motor. And Dirk also said to use the unipolar configuration. So, the currently recommended "MechMate motor", the Oriental PK296_2A-7.2, should have a supply voltage of say 35 to 40 volts (37 from inductance formula, 28 from voltage formula) and 4 of those motors will want a power supply current of 8 Amps. That means around a 300 VA supply. Right?
  #34  
Old Thu 11 October 2007, 07:19
Gerald D
Just call me: Gerald (retired)
 
Cape Town
South Africa
Mike, for that MotionKing motor, I would still go for the Unipolar, even though it has 8 wires. Still 56V but on a 600 Watt supply. Can't remember now why I favour unipolar over parallel . . . .
  #35  
Old Thu 11 October 2007, 10:43
Alan_c
Just call me: Alan (#11)
 
Cape Town (Western Cape)
South Africa
Send a message via Skype™ to Alan_c
Richard

What is the size (VA) of your transformer to get nice toasty steppers? I have the same motors, but in testing with the kitchen table project they hardly rise above ambient - I have them wired unipolar on a 300VA transformer.
  #36  
Old Thu 11 October 2007, 12:16
Richards
Just call me: Mike
 
South Jordan, UT
United States of America
Alan,
The power supply that I used when I last tested the PK299-F4.5 motor was an 800VA unit wired to give 35VDC. The transformer never got above room temperature, but I was really exercising the stepper motors that I had attached to that power supply. Even the 250VA toroidal transformers that I often use in the 27VDC power supplies stay at room temperature when I run three 3A motors. Maybe I should also add that 'toasty' is defined in my shop as being between 130-degrees F. and 145-degrees F., well within the design range of the motors. (I have had severe transformer heating problems when I've used standard, non-toroidal, transformers. One standard Triad F-258U transformer always ran too hot to touch, even when the four steppers had been sitting in reduced current mode for more than an hour. The stepper motors were at room temperature and the Gecko G203v stepper drivers were at room temperature, but the Triad F-258U was HOT.)
  #37  
Old Wed 23 January 2008, 07:30
J.R. Hatcher
Just call me: J.R. #4
 
Wilmington, North Carolina
United States of America
Send a message via Skype™ to J.R. Hatcher
I have a question. Does a TA7812S voltage regulator work only with a DC input or will it work with a AC input as well?
http://www.questcomp.com/PdfDir/D8204487.pdf
  #38  
Old Wed 23 January 2008, 08:42
Gerald D
Just call me: Gerald (retired)
 
Cape Town
South Africa
Looking at the internal schematic, there is a diode across input and ground. AC will make the diode (at least) go *pop*. DC only......until someone else verifies.

Some ideas:
http://www.explorecircuits.com/cir_p...wer_supply.htm
  #39  
Old Wed 23 January 2008, 09:29
domino11
Just call me: Heath
 
Cornwall, Ontario
Canada
JR, Gerald,
Yes this is a DC Voltage regulator. Only use Dc as an input. If you only have AC then hook up a rectifier bridge and a filter capacitor to give you the proper DC for the regulator. I can provide a schematic if anyone needs it.
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