Which one should you buy, regulated (switching) or unregulated power supply?

Both regulated and unregulated power supplies can be used to supply stepper drivers and motors. However, unregulated power supplies are preferred due to their ability to withstand current surges.

Regulated power supplies were designed to be used with sensitive equipment, such as computers and electronic parts. The idea of the regulated power supply is to always maintain a clean and consistent power source. Something electronic parts desperately require. To do this, the regulated power supply is always adjusting and manipulating voltage and current levels. If the power supply can't maintain proper levels, it shuts down and "faults out ". Which is a good thing. This will protect the electronic components.

Regulated power supplies are also nice because they are already in a finished form. Add a power cord, wire in your driver and your done. No need to build a power supply from many parts. Prices are reasonable. Overall size and weight make them a good choice as well. Built in fans and multiple outputs, again make them attractive to the buyer.

Now here are the inherent problems.

If a regulated power supply (switching) is chosen, it is important to have a large current output rating to avoid issues such as current clamp. If your power supply can't maintain voltage and current levels, it will shut down. To avoid this issue you must choose a power supply that is bigger then the load it is to drive. For example, use a 4 amp supply for 3 amp motor driver operation. This is required mainly due to the fact that when a motor is first started up, it will briefly draw more then it's rated current (in rush current), albeit for a very brief moment but enough to "fault" the driver.

Another issue is to understand the relation between the motor and the power supply. Stepper motors are not very power "friendly". Steppers are constantly, speeding up, slowing down, holding, braking etc. There is nothing consistant about their power requirements. This is tough on a regulated power supply, who's job is to be consistant. It would rather power electronics, the demand is much easier.

One of the most common and destructive issues with stepper motors on regulated power supplies is current feedback to the power supply. This is when a stepper motor is (usually) slowing down or is being driven by a load on the motor. This turns the stepper motor into a generator rather then a motor. If the current produced by the motor reaches the power supply it will, at the very least, "fault" the power supply. Or worse, damage the power supply.

With this said, it would be easier on the power supply to have multiple motors connected to it. This way the power requirements are not as crazy. When one motor is slowing down, another is speeding up. The accelerating motor can actually pull current from the slowing motor. This makes it much easier on the regulated power supply to maintain voltage and current levels with out "faulting". This can also be corrected by adjusting acceleration and de-acceleration times to be much longer and at slower rates. As we add with multiple motors, we have to worry about start up current. Again, we must size up our power supply to avoid "faulting" the power supply on start up.

During testing, it was found that when one motor was connected to a regulated power supply, it "faulted" more often on de-acceleration then any other time. This was finally corrected by increasing the size of the power supply to a size much larger then the draw of the motor.

The "oops" factor. Once in a while we find ourselves goofing up and making mistakes. The nice thing about a regulated power supply is it will "fault" out when you most need it. Years ago a customer wired 3 drivers to a regulated power supply. He got confused and reversed the feed wires to the drives. Lucky for him all that happened was the power supply shut down. If he had done that with an unregulated power supply things may have been much worse. So the very problem of avoiding a "faulting" power supply, saved him in the end.

Unregulated power supplies.

If you were to look at a Toroidal transformer, it's just wires and a core. It has no care in the world about regulating current or voltage. It will give all it can no matter what the demand is. If it is rated at 3 amps and your motor is drawing 10 amps. It will give you the 3 amps and try to give you more. So is this a good thing? Well the unregulated power supply wont "fault" out. So the good news is, your motors will keep moving or at least keep trying to move. The bad news is that this may cause your transformer to overheat and burn up. So again, we must size correctly. A quick current surge is fine but if you are greatly exceeding the power requirements of the power supply things will start to burn up.

If an unregulated power supply is used, one may use a power supply of lower current rating than that of motor (typically 50%~70% of motor current). The reason is that the driver draws current from the power supply capacitor of the unregulated supply only during the ON duration of the PWM cycle, but not during the OFF duration. Therefore, the average current withdrawn from power supply is considerably less than motor current. For example, two 3A motors can be well supplied by one power supply of 4A rating.

Unregulated power supplies require that you have to build them with rectifiers (changes transformer current from ac to dc) add in a large capacitor (for storage of electrical energy) and an over current device (ie, a fuse, to protect the transformer and connected equipment).

In conclusion what should you buy?

Right now the industry is coming out with stepper drivers that are AC input. So to connect up a Toroidal transformer is very easy to do. You don't need to build a power supply with capactitors and rectifiers etc. Just wire it into the drive. So that would be the number one pick if you are building a large Nema34 motor set up.

If your driver requires DC input then it really depends on your experience and how smart you are at building things. It would be better to build an unregulated power supply but it's splitting hairs at this point. Buying a regulated power supply (correctly sized) will work very well and there will be no issues.

If you are using small Nema 23 or Nema 17 motors, just purchase the regulated power supply. That's all you'll need.

Should I feed my stepper drivers with AC or DC power supply?

If the stepper driver you have purchased requires DC as it's power requirements, then you can only supply it with DC power. If your driver requires AC then it can either take AC or DC power.

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A note about power supplies.
Regulated Power Supply
Unregulated Power Supply