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A4988 Current Drawn

Hello,

I think this is a relatively matter, but somehow I’ve not been able to find this information. Do anyone knows what is the current drawn by the 5V pin in the A4988? I know from the motor it can draw up to 4 amps, but the other 5V pin its not clear.

The reason for this question is that I have connected a an LCD screen which draws 400mA from the power supple (12V, 3 amps). When I connect this LCD in conjuction with a stepper motor, the motor stall initially, and I have to give it a push to start running. My stepper motor operates at a current of 0.95mA, and I’ve set the vref to 0.544 volts (0.068 rs). I am also using an Arduino UNO board, which apparently can draw up to 200mA. I am not sure why would my motor stall with this LCD connected to it.

Any insights would be gladly appreciated

Hi.

According to the datasheet for the A4988 the logic supply should draw a maximum of 8mA. You mentioned a 12V supply, but not your logic supply. What are you using to supply 5V? Could you post pictures of your setup that show all connections?

-Claire

I used a L7805 regulator to supply all of my 5V componets (the arduino uno, the lcd and the a4988). I previously connected the arduino via USB to power both the arduino and LCD (still had the same result).

I should mentiont that the LCD being used is a Nextion 5in LCD. I also have 3in nextion LCD which draws 87mA, and the motor works fine using this one. When I use the 5in LCD the motor stalls and the screen gets flickery. My believe is that not enough current is being drawn from the power supply, even though it is rated to output 3A.

Could you measure the voltage at your 12V supply and 5V output of the L7805 regulator both before and after adding your 5 inch LCD?

-Claire

Hi Claire,

I tried what you mentioned. Before and after adding the LCD, on the 12V side, nothing changes, but on the 5V side, the voltage dropped by about 2.5V when adding the LCD. Not sure why this happens though since it is connected in parallel.

Danny

Since the output of your 5V regulator is dropping but the output of the 12V regulator is fine, it seems clear that your L7805 is not able to supply enough current. One solution would be to add a separate 5V regulator for the LCD.

-Claire

Hi Claire,

Thank you again for your response. I have tried adding a separate regulator to power just the LCD, but the same occurs where flickering happens and the motor stalls. I tried adding a 470uF capacitor (advised by some other forum) in patallel with the output of this isolated L7805 regulator. With this method, the LCD and the motor worked fine, but after the motor stop (where the motors are still energized with holding current) the LCD starts to flicker again with the addition of burning smell.

I contacted Nextion but were not particularly helpful. The only suggestion they gave was to use a separate power supply of a clean 5V and 1A. If this is the only safe way to protect the LCD, then i’ll resort to this option. But would you happen to know a good way to step down a 12V to 5V, and protect this 5V from any changes in voltage and current on the 12V circuit? Will a buck converter be a better option?

Thank you for your support.

Danny

The capacitor making your LCD and motor work better implies to me that your 12V supply is probably not powerful enough. Linear regulators are inefficient, so changing to a step-down switching regulator might also help enough. It sounds to me like your A4988 is working properly, so I cannot help too much with the rest, but here are some thoughts to get you started.

First, I would figure out where the burning smell is coming from. Keep in mind though, whenever you smell burning, some component might be in danger of getting damaged. Next I would monitor the voltage of the 12V supply and input and output of each 5V regulator under various conditions (preferably with an oscilloscope) to see where the voltage is dropping or cutting out. It might be helpful to compare a working system with your lower power, 3 inch LCD to the setup with the 5 inch LCD.

-Claire

Hi Claire,

Thank you for your tips. Unfortunately I do not have an oscilloscope with me at the moment so I am only relaying on a multimeter.

Fortunately, after recieving the buck converter It seemed to work fine. The linear worked great for the controller, but not for the LCD. Since I dont have an oscilloscope, can only assume that the linear regulator was shutting down with the amount of current passing by. I still added the 470uF capacitor on the 5V side of the buck converter just to smooth out the signal further.

Thank you for your support Claire.