control speed of motor (help)

Discussion in 'General Electronics Chat' started by fadelo, Apr 12, 2011.

  1. fadelo

    Thread Starter New Member

    Apr 12, 2011
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    hi there

    I was thinking of what is the simple way to control the speed of a motor

    I'm planing to build a circuit consisting of tow motors..

    while surffing the net I found topics about the motor controller and it's the

    first time to hear about it!

    mmm what about using a variable resistor??

    regards
     
    Last edited by a moderator: Apr 12, 2011
  2. Wendy

    Moderator

    Mar 24, 2008
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  3. fadelo

    Thread Starter New Member

    Apr 12, 2011
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    thnx for reply..
    I will try to look for it
    regards
     
  4. fadelo

    Thread Starter New Member

    Apr 12, 2011
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    mmmm

    ok I have a 12v dc fan 0.19 A .. it operates at 5 v mostly

    how could I possiblly increase the votage taken by it in order to i
    ncrease the speed?

    what if I connect a capacitor ? would it be useful?

    Im using 12v battery 3 A :D

    Regards
     
  5. jpanhalt

    AAC Fanatic!

    Jan 18, 2008
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    Does you fan happen to be from a computer or other electronic device?

    John
     
  6. fadelo

    Thread Starter New Member

    Apr 12, 2011
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    no I bought it from an electronics shop who sell most what student need for making projects...

    my idea is to decrese the speed of a fan by conncting different values in series with a rotary switch so every position has a vaoltage drop which make the fan slower

    and it work pretty good :D

    but what about if I wanted to increase the speed even faster? what I could do??

    what is the simple method ever?

    I connect a 300v 240 micro farad capacitor :D but nothing changed

    thnx
     
  7. fadelo

    Thread Starter New Member

    Apr 12, 2011
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    any thought please :)
     
  8. jpanhalt

    AAC Fanatic!

    Jan 18, 2008
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    Is the fan a brushed or brushless design?

    John
     
  9. fadelo

    Thread Starter New Member

    Apr 12, 2011
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    I couldnt tell really :confused: but I did connect a 224 capacitor in parallel with the fan and from the sound it seems faster and it took half the time to reach maximum speed (edit the power factor I guess)

    thnx for reply sir

    ok here is another issue
    [​IMG]

    this is my circuit it's quite simple the idea is to reduce the speed of the fan by resistors!! it's working good.. what I was trying to do is to put
    LEDs between each position of the rotary switch so when I start at the fan with low speed a Yellow LED turn on .. when I change the rotary switch to the second position a red Led is turn on it doesn't matter if they where all on when I change to the last position ??
    I'm still trying

    any help :D
     
  10. hgmjr

    Moderator

    Jan 28, 2005
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    There is a problem that arises when attempting to use a resistor in series with a motor to control its speed. That problem is the potentially severe loss of torque that results. As you apply a load to a motor, it draws more current from its power source. With a resistor in series with the motor, this increase in current results in a larger voltage drop across the resistor as the load on the motor increases. With more voltage dropped across the resistor there is less voltage available to power the motor. The motor is then more prone to stall due to voltage starvation.

    It is for this reason that most of the members will recommend that you use PWM to control the speed of your motor. It may mean a bit more complexity to the control circuitry but the result is a motor that provides the maximum torque for the speed change range.

    I notice that you have used resistors to control the speed of a fan. This is permissible as you do not usually make heavy torque demands on a fan unless you are trying to achieve negative or positive levels of pressure. However, the use of PWM on the fan will give you the best fan performance across the range of operating speeds.

    hgmjr
     
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  11. fadelo

    Thread Starter New Member

    Apr 12, 2011
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    thnx a million.. now I can understand
    what's wrong with using the resistors
    I will give it a shot and try to design the
    PWM
    thnx again
     
  12. jpanhalt

    AAC Fanatic!

    Jan 18, 2008
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    I hope you are aware that PWM with a standard DC brushed motor will only decrease speed. It will not allow you to increase speed greater than its speed when directly connected to your supply.

    If you still want to increase speed, you need more voltage or a different type of motor. More voltage can be provided by a boost converter, but that is more complicated.

    John
     
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  13. strantor

    AAC Fanatic!

    Oct 3, 2010
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    Another idea, if you are happy with having the 3 speed selection would be to put 3 voltage regulators.
     
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  14. fadelo

    Thread Starter New Member

    Apr 12, 2011
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    what I was trying to do is to put
    LEDs between each position of the rotary switch so when I start at the fan with position one,, a Yellow LED turn on .. when I change the rotary switch to the second position a red Led is turn on it doesn't matter if they where all on when I change to the last position ??
    I'm still trying any help?
     
  15. hobbyist

    Distinguished Member

    Aug 10, 2008
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    Hi,

    will something like this work for you?

    led fan.jpg
     
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