4-phase motor and wiring questions

[DmitryZ]

My first post!!!

I just got my steppers in the mail today .

I ordered them from this place:

http://www.clickautomation.com/produ...id=395&cid=158

The funny thing is the back of the motor says it is a 4-phase motor? I never heard of a 4-phase motor and almost thought they sent me the wrong part but I figured I am just missing something and hopefully someone can explain this to me.

Another question: I would like to wire these motors as Bipolar Half-Coil i.e using the center tap wire. How does this affect the amperage rating of the motor? From reading the other posts I still cannot figure out if I need to half the amps or if that only applies to 8 wire motors wired in parallel.

This probably will sound dumb but the way I see it is if my motor is rated at 2amps/phase I would have to apply 4amps if full winding is connected and 2 amps if half winding is connected. Is this correct?


I would appreciate any input

thanks,

Dmitry

[DmitryZ]

Ok I just noticed this thread right below - Do'h
http://www.cnczone.com/forums/showth...&threadid=3730
and I read the white paper from gecko drives as posted by Mariss.

I am now confused more then ever. The paper has the following statement "The drive will always draw less than 2/3 of the motor's rated current when it is in parallel (half-winding). Does this mean that I have to set up my Xylotex board for 2*(2/3)=1.33 amps when I am installing the motors?

Dmitry

[Mariss Freimanis]

Dmitry,

Wrong. Use 2A in half-coil (CT and end-wire) or 1A in full-coil (end-wire to end-wire). This is a low-current, high inductance motor. I suggest you run it half-coil to get decent performance.

Here's the deal with that. Step motors need only 2 coils to work. That means 4 wires. Some motors have the coils center-tapped (like yours) and have 6-wires. 8-wire motors have these center-taps seperated so you can wire the coils in parallel or series.

Series on a 6-wire motor is identical to using the end-wires and ignoring the center-taps. Parallel on a 6-wire motor is using the center-tap and 1 end-wire. DO NOT connect the remaining wire!! The performance is within 1% of what you get with a true 8-wire motor.

In all respects it is an ordinary 2-phase motor. There is no reason the mfg should call it a 4-phase motor. Ignore that entirely.

Mariss

[radio-op]

I think by '4 phase' they are noting the fact that the coils are center tapped.
After looking over the specs from the site, they are listing the current per phase @ 2A, I.E. 4.5V/2A=2.25Ohms per phase. So for a full winding 4.5V/4.5Ohms=1A. Running half winding bipolar would draw 2A per phase. With an 8 wire parallel bipolar, the 2 halves are a parallel resistance, 1/(1/R+1/R); so the resistance would be 1.125 Ohms, and 4.5V/1.125Ohms=4A.
For half winding, your motors will draw 2A per phase at the 4.5V rating. For a full winding, the current will go down to 1A from the same supply voltage, due to the increased R.
Now, you power supply will need to supply 2 x the phase current per motor.
As you may know, if you run a higher Voltage, you must still limit the current to these values.
Hope this helps,
Bill

[DmitryZ]

Thanks for the instantaneous replies guys!!! I actually understand this now!!!

Originally posted by radio-op Now, you power supply will need to supply 2 x the phase current per motor. As you may know, if you run a higher Voltage, you must still limit the current to these values. Hope this helps, Bill

If I have 3 identical motors utilizing half winding I will need a power supply capable of 12 amps? That would mean I am about 6 amps short with my 24V 6.5 amp PS. Grrrrr - Story of my life – never enough power.

From reading all the posts in the past couple of months, I realized that my first machine should be a learning project. I have my power supply already and would rather not buy/make a new one (I will save that for the monster CNC that I envision in my dreams). Since my PS lacks proper amps for a half winding configuration, should I wire it for full winding instead?

Dmitry

[radio-op]

On your second post Dmitry, are you quoting from the Gecko white paper? I believe they are derating the current demand from the power supply to the driver, due to the efficiencies of the Gecko drive. In other terms, I think they are saying you can reduce the current capacity of the power supply. I may be very wrong on this, anyone know for sure?
I would follow the directions for the Xylotex board to be on the safe side.
Bill

[radio-op]

Based on what I know from a different motor, you should be able to run them full winding bipolar and your holding torque should be nearly the same as parallel bipolar, but it will drop off faster as the RPMs increase. What this will mean to you is a lower top speed for rapids without losing steps.
Bill

[DmitryZ]

Originally posted by radio-op Based on what I know from a different motor, you should be able to run them full winding bipolar and your holding torque should be nearly the same as parallel bipolar, but it will drop off faster as the RPMs increase. What this will mean to you is a lower top speed for rapids without losing steps. Bill

Thanks!

[radio-op]

If your still out there Mariss, let me ask this question. Wouldn't running a 6 wire in half winding bipolar yield the same holding torque as unipolar, both are only using half the total coil length at any given time? What is getting me confused is the ratings from Pacific Sci on their motors, they list the torque and amps drawn for unipolar, series bipolar and parallel bipolar. From their ratings, series bipolar has the lowest current load but the same holding torque as parallel, whereas unipolar has the lowest holding torque but more current draw then series. They don't list ratings for half winding, so I'm trying to make sure I understand.
Bill

[Mariss Freimanis]

Radio-op,

Easy soft-ball pitch. 8-wire motors have 3 current ratings; series, half-coil (unipolar) and parallel.

Let's say the motor (a wierd one because of purposes of illustration) has a 1 Ohm half-coil resistance and is rated at 1A unipolar.

Its series rating would be 0.707A
Its unipolar rating would be 1A
Its parallel rating would be 1.414A

Why? To keep I squared R dissipation constant.

For that, look at the coil resistance and resulting dissipation:

Series, 2 Ohms, 0.707A = 2*(0.707 squared) = 2*0.5 = 1 Watt
Unipolar, 1 Ohm, 1A = 1*(1 squared) = 1*1 = 1Watt
Parallel, 0.5 Ohms, 1.1414A = 0.5*(1.414 squared) = 0.5*2 = 1Watt

In all cases the currents result in a constant 1 Watt dissipation!

Take a look a various motor mfg data sheets for 8-wire motors. Pick the series rated current. Multiply it by 1.414, that will match the data sheet unipolar rating. Multiply it by 1.414 again, that will match the data sheet parallel current rating.

Every mfg's data sheets will agree with what I wrote. I'll bet my dinner on it (Oh-oh. I've not done so good betting people recently but I'll still go for it) :-)

Mariss

[radio-op]

Mariss, thank you very much, very informative. Your insight is helpful, as Pac Sci does not list a rated voltage but rather a max voltage rating. I hadn't realized the constant power dissipation relationship. Had only applied Ohm's law solving for either rated voltage or resistance depending on the published specs.
The core of my confusion is the relationship with the torque ratings, in regards to the amp/turns and the difference between parallel bipolar and half winding bipolar. I have seen it stated a few times that a half winding and a parallel bipolar are nearly identical and one source (Gecko's white paper) recommended the half winding over the parallel. As I understand, half winding seems like it should yield the same holding torque as unipolar, both should have the same amp/turn ratio. With Parallel your amp/turns would be much greater (2x as many turns) then a half winding. The published holding torque for say a 100oz/in type single stack motor lists unipolar as 97oz/in @ 3.3A and parallel bipolar as 137oz/in @ 4.6A; a 40oz/in difference. The same motor has a series bipolar rating of 137oz/in @ 2.3A. I understand that the holding torque does not represent the whole picture, but is a figure of merit. Is this recommendation for half winding based on the torque/speed performance curve as apposed to just the holding torque?
Is the half winding resistive reactance different then the resistive reactance of a unipolar winding? This really bugs me 'cause there ain't no free lunch
Thanks again,
Bill