1. Welcome to our site! Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.
    Dismiss Notice

Circuit Simulation and Modeling a Motor using a Resistor

Discussion in 'Circuit Simulation & PCB Design' started by Vsh3r, Jul 7, 2010.

  1. Vsh3r

    Vsh3r New Member

    Joined:
    Jun 23, 2010
    Messages:
    12
    Likes:
    0
    Hi,

    I have a circuit that I'm simulating and would like to substitute a resistor for a motor.

    I don't know much about the motor other then that it runs "kinda fast" when a 5 volt battery is connected to it... I'm not sure how much current is going through the motor and I don't have a good way to test it...

    Here is the circuit that I'm using to simulate my design now...

    (see attached schematic & simulation)

    the current through R3 is about 100 mA... is that kinda typical for a motor?

    Thanks,

    V$h3r
     

    Attached Files:

  2. ericgibbs

    ericgibbs Well-Known Member Most Helpful Member

    Joined:
    Jan 4, 2007
    Messages:
    21,242
    Likes:
    645
    Location:
    Ex Yorks' Hants UK
    hi,
    There no such motor as a typical motor.
    The current thru the motor depends upon the load on the motor shaft.
    When the motor is just starting or stalled it can draw up to ten times it normal operating current.

    For simulation you can use a resistor or an inductor and resistor in series, also you require a diode across the motor in order to clamp the back emf generated by the motor
     
    Last edited: Jul 8, 2010
  3. Vsh3r

    Vsh3r New Member

    Joined:
    Jun 23, 2010
    Messages:
    12
    Likes:
    0
    Thanks Eric,

    Do you have any ideas what resistor and inductor values I would use?

    Thanks,
    V$h3r
     
  4. dave

    Dave New Member

    Joined:
    Jan 12, 1997
    Messages:
    -
    Likes:
    0


     
  5. ericgibbs

    ericgibbs Well-Known Member Most Helpful Member

    Joined:
    Jan 4, 2007
    Messages:
    21,242
    Likes:
    645
    Location:
    Ex Yorks' Hants UK

    hi,
    Its important that you get the motor specification.
    If thats not possible measure the motors resistance, that will only be a rough guide.
     
  6. MrAl

    MrAl Well-Known Member Most Helpful Member

    Joined:
    Sep 7, 2008
    Messages:
    11,049
    Likes:
    961
    Location:
    NJ

    Hi there,


    The equation for a motor includes resistance and inductance as well as rotor inertia and friction, however as Eric pointed out already if you dont know the motor spec's you cant simulate it very well.
    If your application can get away with just a constant voltage however then you can get away with measuring the current and voltage when the motor has a load and when the motor does not have a load and go from there. Without any data like this however it will be impossible to get it right.
     
  7. colin55

    colin55 Well-Known Member

    Joined:
    Feb 14, 2009
    Messages:
    3,534
    Likes:
    82
    Location:
    Melbourne Australia
    You cannot simulate a motor or a globe. Both take a very high current at the beginning and the driving device plus the power supply must be able to deliver this current.
     
  8. Mikebits

    Mikebits Well-Known Member

    Joined:
    May 24, 2008
    Messages:
    6,217
    Likes:
    175
    Location:
    San Diego, Ca
  9. colin55

    colin55 Well-Known Member

    Joined:
    Feb 14, 2009
    Messages:
    3,534
    Likes:
    82
    Location:
    Melbourne Australia
    Anyone who tries to immitate a globe or a motor is a fool.
    You have absolutley no idea how the item will behave in real life.
    I have had problems with both motors and globes not turning on and would not waste my time trying doing anything other than getting the actual device to work.
     
  10. ericgibbs

    ericgibbs Well-Known Member Most Helpful Member

    Joined:
    Jan 4, 2007
    Messages:
    21,242
    Likes:
    645
    Location:
    Ex Yorks' Hants UK
    Motors and lamps can and are simulated during the design phase of these components.
    Anyone who says they cannot be simulated is the fool.

    Perhaps it would be more correct so say they dont know how to use simulations to help in the design process.

    EDIT:
    Sim example added.
     

    Attached Files:

    Last edited: Jul 10, 2010
  11. MrAl

    MrAl Well-Known Member Most Helpful Member

    Joined:
    Sep 7, 2008
    Messages:
    11,049
    Likes:
    961
    Location:
    NJ
    Hello,


    Im sorry but i have to second what Eric says. I have used motor models in the past to analyze and design analog speed control systems and without that i would not be able to tune the components correctly. There may be limits of course, as with any theory applied in practice. The trick is to know if and when those limits are exceeded.
     
  12. Mikebits

    Mikebits Well-Known Member

    Joined:
    May 24, 2008
    Messages:
    6,217
    Likes:
    175
    Location:
    San Diego, Ca
    Thanks for the model Eric, this fool will use it.
     
  13. ericgibbs

    ericgibbs Well-Known Member Most Helpful Member

    Joined:
    Jan 4, 2007
    Messages:
    21,242
    Likes:
    645
    Location:
    Ex Yorks' Hants UK
    hi Mike,
    I should point out that the model is not my creation, its downloaded from the Yahoo LTspice users group.
     
  14. Mikebits

    Mikebits Well-Known Member

    Joined:
    May 24, 2008
    Messages:
    6,217
    Likes:
    175
    Location:
    San Diego, Ca
    At any rate, it is a nice contribution and thanks for posting it. I am a happier fool now :)
     
  15. MrAl

    MrAl Well-Known Member Most Helpful Member

    Joined:
    Sep 7, 2008
    Messages:
    11,049
    Likes:
    961
    Location:
    NJ
    Hi again,


    Yes thanks Eric, too bad they got rid of that 'thank you' button :)
     

Share This Page