How to beef up a motor control board?

Discussion in 'General Electronics Chat' started by ceefna, Feb 21, 2012.

  1. ceefna

    Thread Starter Member

    Feb 21, 2012
    31
    0
    Hi experts,

    I have a motor control board that uses a L293DD chip which is rated at 600mA. I am wanting to upgrade the motors it drives to 1.5A.

    What are my options? I have found that the L298 is a 2A motor driver. Do you think it would be possible to remove the L293DD and add jumper wires to run a L298 off board on a seperate heatsink.
    I have done a rough pinout diagramme and it seems compatable? Have a look at the attachments of the board.
    I have also included 2 pics of differences in the spec sheets of the 2 chips.
    I don't know weather these differences would be a problem?

    Or am I making this more complicated than it needs to be? can you think of an easier way? piggy backing maybe?

    Thanks for your time.

    Ceefna
     
  2. Felo

    Member

    Feb 20, 2012
    91
    13
    This looks ok to me, just make sure that Vss on the original does not exeed 7v, the 293 can take a logic supply from 4,5v to 36v the 298 from 4,5v to 7v that's the only thing to worry about.

    Let us know how it worked!!
     
  3. ceefna

    Thread Starter Member

    Feb 21, 2012
    31
    0
    Thanks for the reply Felo, just got to pluck up courage to take the chip off!

    Do you know if there is any sort of header socket I can solder in place of the chip to connect the wires to? I am just worried that soldering jumper wires straight to the surface of the board may break off.

    Anybody in West Yorkshire that does surface mount soldering!!!!

    Ceefna
     
  4. Felo

    Member

    Feb 20, 2012
    91
    13
    Straight solding cable to the boar WILL eventually break if subjected to mechanical stress, a good solution here would be to make a small PCB imitating the soic20, drill holes through it, run short wires, finally solder to end PCB, this way any stress to the board wil be shared by 20 pins instead of 1, less likely to break.

    On the desoldering matter, you can acomplish that by means of a hot air blower, (not hair dryier but a really hot PVC piping bending type) I have personally done this a few times with good result, of course if can have it prodessionaly done, play it safe.

    Be carefull not to overheat the PCB, or desoldering other small components
     
  5. ceefna

    Thread Starter Member

    Feb 21, 2012
    31
    0
    Thats a good tip for the PCB, the motor drive board is from a telescope so once the new chip is fitted there wont be any mechanical stress as all will be fixed solid.
    I was worried about breaking the connections moving the heatsink etc before I got it fixed in place.



    I work in a large vehicle repair shop and we do a lot of plastic repairs to bumpers and other car parts. We use hot air guns with quite fine tips to plastic weld parts back together and I have tried soldering with one before which resulted in removing all the parts within a 2 inch radius on the board!!

    Wonder if I could fabricate a nozzle to vent off some of the blow force an the guns are temperature controllable they might work.

    these are the guns
    http://www.welwyntoolgroup.com/leister-plastic-repair-kit.aspx

    Do you think this would work or is it too big?

    Ceefna
     
  6. Felo

    Member

    Feb 20, 2012
    91
    13
    It will surely work!! finer tips should prevent you from removin other components, at this point it is all in the wrist....

    good idea about the nozzle, when I had to use the hot air gun, I din't had any nozzle and still turn out OK. (maybe it was just begginers luck!!......)

    I still advice you to exercice care, it seems like an important PCB, and if it gets ruined would like you to blame it on me...hehheh
     
  7. ceefna

    Thread Starter Member

    Feb 21, 2012
    31
    0
    It will obviously be your fault :D

    Last question, would you add capacitors to the L298 as they will already be on the board?
    I found these pre built boards on ebay using the L298. Do you think one of these wired to the old chip pins would work? They seem to use all the same pins.
    http://www.ebay.co.uk/itm/L298N-Dua...deo_TelevisionSetTopBoxes&hash=item43ace720f4

    Or would you just stick to the bare chip? I don't know how critical the circuit is and whether even extending the wires will change the drive rate. The board drives two DC servo motors at very specific rates for astronomy so I hope my modifications will not ruin it.

    Ceefna
     
  8. Felo

    Member

    Feb 20, 2012
    91
    13
    I woul probably go for the bear chip due to space/availability/downtime, besides if its gonna blow, let it blow already......hehehe

    you original pcb seems to have all the support and proteccion needed so it would be a little overkill to throw in the ebay, still both should work
     
  9. ceefna

    Thread Starter Member

    Feb 21, 2012
    31
    0
    Modified the hot air gun nozzle to make it safe for removing the chip. I had an old board with a L293DD on it as a test, the hot air gun worked perfectly to remove the chip.

    I have got a L298N but before I remove the L293DD from my good board I need to test the Logic Supply Voltage. Can I just use a multimeter on Pin 20 and ground to find the voltage? I think it will be 5V but I want to make sure it is not over 7V.
    The board is supplied by 12V but has a 5V regulator.

    Ceefna
     
  10. ceefna

    Thread Starter Member

    Feb 21, 2012
    31
    0
  11. ceefna

    Thread Starter Member

    Feb 21, 2012
    31
    0
    Well for anybody that cares if anyone is actually reading this today I knackered the board testing the logic voltage on the L293.
    Tested between pin 20 and ground but had the multimeter steup for amps and shorted the board!
    Still works but after moving one of the motors it takes about 10 seconds to start moving at tracking speed again, should be instant.

    can I find what part is damaged?

    Ceefna
     
Loading...