I recently purchased an Arduino Mega 2560 with a Ramps 1.4 Shield and some A4988 Motor drivers (Link:https://www.amazon.de/gp/product/B01NCZ09Q5/ref=ppx_yo_dt_b_asin_title_o00_s00?ie=UTF8&psc=1)
to drive a Nema 17 59Ncm/2A Stepper Motor. After reading up on the Topic I found a lot of threads talking about how to Limit the Current provided to the Motor and followed their Instructions.
As you can see the A4988´s are not Original Polulu´s and so my Rces 0,05 Ohm but 0,1 Ohm wich means with this Formula: Vref = Imax8Rces i should set Vref to 1,12V to drive my Motor with 70% of its maximum Current (The Reference Voltage on my A4988s jumps back down to 0 if i turn it "above" ~1.25). I power the Ramps Board with an old Pc Power Supply rated to 12V 15A.
Now to my Problem wich is that no matter what i set the Reference Voltage to, if I measure the Current through one Coil (with the Step Pin set to High) it draws 2.3 Amps wich obviously is way too high.
I havent found anyone having this Problem and I am 100% shure i followed the Steps to set the Currentlimit correctly. All 5 drivers behave the same way and switching from the X-Axis driver "Spot" on the 1.4 Ramps to the Y-Axis Spot did not change anything either.
An A4988 is not capable of delivering the 2 amps your motor requires. The DRV8825 which is a plug-in replacement will also struggle to deliver 2 amps.
For a 2 amp motor I would use a driver than can deliver at least 3 amps and those driver probably don't fit onto a RAMPS shield.
Be VERY CAREFUL never to connect or disconnect the wires between the motor and the stepper driver while the driver is powered up. The driver will be instantly destroyed.
I also have a smaller stepper motor rated to 0.8A I´ll have to try if its the same with that motor. I dont believe i destroyed it because if I run the Test Code for the Ramps 1.4 the Motor turns just fine and the Controller doesnt get that hot.
conseil:
Now to my Problem wich is that no matter what i set the Reference Voltage to, if I measure the Current through one Coil (with the Step Pin set to High) it draws 2.3 Amps wich obviously is way too high.
How exactly are you measuring this current? You realize that the motor driver must either have no load, a very
light load (resistor+led for instance) OR it must have the motor winding as an inductive load.
If for instance you tried to measure the short-circuit current of the driver you'd risk burning it out and
the reading would be essentially meaningless. Measuring current requires breaking the circuit and
putting the meter in series with the motor, which begs the question can you guarantee that connection
is rock-solid (if not you can easily blow up the driver). And of course any connections and
disconnections can only be carried out with the circuit powered down.
I'd just check that the shunt resistor is 0.1 ohm as you think and set up the chip as per directions.
Don't expect to get more than about 1.2A from an A4988, so don't try to set it higher.