help to 30Amp motor controller

Discussion in 'The Projects Forum' started by mejlby, Apr 26, 2013.

  1. mejlby

    Thread Starter New Member

    Apr 26, 2013
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    Hi All
    I am looking for a circuit for 30A motor controller 24V. I need it for an electric gokart. Is there anyone here who has etelectrical Circuit or can refer to a website where I can find it ?

    I made ​​a motor controller from this link http://electronica.mk/all_articles/Electric_Car_Projects/PWM_Motor_Control/PWM_Motor_Controller.html

    but it does not work. I have corresponded with support but I have not received any explanation of the problem

    the problem is that the potentiometer only works on 50% of 300 degrees rotation of the potentiometer. it means that I can not control the speed from 0V to 24V full speed.

    Perhaps there is anyone who has tried to make this motor controls and know what the problem is with this circuit.

    It will be very happy if someone has a circuit that can handle 30amp and 24V

    Sincerely,
    Tonny
    (From Denmark)
     
    Last edited: Apr 26, 2013
  2. mejlby

    Thread Starter New Member

    Apr 26, 2013
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    Last edited: Apr 26, 2013
  3. panic mode

    Senior Member

    Oct 10, 2011
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  4. mejlby

    Thread Starter New Member

    Apr 26, 2013
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    thanks for your quick response

    do you have a completet Circuits for a 30A motor controllers 24V ?

    Tonny
     
    Last edited: Apr 26, 2013
  5. #12

    Expert

    Nov 30, 2010
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    Your circuit is designed for 250 watts. You need 720 watts, and you have no heat sinks for the transistors.

    "The circuit diagram for the motor driver using MOSFET. Especially for this circuit can drive a DC motor with 250W power. We had use 120A/60V MOSFET and one diode MBR3045V. On start up motor draw more than 30 Amps."


    Perhaps one of these for $20?


    http://www.ebay.com/sch/i.html?_nkw=dc+motor+speed+controller


    http://www.ebay.com/itm/DC-9V-28V-3...430?pt=LH_DefaultDomain_0&hash=item27cb652a96
     
  6. Dodgydave

    AAC Fanatic!

    Jun 22, 2012
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    The circuit with the TL494 is used for Smps, pin 4 is the dead time control, does it work from zero to half speed or from half speed to full?

    Try the variable resistor across pin 12 and 7, instead of pin 14-7, see if works better.


    http://www.555-timer-circuits.com/pwm-controller.html
     
    Last edited: Apr 26, 2013
  7. panic mode

    Senior Member

    Oct 10, 2011
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    just add 12V regulator for the LM324 and use transistor(s) rated properly for your load. i used on couple jobs nice mosfet from ST and it worked quite nicely. max current is some 180A and they are good for 75V. best of all Rds_on is just 0.002 Ohm so at 30A, they dissipate <2W. beauty if you ask me.
    http://www.digikey.ca/product-detail/en/STH260N6F6-2/497-11217-1-ND/2643202
     
  8. mejlby

    Thread Starter New Member

    Apr 26, 2013
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    YES I know you can buy some cheap motor controls on Ebay. I already have a motor controller that I bought on Ebay - BUT it's more fun to make them by myself.

    Jes I know that I have no heat sinks for the transistors....... but I make this if I get it to Work. ( I know i only need max 20A )

    see the Picture
     
  9. mejlby

    Thread Starter New Member

    Apr 26, 2013
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    The potentiometer works only after I turned 50% of 300 degrees rotation - then adjust it from 0 to full speed 24V

    This link to 555 motor controller can only handle 12V

    I will try your suggestion
     
  10. panic mode

    Senior Member

    Oct 10, 2011
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    did you wonder how TL494 handles 24V?
    it does not, it uses 12V which is stepped down using 7812...
     
  11. mejlby

    Thread Starter New Member

    Apr 26, 2013
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    Åhhh yes ofcause i did'nt think of that

    Do you know how many hz its work on ?
    Can i adjust the hz - maybe to 2 khz
     
  12. Dodgydave

    AAC Fanatic!

    Jun 22, 2012
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    Well use the 555 timer cct that i gave with a Lm7812 regulator feeding the 555ic and take the motor across the 24v side.
     
  13. panic mode

    Senior Member

    Oct 10, 2011
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    1. How did you make your circuit without realizing that there is a voltage regulator? How did you connect 7812?
    2. Why would that be important? Do you know how PWM works? Yes, with circuits in link I posted you can independently adjust frequency and duty cycle. it is 500Hz now so if you change 10nF capacitor to 2.5nF or reduce R2 to 27k (as a close enough value for 25k), you will get 2kHz. Get simulator like LTSpice and play with it. you can learn a lot about circuit by simulating.
     
  14. mejlby

    Thread Starter New Member

    Apr 26, 2013
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    I built the circuit on the basis of the link which I sent - that's why I forgot there was a LM7812

    Yes I know the principle in a PWM motor controls.

    It is also not because I need an motor controller to the go kart I just have made for my little daughter as you look at the attached link run the go kart fine (I only need to make a speed pedal)

    The reason I want to make a motor controller is to learn a little more about electronics. And I do not understand why it works. If you see the video from the link then you see its works very good. And if there is something I do not understand, then I will continue until I understand it.

    I have no doubt about you are very good at electronics - I'm only an engineer working with building construction -so I am sure you can be very helpfull for me.

    http://www.youtube.com/watch?v=qD8NtmhRVOU&feature=youtu.be
     
    Last edited: Apr 27, 2013
  15. panic mode

    Senior Member

    Oct 10, 2011
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    nice video. it is enough if you can make circuit from working schematic. frequency is not that important. 500 or 2000Hz makes not much difference. In fact I'd probably keep it at 500Hz because it is fast enough. if it was 10Hz, you would get noticeably choppy response but at 500Hz it will be very smooth. Going faster makes no sense unless you are trying to get above 20kHz (above audible range) but that is another ball game.
    Every time you switch the motor on or off there is a transient (notice in attachment that green V-out wave is not perfectly square but is just slightly rounded near top). Also power mosfets have quite large capacitance at the gate. this means that gate voltage cannot rise and fall instantly (it takes time to charge and discharge capacitance). this "deformity" causes transistor to act not as a switch but as a resistor for brief period of time. during that time transistor heats up. by lowering frequency, we reduce how often transistor goes through this and increasing frequency from 500Hz to 2KHz means that we get 4x as many such transitions and more heat build up on the mosfet transistor(s).

    opamp in the bottm left is just voltage follower that duplicated 50% of the 12V (making so called virtual ground). most opamp circuits are meant for symmetrical supply (for example +/-12V or +/-15V). to make them work on single supply (here we have 12V), virtual ground is created by splitting that 12V into two 6V voltages. lower left opamp is a voltage follower that basically just duplicates the 6V as virtual ground.
    the top two opamps form an oscillator. output with triangular wave is compared with fixed voltage (set by potentiometer). when triangular wave is higher than setpoint, output is high and motor turns on. when triangular wave is below setpoint, output is off. by changing setpoint you can control 0-100% duty cycle. if you install that potentiometer into an accelerator pedal, you can get convenient way to control cart speed. attached file shows the basic idea. note that because of linearity of the slopes of the triangular wave you get very nice, clean and repeatable output because last opamp works as a comparator, regardless of oscillator frequency.

    Version with 555 is also nice. the frequency is not fixed, it changes slightly with duty cycle or changes of position of the potentiometer (which is fine in this case). also you don't get perfect linearity or full 0-100% range, probably more like 2-98%. But normally this is just fine, given benefits of lower component count and smaller PCB.
     
    • PWM.pdf
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  16. Dodgydave

    AAC Fanatic!

    Jun 22, 2012
    5,000
    745
    On your circuit what is the voltage at these points when you adjust the pot from zero to full speed,

    (1)Pins 9,10

    (2)Emitters of transistors Bd139/140

    (3)Anode of diode Mur120

    (4) pin 4

    here is the datasheet of this ic it works upto 42V, no need for a regulator.


    http://www.datasheetcatalog.org/datasheet/motorola/TL494.pdf
     
  17. mejlby

    Thread Starter New Member

    Apr 26, 2013
    28
    1
    thanks for your reply

    When I measure the potentiometer starts the engine not running until I reach about 1.9 V. 0 to 1.9 V, nothing happens.

    I will measure the places you've described

    Tonny
    Denmark
     
  18. mejlby

    Thread Starter New Member

    Apr 26, 2013
    28
    1
    thanks for your reply

    When I measure the potentiometer starts the engine not running until I reach about 1.9 V. 0 to 1.9 V, nothing happens.

    I will measure the places you've described

    Tonny
    Denmark
     
  19. mejlby

    Thread Starter New Member

    Apr 26, 2013
    28
    1

    Thank you for a very good explanation of how a PWM Controller works. I will try me slightly forward with a LM324 (I have a few)

    As you look at the attached picture then I have made several things to control

    Since it's for my little daughter, I have put a transmitter and receiver on, so that I am on a remote control can turn off the motor if she can not handle the go kart.

    I also made it such that she can not put it in reverse until there is less than 2V on the motor - this in order to protect the motor. So far, there are only a pot to control the speed, but I'm going to make an accelerator pedal. My daugther is to little to control the speed with a pot and i will be easier for her with a foot pedal

    Best regard
    Tonny
    Denmark
     
    Last edited: Apr 29, 2013
  20. mejlby

    Thread Starter New Member

    Apr 26, 2013
    28
    1
    hello Dodgydave

    Now I measured on the points that you have recommended.

    I have also taken some pictures from my oscilloscope which maybe provide an explanation as why the motor does not respond before potentiometer turned up at approximately 2,8V and 4.9 V (From 0V to 2,7V no respond)

    I hope you have time to look at the attached and maybe have an idea what is wrong.

    Many greetings
    Tonny
     
    Last edited: Apr 30, 2013
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