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Use of ULN2003 motor driver to run 150W motors — Parallax Forums

Use of ULN2003 motor driver to run 150W motors

ViVekITOViVekITO Posts: 1
in Robotics
Hi,i want to interface the ULN2003 motor driver using ATMEGA16A . Then connect the outpins of ULN2003 to motors of 150W and 24 volts with RPM of 3000 .is it okay to use 12V relays between the outpins of 2003 and the motors? 
help needed asap :) ThanksVivek

Comments

  • kwinnkwinn Posts: 8,697
    As long as you make sure the relay coils draw less current than the uln2003 can supply, and that the relay contacts can handle the motor current it should be fine.
  • PublisonPublison Posts: 12,366
    edited 2015-07-17 15:20
    http://www.ti.com/lit/ds/symlink/uln2003a.pdf

    The collector-current rating of a single Darlington pair
    is 500 mA. The Darlington pairs can be paralleled for
    higher current capability. Applications include relay
    drivers, hammer drivers, lamp drivers, display drivers
    (LED and gas discharge), line drivers, and logic
    buffers.
  • LoopyBytelooseLoopyByteloose Posts: 12,537
    edited 2015-07-17 18:54
    What you are talking about doing is to control your motors in several stages.

    The UNL2003 can take 12 VDC for 12V relay coils. And that is a pretty good objective. 
    Publison is reading the 'Absolute Maximum Ratings' at 500ma.  Don't get close to that.

    But each of its Darlington pairs may only handle about 350ma. 12relay coils may require 120ma to properly drive the coils.  Much depends on whose UNL2003 you buy.  Publison's PDF claims 200ma to 350ma loads work well.  These are 2013 chips.


    As for your 12VDC coil, the contacts of the relay will need to be rated high enough for your voltage and motor.   RPM doesn't mean much.  But 150watts at 24VDC provides an amp target 150/24 = 6.00+ amps.

    Considering that the load is a motor, it would be best to have 10amp or higher rating on the contacts, and maybe some spark suppression.  These features would make the relays last a lot longer.  For DC motors, just a 10 amp 100 volt rectifier diode backwards across the contacts will add a lot of useful life.
  • Mark_TMark_T Posts: 1,981
    150W 24V motor means 6A nominal current, probably up to 30A stall or more.
    30A of inductive DC load is a lot for a relay, a big MOSFET plus beefy free-wheel
    diode might be more appropriate - certainly the free-wheel diodes are a good idea
    even with the relay to reduce arcing.
  • LoopyBytelooseLoopyByteloose Posts: 12,537
    I presume that the OP will supply 12VDC to the UNL2003 AND 24VDC to the motor.

    Now I wonder if the OP was hoping to us a 12V relay with 24VDC to the coil rather than having to supply 12VDC.  One could use a 24VDC relay and have the UNL2003 power it -- thus avoiding the problem of supplying 12VDC.

    But as Mark T points out, the stall current is always a problem in motor control.  A bigger 30Amp relay or more would be ideal.  There are inexpensive 12VDC and 24VDC relays rates at 30amps and higher available for automotive use.  Trucks use the 24VDC relays, while passenger cars use the 12VDC.

    The 'free-wheel diode' is a very cheap component.  Rather than getting a  10amp 100 volt item, one easily can acquire a 30 amp 1000 volt item for not much more in cost.  But one will notice that there is a significant increase is component size.

    And yes, MOSfets will work.  But it is a whole separate design problem.  One has to build a board and the design of stages to drive a power MOSfet are a bit different.
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