HELP motor control

Discussion in 'The Projects Forum' started by hamadashedid, Nov 30, 2012.

  1. hamadashedid

    Thread Starter New Member

    Nov 23, 2012
    3
    0
    hello,
    i have big problem with my friend wheelchair
    damaged control unit
    i need to design new one with simple draw
    the motor is MBT1141M 24 volt 0,55kw
    i try make simple an555 ic pulse width with 10v and i sucsess with it
    but i don,t know the mosfet to put i try irfz44n heat and damage
    irf3205 same irfp460 same
    really i pay too much for trying mosfets what i do? please help
     
  2. tubeguy

    Well-Known Member

    Nov 3, 2012
    1,157
    197
    Looking at a couple of the Mosfets chosen, it looks like you are on the right track.
    For some help please post a schematic of the circuit you are using.
    I'm assuming you need forward/reverse and speed control.
    Edit: And there are two motors -- correct ??
    Do you have a schematic of the original damaged circuit also ??
     
    Last edited: Nov 30, 2012
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  3. wayneh

    Expert

    Sep 9, 2010
    12,118
    3,042
    If by 10V you mean the supply voltage to the 555, then the output driving your MOSFET will be less and is not enough to turn it fully on and reduce to Rds, causing too much heat. I'd like to see maybe 12V at the gate of the MOSFET, to eliminate this issue.

    Even fully on, the MOSFET will be dissipating more than 10W, and requires a BIG heat sink.
     
    Last edited: Nov 30, 2012
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  4. hamadashedid

    Thread Starter New Member

    Nov 23, 2012
    3
    0
    yes you are right i need forward/reverse and speed control schematic real one working
    to do it
    i don,t have schematics i do it by manual
    can you help
    if you have one with forward and speed control OK no problem he need to move only because of his legs can,t walk
    thanks for your time
    best regards
     
  5. tubeguy

    Well-Known Member

    Nov 3, 2012
    1,157
    197
    Have some more questions.

    1. What do you have for a controlling device - Is it a joystick with pots? - for example. Be specific

    2. Is the battery voltage 24vdc or something different ?

    3. How are you getting the 10 volts for the 555 ?

    4. How are you controlling the 555 to get the PWM ?

    5. How did you connect the Mosfets which (unfortunately) burned up. ?

    You really need to post a wiring diagram of what you have done or tried so far.
    There are various ways to accomplish this project, but more details are required to give you accurate advice.

    As wayneh pointed out you need 10-12VDC driving the lower Mosfet gate in a bridge circuit and if using all N-Channel Mosfets you need 10-12v MORE V+ than the voltaje on the top Mosfet Drain.
    Note: There are many circuits posted on the internet of this type which are just plain WRONG !
     
    Last edited: Dec 1, 2012
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  6. hamadashedid

    Thread Starter New Member

    Nov 23, 2012
    3
    0
    1. What do you have for a controlling device - Is it a handle with switch on-off

    2. Is the battery voltage 24vdc -2battery 12v 55ah

    3. How are you getting the 10 volts for the 555 - 78L10

    4. How are you controlling the 555 to get the PWM ? PIN 3 OUT (+) TO MOSFET GATE WITH RESSISTOR 220 OHM

    5. How did you connect the Mosfets which (unfortunately) burned up. ? PARALLELED
     
  7. tubeguy

    Well-Known Member

    Nov 3, 2012
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    How is the switch handle connected to the 555 circuit. ?
    How are the Mosfets wired to the motor ? Where is V+ in relation to motor
    to Mosfets to gnd?
    Are the batteries wired in parallel or in series?
    NEED diagrams of what you have tried. Cannot help without those

    This is the type of Mosfet circuit you need to control a motor with speed control and forward-reverse.
    Example only - you need the higher current N - Mosfets, plus P Mosfets, plus variable PWM fed to A or B for forward or reverse.

    You need more than a handle with a switch to vary speed.
    Does the handle have potentiometers in it ?
     
  8. tubeguy

    Well-Known Member

    Nov 3, 2012
    1,157
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    How did the original control system work on the wheelchair ?

    Edit: Explain it like you are teaching someone to operate it for the first time.
    How to go forward, backward, turn stop etc.

    It may seem like too many questions but all of these details are extremely important to figure out how to use some of what you already have. :)
     
    Last edited: Dec 1, 2012
  9. tubeguy

    Well-Known Member

    Nov 3, 2012
    1,157
    197
    The schematic in post #7 had the PMOS upside down
    Here's the correct image
     
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