stepper motor voltage and current

Dear all,

I have problem with my stepper motor. It was working fine previously. But under exactly the same condition, now its moving pattern becomes a repetition of 4 steps, i.e. after turning from step 1 to 4, it goes back to the step 1 position.

I'm not sure if it is the problem with the supplied current and voltage. The motor I'm using is RS_441_0401_16HS_012, the datasheet (attached) specifies 36V supply voltage, 0.6amp/phase and 6.6 ohm/phase, why it doesn't obey ohm's law? For my previous experiments, I tried to supply 12V and it worked fine. But even if I supply more than 12V now, it doesn't work properly again.

Some additional info:
1. I'm sending a sequence of signals: 1010, 0110, 0101, 1001 from BasicX to L298N
2. the circuit is similar to that I've attached.
3. when driving at a high voltage, say 20V, the power source jumps from 'constant voltage' to 'constant current' mode at the end of each 4-step repetition.

Thanks a lot in advance!

The motor will obey Ohm's law so at 0.6A and 6.6R it will be a 3.96V motor. The performance curves at higher voltages are for a constant current drive. These initially apply the high voltage until the current reaches the target value and then switch off until it falls a little and then on again, etc.

Your circuit has nothing connected to the sense resistors to control the current so you have constant voltage drive. In which case, even with a 12V supply you will be overdriving the motor.

The maximum voltage on the sense pin should be limited to 2.3V, so if you have no current control loop then you should connect the sense pins to ground. If you applied more than 15V then the current would be enough to drop more than 2.3V across 1R so you may hve damaged the chip.

Also you don't have any clamping diodes so that also may have damaged the chip.

It looks like one of the transistors has gone short circuit so the last phase pattern short circuits the supply.

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[www.hydraraptor.blogspot.com]

Thanks a lot nophead, what you suggested is very reasonable. I will try a new L298N.

In my circuit, I grounded the sense pin, but I didn't put the diodes, I guess the later might cause the damage.

I don't quite understand the difference between constant current and constant voltage driving. Which one would be more advantageous? If possible, could you show me a sample schematics of using constant current to drive stepper motor?

Constant voltage is the cheapest and simplest, but torque falls off with speed because of the time taken for current to build up in the inductance of the coils.

Constant current gives better torque at high speed by using a higher voltage which causes the current to build up quicker.

Here is an example of a constant current chopper circuit using the L298 with an L297: [reprap.org]

These chips are very out of date now, so the modern way to do it is with a single chip that does not need external diodes. [reprap.org]

A halfway house between CV and CC is to use resistors in series with the coils. It wastes a lot of power but gives better performance than CV, not quite as good as CC.

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[www.hydraraptor.blogspot.com]

Master Nophead, share with us your wisdom and guide us to the path of truth and enlightenment. *bows*

It seems this is a reoccurring question. It would be helpful if there was a page on the wiki that explained how these things work and the differences between the different drivers. I would do it myself, but I'm still not 100% sure how all of the math works. I thought I understood it after the thread I started on the subject, but once I tried to apply it to a different motor it became all fuzzy again.

Jeremy

OK, Forrest has made a similar request so I will have to do a post but I am a bit busy at the moment.

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[www.hydraraptor.blogspot.com]

Understand and thank you.

Hi nophead, thanks a lot for the previous help. I added a L297 and followed the V1.2 schematics to make my own circuit. However, I have a couple of questions which I want to clarify before I make the first try:

1. Some other sources specified to use non-inductive resistor for R1 & R2, is it necessary?

2. If I were to use normal 1N4001 instead of fast 2A diodes, what will be the consequences? (The fast diodes I got is too big to be mounted on the breadboard.)

3. When I refer to the schematics provided by L298N datasheet(attached), I found that they simply connect sens1&sens2 to sen_A&sen_B without using C3&C4,R4&R5. What will be the consequences then?

4. If only the direction and speed of the stepper motor were my concern. Is it correct if I just connect 'clock' and 'CW/CCW' to my microprocessor; connect 'half/full', 'reset' & 'enable' to 5V and leave 'Vref', 'control', 'sycn' & 'home' floating?

5. Could you explain to me the function of 'reset', 'Vref', 'control', 'sycn' & 'home' when time permits?

6. Since my motor (RS_441_0401_16HS_012) has specified 36V, but also 6.6Ohm and 0.6A per phase. The L298N datasheet here also suggested 36V. So after I add the L297, what voltage should I input for L298N?

Thanks again!

Edited 1 time(s). Last edit at 10/13/2009 12:15AM by hawkoli1987.

1. Yes they should be non inductive. Wire wound resistors will have some inductance which will give less accurate current measurement.

2. Some power will be wasted and the chip and diodes may get hotter than they would with fast diodes.

3. They are filters to remove high frequency noise. Ringing on the current waveform may cause instability in the chopping. Especially if your sense resistors are inductive.

4. You can leave outputs floating but inputs should always be connected to something.

If you tie reset high then the motor may start on a random phase which doesn't matter in most cases, only if you want to keep track of the phase in software.

Control should be tied high or low depending on if you want fast or slow decay. Slow decay is more efficient but not as good at high speeds. Fast decay is probably what you want, which would be tied high. You could put it on a jumper and experiment or drive it from your micro such that is is slow decay when stationary or moving slowly and fast decay when moving fast. [hydraraptor.blogspot.com]

You may want the enable under s/w control to keep the motor cool when stationary but otherwise tie high.

5. Vref should be connected to a potentiometer to set the current.

Home is an output that indicates phase 0. Only needed if you want your s/w to keep track of the motor phase. You can use that to increase the resolution of your limit switches: [hydraraptor.blogspot.com]

Sync is to allow several choppers to all switch together. That stops the noise caused by one drive switching from affecting the others. Most people seem to get away without it.

6. You should run the L298 from 36V and pick sense resistors and vRef to set the current to 0.6A.

If you play by all the rules with electronics then it will always work. If you don't then it a may or may not work, so you might get away with some of these things, but be prepared for problems if you do.

Edited 1 time(s). Last edit at 10/13/2009 02:26PM by nophead.

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[www.hydraraptor.blogspot.com]

Thanks again nophead, one more question: if I were to use driver V1.2 to drive uni-polar motor of 6 wires, what will be the modification?

You just use half of each coil. I.e. connect the centre tap and one end to the two bipolar connections and leave the other wire floating.

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[www.hydraraptor.blogspot.com]

That's a brilliant idea to me. Thanks!

Yet I still three more question:

1. As I understood, high 'control' is good for higher speed while low it is good for slower speed. If that's the case, what is the speed considered as high? If in my case I need it to be low, but the board has by default set it to high. Is it possible for me to change it?

2. My motor rating is 36V, but I it works well at 10V. Does it necessary to supply a high voltage as 36V? If I had to supply 36V, would it still be possible for me to supply the board with a single voltage?

3. I saw others driving unipolar stepper with UCN5804, which requires much less circuitry than L297/L298N combo. Therefore, is there any advantage of using this combo for driving unipolar stepper?

1. With it high the motor will still work at low speed but may use a bit more power. To make it low you would have to cut a track or lift the leg of the chip.

2. The motor is not really rated at 36V, it is a 3.96V motor as ohms law states V=IR. The data sheet simply shows the performance when running it from a 36V chopper drive. Chopper drives can be any voltage within reason. The only limit as far as the motor would be concerned is the insulation breakdown voltage on the coils, which would be much higher than 36V.

The higher voltage just gives more torque at high speed.

The V1.2 board is designed for 12V. You may need to change the voltage rating of C2 and make R2 bigger if you increase it. You also need to provide it with 5V.

3. It is cheaper to drive a unipolar motor with a unipolar driver, that is why unipolar motors are made. Bipolar motors need more transistors to drive them but they give more 1.4 times more torque for the same size of motor.

You can connect the bipolar driver to the full coil of the unipolar motor. You have to drop the current by a factor of 1.4 but you get 1.4 times more torque. The down side is that torque falls of 4 times faster with speed.

If you are not interested in high speed running then a simple constant voltage drive will be the cheapest solution.

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[www.hydraraptor.blogspot.com]

Hey nophead -

I have some geckodrive stepper drivers that use current-limit resistors. Are you basically saying that I can run my motors at any voltage, as long as I set the current limit resistor properly? In particular I have some small nema 17's (0.84 amps, 9.3mH) and larger nema 23's (3.5 amps, 3mH) that I would like to run off a 48V power supply.

Thanks
Ivan

Yes as long as the current is limited you can use any voltage up the the limit of the winding insulation.

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[www.hydraraptor.blogspot.com]

thank you very much for the quick reply!

A Stepper motor converts electrical activity into detached motions or steps. The motor consists of assorted electrical windings captivated in pairs (phases) about the alien anchored allocation of the motor (stator).

The close allocation (rotor) consists of adamant or alluring disks army on a shaft and abeyant on bearings. The rotor has bulging teeth which adjust with the alluring fields of the windings. When the coils are activated in arrangement by absolute current, the teeth chase the arrangement and circle a detached ambit all-important to re-align with the alluring field.

A Stepper centrifugal convinces electrical activity into separate movements or steps.Well as extended as the current is restricted you can purpose any voltage up to the limit of the serpentine insulation.