stepper wiring and parameters

[Ferenczyg]

I got some steppers 1.3V, 3.9V nema 23, 6 wires. These are the specs at the stepper label. My questions are:

1) if a unipolar stepper is wired bipolar, how the specs change? I mean, wired bipolar the coils have double length so have double resistance, so the A is the same and V is double? As they have 6 wires they only can be wired bipolar series, not bipolar parallel.

2) what are the relations in wiring 8 wire steppers from bipolar series to bipollar parallel? I was thinking that wiring two coils in parallel makes the resistance the half (like resistors), so the current is double and the V the same, but looking at other posts and some datasheets the ratio between Amps serie and Amps Parallel is 1.4, someone of you know why? I am not considering inductance or something similar?

Thanks in advance

Fer

[ger21]

I *think* the 1.4 is 6 wire unipolar wired bipolar. I know that 8 wire motors wired parallel need twice the current, half the voltage of those wired series.

I just checked my PacSci chart I have, and the 1.4 is an 8 wire motor wired unipolar, needs 1.4 times the current of an 8wire motor wired bipolar series. So I think the first thing I wrote is wrong.

[ESjaavik]

If you want low speed, high power, try serial. If you need high speed wire parallel. Or if your drive electronics can push the amp's quoted for parallel, wire them that way and you'll get the best high speed power and the same at low speed. When run bipolar each winding gets to cool down while the other winding carry the current. it doesn't when unipolar as then it always carry current. The fact that the current change polarity in bipolar does not allow it to cool down, so it is derated.

[radio-op]

A stepper motor is composed of 4 coils, 2 per phase. A 4 wire motor has the center tap between coils tied internally. A 6 wire has the center tap for each coil pair brought out and a 8 wire has a lead for each end of each coil.
A 4 wire motor can only be run as a series bipolar. Where as a 6 wire can be run as a series bipolar or as unipolar. With a 8 wire you can wire it as above or parallel the 2 coils of each phase for parallel bipolar. So the resistance of series bipolar windings are twice that of parallel bipolar but half the current, no changes to applied Voltage
To run a stepper in unipolar mode, the center tap for each phase is tied to pos voltage and the driver engerizes (pulls to GND) only one of the coils in each phase to take a step. Where as bipolar mode will require the driver to reverse the voltage phase of the coil, appling a pos voltage to either the top of the coil or the bottom for a step. So
I=V/R per phase, unipolar
I=V/2R per phase, series bipolar
I=V/(1/(1/R)+(1/R)) per phase for parallel bipolar
Bill

[radio-op]

"So
I=V/R per phase, unipolar
I=V/2R per phase, series bipolar
I=V/(1/(1/R)+(1/R)) per phase for parallel bipolar"
P.S.
Let me add that the above is misleading in that the DC current for a stepper should be constance reguardless of the applied voltage; the above is the current draw for a given R and V. If the supply voltage is higher then the spec of the motor, the current must be limited to the design current spec. If you use the the manufacture's design voltage and resistance the above equations will yeild correct current draw for the wiring configurations. Using the above for a linear driver
P(bias)=V(Idraw-Idesign)
Where
P=power in watts dissapated by the bias resistor
V= voltage applied
Idraw=the motor's DC current draw
Idesign=the motor's design DC current
Bill

[rimcanyon]

"A stepper motor is composed of 4 coils, 2 per phase. A 4 wire motor has the center tap between coils tied internally. A 6 wire has the center tap for each coil pair brought out"

If I interpret this right, then to convert a 6 wire stepper to bipolar series, I would identify the two center tap leads and tie them together, then connect the remaining 4 wires to the driver. I checked the resistance between leads: 1,3 & 6 have approx. zero resistance, as do 2,4 & 5 (using a VTVM). Do I need to disassemble the motor to figure this out? The motors are SloSyn M092-FD-310

-Dave

[ESjaavik]

DON'T DISASSEMBLE A PERMANENT MAGNET STEPPER MOTOR! ! !

Yes, I'm shouting, because it's important. Disassembling it WILL demagnetize it. And after that you have just a fraction of the torque left. In other word thenyou can strike out the word "permanent".
BTW: the same goes for a synchronous BLDC servo motor.

Use your VOM to find out which lead goes where.

[DR-Motion]

Dave, Definitely listen to ESjaavik. Disassembling a stepper motor will definitely result in lower torque. I don't know if you are demagnetizing it but it is extremely difficult to realign the gaps between the stator and the magnets. Don't ask me how I know this, ahem.

You say that you measure a zero resistance among two sets of three wires 1,3 & 6 and 2,4 & 5.

This identifies the separate coil phases but you are going to have to take more accuate measurements to determine which wire is the centre tap... although its been my experience that the motor manufacturers DO try to make it easy for you.

So my guess would be that 3 and 4 would be the centre taps.

HTH Gary

[Stevie]

I had to dissaemble one of mine; it got dropped somewhere along the line before I got it; I could hardly turn the shaft; the other 2 spun freely compared; so I though must be out of line (one corner was all banged in) I made sure to not rouch the rotor to the windings as i removed it; then I replaces once i saw there was no damage inside; it now moves just as well as the other 2; if I cross the leads on all 3 the drag increases; So I figure I missed that demag bullet

[rimcanyon]

"So my guess would be that 3 and 4 would be the centre taps"

Gary, that was my guess too for the same reason. If the guess is wrong, but I hook the motors up and try it out, what is the worst that could happen? Would it be pretty clear that it was wired wrong?

"DON'T DISASSEMBLE A PERMANENT MAGNET STEPPER MOTOR! ! !"

ESjaavik, thanks for the message, I had no idea this would be a problem.

I also saw in other posts someone's suggestion not to run the steppers without a load. Is that really an issue? I want to hook up the motors and controllers and try the trial version of Mach1, to see if I can get the SloSyn controllers to respond to the pulse/direction signals, or if I will need to buy new controllers.

-Dave

[radio-op]

"If I interpret this right, then to convert a 6 wire stepper to bipolar series, I would identify the two center tap leads and tie them together, then connect the remaining 4 wires to the driver. I checked the resistance between leads: 1,3 & 6 have approx. zero resistance, as do 2,4 & 5 (using a VTVM). "
To use a 6 wire as bipolar you would not connect the center taps to anything and just use the 2 ends of each coil for full winding bipolar I.E. Phase A=1-6 and Phase B=2-5. Or if you want half winding bipolar, use the center tap and one end of the coil for each phase, leaving the other end open. You will need to identify the same ends of the 2 coils, use both tops or both bottoms of the phases, I.E. Phase A=3 & 6 , Phase B=4 & 5 or Phase A=1 &3 and Phase B=2 & 4.
1,3,& 6 are one phase (call it A) and 2,4,& 5 are the other (B). Set your DMM/VOM to the lowest ohms setting and test for the centertaps I.E. 1-6=R, 1-3=1/2R & 3-6=1/2R would mean 3 is the centertap. Finding the 'top' of the coil is a matter of trial and error. You'll have to hook up to a driver and try stepping. If it won't move, reverse the wires to the ends of one phase, I.E. 6 and 1 for full winding. If it moves CCW when you step CW, reverse the wires to the phases.
Hope this helps.
Bill

[radio-op]

"I also saw in other posts someone's suggestion not to run the steppers without a load. Is that really an issue? I want to hook up the motors and controllers and try the trial version of Mach1, to see if I can get the SloSyn controllers to respond to the pulse/direction signals, or if I will need to buy new controllers."
What you may have seen is not to run a driver without a load ( stepper motor). A chopper drive can be burned up without a load connected. Running a stepper motor unloaded (on the bench) is no problem.
Bill