You haven't specified how you are driving this motor, it sounds like you aren't sending pulses in the correct sequence.
Look at **broken link removed** in this NXP document for an example.
Hi am using unipolar stepper motor by using 4 NMOS chip each source connected to ground and each drain connected to corresponding coil and gate from Microcontroller .and common connected to 12v .
i dont know the rated current /voltage of this motor , but i measured the coil resistance [common to A pole 2E and A to -A is 4E like in B side also same ] . when i connected to 12v which heating more and not rotaing but vibrating with big sound , and wire got burn , please help me.
Hi am using unipolar stepper motor by using 4 NMOS chip each source connected to ground and each drain connected to corresponding coil and gate from Microcontroller .and common connected to 12v .
i dont know the rated current /voltage of this motor , but i measured the coil resistance [common to A pole 2E and A to -A is 4E like in B side also same ] . when i connected to 12v which heating more and not rotaing but vibrating with big sound , and wire got burn , please help me.
yes you are correct , Can you provide any constent current source circuit for this application ? by using MOSFET and no need any inbuild driver chip .If I get what you describe correctly then you have a five wire (or is it a six wite with separate common wires?) unipolar motor with 4 Ohm resistance in each coil (2 Ohm for each side of the coil) and you have it connected like the following image
View attachment 127790
The problem is that the resistance of each half coil is 2 Ohm so with 12v supply it leads to 6A current which is way too much.
If you want to use them with a DC supply without current limiting circuit then you have to decrease the supply voltage to about 1.5v or even less but this in not the way they are intended to be used. Low resistance steppers are intended for constant current operation rather than constant voltage, the low resistance of the coil in conjunction with a current limited high voltage can achieve higher torque at higher speeds.
The circuit is ok but you need to put short pulses to the four mosfets. The width of the pulses will determine the current and should not be too long (the mosfet should be off before the current reaches 6A DC limit). None of them should be on for long duration and that is the cause of the motor burning out in your earlier experiments.
The sequence of pulses applied to P0.0, P0.1, P0.2, P0.3 is critical. First try and convince yourself with the regular full stepping mode and get it running. You need to turn on and off each pin at the right time through your software.
In the preliminary experiment, use a low power 12V supply so that you do not burn out your motors by mistake. Once you have debugged the circuit, you can use a full power battery (as you have now done).
That's the usual way to operate stepper motor with constant current. Unipolar motors like yours are more often operated with constant voltage, yours is obviously designed for a lower voltage than 12V.so i think i need keep on read current through shunt res ? and need to control through PWM right?
so i think i need keep on read current through shunt res ? and need to contrlo through PWM right?
Operating a step motor with constant voltage gives the lowest possible speed. Constant current achieves a considerable faster current settling and respective higher step rate.
Next point for faster step motor operation is using acceleration and deceleration ramps.
If each pulse is lasting for 5 ms, then you will get have 200 pulses per sec. That makes about 100 steps (or, is that 50) per sec. Each step is 1.8deg (please verify!) and that makes 90deg per sec. That is about 15 rpm. Something is wrong (I do not know)- please check.
As per the diagram each pulse appears to be about 10 ms. In this time, the current in the coils have come to the steady value. You can certainly increase the pulse frequency and increase the pulse duration. It should rotate faster. If it does not, the voltage need to be increased to the full 12V as per the rating.
For steady acceleration without missing a step: start with a low pulse frequency and low pulse width. Increase the pulse frequency and the the width but make sure that the pulse sequence diagram is correct (no pulse cross over).
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