Determining ratings on stepper motor

Discussion in 'Datasheets, Manuals and Component Identification' started by musehcl411, Aug 19, 2015.

1. musehcl411

1
0
Aug 19, 2015
I have three identical stepper motors, but I can't seem to find data sheets for them. I have scoured the internet for long and come up with nothing. Since the ratings are not given on the motors, I would like to know if there is a way to find the actual ratings (Voltage, current, resistance etc) of stepper motors by myself.

2. Minder

3,214
700
Apr 24, 2015
Very difficult without the spec's what make/model are they?
You could apply a increasing DC voltage and monitor for typical max temperature for a similar sized motor.
M.

3. Colin Mitchell

1,416
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Aug 31, 2014
Start by measuring resistances and work out where the coils start and stop and maybe have a centre tap and then come back to us.

4. Hellmut1956

63
4
Aug 11, 2014
Here I try to give some initial hints:

This picture of a very simple 2-Phase-Stepper that has 4 cables coming out explains graphically what Colin Mitchel suggested. Each of the phases "A" and "B" consists of two coils connected in series. Measuring the resistance over each phase helps first to identify which 4 cables belong together and which not. Those of different phases will show an infinite resistance-

This a bit more complex graphic displays to which of those styles of steppers your motor belongs and if they can be operated "unipolar or bipolar" If you have i.e. a stepper with 6 cables coming out then you will find that over 2 of those cables there is a certain resistance value and that if you measure between a cable belonging to one of the coil circuits an the center point the resistance value only shows half the resistance value. This way you should be able to find out what kind of motor you have!

Next comes the question about what is the nominal "current" the stepper motor has. With no data about the stepper motors comes the question if you know from where it comes. Often in inexpensive printers you still find unipolar motors. I have taken the decision not to bother about them. This was just my personal decisions and does not say anything about how adequate a unipolar motor is. It just says that I have decided for me to only deal with bipolar stepper motors.

Kind of the only way to find what current is adequate for your 3 stepper motors is to start with applying a low tension to the 2 phases. This would put the stepper motor in a certain position. Then, while you keep an eye on the stepper motors temperature, apply a certain tension and let it applied for an adequate amount of time. If the current that flows trough the coils of a phase does not heat the motor, then the motor can handle that current. You keep increasing the applied tension in steps repeating the exercise until you find out when the motor starts to heat up. You should know that i have met experts in stepper motors that told me that those are the kind of motors where you end up being burned by its high temperature! This is true when, as it was in the past and still is in many case typical for a stepper motor that independently of the load is always fed with the full current amount. This tells you that a stepper motor under such operating modes, not unusual in the past and not damaging it, heat up quiet a lot!

Often your choices of tensions you can apply to the stepper motor will limit your choices of operating the stepper motors! So 6 VDC should not damage any stepper motor. 9 VDC probably either. 12 VDC could and could be not. 24 VDC would probably be a lees frequent tension you have available.

5. hevans1944Hop - AC8NS

4,691
2,196
Jun 21, 2012
Most modern stepper motors are driven with pulse-width modulated constant-current drivers to provide high torque without excessive heating. There are integrated circuits available for just this purpose. Measuring the heat increase with steady DC applied to the windings will provide a very conservative estimate of what the motor is capable of providing, but it is a good place to start if you know nothing about the motor. Another clue is the case dimensions. Motors of similar size will have similar power ratings, although specific operating voltages and currents will differ. The allowable temperature rise depends on motor construction: you must avoid damaging the wire insulation and cooking the bearings too much. Many stepper motors operate at temperatures too high to comfortably touch their cases, but if that bothers you a fan will help lower the temperature.

Can you post a picture of your "three identical stepper motors" perhaps along side a ruler to help estimate their dimension? How many wires does each motor have? What is the wire gauge? Measure the resistance between all possible wire pairs and post the results, preferably with some means to identify the wires.

6. Hellmut1956

63
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Aug 11, 2014
Dear hevans1944, you should have a look at the site of "trinamic.com. Their controllers take benefit of a deep understanding of the internals of the stepper motors and implement functions that increase the efficiency of stepper motors usage, allow to use lower performance stepper motors by being able to apply for short period of time higher currents to catch load peaks. Have a look over technologies like "Stallguard", "Microplyer", "Spreadcycle", "stealthChop" to name a few. i learned a lot by studying their documentation and making my experiments with their "stepRocker evaluation board". Also the new version of their IDE offers extensive tools to find the most appropriate parameter settings for specific motors and applications. I see today more a trend towards implementing the controller in software taking Texas Instruments as an example. But I also see that the general technical public has relatively little knowledge if the intrinsics of a stepper motor. Just to relate to your correct statement that today the stepper motors are fed with a constant current supply using PWMs I want to point to a Trinamic technology implemented in their controllers were the current flow is managed to follow the actual load a stepper motor has to take. Just a short explanation. A stepper motor with no load will position its rotor in a certain position according to the step pattern applied. Does a load be put on the stepper motor the rotor will turn a bit proportional to the load torque. This can be sensed by the electronics in the controller, using no extra sensors, monitoring the electromotive force. This way with no load or low load torque on the stepper motor the current can be reduced up to 75% as Trinamic claims and load peaks can be managed by exceeding for a short time the current limit and so generating extra torque to handle that load peak for a short time. Another nice use of this same technology is that it makes possible to detect when something is blocking the move of a stepper motor driven device. This for me as a naval modeler is very useful as i do not want the stepper motor with its huge torque capabilities to damage my model if something accidentally blocks a certain movement. A nice side effect of this is a dramatic reduction of the energy consumption of such a stepper motor driven application. My models are battery driven, so that energy efficient allows to reduce the capacity of the batteries used. It is even specially of use to me in my application as stepper motors have their highest torque when holding a position and as consequence highest energy consumption. I am considering not to use an electrical brake, as this technology makes possible to reduce the power consumption!

7. hevans1944Hop - AC8NS

4,691
2,196
Jun 21, 2012
@Hellmut1956 Good old German engineering shines again! I haven't had time to pursue this in depth yet, but Trinamic appears to offer excellent cost-effective solutions to stepper motor drivers and positioners, and they have authorized USA distributors. Thanks for the link.

8. Hellmut1956

63
4
Aug 11, 2014
@hevans1944 Share with us when you investigate the topics at Trinamic. I had written that I did chose the "chat forum because it should neither be a "tutorial" kind of thing, I am not even close enough to be really knowledgeable in the field of stepper motors. As I wrote I see in the market s strong trend to implement motor control systems using microcontroller with required dedicated hardware, but mainly using software. I think it could be interesting if in a chat like this one we can not only get deeper into the field of bipolar stepper motors with special focus on hybrid stepper motors. I might find the energy to present the different kind of bipolar stepper motors and in what they differ and what those difference mean for a choosing a stepper motor for am application. But also I want to learn more about the software based approaches. My objectives in my naval model building already and intentionally are being slowed down due to the interest I do develop in fields I am getting in touch with and skills I need to refresh and extend required for those topics. Right now my focus is on refreshing and extending my decades old fluency in mathematics that as I see has strongly eroded in this decades.