Unipolar, Bipolar wiring, driver options

[joel0407]

Ok guys, I've been searching and reading for 2 days, 10 hours each day and I can't find answers to my questions so I'm resorting to asking.

My question All of the drivers I have been looking at have 4 wire connections for the/each stepper. Wiring an 8 wire stepper in unipolar has "A+", "Tap", "A" and "B+", "Tap", "B". My question is where does the "Tap" go?

I've found all the answers for Bipolar Parallel and Serial but not Unipolar.

Reason I am asking is I am looking at purchasing these motors Nema 23 Dual Shaft Stepper Motor 2.83Nm(400 oz.in) 4.0A 23HS33-4008D|AU095|Nema 23 Stepper Motors. I have been using this site to calculate max RPM Stepper Motor Calculator. I know Bipolar will give me more torque but as I get much lower mH with unipolar, I get higher max speed.

I have already purchased RM1605 ball screws. Yes I know I was advised to get 1610 but 1605 was easier to find cheap than 1610 and I figured it was better to have too much torque than not enough speed. This is only a hobby machine and I can afford time but maybe not money for bigger motors and more power handling electronics.

So running those motors Bipolar Parallel rates the motors at 5.66amp and 1.8mH. At 48v that'll give me 11.8 Rev/Sec. That calculates out to 59mm/sec = 3540mm/Min = 139IPM. I figure that's respectable for a hobby machine but if I find I have more than ample torque to drive my machine at that then I'd like to have the option to change my wiring to Unipolar. Unipolar rates the motors at 4.0amp and 1.8mH. At 48v that gives me 16.7 Rev/Sec. That calculates to 83.5mm/Sec = 5010mm/Min = 197IPM.

The 2 drivers I have been mainly looking at is the MA860H or the M542T. I can't find anything on how to wire motors to these in Unipolar configuration. The MA860H will give me plenty of over head but the M542T will save me some coin.

Happy Days

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[john-100]

Hi Joel

" The 2 drivers I have been mainly looking at is the MA860H or the M542T. I can't find anything on how to wire motors to these in Unipolar configuration."


the MA860H and M542T are Bipolar stepper drivers and can not drive a motor in uni polar configuration



to use the 6 wire uni-polar motors with the bi-polar MA860H and M542T stepper drivers you can either

use the full coil with the centre taps insulated
or
use only half the coil , connecting the centre tap and one end of the coil to the driver





John

[joel0407]

Thanks mate.

I kept researching after I posted this and found Unipolar drivers are older style. Do you know of any drivers that do both?

Currently thinking I'll just go the MA860H and then that'll leave me head room if I want to go higher voltage or higher current motors.

Happy Days

[A_Camera]

Ok guys, I've been searching and reading for 2 days, 10 hours each day and I can't find answers to my questions so I'm resorting to asking.

You must be joking....

Googling "stepper motor wiring" gives millions of answers...

My question All of the drivers I have been looking at have 4 wire connections for the/each stepper.

If you have a 8 wire motor then you have a choice of connecting the coils in series or in parallel. You can also just use one coil in single coil mode. In all cases you have 4 wires which are connected to the driver. You must be careful with the phases.



If you have a 6 wire motor then you have a choice of using the coils in series or in or just as a single (half) coil of each phase. In both cases you have 4 wires which are connected to the driver. In a six wire motor the coils are connected in series and the tap is the center connection.

Wiring an 8 wire stepper in unipolar has "A+", "Tap", "A" and "B+", "Tap", "B". My question is where does the "Tap" go?

This does not make sense to me. "A+", "Tap", "A" and "B+", "Tap", "B" means six wires, not eight.

[joel0407]

You must be joking....

Googling "stepper motor wiring" gives millions of answers...

Yes. 99% relate to wiring Bipolar parallel or serial though.

If you have a 8 wire motor then you have a choice of connecting the coils in series or in parallel. You can also just use one coil in single coil mode. In all cases you have 4 wires which are connected to the driver. You must be careful with the phases.
.

That's almost right. Just have to add Unipolar. Wiring in single coil mode is a quarter of the way there.

If you have a 6 wire motor then you have a choice of using the coils in series or in or just as a single (half) coil of each phase. In both cases you have 4 wires which are connected to the driver. In a six wire motor the coils are connected in series and the tap is the center connection.



Again, almost right. Leaving the tap disconnected (just joined) is just a 4 wire motor. For it to be unipolar, the tap gets connected.

This does not make sense to me. "A+", "Tap", "A" and "B+", "Tap", "B" means six wires, not eight.

Yep. That's right. 6 wires for unipolar. I'm thinking a unipolar driver had 6 connections. Or maybe 4 and then the "Taps" get connected to positive or ground?

I'm still researching.

Happy Days

[joel0407]

This is the picture I've been sent from the supplier.

I'm not sure if this is full unipolar or a botched up way to get unipolar from a bipolar driver?

Happy Days

[john-100]

thats the half coil option that has a lower inductance than the full coil



with the higher inductance of the full coil connection
you will need a higher supply voltage

John

[joel0407]

thats the half coil option that has a lower inductance than the full coil



with the higher inductance of the full coil connection
you will need a higher supply voltage

John

Isn't that picture of Bi-polar full coil just Bi-polar series?

[joel0407]

Holding Torque(Bipolar) 2.83Nm(400oz.in)
Holding Torque(Unipolar) 2.0Nm(283oz.in)
Rated Current(Bipolar Serial) 2.83A
Rated Current(Bipolar Parallel) 5.66A
Rated Current(Unipolar) 4.0A
Phase Resistance(Bipolar Serial) 1.6ohms
Phase Resistance(Bipolar Parallel) 0.4ohms
Phase Resistance(Unipolar) 0.8ohms
Recommended Voltage 24-48V
Inductance(Bipolar Serial) 7.2mH±20%(1KHz)
Inductance(Bipolar Parallel) 1.8mH±20%(1KHz)
Inductance(Unipolar) 1.8mH±20%(1KHz)

These are the specs for the motor. The ratings for Bi-polar Serial is different to Uni-polar

Happy Days.

[joel0407]

I just found this:



So looks like the "Tap" goes to "+". The question is now will a normal Bi-polar driver operate like this?

[john-100]

Using all of the 6 wire uni-polar motors coil is equivalent to bi-polar series connection of an 8 wire motor




your diagram in post 10 is for a unipolar motor and unipolar driver

with a bi-polar driver you must not connect the centre tap to the motor supply



john

[A_Camera]

I don't actually know what you are trying to do. The way I understand is that you bought motors with eight wires. Those are the best because you can connect them and use them any way you like, as long as you keep track of the phases. You can use them in half coil mode and in that case the inductance is X uH. You can connect the coils in parallel and in that case you get an inductance of 0.5 x X uH. You can connect the coils in series and in that case the inductance is 2 x X uH. The driver voltage and current is needed to be adjusted accordingly.

I think you worry too much. Just wire the motors like this:



If you start with the motor coils in series, if you are happy then you are fine. If not then you can try connecting them in parallel. That gives you the highest possible speed, but also draws more current and generates more heat. Don't worry, unless you mix the phases everything will be fine and it will work, assuming you have enough voltage and current.

BTW, you must go from theoretical calculations to reality. Your maximum speed is not only motor and driver dependent, but also the mechanical design and the quality of your work. Maximum speed of the motor is one thing, but don't expect that to be the real speed. That will depend also on your own abilities to build a quality machine. Typically, with a moving gantry machine you will NOT get the maximum motor speed anyway.

[joel0407]

So can I still buy Uni-polar drivers?

[A_Camera]

So can I still buy Uni-polar drivers?

Of course you can. Why would you buy anything else?

Just watch out for the phases and get the power supply needed for the motor.

[joel0407]

I don't actually know what you are trying to do. The way I understand is that you bought motors with eight wires. Those are the best because you can connect them and use them any way you like, as long as you keep track of the phases. You can use them in half coil mode and in that case the inductance is X uH. You can connect the coils in parallel and in that case you get an inductance of 0.5 x X uH. You can connect the coils in series and in that case the inductance is 2 x X uH. The driver voltage and current is needed to be adjusted accordingly.

I think you worry too much. Just wire the motors like this:

I already know from the calculations that these motors in Bi-Polar Serial will be too slow. From the specifications, Uni-polar will give me much greater speed but not as much torque as Bi-Polar Parallel. I don't need the torque of Bi-Polar Parallel so Uni-Polar seems like the most sensible place to start.

Happy Days

[joel0407]

Of course you can. Why would you buy anything else?

Do you have any suggestions for a Uni-polar driver up to around the 4.5 - 5 amp range?

[ger21]

You're better off using bipolar parallel. Good quality Unipolar drives in the 5 amp range might be quite expensive. Virtually all of the inexpensive, higher quality drives you'll find are bipolar drives.

[A_Camera]

Do you have any suggestions for a Uni-polar driver up to around the 4.5 - 5 amp range?

I have no idea, sorry. Anyway, my previous post was not what I meant...

I meant that you should buy a bipolar driver. Why would you buy anything else? Like I said, you worry too much about things which will not be a problem and which you don't seem to understand. What you should think about is that the driver and the power supply is for the motor. The M542T is limited to 4.5A peak and 3.2A for continuous use, so it may be too weak for those motors. However, speed is not going to be an issue if you have a voltage for that driver, which is 50V maximum.

[joel0407]

I meant that you should buy a bipolar driver. Why would you buy anything else? Like I said, you worry too much about things which will not be a problem and which you don't seem to understand. What you should think about is that the driver and the power supply is for the motor. The M542T is limited to 4.5A peak and 3.2A for continuous use, so it may be too weak for those motors. However, speed is not going to be an issue if you have a voltage for that driver, which is 50V maximum.

Why should I buy Bi-Polar when my motors will give me the performance I need in Uni-Polar configuration. Bi-polar Serial will be too slow and Bi-Polar Parallel will need too much current and give me more torque than I need. Yes I am thinking about the driver. That's sort of the point. If a driver rated high enough to run the motors at 5.66amp required for Bi-Polar Parallel was no more expensive then I'd just run it Bi-Polar Parallel. As "ger21" has said above that a Uni-Polar driver maybe more expensive if that's the case then I'll just go Bi-Polar Parallel.

Happy Days

[Torchhead]

True unipolar connection is where the full + volts are wired to the center tap of a winding and the two legs are pulled sequentially low . its sometimes referred to as a Push-Pull circuit . The unipolar driver is easier and cheaper to make and the early ones just used a big series resistor in the + leg to limit that current. With the cost of chopper stepper drivers now almost as cheap as the unipolar drivers and the distinct advantages you get with a bipolar setup there is no logical reason to try and move back to the older technology.

The other factor you are not thinking about is the loss of torque with RPM . Just because you can spin a motor faster does not mean you can use all that extra RPM. Yes, inductance does predict the slope of the torque curve (and where the torque "knee" happens ) but as stated you have a lot of connections options with an 8 wire motor. A true unipolar motor only has 6 wires: 3 on each winding.

The correct question is what level of torque and RPM go you NEED. You can get a ballpark on paper but there are too many variables to get really accurate ones. The max theoretical RPM of a motor is a combination of many things including the applied voltage, torque curve at that voltage , series or parallel connection and even the "purity " of the pulse (step) signals. Then you have "microstepping" and step morphing that changes the dynamics of the RPM / torque curve at higher RPM (some drivers have it, some don't) . We have seen a 25% increase of top RPM just from moving from a PC generated step to a pulse train generated by a separate pulse card.

I use the 1/2 rule. You can usually get about 50% of the max numbers in real live moving a load. Its conservative but when you start to push boundaries you start to see problems. With 1605 ballscrews your linear feedrate will be 1/5 of your motor RPM. That RPM has to be at a point where you still have enough torque to both accelerate and decelerate the motion of the toolpath and handle the inertia of the total mass of the object you are moving and any cutting forces .

So---- at 48VDC you can expect to see from 800 to 1000 RPM unloaded motor RPM before it self stalls. USABLE RPM can be 1/2 that . Lets take 500 as a good number. Put that though the 1605 and you are at 100 IPM . Torque and speed and on opposite sides of the equation so while you can get more RPM that often results in less torque (especially through a transmission) so its faster, but won't pull a sick cat out of a litterbox.

The best advice I can give is to look at designs that are similar to what you want to do and use that as a baseline. As they say "your results will vary". There are no simple formulas to predict the overall performance of a set of electronics and motors on a specific mechanical structure