I need help about (stepper motor simple driver)

Discussion in 'The Projects Forum' started by tracker, Jun 1, 2011.

  1. tracker

    Thread Starter Member

    Jun 1, 2011
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    HELLO EVERYBODY
    i'm supposed to design a simple stepper motor drive circuit, i did a simple one but the problem is the limiting current resistor i don't know how to calculate it . therefor i don't have enough informations about the motor neither the current nor the voltage etc (motor:SANYO DENKI 103H-546-0741 impossible to find the datasheet!! 6 wires unipolar 1.8 Ω resistance 1.8°step)
    today i made an experiment with a 47kΩ power resistor the motor turns with coggs at 50hz when i increase the STEP frequency it vibrates and stops and the power resistor become insanely hot i don't know why is it current (low )?

    this is the schema :
    http://www.imagup.com/data/1121635644.html
    best regards
     
    Last edited: Jun 1, 2011
  2. tracker

    Thread Starter Member

    Jun 1, 2011
    41
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    This is my 1st post here so I hope I am posting in the right section.
    I know that I could just go out and buy a driver board but what’s the fun in that, plus I will not learn
     
  3. SgtWookie

    Expert

    Jul 17, 2007
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    The scale used for the schematic export was FAR too high; I can't fit it on my screen.

    Please scale it down to somewhere between 75 and 120 DPI resolution so that it doesn't require scrolling all over the place.
     
  4. tracker

    Thread Starter Member

    Jun 1, 2011
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    i'm sorry i'll put another capture. thnx
     
    Last edited: Jun 1, 2011
  5. SgtWookie

    Expert

    Jul 17, 2007
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    OK. In your schematic, you have R3 in the wrong place; it should be to the right of D4. Otherwise, you are getting the noise from the stepper motors on your supply inputs.

    You're using 24v for a supply, and your motors have 1.8 Ohms for resistance.
    With 47 Ohms in series with the motor, you would wind up with 24/(47+1.8) = ~0.5A current through the motor when it is stopped, and you would be dissipating 24v*0.5A = ~12 Watts total, most of that (~96.3%, or ~11.56 Watts) in the resistor, so you would need about a 12W * 1.6 = 20 Watt resistor minimum to keep it from getting too hot.
    Alternatively, you might use a pair of 100 Ohm 10 Watt power resistors in parallel. Be advised that they will need air circulation around them to get rid of the heat.
     
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  6. tracker

    Thread Starter Member

    Jun 1, 2011
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    thank you very much for replying
    i totally agree with you BUT don't you see that 0.5 AMPS is too low to energize the stepper motor winding.
    and if it the case i have to put another small resistance like 10 OHMS but the resistor whould dessipate (P=≈2²*24=41.36WATTS ) it's will be veeery hot doesn't it.
    i didn't understand the 1.6 from the formula u used (12W * 1.6=20W)
    thanks a lot i appreciate your help
     
  7. SgtWookie

    Expert

    Jul 17, 2007
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    You're welcome. ;)
    I don't know what your stepper motors are rated for.
    I don't even know what size they are.
    Perhaps 2A would be more appropriate to try if you're having trouble with "cogging" even at low speeds.
    Yes.
    You might investigate using a couple of automotive lamps in series to get the 24v rating.
    A pair of lamps rated for somewhere between 20W and 30W each might take care of the problem.

    The old "rule of thumb" for resistor wattage requirement is twice the actual value; so with 12w actual power dissipation, you would need resistors rated for 24W. However, you can actually get by with somewhat less than double the actual power dissipation without getting the resistors too warm. 1.6 times the actual power works out pretty well - just don't go under that, or you'll have some hot parts.
     
  8. tracker

    Thread Starter Member

    Jun 1, 2011
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    I DON'T know how to thank you. any way, you said that the lamps may help of power dessipation so i can put a 10 W lamp in the first case (12W) and it will still just 2 W that i can handle it by a simple power resistor, instead is there another solution to dessipate power but lamps.
    for the motor how i can determine current rated?
    thanks i'm sorry for those questions, but i'm so excited to know.
     
  9. SgtWookie

    Expert

    Jul 17, 2007
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    Well, automotive lamps or other small 12v incandescent lamps would be an inexpensive way to go about limiting the current. You would select the wattage based on how much current you want; the bulbs would have to be rated for the same wattage though.

    You wouldn't want to mix resistors and bulbs.

    More sophisticated stepper driver circuits use "chopper drivers" to limit current, while allowing the use of voltages higher than the stepper is rated for. The high voltage gets the current flow going quickly in the coils, and the chopper circuit limits the current by sensing the voltage across a resistor - or the use of a Hall-effect sensor and a current loop. But, I'm not sure if you are ready for that sort of thing.

    You can get an idea of chopper driver circuits by looking at the L297 and L298 driver pair datasheets, but I don't recommend their use. You will probably be confused the first couple of times you read through the datasheets.
     
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  10. tracker

    Thread Starter Member

    Jun 1, 2011
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    Well, automotive lamps or other small 12v incandescent lamps would be an inexpensive way to go about limiting the current. You would select the wattage based on how much current you want; the bulbs would have to be rated for the same wattage though.
    .............................................................................................
    do you mean if i want 2AMPS to flow through the coil windings i have to put (P=I*V=2*24=48W) lamp in series with the coils ? can you please modify my circuit to make me see the differences.
     
  11. SgtWookie

    Expert

    Jul 17, 2007
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    I'm sorry, I don't have the time.
     
  12. tracker

    Thread Starter Member

    Jun 1, 2011
    41
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    no problema :)
     
  13. tracker

    Thread Starter Member

    Jun 1, 2011
    41
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    no problema :)
     
  14. tracker

    Thread Starter Member

    Jun 1, 2011
    41
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    please help me :eek:
     
  15. SgtWookie

    Expert

    Jul 17, 2007
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    I really don't have much time right now, but I put the light bulbs in where they go, and removed R3, the 47 Ohm resistor from where it was before. See the attachment, below.

    I also moved the supply wire for the lower side of the motor over to the right side to make the schematic a bit less cluttered.

    Your transistors don't have current limiting resistors on their bases. Use values somewhere between 400 Ohms and 1k Ohms. The transistor Q5 on the left is shown as a PNP, but it should be an NPN, and the high side of the DIR switch should be connected to +5v.

    Your optoisolators/optocouplers (U4, U5) do not have current limiting resistors on the emitter side. I suggest using 360 Ohms.

    The 7805 regulator must have capacitors from it's input to ground, and output to ground;l 0.33uF (330nF) on IN, and 0.1uF (100nF) on OUT - otherwise it may oscillate unpredictably.
     
  16. tracker

    Thread Starter Member

    Jun 1, 2011
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    it's very helpful thank you very much ;)
     
  17. tracker

    Thread Starter Member

    Jun 1, 2011
    41
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    kind man i just started the modifications but when a switch the DIR to +5 the LED D5 start to blink i don't know why?
     
  18. tracker

    Thread Starter Member

    Jun 1, 2011
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  19. SgtWookie

    Expert

    Jul 17, 2007
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    If you did not add a base current limiting resistor for Q5, the transistor would act almost as a short to the output of the regulator; the base-emitter junction will act like a forward-biased diode.

    I don't see the base current limiting resistor for Q5 in the circuit.

    I don't know what you are doing with D5 and R7 being in the regulator input path; you will not get much current out of the regulator.
     
  20. tracker

    Thread Starter Member

    Jun 1, 2011
    41
    1
    D5 & R7 i just add them to emphasize the well working of the circuit
     
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