Hi, I am new to circuits and electronics in general, and have several confusions when it comes to driving multiple stepper motors. I am intending on driving two nema 17 stepper motors (17HS4401) with two A4988 drivers. I will be trying to microstep (~1/4) at a low RPM. I have a few questions that are mostly related to supplying power to the circuit.
I am not entirely sure if it is correct. Feels strange to see the two decoupling capacitors in the schematics side-by-side. Please help me check the layout of my circuit. The GND for the power supply was also labeled as (-) in the schematics. Not sure if that is normal or if I just connected them incorrectly.
On the Amazon listing for the motors, it said it has a current of 1.5A and a phase resistance of 1.5ohms. It also states it has a rated voltage of 3.6V. I am not sure how they got that voltage since I couldn''t get that same number no matter how I multiply. If I go by this datasheet, 17HS4401 has a rated current of 1.7A and a phase resistance of 1.5ohms. After following the formula I found in this forum thread, I assume the wattage of each motor is 1.7A^2 * 1.5ohm * 2 = 8.67W, which is about 18W for 2 motors, and 36W if doubled for inefficiencies. Am I correct in thinking that I can use a 18V 2.5A (45W) power supply?
In addition, if I want to use a power supply with a DC power jack, would I be using a screw terminal adapter to connect it to a breadboard? Also, since the datasheet for the driver specified a minimum 47 µF capacitor, does that mean I can use any capacitor that has larger value than 47?
The cap should be close to the driver module. A single cap can only be close to one module.
A supply can be labled (+) and (-)
In this case (-) is ground.
Those motor drivers working like switching buck converters, so you should calculate with power, not current. An 18volt/2.5A supply seems ok for two motors.
The A4988 is a 1Amp driver. If you need the full torque of the motor (1.5A setting) then you should use a different driver.
Never use a breadboard for motor connections.
A poor contact will instantly fry your driver.
The cap should be close to the driver module. A single cap can only be close to one module.
I see. That is why it seems odd in the schematic diagram for me. I assume their positions are correct on the fritzing diagram. Here's the updated schematics:
Since you have an Uno you might want to consider using a CNC shield V3. Really does simplify using steppers and is more secure than a solderless breadboard.
It has spaces for 4 stepper drivers like A4899 or DRV8825 and connections for limit switches and other peripherals. The caps are installed and there are jumpers for setting microstepping.
I am having trouble understanding the max power/current I can use for the power supply. I understand that the drivers need 8-35V of voltage (min 12V with the shield), and that you need proper amount of total wattage from the power supply. But there was no mention of maximum supply current on the datasheet I showed in the original post . When I was trying to buy a power supply online, I saw one that is 20A (240W). I didn't go through with the purchase as I was worried it was too much power/current.
I asked the guy at my local electronics store and he said the maximum should be around 2A. I checked the datasheet for the driver on their website, and it seems to say ±2 A. But I suspect it might be referring to the max current it can output to the motors and not the current it can take.
Are there limits to how much wattage/current you can supply to the drivers from the power supply? How can I find out about that information? Or does that not matter since the power goes through the built-in translator and has nothing to do with the logic of the driver, meaning I can go as high as I want for the input current?
The driver can limit the current to the motor. You could have a 12V 20A power supply feeding several drivers, and the drivers can limit the power to the steppers so the coils and driver aren't overloaded.
I ordered 4 a4988's to work with the cnc shield. As I was testing them, uno keeps turning off (onboard led gradually dimming till off) once I connect it to the shield. It kept happening and I was very confused. After some isolation tests, I realized the problem came from one driver—as soon as I use it, the uno turns off.
While I found the culprit, I am very curious as to why the driver caused that problem. Does anyone have an idea?
