Laptop Power Supplies And Stepper Motors?
idbruce
Posts: 6,197
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?
Does anyone here have experience with powering their stepper motors with laptop power supplies? And if so, was it a good or bad experience?
Comments
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.
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.
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.
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.
Needed compact 24V at 2A or above here for a bilge pump recently, and a 90W laptop universal model (included 24V) worked fine.
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.
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?
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.
-Phil
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.
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.
-Phil
A transorb would cook in an instant.
-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.
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 would have never guessed that this topic would attract so much attention
-Phil
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
Consumer device power supplies in a machine, to me, screams "cheap"....first impressions and all that stuff.