Problems with power supply for stepper motors connected to A4988 drivers

Hi,

As mention in the title, I may have problems with the power supply. The power supply I have chosen for my project is just 8X1.5V AA batteries to provide a voltage of 12V. I have attached a wiring diagram as well.

The goal is to have 2 motors rotating together to drive a robot and another to actuate a movement hence the 3 motors. Stepper motors are required so I can't change them to another motor or anything. I have set the potentiometer in the A4988 drivers to only supply an output current of 1.9A

The problem is that the motors starts turning sluggishly and then just vibrates without turning. This occurs during the 4th or 5th time of re-running a simple program like turning clockwise 300steps and back. The first couple of times works fine so I do not think it is the wiring issue like the motor's wire is connected to the wrong pins.

What I have tried so far,

  1. Changing batteries which work for the first couple of times and then the problem comes back.

  2. Adding more batteries(4 more 1.5V batteries so total voltage would be 18V) but the problem still persists.

  3. Setting the potentiometer to provide an output current of 1A. The problem comes back but is delayed further.

From my understanding, if a certain amount of current is drawn from the battery, the voltage of the batteries drop. Could the drop in voltage and not having a constant DC voltage to the a4988 driver be the issue?

Since the robot only needs to work once, this issues isn't a big deal but I need to constantly test it to see whether the motors are turning properly and this issue is preventing me from doing so. I do not have a 12V DC adapter or a variable power supply.

To summarise, I would like to know,

  1. Is my power supply really the problem?

  2. If I set the driver to have an output current of 1A for the stepper motor? Does it mean that I only draw 1A of current from my power source, aka batteries? So if I run 2 stepper motors at once, the current drawn would be 2A?

  3. Could a voltage regulator help fix this issue?

The wiring diagram is here.

The motor driver and battery supply are both inadequate for your project.

The A4988 can't provide 1.9 Amps on a continuous basis. It will overheat and shutdown. You can expect only about 1 Ampere steady state, without extra cooling. With the DRV8825 driver, you might be able to get 1.5 amperes steady state.

Fresh alkaline AA cells can provide up to 2 Amps for a few minutes, then the internal resistance starts to go up and the voltage will drop.

NiMH batteries have much higher current capabilities than alkaline batteries and would be a much better choice, as they are easy to charge, tolerant of abuse and don't have the very serious problems associated with LiPo batteries.

Thanks for your quick response.

The drivers I used has a heatsink on them so it should be fine and should be able to handle 1.9Amps without any issue according to the Polulu webpage. I have spares but to be on the safe side, I will set it to 1Amps in that case.

For the power source, I will take your advice for it, using NiMH batteries instead of the LiPo batteries.

Before I go buy myself the new batteries, can someone kindly provide me with an explanation to my problem? :slight_smile:

cmleong2618:
The drivers I used has a heatsink on them so it should be fine and should be able to handle 1.9Amps without any issue according to the Polulu webpage. I have spares but to be on the safe side,

If you set the current too high the driver will shut down from over-temperature which will give very erratic behaviour that might look like a software problem. It should not result in damage to the driver.

As far as the batteries are concerned you need to know how many watts the motors require. You need to post a link to the datasheet for the motors. For example a motor that requires 2 amps at a nominal 3 volts uses 6 watts per coil or about 12 watts total. And 12 watts from a 12v battery amounts to 1 amp. But I would double that to allow for inefficiencies.

...R
Stepper Motor Basics
Simple Stepper Code

  1. Yes

  2. Not exactly. The current is per-coil and there are 2 coils in 1 stepper. But they are never both driven together.

  3. No.