Confused about selecting the correct Amperage for a stepper motor

Projects General Guidance
1

Hi!!!
I've been reading a lot about stepper motors lately and every time I find a new piece of Information all the things I believed come apart. I'm still confused when selecting the correct amperage for different kinds of stepper motors. Please , correct me If I'm setting up some of these settings wrong.

I'm using DM542 Fully Digital Stepper Drive which lets you decide which amperage to use using switches on the side.

Switches
Switches960×297 26.1 KB

dm542.pdf (385.0 KB)

In the first set up I'm using the 17HS8401 Stepper motor, which documentation says Rated Current(A) is 1.7.
17HS4401-MotionKing.pdf (94.9 KB)

Following the documentation of the stepper driver I should multiply the value of the rated current by 1.4 and select it as a setting:

4 lead motors are the least flexible but easiest to wire. Speed and torque will depend on winding inductance. In setting
the driver output current, multiply the specified phase current by 1.4 to determine the peak output current.

So I should use the 2.37 Peak current 1.69 RMS Current.

In different posts I've read the Rated current the step motor provides means that is the maximum you should provide to the motor.

  1. Am I frying the motor by saying the peak current is 2.37? Should it be lower?
  2. Does this value determine how fast the stepper motor can go?
  3. Can modifying this value result in missing steps on the motor?

In the second set up I'm using a stepper motor Rated 3A so using the same method the settings I should use is 4.20 Peak current and 3A RMS current? Is this right?

I'm aware the controller has an autoconfiguration for the current so you don't have to worry about these things but I want to understand how it works in case I work with other controllers.

Microstepping
This driver, doesn't allow fullsteps , so I'm forced to use Microstteping.
I've also read in some tutorials that when you are microstepping , you should use more Amperage than normally. Is this right? Does it apply to my case?
If I decide to switch to another driver , and I don't use microsteps, does this rule of currentAmp * 1.4 apply? I'm guessing I should follow only the instructions of the driver and nothing more , but I've read so many things I don't know what to believe anymore.

Sorry if you read this and you thing the answer is very obvious, I have a very hard time understanding currents and circuits.

2

Stepper motors are rated for steady state (DC) current, the problem being heat generation. In terms of heat generation, steady state and RMS current are equivalent. So 1.69 A RMS is fine.

Steppers are designed to run hot (too hot to touch), but do not exceed the manufacturer's recommend casing temperature.

3

Use the RMS current, since wattage varies with the square of current, 1.414 squared times 1.69 = 3.38, 2 times the wattage (heat).

4

Don't over-think. Just use the settings table on the motor.
1.7A motor > closest setting 1.46A.

Google "A4988 datasheet", and look at the table in the datasheet what the current does during micro stepping. Motor current could vary between 100% and 142% (over two coils), depending on position.
Leo..

5

See what I mean , I recieved different answers for the same question, I'm still unsure what's the correct set up.

6

All the replies say 1.7A

7

No they don't.

8

ON ON ON ON is 200 which would be full step

1 Like
9

Motor current is not as important as you might think it is.
If you set the driver to 1Amp for a 1.7Amp motor it will still run.
Just with a bit less torque. Which is fine if you don't need it.
If you set the driver to 2.5Amp it will also be fine.
The motor (not the driver) will just will get (too) hot after a while.
Recommended current is a compromise between torque and heat.
Leo..

2 Likes
10

I've tried to ; the motor starts vibrating a lot and rotates incorrectly. That's why I assumed it doesn't support fullstep. Even the driver name says MICROSTEPPER controller.

11

I need to find the right settings for different motors:
1.high speed with good amount of torque so I don't have missed steps.
2. Motor has to operate for long times. I am disabling them after a while if they are not in use, but I don't want to break any more motors.

Thank you , I think I will play with lower current and see if I have any missed steps to find what fits best.

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