How to check the real current of the stepper motor

Phaedrux

@moth4017 said in How to check the real current of the stepper motor:

M98 P/macros/3zhome

What do you have in that macro?

zapta

@moth4017 , oscilloscope is tricky for this application because it doesn't measure current and because one of it's wires is grounded.

A simple DVM in amps range should be sufficient because the current is stable when the motor does not move. Have a gcode macro that will move the motor in tiny steps and see when you have the max reading. If you want to get fancy, you can have a bidirectional analog meter like this +/-2A one https://www.aliexpress.com/item/32400650799.html

Edit: just make sure to make all the connections when the printer is off because stepper drivers don't like when motors connect/disconnect under power.

zapta

@moth4017 , I haven't tried it myself but I believe that running a macro like this one while observing your current meter connected in series to any X or Y stepper coil will allow you to measure the max current.

; Move slowly to identify peak stepper current.
; Assuming XY are already homed.

G90   ; absolute positioning
G1 X100, Y100 ; starting point

G91  ; relative positioning

while iterations < 500
  echo "Iteration " ^ {iterations}
  ;G1 X0.001 Y0.001  ; for cartesian printer
  G1 X0.001               ; for core XY printer
  G4 P250   ; Wait 250ms

G90   ; absolute positioning

moth4017

@phaedrux said in How to check the real current of the stepper motor:

What do they report?

2/20/2022, 2:31:05 PM: Connected to 192.168.0.19
2/20/2022, 2:31:24 PM: M906: Motor current (mA) - X:800, Y:800, Z:600, E:1200, idle factor 30%
2/20/2022, 2:32:40 PM: M913: Motor current % of normal - X:100, Y:100, Z:100, E:100

moth4017

@phaedrux
M400
M569 P0.4:0.5:0.6 V10
G4 P100
M574 Z2 S4
M906 Z300 ; set motor current
G91 ; relative positioning
G1 H2 Z0.2 F3000 ; power up motors to ensure they are not stalled
G4 P100 ; wait 100ms
M400 ; wait for current moves to finish

G4 P200
M915 P0.4:0.5:0.6 S0 H10 F0 R0 ; Configure Z-Axis Stall Detection

G4 P200
G91 ; relative positioning
G1 F4000
G1 H1 Z350 ; Home Z-Axis actuators independently
M400 ; make sure everything has stopped before we make changes
M906 Z600 ; Reset motor current
G90 ; absolute positioning
G92 Z301 ; set position
G91 ; relative positoning
M84 ; Motors off

then run
m906
Motor current (mA) - X:800, Y:800, Z:600, E:1200, idle factor 30%
m913
Motor current % of normal - X:100, Y:100, Z:100, E:100

moth4017

@phaedrux
ill give it a try tomorrow. Thanks very much

moth4017

@zapta hi was going to do a differentual measurment using 2 channels on the scope with a very small resistor in line e.g 0.01ohms

zapta

@moth4017 said in How to check the real current of the stepper motor:

@zapta hi was going to do a differentual measurment using 2 channels on the scope with a very small resistor in line e.g 0.01ohms

I think that should work, assuming the scope's sensitivity and offset or good enough. You can use x1 probe since bandwidth is not an issue. I got recently an OWON HDS242s for similar applications since it's floats when running on battery. BTW, I just tried here the approach with a Amp meter and very slow movement and it seems to work. I got about 950ma DC max with RRF configured to 1200ma (?).

https://www.youtube.com/watch?v=xaELqAo4kkQ

zapta

Here is a better macro for measuring current. Simplify connect a current meter in series to one of the stepper coils, turn on the printer, home, run the script, and observe how the current changes slowly between negative and positve max currents.

; Assuming x,y are homed.
G1 X100 Y100 ; move to starting point
M203 I1      ; allow slow movements
G1 X103 F1   ; move both motors slowly, corexy version
; G1 X103 Y103 F1   ; cartesian version

moth4017

@zapta its ok used you first macro
M906 600 measured max 0.5179mA
M906 1000 Measured max 0.6414mA

i tried to test the extruder but couldn't get to extrude for some reason

moth4017

@moth4017 said in How to check the real current of the stepper motor:

@zapta its ok used you first macro
M906 600 measured max 0.5179mA
M906 1000 Measured max 0.6414mA

i tried to test the extruder but couldn't get to extrude for some reason

values in Amps not mA

dc42

@moth4017 bear in mind that when the stepper driver is moving slowly, standstill current reduction will kick in.

zapta

Thanks @dc42. A couple of questions if you don't mind. Having a simple technique to measure actual current would be very useful.

The code that @moth4017 used moves 0.001mm every 250ms. Will this kick in the standstill current?
What about the code below, will it kick in the standstill current?

G1 X100 Y100 ; move to starting point
M203 I1      ; allow slow movements
G1 X103 F1   ; move both motors slowly, corexy version

Any suggestion for a reliable way to measure the actual current using simple means?

dc42

@zapta on the TMC2209, standstill will kick in when the frequency of step pulses is less than approx. 12Hz. So the axis speed below which standstill current reduction kicks in depends on your steps/mm. For example, if you have 100 steps/mm, then 12Hz corresponds to 12/100 mm/sec = 0.12mm/sec = 7.2mm/min.

When measuring motor current you can use M917 to set the standstill current to 100% of the running current for a particular axis. At high currents, on the MB6HC and EXP3HC RRF will impose a maximum standstill current below 100%, but this doesn't apply to the Duet 3 Mini.

zapta

Thanks @dc42. I updated the macro to disable standstill current reduction and am getting now very consistent current readings, peaking at ~1250ma with 1200ma configuration (good). This is with a Mini 5.

G1 X100 Y100   ; Starting location
M203 I1        ; Allow very slow movements
M917 X100 Y100 ; Disable standstill current reduction.
G1 X103 F1     ; Move slowly. Moves both motors with coreXY

I also ordered this +/-2A meter, may be more visual https://www.aliexpress.com/item/32400650799.html

moth4017

@zapta
M1000 requested measures 0.8379A with you new script

moth4017

@zapta
ive deleted the macro that contained
; Move slowly to identify peak stepper current.
; Assuming XY are already homed.

G90 ; absolute positioning
G1 X100, Y100 ; starting point

G91 ; relative positioning

while iterations < 500
echo "Iteration " ^ {iterations}
;G1 X0.001 Y0.001 ; for cartesian printer
G1 X0.001 ; for core XY printer
G4 P250 ; Wait 250ms

G90 ; absolute positioning

but it is still continuously running , where would it be hiding so i can stop it

zapta

@moth4017 said in How to check the real current of the stepper motor:

but it is still continuously running , where would it be hiding so i can stop it

It should stop after a minute or two. What I do is pressing on the red STOP button on PanelDue or DWC to reset the machine. This also resets any configuration changes the script may do.

zapta

@moth4017 said in How to check the real current of the stepper motor:

M1000 requested measures 0.8379A with you new script

I guess it's now a question to the Duet team, is this a reliable measurement and is the result within the expected range.

dc42

@zapta I would expect it to be closer than that, it should be less than 10% out.