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MOTOR SPEED CONTROL

Discussion in 'Sensors and Actuators' started by arg733, Jul 21, 2012.

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  1. arg733

    arg733

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    Dec 14, 2010
    MOTOR SPEED CONTROL (DC)

    Hi.
    I need a device that can count RPMs from a hall sensor on a motor and keep the RPMs at 5000 ± 200 with highly variable loads.I tried lowering and increasing the speed of the motor by increasing hertz , what I need now is a circuit that will do that automatically when the RPMs go more or less than 5000 by constantly measuring the RPMs. Is there something on the market that can do this or can you tell me how to make one? I don’t have a pic programmer so I can’t make something that includes PICs.
    Thank you.
     
    Last edited: Jul 22, 2012
  2. CDRIVE

    CDRIVE Hauling 10' pipe on a Trek Shift3

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    A Picaxe doesn't require a PIC programmer.
    http://www.picaxe.com/
    Getting started is inexpensive.

    BTW, since you referred to frequency I'm assuming it's an AC motor but I'm not familiar with induction type motors that run at 5000RPM? Are you sure you're not referring to PWM?
     
  3. arg733

    arg733

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    Dec 14, 2010
    Hi.
    Thanks for the quick reply and sorry for the lack of information. I need it for a DC motor I have my own driving circuit with MOSFETs and Hall sensor. I tried giving some hertz and the motor’s RPMs dropped dramatically. I don’t need anything fancy just something that will compare the RPMs from the hall and keep them at 5000 ± 200-500 by increasing the frequency when the RPMs go higher and lowering the frequency when the RPMs get lower than the given value. I would also like to be able to change the “threshold” RPMs from 5000 to any value from 1000-10000. I don’t have much experience with IC’s other than MOSFETs and NE555 so if you have any circuit or link it would be very helpful.
    A friend told me that what i need is called “electronic governor” so I googled it but with no luck.
    I think that there should be something like what I need but I don’t know how it’s called and for what to search for.
    Here is the basic idea of my circuit.

    Thank you.
     

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    Last edited: Jul 22, 2012
  4. CDRIVE

    CDRIVE Hauling 10' pipe on a Trek Shift3

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    Do you own a scope? What's the output voltage and current specs of the hall sensor?
     
  5. CDRIVE

    CDRIVE Hauling 10' pipe on a Trek Shift3

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    I started to sketch a schematic centered around 555 technology but stopped because the complexity and would never match the simplicity and elegance of a microcontroller.

    BTW, there are many off the shelf PWM controllers available. Here's just one.

    http://www.electronickits.com/kit/complete/motor/CKMX033.htm

    It doesn't meet with your supply voltage but there are many more out there. I'm sure that you can find one >50V. Yes, I know that you need speed governorship. My guess is that's available too. How extensive was your search?
     
  6. CDRIVE

    CDRIVE Hauling 10' pipe on a Trek Shift3

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    Last edited by a moderator: Jul 23, 2012
  7. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    I suspect the OP is trying to use PWM to control speed and wants feedback via a hall sensor to allow automatic changes to duty cycle to maintain speed under varying load.
     
  8. CDRIVE

    CDRIVE Hauling 10' pipe on a Trek Shift3

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    Yes Steve, I understand that. I thought that the last link I posted might have an input for that. The data on that page didn't define that though. If he wants to roll his own I could draw a Picaxe option for him but I need more info from him, including motor current..
     
  9. arg733

    arg733

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    Dec 14, 2010
    Thanks but I was looking for something less complex and less costly.
    You don’t need to be concerned about motor current. As you see in the sketch the output from the microcontroller/governor/picaxe goes to the gate of the Q1 which will interrupt the Q2s source and won’t allow it to give a steady signal from the hall. As far as I can tell it works great and I can drop the RPM from 5000 to 10 and even stop the motor completely (manually controlling the frequency ofcourse)
    Though I have maid a dozen of PCBs with MOSFETs and NE555s I don’t know anything about microcontrollers or PICs but if you give me complete schematic I think I can make about anything.
    I apologize if my English isn’t that good.
     
  10. CDRIVE

    CDRIVE Hauling 10' pipe on a Trek Shift3

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    Please don't tell anyone that asks you a question that they need not be concerned about it. Just because you're using a FET doesn't mean that we don't need that information.

    The FET you're using is rated at Vdss(MAX)=55V. Your motor and power supply are operating at 50V! This is the wrong transistor to use. It will eventually pop! More probably sooner than later. :rolleyes:

    Besides that it's not a logic level FET. So, we can't use it to directly interface to TTL logic levels.

    I also asked you for the Hall Effect output (V & I) and didn't get that either.


    I suggest that you read back over this thread and answer all the questions. The more information you give the better.

    Absolute Max Supply Voltage... Is it really 50V?
    Motor Type and Specs.
    Hall Effect Module: Vo Io. or part number.
     
  11. arg733

    arg733

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    Dec 14, 2010
    My hall (CS3020) is rated at 24V but it’s an N-channel so the output is negative. I use a 10k resistor to give 12v to the gate of the Q2 when the hall is off.
    The sketch I gave before is wrong the Q1 takes 12V and not 50, sorry.
    The motor is just a simple brushless dc motor of my own making and it draws about 4A at 50V (can’t understand how that helps…) and it’s almost always on 50V.
    As for the irf540 it blows up at 120V so it’s ok at 50.
    The datasheet of the irf9540 also states that it is 100v
    I can also replace the irf9540 with irf9204pbf which says that it has logic level gate.
    To answer to a previously asked question: no I don’t have a scope or any advanced electronic equipment for that mater.
     
  12. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    First thing to do is to place a reverse biased diode across the motor to protect your mosfet.
     
  13. arg733

    arg733

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    Dec 14, 2010
    Steve if I do that the current from the bemf goes back in the coil and the RPMs drop dramatically. My fet is ok. It blew up when I gave it 120V :) .
     
  14. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Seems I can't be of any assistance.
     
  15. CDRIVE

    CDRIVE Hauling 10' pipe on a Trek Shift3

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    Sorry about that. Brain fart over here. I thought you were using a IRFZ46N. This happens when I'm involved in too many topics simultaneously.

    I assume that you mean the Drain of the 3020 is normally low - not negative?

    EDIT: Never mind. I found a schematic of the CS3020. The output is an open collector NPN BJT not an NChan FET as you describe.. So the output sinks low when on.
     
    Last edited: Jul 24, 2012
  16. arg733

    arg733

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    Dec 14, 2010
    Yes that's correct.
     
  17. CDRIVE

    CDRIVE Hauling 10' pipe on a Trek Shift3

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    Since this will not be a fixed RPM I've totally abandoned any 555 concepts. Yes, I think a circuit based around 555's is doable for a fixed RPM. Since you want user speed control along with speed governorship I think it would be very complex, ... if it could be done at all.

    Here's the uC rout I'd take but with some caviats...

    The IRF540 isn't specifically a Logic Level FET. No guarantee that the Gate (Vgs) will get sufficient voltage for Vds(ON).

    Since your (BDCM) motor design is sensor-less and requires non suppression of BMF, I give no guarantees that BMF won't pop anything.
     

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  18. arg733

    arg733

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    Dec 14, 2010
    Hi.
    Don’t try to make a circuit that can drive the motor directly because as you say the bemf will blow up something , I only need TTL output and then I can pass the signal through a couple of amps and that way protect it as I have protected my frequency generator.
    Will that circuit do what I need? Does the picaxe08M2 need programming?
    Thank you very much.
     
  19. CDRIVE

    CDRIVE Hauling 10' pipe on a Trek Shift3

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    Yes & yes. Here's a link to get you started.
    http://www.picaxe.com/
     
  20. arg733

    arg733

    89
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    Dec 14, 2010
    Thanks I will get the parts and try the circuit and post the results.
    But I don’t get it how do I program it? Can I just run some cables from the serial port of my computer to the breadboard and connect it to the picaxe pins? Or I need to buy one of those boards that connect with my computer? Can you tell me the code with which to program it? Sorry for the dumb questions.
     
    Last edited: Jul 26, 2012
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