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12V/5A from 19.5V/4.6A laptop charger

Discussion in 'General Electronics Discussion' started by abuhafss, Jun 28, 2018.

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  1. abuhafss


    Aug 3, 2010

    In my current Arduino based project, I need to power

    a) 2.7A Stepper Motor
    b) 12V-5A Solenoids (2 pcs, either would be used at a time)
    c) Arduino

    For that I am considering to use a 19.5V-4.6A laptop charger.
    My question is what would be the efficient way of stepping 19.5V to 12V and 5V?
  2. BobK


    Jan 5, 2010
    A switching DC to DC converter. Look for buck converter on EBay. The practically give them away.

  3. jaredwolff


    Jun 11, 2018
    Not quite sure if a solenoid will work with a stepper motor. You can also use some beefy FETs, solid state relays, or a solenoid specific driver if you need some kind of control from the Arduino. If you are building something CNC related then you'll need some feedback for the solenoids. (linear encoder, etc)

    There are TONs of 12V power adapters out there for computers, routers, printers (this is where I would look), old ATX power supplies (also another good choice if you're on the cheap), etc you just have to check those labels to make sure it works with your current spec. That may save you some time rather than mucking around with a fiddily Chinese buck converter.

    Happy hunting.
  4. kellys_eye


    Jun 25, 2010
    ...that are inevitably OVER-RATED as to their capabilities.
    jaredwolff likes this.
  5. abuhafss


    Aug 3, 2010
    Would you please elaborate.

    Do you mean, I should not use normal relays? Why?

    By the way, its not a CNC stuff.
  6. abuhafss


    Aug 3, 2010
    Thanks for the tip but ATX supply does not have higher voltages like 18-24V which are required for the stepper.
    Last edited: Jun 29, 2018
  7. abuhafss


    Aug 3, 2010
  8. hevans1944

    hevans1944 Hop - AC8NS

    Jun 21, 2012
    You measure the current that actually flows when the rated voltage is applied. Do this with a multimeter using its 10 A DC current measuring function. Place the multimeter leads in series with one of the solenoid leads. Apply rated voltage between the free multimeter lead and the other solenoid lead. Apply power and read the current on the multimeter.

    The current required to initially energize and move the armature (the moving part) of a solenoid is generally greater than the current required to hold the armature in the energized position. Some applications will reduce the solenoid current to the lower holding current level after the solenoid is energized. This is mainly important if the system is a marginal design that overheats when the solenoid is energized continuously at its rated voltage.
  9. Minder


    Apr 24, 2015
    Although this only generally applies with a AC version, the DC should be the same when energized.
    This is why the AC version only has the edge at switch on, current is high until the inrush and the armature has moved over and inductive reactance takes over, apart from this the DC has the edge.
  10. jaredwolff


    Jun 11, 2018
    Relays work just fine for servos. Though, they have some time delay and definitely have a higher "On" current than say a MOSFET.

    A stepper driver may work fine for a servo but you would have to continuously step the output for it to spin continuously. A stepper driver, of course, is meant for a stepper motor so you can always use it there.

    Either way I recommend you get separate supplies for the voltages you need. An ATX supply can give you the 5V and 12V for sure. Then your laptop charger can potentially supply the single stepper. No need to go further than that!
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