stepper motor problems

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mikeb
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stepper motor problems

Post by mikeb » Tue Jul 29, 2003 6:57 pm

i have a unipolar stepper motor thats rated 5 volts 3.6 ohms, step angle 7.5 degrees 1.38 amps/phase, my questions is whether this is the maximum allow current that the coils can handle per step angle or is this the current that is required to make the motor rotate.the motor is from a surplus source but has never been used.
im trying to figure out the wiring to connect this motor, the motor has 6 wires an i have successfully figured out the 2 common wires an now im trying to figure out which is for the different coils. i have information as far as how to connect the motor to a volt souce by connecting both or either common wire then grounding 1 of the remaining four wires assuming that its connected to coil 4 then connecting each of the 3 remaining wires in turn an watchiung the results of the motor, whether its direction is clockwise indicating coil 3 or counter clock wise indicating coil 1, an no response from coil 2. after connecting the coils in this manner i get a response from the motor but it wont turn but the response seem to indicate the coils are not energized enough to turn the motor. but 2 wires respond by making a clicking noise while one does not so it appears that the wires are responding as the diagram has said. my question is whether the rating of the motor is its maximum rating, or is it the requiredcurrent an voltage to turn the motor. i connected the motor to a 12 volt source at 1.21 amps still with no respond other then it clicks like it wants to energize but it doesnt. if any one can help me with this id be most appreciative.
thanks in advance

grant fair
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Re: stepper motor problems

Post by grant fair » Tue Jul 29, 2003 9:17 pm

The rated current is the maximum current per phase that the stepper can handle without overheating and eventually destroying itself. Steppers can operate (with reduced torque) at reduced current levels. <p>It is possible to use a power resistor in series with a higher than rated voltage and thereby increase stepper torque. The important thing is to use Ohm's law to ensure that the resistor is the right value for the voltage used to provide the specified current. But you would not need to do this to test the motor.<p>I hope this helps; I am not sure what to make of the symptoms you describe but perhaps someone else on the list will be able to help you out.<p>Grant
Grant

Chris Foley
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Re: stepper motor problems

Post by Chris Foley » Wed Jul 30, 2003 9:32 am

You might want to look at one of the better stepper motor tutorials available on the web...<p>http://www.cs.uiowa.edu/~jones/step/<p>This will answer most of your questions.

Will
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Re: stepper motor problems

Post by Will » Wed Jul 30, 2003 11:45 am

Grant,
Satisfy my curiosity - Why would including a resistor increase the stepper torque ?
BB

grant fair
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Re: stepper motor problems

Post by grant fair » Wed Jul 30, 2003 12:13 pm

Will -<p>It takes time after the power to a stepper coil is switched on to achieve a magnetic field in the coil. The time to achieve this is reduced with a higher voltage which is allowable with the current limiting resistor. It has to do with the inductance of the coil.<p>I'm not entirely clear on the reasons for this, so someone else may be able to add or clarify it. But I do know that I have been running steppers at voltages up to 30v from a current limiting supply I made (the current limiting is instead of the resistor) and subjectively, the torque is increased noticeably (the old grab the shaft and try to keep it from turning "measurement").<p>Grant
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grant fair
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Re: stepper motor problems

Post by grant fair » Wed Jul 30, 2003 12:30 pm

Will - the Jones site above explains it in more detail.<p>Grant
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mikeb
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Re: stepper motor problems

Post by mikeb » Wed Jul 30, 2003 7:47 pm

HELLO GRANT ,WILL,CHRIS I WAS JUST STOPPING BY TO THANK ALL U GUYS FOR THE INFO U GAVE ME ON STEPPERS, THE JONES SITE WAS REALLY HELPFUL AS WELL. THE PROBLEM TURNED OUT TOP BE THAT I NEEDED TO APPLY POWER TO BOTH COMMON LEADS AT THE SAME TIME IN ORDER FOR THER MOTOR TO ROTATE. THE ARTCLE I WAS USING SAID ONLY ONE COMMON LEAD NEED TO BE CONNECTED ONCE AGAIN THANKS A BUNCH

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