Ian or Ian - sorry are you saying from coils in parrallel I should settle at 3.5amp - not 5amp.

If you don't want to exceed the manufacturer's rated values, yes.

Certainly where I went wrong was - when the motors said they were rated at 2.5amp at 7.5 volts - per coil - I then opted for 2.5amp drives. There are four coils of course - two pairs - and it follows that you need more current capability.

It depends on the application, you might decide that series winding is advantageous, in which case a 1.77A driver would do it. I'm currently working through this very process for a system I'm designing and at the moment it's looking like serial may be the way to go - but I need to learn more first. Like Ian R say's - it's a long and steep old learning curve.

I better stay as I am for the moment (otherwise the financial director will complain) - I have the two motors using only 2 coils on the y and z - using their original drives upped to the Max at 2.5amps.

post #28?

Jim,

Congatulations on the increased speed! You might have got similar results with the Leadshine driver from Arceuro or Motion Control but I have not tried them.

You asked  "Ian or Ian - sorry are you saying from coils in parrallel I should settle at 3.5amp - not 5amp."

Ah - Here I think Ian S and I have a different view. For the Routout drives set it to 2.5 Amps (single coil). For the Gecko - set the output control resistor for 5 Amps (2.5 + 2.5) ( Edit by Ian R. This wrong see later) and note that the Gecko needs to be mounted on a heatsink above 3 Amps. It is recommended to match the driver output to the coil and not overdrive it as Ian S said.

Ian

For the Gecko - set the output control resistor for 5 Amps (2.5 + 2.5)

LOL - I'll come clean - up until a short while ago I'd have agreed with you Ian.

As I think we agree, the rated values are specified such that we don't overheat a coil.

The problem comes about because we all get too hung up on the purely electrical side of things and we forget that motors are physical beasts - like when you drop one on your foot it hurts.

The two coils that make up a single phase are not two isolated coils. They are inter-wound together forming one physical mass of copper. Each winding is not just heated by the current induced in it, it's heated by its partner as well. Because heating is a function of power (and hence why we buy 250W kettles and not 10 Amp 2.5 Ohm kettles or whatever), the total power and thus heating of any wiring combination is arrived at by summing the power of the individual windings that make up that phase and not by summing the currents.

Ian

Jim,

Excuse us for a moment we have come to a fork in the road . It is relevant to how you set up the drivers, but as long as neither the driver nor the motor are overheating, you should be OK.

Ian,
I was under the impression that the steppers we use were all four pole devices and that in an eight lead motor they were just brought out separately. Are you saying that they are wound as a pair of wires serving two poles? Can you point me to a diagram, as I have yet to dismantle a motor. What are the advantages?

Ian

You two chat amongst yourselves - I had the back off one of the motors - it fouled the lathe bed and cut the wires (lost a drive) - it needed re-wiring so -

It looked to me as though there were eight coils in my motor - wired as four pairs (one pairing the opposite).

On diagrams I have seen of stepper motors, there have always been four magnets - which mean that they must be seperately wound. If they make eight wire motors - they must be four seperate coils, but having said that - how you wire them gives several choice

Ian,

I dropped the map! Jim's motors are 8 wire 2.5A per phase, so he should set his Gecko to 2.5A max for parallel connection.

I was also confusing the number of poles with the number of phases and being missled by the simple diagrams that are used to describe stepper motors. A bipolar stepper has two phases 4 wires or 8 wires. This to enable the motor to be stepped by alternately feeding each phase with a pulse of current. It may have many poles depending on it's design.

I think I am begining to understand why the torque drops off with speed. More later.

Ian

Hi Ian EDIT: posted this before I realized you'd posted again.

just to be clear we're on the same page, we're talking 2 phase motors - yes?

So, yes - 4 poles, 2 phases (each and every magnet, electro or otherwise has two poles - yes?). A four wire motor has 2 coils - 1 per phase, an 8 wire motor has 4 coils - 2 per phase. You don't need to take a motor apart to consider what would happen if the coils of a phase were in different physical locations. Apart from anything else - how would you pack them in to the available space optimally?. Will try to find a diagram.

Meanwhile, here's some datasheets for motors where the manufacturer has been good enough to give the ratings for each wiring option so we don't have to work them out. If what I'm saying about heating is wrong - why else are the rated values as they are?

http://www.kelinginc.net/NEMA23Motor.html - some are 4 some are 8 - for our purposes check the 8s. Obviously 4 wire motors only have one wiring option.

PS The reason I suspect Jim's motors never get particularly warm is that with the voltage he's using I doubt if they're ever conducting the excess current for long enough. When Jim was running his motors in serial he was also over currenting them by around 100% and they didn't get warm then. What this shows (to me anyway) is that Jim has never been running his system optimally and until he ups the voltage he never will be. The original question concerned getting more speed - voltage not current, gives speed.

Ian

On diagrams I have seen of stepper motors, there have always been four magnets

Then you're not looking at 2 phase motors.

My apologies - four poles - two magnets.

I don't think we are going to resolve this unless the manufacturers give figures for their motors - all from the same Hymnbook.

If I can run a motor at different voltages - Routouts sheet with the driver say it is the normal to drive motors with 3 or 4 times the rated voltage, then how are we ever to know the current they will draw (at that voltage). I noted the figure given for the motors above and the current drawn by the various different wirings was in the ratio   Unipolar 4, Bipolar series 3, bipolar parrallel 6 - but in quoting the current, nowhere was an appropriate voltage quoted - except one, where the voltages were different for each method of wiring.

I think it is going to be a matter of intuitive guesswork - and a continuous check on the warmth generated to see if your setting have any adverse effect. Yes - I must admit I try and stay conservative - I am only a hobby/part time pro - I build maybe two engines a year - so I do not need to try and get every last ounce from the machine.

It would still be nice to know though - and to be able to advise others - what is the best way to wire steppers for the quickest, reliable performance,

I don't think we are going to resolve this unless the manufacturers give figures for their motors - all from the same Hymnbook.

I don't know what to say Jim. I've tried to explain the best I can HOW and WHY you calculate the rated values. I'm not sure I can improve on what I've already said.

If I can run a motor at different voltages - Routouts sheet with the driver say it is the normal to drive motors with 3 or 4 times the rated voltage,

Maybe with their drives - I don't know - but as a general rule this is a pretty meaningless statement. The torque curves for the motors I use are generally calculated at around 8 times. Gecko drives recommend a minimum of 4 and a max of 25.

then how are we ever to know the current they will draw (at that voltage).

Again I'm not sure what to say. I've tried to explain that motors "draw" the current made available to them by the driver. Voltage is effectively independant of current in a dynamic system. That is the whole point of how motors and drives work together.

I noted the figure given for the motors above and the current drawn by the various different wirings was in the ratio Unipolar 4, Bipolar series 3, bipolar parrallel 6 - but in quoting the current, nowhere was an appropriate voltage quoted - except one, where the voltages were different for each method of wiring.

Again.... These are STATIC RATED values.

I think it is going to be a matter of intuitive guesswork - and a continuous check on the warmth generated to see if your setting have any adverse effect. Yes - I must admit I try and stay conservative - I am only a hobby/part time pro - I build maybe two engines a year - so I do not need to try and get every last ounce from the machine.

It would still be nice to know though - and to be able to advise others - what is the best way to wire steppers for the quickest, reliable performance

Jim - do you remember Chioticones animated avatar where the guy beats his head on the keyboard until he's a bloody mess - well that's me now...