GUIDE TO STEPPERS and wire in parallel or series AND 8 wire series connection

--- In CAD_CAM_EDM_DRO@y..., "mszollar" <kenargo@v...> wrote:

> I can wire my motors (8 wire) in series or in parallel. The only

difference I can see is that parallel is 2x the current of series.
The specs look like the torque is the same.

>
> Any benefits of 1 wiring scheme over the other?
>
> Thanks, Ken

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To Ken,

This should clear things up.

To the rest of the group,

If I may post some notes from other messages. Mostly quoting Mariss.
These are old posts in their entirety. You may have already read
them before.

I am working on assembling my notes and will post this in the files
section once I get the OK from those concerned.

I want to include the mystery motors, but found that a spreadsheet
would work better. still working on that.

Dave

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Message 40388 "mariss92705" Fri Feb 22, 2002 2:41 am

UNIPOLAR, BIPOLAR, SERIES, PARALLEL, FULL-WINDING, HALF-WINDING

These terms can be confusing but they don't have to be. Unipolar and
bipolar properly refer to motor drives, the other terms refer to
motors.

In the end, 4 wires from the motor must be connected to the drive;
it's all a matter of which ones go where. The following definitions
will clear things up.

DRIVES FIRST:

UNIPOLAR: An outdated motor connection requiring only 4 power
transistors. It also refers to 6-wire motors, (not outdated). Motor
current is applied to the center tap of a winding. One end of the
winding or the other is switched to ground by the power transistors
but never at the same time.

ADVANTAGES: Simple

DISAVANTAGES: Many. The connection acts a 2:1 step-up transformer, so
the transistors "see" twice the power supply voltage. Inductive
energy is not inheirently clamped, so complex and inefficient
clamping circuits must be used to prevent damage to the transistors.

BIPOLAR: Almost universally used in modern, high-performance drives.
Bipolar refers to how the winding is driven; when one end of the
winding is grounded, the other end is connected to the power supply
voltage and visa versa. This method requires a full-bridge driver per
winding for a total of 8 transistors.

ADVANTAGES: Many. The transistor voltages never exceed the power
supply voltage. Inductive energy is clamped to the power supply
voltage rails and is efficiently recirculated back to the power
supply. No circuit voltage is above or below the power supply voltage
rails at any time.

DISADVANTAGES: More complex than unipolar.

NOW, THE MOTORS:

SERIES: A method of connecting a split winding (8-wire motor) end to
end so that the current flows through one winding and then through
the other one. Mind the phasing of the windings; they must be
connected so that they "add" (boost). If they are connected
to "subtract" (buck), the result will be no torque and possible
damage to a switching drive since the inductance will be zero as well.

ADVANTAGES: Smaller power supply because only half of the rated
current is necessary for the same holding torque. Less motor heating
at a given voltage.

DISADVANTAGES: The motor will develop only half the power at higher
speeds because this connection has 4 times more inductance.

PARALLEL: A method of connecting a split winding (8-wire motor) side
by side so that current flows through both windings simultaneously.
Mind the phasing again (see SERIES: above).

ADVANTAGES: Develops maximum power at higher speeds.

DISAVANTAGES: Greater motor heating at a given power supply voltage
when compared to the series connection.

FULL-WINDING: A method of connecting the end wires of a 6-wire motor
leaving the center tap unused. It is exactly identical to a series
connected 8-wire motor since the winding is internally connected in
series at the center tap. The advantages and disadvantages are
identical to the series connection as well (see SERIES: above).

HALF-WINDING: A method of connecting the center tap and one end wire
of a 6-wire motor leaving the other end wire unused. It makes no
difference which end wire is used. It is almost identical to a
parallel-connected 8-wire motor.The single difference is only half
the copper (hence half-winding) is used, so the winding resistance is
twice what it would be for an identical 8-wire motor. At higher
speeds this higher resistance develops a slightly greater voltage
drop, leaving a little less for the motor to work with, and so the
motor develops a little less power compared to an 8-wire motor.

The difference is almost insignificant; dynamometer tests show only a
3% difference in power output between a half-winding 6-wire motor and
a parallel-connected 8-wire motor. It only stands to reason; at
higher speeds phase currents decrease and therefore the I squared
Rloss differences decreases as well. The advantages and disadvantages
are the same as a parallel connection (see PARALLEL: above).

CURRENT SETTINGS FOR WINDING CONNECTIONS:

The proper phase current is very important for best low speed
performance of a microstep drive. It relates to how smoothly and low
speed resonance free a good microstepping motor will be.

There is a common misperception some users make regarding current set
with microstep drives. It has to do with the fact microstepping
drives the motor with sine and cosine weighed currents. When the
current in one winding reaches its maximum the other winding current
is at zero. From this some surmise that it should be possible to
increase the set current to 141% of rated since the motor power
dissipation would then be identical to a full step drive. That is
correct as far as power dissipation goes but it neglects a very
important point most are not aware of.

The magnetic flux path is not shared by the windings. This means the
current in one winding does not contribute by adding or subtracting
to the to the magnetic flux of the other winding. Though the
dissipation may equal a full step drive by running the current at
141% of rated, the iron magnetic saturation is dependent on the
current of one winding entirely.

The result is the iron in the motor saturates at the higher current
and degrades the motor's linearity. Consequently the microstep
placement is not optimal anymore and the motor will exhibit greater
low speed resonance than it otherwise would have.

A microstepping drive may not have as much holding torque as a full
step drive, but this is meaningless in practical terms. A full step
drive invests about 35 to 40 % of its available torque in vibrating
the motor and mechanism once it begins to turn. A microstepping drive
wastes less than 1% of available torque this way.

Though it may have less torque to work with, a microstepper applies
nearly all of it to the load, so in the end it is at no disadvantage
compared to a full step drive. There is no point to trying to bring
up a microstepper drive torque to the same level as a full step drive.

The conclusion is: set the current to the motor's rated current. If
it is a unipolar (6-wire motor) use the nameplate rating. If it is a
parallel wired 8-wire motor, use the parallel rating.

UNIPOLAR: Use the motor's name plate rating
SERIES: Use one-half the parallel rating
PARALLEL: Use the motor's name plate rating (usually the parallel
rating)
FULL-WINDING: Use one-half the name plate rating
HALF-WINDING: Use the motor's name plate rating

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Message 44436 "mariss92705" Wed May 8, 2002 5:46 pm

Full-stepping vs. Microstepping.

If you have a 5V 1A per phase unipolar rated, 8-wire motor, then you
would run it at 1A unipolar (half-winding) and it would dissipate 5W
(1A squared times 5 ohms).

If you connect the windings in parallel, then the winding resistance
is 2.5 ohms (1/2 what it was in half-winding). The current can be
increased to 1.41A and still dissipate 5W (1.41A ^2 times 2.5 ohms =
5W).

What matters here is your torque (from the URL you referenced)
increased 30%. It should have increased 41%; the reason it didn't is
because the iron has magnetically saturated.

If you are full stepping, you don't care. There is no negative
positioning effect from saturating the iron except for a drop in
inductance.

If you are microstepping you do care because saturated iron means a
non-linear motor and the microstep positions will begin to bunch-up
at the full step locations.

An analogy is an audio amplifier. If you overdrive it with a sine
wave, the output will limit or "clip" and produce distortion. If all
you are amplifying is a square wave, then who cares if it clips?

Second point. Take the same motor and drive it at 1.41A half-winding.
You will not be able to tell it apart from the parallel connected one
at 1.41A torque-wise. The only difference is it will dissipate 10W
(1.41A squared times 5 ohms).

Third point. This 30% increase in torque occurs at low speeds where
step motors usually have surplus torque anyway. It does not get you a
single extra oz-in of torque at high speed, where improvement would
be appreciated.

Inductive reactance becomes the bottleneck that limits the winding
current. The drive may be set at 1A or 1.41A, it will make no
difference. 10 mH of inductance will have 62.8 ohms of inductive
reactance at 4,000 full steps per second and will limit winding
current to 0.5A for a power supply voltage of 31.4VDC.

I = 31.4V / 2 pi times 1kHz times 0.01 Henries
4 full steps is one electrical cycle, so 4,000 full steps/sec = 1kHz

============================================================
Message 36945 "mariss92705" Fri Jan 11, 2002 4:54 pm

Running Uniploar motors as Bipolar motors.

If an 8-wire motor has a 1A unipolar rating and you have a full step
or half step drive, then:

Use 1A if you are running the motor with a unipolar drive (6 wire)
Use 1A if you are running half-winding bipolar.
Use 1.41A if you are running parallel bipolar.
Use 0.707A if you are running series bipolar.
Use 0.707A if you are running full-winding bipolar.

If you are using round motors, are using a microstep drive and you
want optimum smoothness,
then:
Use 1A if you are running half-winding bipolar.
Use 0.500A if you are running full-winding bipolar.

If you are using new SQUARE motors, a microstep drive, you want
optimum smoothness
then:
Use 1.41A if you are running half-winding bipolar.
Use 0.707A if you are running full-winding bipolar.


8 wire stepper connected in half winding , the performance will be
identical to a 6-wire motor wired in a half-winding configuration.

You can also try to connect the motor in parallel. The test to see if
you have it right is easy. Simply compare the motor's detent torque
after you have paired the windings to what the detent torque was
before you connected anything.

If you have it right, the detent torque will be the same (easy to
turn). If you have it wrong, the motor will be difficult to turn.

If it is easy to turn, connect the windings to the drive connector
and try running it.

==================================================================
Message 49179 "JJ" Wed Sep 4, 2002 8:26 pm

WIRING FOR AN 8 WIRE SERIAL CONNECTION

Okay, I did a lot of driving today, so I had time to think about this.
This may or may not work.

Use a DVM to find the coil wires by checking resistance between wires.
Label them something like A, B, C and D.

Now, switch the meter over to DC volts. Connect coil A to the meter.
Give the motor a spin, and note the polarity of the voltage. If it's
positive, label the motor wire connected to the red meter lead +, if
negative, label the wire connected to the black lead +. Label the
other wire - if you want. Repeat for B, C and D, turning the motor
the same direction each time.

Go get a flashlight battery. If your motor is less than 1.5 volts,
use a 10ohm resistor in series with it.
Put a little mark on the motor shaft so you can see it move.
Connect A-, B-, C- and D- to the - end of the battery. Leave them
there for the remainder of the test.

While watching the motor shaft, connect A+ to the plus end. You
should see a twitch in one direction or another. If you don't see a
twitch check A- and A+ with the ohm meter, then check the battery
with the volt meter.

Now while holding the A- and A+ wires on the battery, connect B+ to
the + end of the battery. If you don't see a twitch, you've gotten
lucky and that's a pair of coils. If you do see a twitch, take B+ off
and try C+, then D+, all the while keeping A+ connected.

Now, if you see a twitch with all the coils, try connecting B+, C+ and
D+ to the - end of the battery, and connecting B-, C- and D- to the +
end of the battery, one at a time. If you still see a twitch, then I
don't have a clue :-)

I don't have any 8 lead motors lying around, but I believe this will
work for you.

BTW, I have unipolar motors and used the battery twitch method to
find out the coil sequence. By connecting both center taps to the -
end of a D cell, I touched the other wires to the + end until I found
the right sequence so all the twitches were in the same direction.

Hope that helps.

Regards,
JJ

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49176 From: "cadcamcenter" Wed Sep 4, 2002

Determining how to connect an 8 wire stepper in series.

First isolate the motor pairs.
1. determine the paired wires with multimeter
2. pick any 2 pairs, connect them to the driver.
3. Test under power. If wrong pair motor will not turn, probably make
noise, but no harm done.
4. Make a note, pick another 2 pairs.
5. At most, you need only 3 trials before you get the motor turning,
and at most 4 to get them turning correctly.

To connect in series, perhaps add the following steps to the above:

6. Note which pair of pairs are A and A', B and B', (pair of pairs
which will miss when connected.

A) connect any pair to any other pair and spin by hand. If the
detent is noticeable hard, you have the wrong pairs. If there is no
change in the indent, Motor spins easily, you have the correct pairs

7. Note which sense motor will turn when, say A and B are connected,
plus the polarity of the wires when connected.

8. Note which sense motor will turn when A' and B are connected, plus
the polarity of the wires when connected.

9. Now you have an idea of where the "+" and "-" of coil A and A'

10. Repeat for, say B and A, and B' and A.

11. Join connect the, say, "+" to the "-" of A and A' and the "+"
and "-" of B and B'

There you are, 8 wires connected in series without knowing the color
code of the wires. Haven't done this before myself. Will appreciate
to get feedback on whether the scheme will work.

Thanks
Peter