Laptop Power Supplies And Stepper Motors?

I normally use linear power supplies to run my stepper motors, but out of curiosity, I recently searched and found that some folks have been using laptop power supplies to run their stepper motors.

Does anyone here have experience with powering their stepper motors with laptop power supplies? And if so, was it a good or bad experience? :)


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  • idbruce wrote: »
    I normally use linear power supplies to run my stepper motors, but out of curiosity, I recently searched and found that some folks have been using laptop power supplies to run their stepper motors.

    Does anyone here have experience with powering their stepper motors with laptop power supplies? And if so, was it a good or bad experience? :)

    I have replaced many linear supplies in autopipetters with 12V laptop supplies. Worked very well for me. Do keep current ratings in mind or you may have intermittent problems. I used supplies rated for about 50% more than the instrument required.
    In science there is no authority. There is only experiment.
    Life is unpredictable. Eat dessert first.
  • Thanks for your input kwinn.

    I had to look up autopipetters :)

    I almost have the structure of the LDI machine completely built and it is looking like a real piece of beautiful craftsmanship. Anyhow, I am now at a point where I must be thinking about the electronics and the user interface.

    For this small machine, I do believe a laptop power supply would be more applicable than a big honking linear supply. At the very least, based upon your input, I will give it a try.



    Novel Solutions - http://www.novelsolutionsonline.com/ - Machinery Design • - • Product Development
    "Necessity is the mother of invention." - Author unknown.

  • Do keep in mind that the laptop power supplies come in different voltages and currents. The more common ones I see are 18-19V, although I have found 12V, 15V, and 24V units as well.
    The PC power supplies are pretty much standardized with +12, +5, +3.3, and -5 volts. Some of them will require a minimum current draw on the +5V and/or +12V supply to operate, although that is less common now than it used to be.
    In science there is no authority. There is only experiment.
    Life is unpredictable. Eat dessert first.
  • In my stepper experiments I have used a 12 volt SLA battery on a stepper rated for 6 volts.
    I insert a PNP transistor into the power supply and use PWM to control the current and voltage.
    I reduce the duty cycle at slower speeds or lighter loads to reduce the noise a stepper can make as it slows down.
    Larry

    If the grass is greener on the other side...it's time to water your lawn.
  • I am particularly thinking of a 12V, 2.5~3A laptop supply.


    Novel Solutions - http://www.novelsolutionsonline.com/ - Machinery Design • - • Product Development
    "Necessity is the mother of invention." - Author unknown.

  • idbruce wrote: »
    Does anyone here have experience with powering their stepper motors with laptop power supplies? And if so, was it a good or bad experience? :)

    Needed compact 24V at 2A or above here for a bilge pump recently, and a 90W laptop universal model (included 24V) worked fine.
  • Just watch out .... the stepper motors have an inductive load, and the Laptop power supply may not like that very much.
    That said, I have used and abused Laptop power supplies throwing all kinds of stuff at them. I have only gotten a few to go into high current shutdown. A simple power cycle on the Power supply usually fixes the problem.


    Beau Schwabe -- Submicron Forensic Engineer
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  • Just watch out .... the stepper motors have an inductive load, and the Laptop power supply may not like that very much.
    That said, I have used and abused Laptop power supplies throwing all kinds of stuff at them. I have only gotten a few to go into high current shutdown. A simple power cycle on the Power supply usually fixes the problem.

    True, motors are occasionally a problem for switching regulators. That high current on startup will sometimes cause the supply to shut down. Often solved by adding a capacitor on the supply output to provide that peak current.
    In science there is no authority. There is only experiment.
    Life is unpredictable. Eat dessert first.
  • Thanks Guys
    Often solved by adding a capacitor on the supply output to provide that peak current.

    Of course, a shut down is the last thing I would want to happen. So are you simply talking about a capacitor across the positive and negative of the output or is it a bit more complicated than that?

    And if so, what kind of value should I be thinking about?



    Novel Solutions - http://www.novelsolutionsonline.com/ - Machinery Design • - • Product Development
    "Necessity is the mother of invention." - Author unknown.

  • A capacitor of about 470 to 1000uF on the supply output, and the capacitance depends on the size of the motor. FYI, most of the DC motors I deal with are in the 5W to 240W range and 24V or less.
    In science there is no authority. There is only experiment.
    Life is unpredictable. Eat dessert first.
  • I had to replace an industrial 48V/10A switchmode a couple of years after new machine was installed. I'm pretty sure it failed due to regeneration causing excessive over-voltage surges. Machine manufacturer wasn't paying much attention me thinks when they didn't provide any regen dump or store. The drives certainly didn't have any.

    I had always noted the power-on indicator going off each time the motors performed a feed operation - taking maybe 100ms. It wasn't until the failure that I realised that maybe it was a design flaw.

    The failure mode was also amusing. The power supply seemed to become slow at turning on. This resulted in erratic servo errors as first move would be fine but following move would discharge the voltage while the power supply was still "off". Reducing the acceleration rates got it back on its feet for a while, but the power supply continued to deteriorate.

    With the replacement power supply I also purchased and added 3x 33,000 uF capacitors to limit the surge voltage to maybe 5 volts over. The power-on indicator is still dimming slightly but no longer goes out.

    Money is a placeholder for cooperation
  • Some of the early switcher designs were not very good at dealing with power supply startup surges and rapid load changes. When I first started working with them it seemed like they were as much black magic as engineering. Took me a while to get used to their quirks.
    In science there is no authority. There is only experiment.
    Life is unpredictable. Eat dessert first.
  • Kwinn, are you sure about your advice? The current to an inductive load builds up slowly. But a capacitive load looks like a dead short when first powered.

    -Phil
    “Perfection is achieved not when there is nothing more to add, but when there is nothing left to take away. -Antoine de Saint-Exupery
  • Wouldn't the stepper driver protect the power supply output?

    The only thing I would avoid is a laptop power supply with more than a two conductor jack. Some have extra pins and rings and get finicky when they aren't connected to anything.
  • evanhevanh Posts: 5,871
    edited December 1 Vote Up0Vote Down
    xanadu wrote: »
    Wouldn't the stepper driver protect the power supply output?

    It'll come down to size of drive's inbuilt capacitors verses the decelerating momentum of the machine. In my example the drives were tiny and inbuilt capacitors were practically non-existent.

    PS: Some drives have an inbuilt dump circuit (connected to a heater element on bigger drives) to pull the capacitor voltage back down if it gets too high.

    Money is a placeholder for cooperation
  • I second Phil's inquiry ... "Kwinn, are you sure about your advice? The current to an inductive load builds up slowly. But a capacitive load looks like a dead short when first powered." ... You can't just slap a capacitor on the output and call it good, the driving circuit "sees" that as a dead short .... you need a choke (inductor) and THEN a capacitor to form a LOW-PASS LC filter... Google "DC output filter schematic"


    Beau Schwabe -- Submicron Forensic Engineer
    www.Kit-Start.com - bschwabe@Kit-Start.com ෴෴ www.BScircuitDesigns.com - icbeau@bscircuitdesigns.com ෴෴

  • Kwinn is talking about adding on to the supply rail going to the drive, same as me, not to the motor wires. The difference is I'm indicating a much much bigger capacitance is likely needed if regeneration is of concern.

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  • Phil Pilgrim (PhiPi)Phil Pilgrim (PhiPi) Posts: 22,093
    edited December 1 Vote Up0Vote Down
    evanh wrote:
    Kwinn is talking about adding on to the supply rail going to the drive, same as me, not to the motor wires. The difference is I'm indicating a much much bigger capacitance is likely needed if regeneration is of concern.
    That's where I assumed he meant. It's still a problem if the supply can't handle the current spike required to charge the cap. Hence the series inductor that Beau suggested. For regeneration issues, it would be better to install a transorb across the supply rails.

    -Phil
    “Perfection is achieved not when there is nothing more to add, but when there is nothing left to take away. -Antoine de Saint-Exupery
  • A switchmode just current limits on power up.

    A transorb would cook in an instant.

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  • evanh wrote:
    A transorb would cook in an instant.
    Not if its breakdown voltage is higher the the supply's output voltage.

    -Phil
    “Perfection is achieved not when there is nothing more to add, but when there is nothing left to take away. -Antoine de Saint-Exupery
  • Phil,
    The regen is significant in some applications. That's why the extra capacitors are used to contain over-voltage.

    In heavier situations I've seen heatwaves come off some equipment with external dumps.

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  • evanhevanh Posts: 5,871
    edited December 1 Vote Up0Vote Down
    "Dynamic braking" is a name I've heard given to that trick. A battery can be used too.

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  • kwinnkwinn Posts: 8,085
    edited December 1 Vote Up0Vote Down
    No, I did mean the capacitor goes on the output of the power supply. The typical switching regulator has a startup delay before shutting down on sensing an over current condition. That delay allows the external capacitor to charge up as long as it is not too large compared to the current rating of the switching regulator.
    In science there is no authority. There is only experiment.
    Life is unpredictable. Eat dessert first.
  • Just watch out .... the stepper motors have an inductive load, and the Laptop power supply may not like that very much.

    Wouldn't worry about that too much.

    Stepper drivers are constant current switch-mode drivers, the power supply won't see the motor
    as a load at all, just decoupling capacitors with heavy switching noise on top, and average current
    that varies with the motor speed and load somewhat.

    Its rare for steppers to be able to backfeed into the supply too, due to their inefficiency.
    Backfeeding on deceleration with a standard PWM DC motor driver can pop the supply through
    over-voltage if there's not a braking circuit/dump resistor.
  • I had wondered about that, Mark. I've almost never dealt with real stepper motors.
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  • The capacitor should do the trick. I know when I've run large steppers with linear power supplies the supply had large caps. maybe 20,000uf + with a bleed down resistors. But expensive caps. would defeat the purpose of using a cheap laptop supply.
  • Hmmm....

    I would have never guessed that this topic would attract so much attention :)


    Novel Solutions - http://www.novelsolutionsonline.com/ - Machinery Design • - • Product Development
    "Necessity is the mother of invention." - Author unknown.

  • If you have a constant-current (i.e. PWM) stepper driver, there's a definite performance advantage in selecting a supply voltage higher than the rated motor voltage. The reason is that the higher voltage will cause the motor windings to come up to their rated current more quickly, which translates to faster slewing and more available torque at speed. I've even used 24V unregulated supplies with 5V-rated steppers. It's all about current regulation, not voltage regulation.

    -Phil
    “Perfection is achieved not when there is nothing more to add, but when there is nothing left to take away. -Antoine de Saint-Exupery
  • idbruceidbruce Posts: 5,701
    edited December 3 Vote Up0Vote Down
    If you have a constant-current (i.e. PWM) stepper driver, there's a definite performance advantage in selecting a supply voltage higher than the rated motor voltage.

    That is the only real intelligent way to go. The heck with all that power resistor mumbo jumbo or transistors. Oh, I remember the headaches when I first started with steppers.

    With the advent of the P2, hopefully we can now get some good CNC support for the Propeller.

    EDIT: Phil - Purchasing PWM stepper drives was the best advice you ever gave me :) There is no turning back now!


    Novel Solutions - http://www.novelsolutionsonline.com/ - Machinery Design • - • Product Development
    "Necessity is the mother of invention." - Author unknown.

  • Hmm, funnily enough, I use standard Android tablets for my machine control HMIs. They are heavily protected by a CNC-machined aluminum enclosure and a Neutrik USB connector. However, for appearance's sake, I prefer to use a DIN-rail mounted PSU. "Meanwell" are reasonably priced and I have yet to have a failure.
    Consumer device power supplies in a machine, to me, screams "cheap"....first impressions and all that stuff.
    3264 x 1836 - 422K
    3264 x 1836 - 408K
    Failure is not an option...it's bundled with the software.
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