Tech Tip: How to Choose and Use Stepper Motor Power Supplies

Tech Tip: How to Choose and Use Stepper Motor Power Supplies


Automation Direct offers a variety of Stepper
System Power Supplies, so how do you know which one is the right one for your application? Before answering that, let’s take a look
at how the stepper system works together. Stepper systems have a power supply, a drive,
and a motor. A PLC or some other kind of controller tells
the stepper drive how to take the current and voltage from the power supply and chop
it up to send positioning pulses to the motor. The Drive monitors the current consumed by
the motor and constantly adjusts it to provide precise positioning of the motor. In general, the more voltage you provide,
the better the motor will perform. You can see that on the motor curves. In this example with a 32 volt supply this
motor is limited to 1200 rpm and the torques falls off real fast. But with a 70 volt supply, the motor can run
out to 1800 rpm and still have about triple the torque. The bad news is the more Voltage and Current
you supply, the more heat you have to dissipate. So normally, you will usually want to choose
the supply with lowest voltage rating that will achieve the speed and torque you need. Beware that the voltage of an unregulated
supply tends to float higher with lighter loads, so make sure your un-regulated supply
stays within the drives tolerance. Of course, you don’t need to worry about
any of that if you are using an appropriate AutomationDirect unregulated SureStep supply
with an AutomationDirect drive– they are designed to work together. You can use this chart in the user manual
to figure out which AutomationDirect Sure Step power supply goes with which drive. These are the drives, these are the unregulated
power supplies. Why doesn’t this supply work with these
drives? Well, this is a 70 volt supply, and these
drives have a max input rating that is lower than 70 volts so we don’t want to use this
supply with those drives. That’s also why none of these will work
with this guy … their voltages are too high. But what about these guys? There are three possible supplies for each
drive. Now which one do you choose? We recommend two different ways to decide
which power supply to use. For a quick rule of thumb, if you select a
power supply with 2/3 the current output of your motors max phase current, you’ll be
in good shape. For example, this Stepper Motor from AutomationDirect
has a max phase current of 6.3 amps. Take two thirds of that – which is a little
overt 4 amps – and we quickly see that this 5 amp supply will handle the worst case load. If you are powering 3 motors, then you will
need three of these which is a 2 x factor. Etc. If you don’t think you will be anywhere
near the worst case load or maybe you are going into production and need to absolutely
minimize the cost of the end system, the second way to choose a power supply is to get one
power supply using the 2/3 rule – because you KNOW that will work – Then power up your
system, run it at it’s full load and simply measure the current out of the supply. To choose the voltage you need, just look
that motor curve and choose a voltage that will get you the motor speed you need. Easy. So far we have been talking about using unregulated
linear supplies. Can you use a switching or regulated supply? Sure! But, there are a couple you need to worry
about. When you first power up a drive system or
quickly accelerate a heavy load, there is a large current draw as the motor stator establishes
its magnetic fields. Regulated supplies may think that is a short
circuit and they’ll reduce – or fold back – to a lower voltage to protect themselves. Of course, the Rhino PSB series regulated
supplies from AutomationDirect are designed to work with the 48volt SureStep drives and
will help reduce these issues when compared to other supplies that weren’t specifically
designed to do this. The other issue with switching regulated supplies
is regen. That is, if you try to slow down a heavy load
too quickly – maybe you turn the power off while it is still ramping down – the motor
now becomes a generator and pushes current back up to the drive. The drive then tries to dump that back into
the power supply which can boost the voltage beyond what the supply expects to see. This can trip the overvoltage protection of
a switching power supply, and cause it to shut down. The best defense when using regulated or switching
supplies is to add a regen clamp. It goes between the power supply and drive. Its job is to take that extra energy and re-route
it to a large resistor to dissipate the power. We call that a braking resistor. This regen clamp from AutomationDirect has
a built in braking resistor that can dissipate 50 watts of power continuous and up to 800
watts peak. If you need to dissipate more power than that
you can just add an additional braking resistor. This one from AutomationDirect adds another
100 watts of continuous power dissipation. Remember, large current surges at startup
and large regen voltages coming back to the supply are only issues with switching or regulated
supplies. None of that applies to linear unregulated
supplies. Which explains why most folks like to stick
with the unregulated supplies – they just do the job without the extra concerns or hassle. AutomationDirect’s SureStep supplies are
all un-regulated so you don’t have to worry about any of that stuff. And one more important thing to keep in mind
– avoid the temptation to power stepper drives in a daisy chain. Wiring them in a star configuration with all
power wires starting at the power supply will help ensure that all drives get the same power
input and one drive doesn’t affect the others. If you have any questions about AutomationDirect’s
Stepper Systems, please contact AutomationDirect’s free award winning support team during regular
business hours. They will be happy to help. And don’t forget the forums! There are lots of experience automation professionals
there that love to share their years of experience. Just don’t post any questions directed at
AutomationDirect’s support team there, they don’t monitor the forums on a regular basis.

8 Replies to “Tech Tip: How to Choose and Use Stepper Motor Power Supplies”

  1. HI, if you can help me in calculating the electrical input and mechanical output powers and the efficiency of stepper motor

  2. Dear sir, I have a power supply which is 12volt and 30 Amps. I need to run Nema 23(3Amps each) 6 stepper motors. Will this power supply be OK for my work?
    Please sir, reply me. I will be grateful to you?

  3. Why does the motor controller need a 5 volt supply and is it a good idea to use the same 5 volt supply to supply the motor controller and the break out board, seems like there is opportunity to fry your expensive stepper circuit and break out board? I would think 2 separate 5 volt supplies could be used but I am not sure why the motor controller needs a 5 volt supply in the first place?

  4. Sir could you help me on how to select the SMPS (voltage, current values) for nema 17 and nema 23 for my project what will be the case if I use more than 2 stepper motors in my project….
    Reply me sir…

  5. I have a polulu stepper motor with a lead screw preattached to it, i used a battery holder with 8 AA baterries 1.5V each but instead of turning it vibrate instead. Is it because of my power supply? Should i used another type of power supply?

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