Basically, I have tried 3 different a4988 chips from Longruner, and none of them seem to work. The circuit diagrams are as shown in the attached url.
I'm using a Nema 17 Stepper motor, Current Rating (single-phase): 1.3A.
I've exercised the current limiting procedure using the formula I = Vref X 2.5, as I couldn't find the datasheet for Longruner a4988. I also factored in the 70% current and tuned Vref to 0.52V.
However on connecting the multimeter in Series to the stepper motor, I get no current reading and understandably, the Stepper motor won't turn.
Need help with my current project! Thank you in advance!
I am using an a4988 clone from Longruner and a LEORX Nema 17 2 Phase 4-wire stepper motor with Single Phase current spec. 1.3 A.
I carried out the current limiting exercise and factored in the 70% current for full step mode and clocked my potentiometer on the a4988 to 0.52 V. I don't see any current coming out of 1A 1B 2A or 2B upon connecting the multimeter in series. I have connected RESET with SLEEP on the a4988. Besides, I have tried this on three different a4988 (all from Longruner), and none work.
With this information, could you suggest something I can do to make it work?
The outputs of a stepper motor driver like this must either be completely open (in which case
nothing happens), or connected to an inductive load like a motor winding. Using a resistive load
can destroy the driver. Having intermittent connections while an inductive load is in circuit can
destroy the driver.
The best procedure is:
Use a multimeter to check the wiring of the motor so you are sure how the windings are arranged,
and that they are of the correct resistance.
Before powering anything connect the motor windings to the stepper driver securely, so there
is no possibility of intermittency.
Then power up and set the current limit as per instructions.
If it then doesn't work you need to power down and check the step and direction pins are actually
connected end to end, and not shorted to anything, and that the chip enable is active, etc etc.
You can use a multimeter to measure winding current, but these precautions are needed:
You must not use a multiranging setting on the meter, use the 10A setting and 10A terminal only...
connect in circuit securely (meter leads into screw terminals or something like that) - any chance
of a poor connection can trash the motor driver.
Another way of measuring the current that is perhaps easier is to add a 0.1 ohm shunt resistor in series with the
motor winding, and measure the voltage across that (then it doesn't matter about meter leads slipping,
continuity is solid). You can also use the 10A setting across that resistor to roughly measure the current
(meter's shunt resistance is much lower than 0.1 ohm typically).
jremington:
This is a very dangerous thing to do, and it won't work anyway, because the current limit is dynamic and very fast.
The surest and fastest way to destroy a motor driver is to disconnect the motor while the driver is powered.
You also need a large capacitor across the motor driver power terminals to avoid inductive spikes.
I suggest to buy motor drivers from manufacturers who document and support their products and clearly explain how to use them, for example Pololu.
Thanks!
I was following the tutorial:
when I put multimeter in series. I'm not sure if my interpretation of the article is correct.
I guess my last option is to let got of working on the seven a4988s I've and get a Polulu. that's where my head is at! it still is frustrating to know that I find myself at dead end with regards to troubleshooting.
Robin2:
This seems to be the same subject as your other Thread which I have already replied to.
I am suggesting to the Moderator to merge them.
Don't double post.
...R
My apologies! It wasn't intentional, but a product of browser issues that were confirming success of the post! I guess the cost I had to pay for using the edge. As I am looking to merge the threads, I can't find it. Not even through my profile. Not sure if anyone else has already done it.
The current measurement is okay as you did it, but if the stepper doesn't move it may indicate a blown meter. You also can check the current from the motor power source to the driver board, which flows through both motor coils together.
Over the weekend, I used a grbl shield I had and tested the a4988 & stepper motor successfully.
So, the issue is somehow with my connections or code. But this is progress! Thanks community for your continued insights.
MarkT:
The outputs of a stepper motor driver like this must either be completely open (in which case
nothing happens), or connected to an inductive load like a motor winding. Using a resistive load
Thank you MarkT. This was extremely helpful in understanding how I was risking my a4988.
Method of shunting is an excellent idea. I tried it over the weekend using a 0.1 Ohm 2W resistor. But I didn't get any reading in my multimeter(in Ammeter mode).
Upon testing my a4988 and stepper motor in the grbl shield, both seem to work fine.
And troubleshooting continues for me! more ideas welcome!
Following this topic I just got an idea and tested it on my stepper, a NEMA 17.
Connect Your multimeter in volt-AC-mode to one of the coils and try to run the stepper. Either I read 0 volts or some 8 - 9 volts. It depends of the position of the stepper. Then I know that the stepper driver delivers power.
Another way to check is connecting the stepper and power up the stepper power supply. Then try to rotate the stepper manually. If the stepper rotates easily You have no power to the stepper. If it rotates stepwise but with some effort from You, the stepper, and driver, is alive.
Yogue:
Method of shunting is an excellent idea. I tried it over the weekend using a 0.1 Ohm 2W resistor. But I didn't get any reading in my multimeter(in Ammeter mode).
If you measure the voltage across the 0.1 ohm resistor you can use the formula V / R = I (Ohms law) to convert the voltage to amps. For example if the reading is 100mV then the calculation would be 0.1 amps / 0.1 ohms = 1 amp
Be sure to do it when the motor is stationary. If there is no reading move the motor by a single step (with the Arduino) and check again.
Railroader:
Following this topic I just got an idea and tested it on my stepper, a NEMA 17.
I like the idea!
I've a desktop cnc milling machine that I am building, and two motors don't quite rotate, but they are stiff, and as you said, that means they have current in them!
Good. If You mechanicaly disconnect Your motors and turn the shafts by hand, how does it feel to rotate them? They should rotate quite easily. Otherwise the problem might be that the motors are overloaded. That should be audioble visible. A stalled, overloaded, stepper, makes a rather characteristc sound very different from normal.
Does Your motors run when being mechanicaly disconnected?
