Merry Christmas~!
I bought a stepper motor yesterday and I am trying to control this motor using arduino according to this great tutorial. http://electronics-diy.com/electronics/stepper_motors.php
I've successfully controlled smaller stepper motor before(with two pieces of ULN2003) which has the speficiation like this.
*Voltage *Current *Holding torque *resistance *Inductance
4V 0.95A 1.6kgf 4.2ohm 2.5mh
Now, I used four pieces of ULN2003 to keep up with the current(A) rating of my bigger stepper motor draws.
But, i am having trouble getting my big stepper motor to rotate.
Its specification is like this.
*Voltage *Current *Holding torque *resistance *Inductance
24V 2A 16kgf 2.5ohm 4.9mh
I used power supply to power this stepper motor.
My power supply is able to supply up to 350watt(DC ouput 24V, Current 14.6A).
When I connect ULN2003's pin 8 and pin 9 to my power supply, all four ULN2003 chips are fried with smoke....
I parallelled all four ULN2003 just like the way I connected them when I used two.
Could you please point me out what have I done wrong?
while your motor may need 2 amps, i think it was actually drawing more. if i remember right, I (current) = V / R, so 24/2.5 = 9.6 amps, probably alot more than those poor darlingtons could handle. you might want to look into current limiting resistors, although they may get hot, so perhaps you might try lowering your supply voltage.
thanks for posting your answer.
oh.. then, may I ask how many resistance do I need to put before darlington pin 9?
I need to have a very stable condition out of this parellel darlington chip circuit as I will often on and off the motor using arduino.
I used AC/DC adapter which converts AC to DC(output 1.5V~14V) before trying to power the motor with my power supply.
14V was too weak for my motor to turn. I only felt some vibration from it.
Could you also tell me what should I do to stablize the heat in case i use resistor?
you would need 12 ohms to limit the current to 2 amps, but the resistors would probably dissipate at least (edit: 50 watts), a large amount that would take huge heatsinks. i should've run the numbers before i suggested it. another thing to look at would be PWM current limiting by running the motor at 20% duty cycle. i've never tried pwm current limiting but i've seen articles on it before, so im sure google has some answers.
OK, then I will try it again with 12ohm resistor on ULN2003 pin 9.
And this time, I will use this circuit to power my motor. http://www.flickr.com/photos/23525729@N06/3137449890/
Ultimately, I will power 15 stepper motors. To power them all, do I need to use an inverter for efficiency?
I heard an analog type power circuit I posted above is low in efficiency in case I power such large number of stepper motors.
There is absolutely no way on earth that you can switch 2A with a ULN2003. Even if the data sheet says you can parallel them up you can't do it to that extent.
Look at the collector emitter saturation voltage, it is 1.6V. So if you are switching 2A that gives a power dissipation of 3.2W.
The thermal resistivity of the package is 70 degrees C per Watt. The maximum junction temperature is 150C.
So if you are dissipating 3.2W the junction temperature will be 3.2 * 70 = 224 C above the case temperature. Therefore in order for the junction temperature to be 150C the case would have to be at -174C.
I don't think you are cooling them at that rate.
Forget that chip and use a FET. Also look into constant current FET drive configuration to linit the current.
thanks MikMo and Grumpy_Mike.
Yes...it is really inefficient to use such motor with darlington chips.
The reason why I am trying to pursue this tutorial(http://electronics-diy.com/electronics/stepper_motors.php) is because of its configuration simplicity but, the motor draws too much current.
so, i better either change the motor or forget using darlington chips.
Few minutes ago, I just supplied 14VDC to darlington chip's pin 9 with 10kohm(1/2W 5%). I used 10kohm for experiment because i don't have 12ohm resistor at the moment.
This motor actually rotated smoothly for about 10 seconds and then it just stopped its rotation and buzzed like before. I was so happy to see its rotating action although it was just a short time.
Anyway, i have no idea why this motor rotated like the way i want.
Do you know what made this motor to turn?
I am amazed that it turned drawing only 1.4mA so no supprise if it stopped because the torque would be very small and most likely under the stalling torque under no load conditions.
Two tings to try:
Help it turn by twisting the shaft between you fingers when it buzzes.
Increase the current by reducing the resistor, even 1K would give you 10 times the current and it would probably rotate at that.
Luckly, I have 1khom(CFR 1/8W) resistor. So I used this resistor on ULN2003 pin9. But I failed to rotate the motor.
And also, i just supplied 12V power to ULN pin 9 without any resistor, I could only feel buzz...
Even if I tried to rotate the shaft of the motor by using vise plier, the motor would not rotate.
Dose my motor connection status look ok?
I think part of your problem is that you're trying to drive a large current through solderless breadboards. The push-in connections on those breadboards are not good enough for large currents. You need to make up a motor driver board with solder, and probably much bigger driver chips than the ULN2003, too. Putting them in parallel is unlikely to work.