# A4983 Stepper Driver

Hi,

I recently got an A4983 Stepper Driver that I am trying to use for a project and running into some issues that seem strange. I have a Lin Engineering 4118 Stepper Motor that has resistance of 2.7 Ohms/Phase and requires current of 1.4 Amp/Phase. Would think this driver could handle this fine with the 2 amp limit. It seems to be switching on an off as I reach about 1.3 Amps measured (not even using the 1.4 scaling factor) while trying to set the correct current limiting. This setup is currently running from a power supply that supplying approx 12V. Cant have a driver that is switching on and off. Any ideas?

Jon Anderson

Hello.

What do you mean by switching on and off? Do you think the thermal shutdown is kicking in? What is your power supply, and can you look at your power lines with an oscilloscope? With the numbers you gave, you’re asking for way more than 2A from the power supply, which could certainly be limiting things; you could also be at a thermal limit.

I’m not sure what you mean by the “not even using the 1.4 scaling factor” comment.

- Jan

By switching on and off, I mean the current at my ammeter reading is droping from about 1.3 amps to very low readings around 0 and then jumping back up. The motor is loosing all of its holding torque when this dropout occurs. This dropout has also occured at lower currents. The driver seems to not be supplying holding current to the motor at all times. The power supply is a GW Instek DC Lab supply 18V 5A, I also have a GW Instek 30V 3A DC Supply. Pretty sure its not a thermal shutdown. 12V / 2.7 ohms = 4.44 A I would think the first supply could supply that.

From the instructions:
The A4983 supports such active current limiting, and the trimmer potentiometer on the board can be used to set the current limit. An easy way to set the current limit is to put the driver into full-step mode and to measure the supply current to the board without clocking the STEP input. The measured current will be 1.4 times the current limit (since both coils are always on and limited to 70% in full-step mode).

This makes me think that I should be measuring about 2 A of current when I am setting the driver to drive a 1.4 A motor.

Jon

Why do you think it’s not a thermal shutdown? What’s the frequency of the cycle? Does the board get quite hot at lower currents?

Your current calculation doesn’t factor in two coils. It shouldn’t actually get that high if it doesn’t rise too quickly, but you are still asking a lot of these parts, and it would be interesting to see what the voltage waveform actually looks like. Can you take a look?

You initially said your motor requires 1.4A/phase; is that something you’ve measured? Do you actually need that? What you’re describing sounds quite a bit like a thermal shutdown kicking in, and if the chip is overheating, it might not be able to handle your application.

- Jan

I am not even trying to step the motor right now, just trying to set the current.

The motor is 1.4 Amp/Phase (as per the manufacturers rating) but my understanding was that this driver can supply up to 2.0 Amp/Phase. Looking at again I see your rating is 2 Amp/Coil, whereas most other stepper driver manufactures rate them in Amp/Phase ratings (as this is the reading that motors are sold with).

Seeing this, I’m guessing this problem may be thermal shutdown. My motors running at 12 V require approximately 4.4 Amp/Coil which is definitely far above the 2 Amp/Coil rating.

I guess my suggestion would be to make sure that the website clearly labels the units on the current rating as it seems to be different than the industry standard (Amp/Phase). This will help prevent disappointment such as my own, getting a driver that at glance looks much more powerful than it is. Also stuck with a driver now that has little or no use for my purpose.

What is the distinction you are making between current/phase and current/coil? By the way, you say you aren’t even trying to step the motor, but the non-stepping case where both coils are driven is the highest-load case. Do you really need the maximum holding torque the motor can provide? I understand that it would be better for the motor driver not to be the limiting factor, but you could set the current limit a bit lower and still use the motor, right?

- Jan