Help needed to identify PWM IC

Discussion in 'General Electronics Chat' started by ceefna, Sep 24, 2012.

  1. ceefna

    Thread Starter Member

    Feb 21, 2012
    31
    0
    Hi guys,
    I need a bit of help to identify the IC on a cheap Chinese PWM motor controller I bought on ebay a while back. As you can see from the pictures the markings have been scratched off for some reason!

    I am trying to include a soft start function to the PWM so I can add it to my observatory dome control as the motor is too harsh on startup.
    I have got a sort of soft start to work by adding a 470uf cap across 2 terminals on the speed control pot (see picture) but this is no good for my application as the PWM controller needs to be powered up all the time and connected to 2x DPDT relays to change motor direction(the relays are controlled by a K8055 USB board). So my solution only works on first power up until the cap charges, I need something that works everytime the motor is connected.
    I have searched the internet for an IC that matches but can't find anything that has Ground on pin11 and the orientation marks on the chip don't match any of the data sheets I have looked at.

    I have added a couple of pics of the PWM controller and a schematic of my observatory control system with a note on where I think the PWM needs to connect. I only need to slow the motor down at startup as it runs at the right speed when operating.

    Any ideas would be much appreciated.
    Thanks for your time
    Richard
     
  2. Dodgydave

    AAC Fanatic!

    Jun 22, 2012
    5,001
    745
    Last edited: Sep 24, 2012
  3. ceefna

    Thread Starter Member

    Feb 21, 2012
    31
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    Hi Dave and thanks for the reply, I have searched and I can't find either of those 2 in DIP14. Think they only do them in DIP16.


    Richard
     
  4. ceefna

    Thread Starter Member

    Feb 21, 2012
    31
    0
    Yes you are right, I think it's a LM324AN.
    The comps on heatsinks are L7812CV and IRF540N
    Thats the way the PCB is marked for motor +/-
    And the circuit looks very close, any ideas on adding soft start?

    Richard
     
  5. Dodgydave

    AAC Fanatic!

    Jun 22, 2012
    5,001
    745
    you need to trace out the circuit, i think it will be the same as the one i posted, so your cap is increasing the wiper on the pot to 12v to slow the motor down, then it charges up and runs as normal, so putting a posative pulse on pin 6 of the lm324 will lower the motor voltage.
     
    Last edited: Sep 24, 2012
  6. ceefna

    Thread Starter Member

    Feb 21, 2012
    31
    0
    Hello again,
    I have been thinking about using the PWM controller with the cap I have added and just fitting the whole unit after the first relay so the cap would not get charged until the relay closed to drive the motor.
    Please have a look at my modified schematic. Can you see any possible problems with connecting it like this?


    Thanks again for your time
    Richard
     
  7. Dodgydave

    AAC Fanatic!

    Jun 22, 2012
    5,001
    745
    looks ok to me, the pwm will ramp up slowly then run normal, only when relay k1a closes.
     
  8. ceefna

    Thread Starter Member

    Feb 21, 2012
    31
    0
    Thanks for the thumbs up Dave, I will wire it in and see how it performs.

    Richard
     
  9. simonvav

    New Member

    Jan 16, 2013
    1
    0
    You might consider reprogramming PC18F24J50. It gives you a whole range od new PWM options to controll a motor.

    I've tried and succeded to program a blank PC18F24J50. And this enabled med to have even 10-bit A/D and to setup PWM by USB. I even managed to write special finctions that enable me to control all teh microcontroller's registers directly over USB
     
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