Duet 3 6HC max pwm is only 3.8V

[Alijambo73]

Im trying to connect a vfd to out 9 using this pwm converter https://www.amazon.com/dp/B091B6LGXB?ref=ppx_yo2ov_dt_b_fed_asin_title

When i measure the pwm signal it is only putting out 3.8 volts when i turn the spindle on at the max rpm of 24,000. The voltage out is only getting to 9V.

; Configuration file for RepRapFirmware on Duet 3 Main Board 6HC
; executed by the firmware on start-up
;
; generated by RepRapFirmware Configuration Tool v3.5.4 on Mon Sep 09 2024 22:47:07 GMT-0600 (Mountain Daylight Time)
 
; General
G90                                          ; absolute coordinates
M83                                          ; relative extruder moves
M550 P"Duet3CNC"                             ; set hostname
 
M453                                         ; select CNC mode
 
; Accessories
M575 P1 S0 B57600                            ; configure PanelDue support
 
; Smart Drivers
M569 P0.0 S1 D2                              ; driver 0.0 goes backwards (X axis)
M569 P0.1 S0 D2                              ; driver 0.1 goes backwards (Y axis)
M569 P0.2 S1 D2                              ; driver 0.2 goes forwards (Z axis)
M569 P0.3 S1 D2                              ; driver 0.3 goes forwards (U or Y2 axis)
M569 P0.4 S1 D2                              ; driver 0.4 goes forwards (V or Z2 axis)
 
; Motor Idle Current Reduction
M906 I30                                     ; set motor current idle factor
M84 S1000                                    ; set motor current idle timeout
 
; Axis
M669 K0                                      ; set Cartesian kinematics
M584 X0.0 Y0.1:0.3 Z0.2:0.4 U0.3 V0.4 P3     ; U=Y2 V=Z2 set axis mapping
M350 X16 Y16 Z16 U16 V16 I1                  ; configure microstepping with interpolation
M906 X1205.2 Y1100.4 Z1100.4 U1100.4 V1100.4 ; set axis driver currents
M92 X100.067 Y100.067 Z400 U100.067 V400     ; configure steps per mm
M566 X60 Y60 Z60 U60 V60                     ; set maximum instantaneous speed changes (mm/min)
M203 X12000 Y12000 Z3000 U12000 V3000        ; set maximum speeds (mm/min)
M201 X600 Y600 Z60 U600 V60                  ; set accelerations (mm/s^2)
 
; Axis Limits
M208 X0 Y0 Z-100 U0 V-100 S1                 ; set axis minimum
M208 X1252 Y2467.8 Z140 U2467.8 V140 S0      ; set axis maximum
 
; Endstops
M574 X1 S1 P"io1.in"                         ; configure active-high endstop for low end on X via pin io2.in
M574 Y1 S1 P"io2.in+io3.in"                  ; configure active-high endstop for low end on Y via pin io2.in
M574 Z2 S1 P"io4.in+io5.in"                  ; configure active-high endstop for high end on Z via pin io4.in
;M574 U1 S1 P"io3.in"                     ; configure active-high endstop for low end on U (Y2) via pin io3.in
;M574 V2 S1 P"io5.in"                     ; configure active-high endstop for high end on V (Z2) via pin io5.in
 
; Probes
M558 P5 C"!io6.in" H5 F120 T6000             ; configure analog probe via slot #0
G31 P850 X-10 Y-10 Z5.89                     ; set Z probe trigger value, offset and trigger height
 
 
;M574 V2 S1 P"io5.in"
;M666 Y+2						   ; move Y1 motor -1.5 from block to adjust for square
 
; Heaters
M140 H-1                                     ; disable heated bed (overrides default heater mapping)
M141 H-1
 
; Tools
M453                                         ; Set to CNC mode
M950 R0 C"out9" Q1000 L0:24000 K1          ; configure spindle #0
M563 P1 S"Makita R0701C" R0 F0               ; create tool #0
 
; Lasers
M950 P2 C"out4"                              ; air Assist solenoid
; Laser offset from spindle is X - 57.5 Y - -49.10
M452 C"io7.out" R255 F500 S1                 ; configure Laser port
;M563 P2 S"Laser"
;M452
 
 
; LED Lighting
;M950 P3 c"out1" Q500
M950 F0 c"out1" Q500
;M42 P3 S1
M106 P0 S0 H-1 C"LEDs" 	
;M563 P0 D-0 R0 ; tool 0 uses extruder 0, heater 1 and fan 0
 
; Emergency Stop
M950 J1 C"io8.in"
M581 T1 P0:1 S1 R0
;M582 T1
;M42 P2 S1
 
 
; Tools
 
M563 P2 S"Laser" F0
;M568 P0 F0                        ; set initial tool #0 active and standby temperatures to 0C
 
; Miscellaneous
;M452                                     ; select Laser mode
T0                                           ; select first tool
M308 S10 Y"mcu-temp" A"MCU"
M308 S11 P"DRIVER_0" Y"drivers" A"X Driver"
M308 S12 P"DRIVER_1" Y"drivers" A"Y Driver"
M308 S13 P"DRIVER_3" Y"drivers" A"Y1 Driver"
M308 S14 P"DRIVER_2" Y"drivers" A"Z Driver"
M308 S15 P"DRIVER_4" Y"drivers" A"Z1 Driver"

What am i missing?

Thanks

[dc42]

@Alijambo73 where are you measuring the 3.6V? Are you using the Laser/VFD connector, or the OUT9 connector?

The exact voltage of the PWM signal doesn't matter as long as it is sufficient to drive the opto isolator at the input of the PWM to voltage converter. However, I think I've seen previous reports on the forum of these converters not going right up to 10V at full PWM.

[Alijambo73]

@dc42 thanks for the reply. I'm using the laser / vfd on out 9. I'm measuring it from the pwm input terminals on the converter.

If there is something you have to suggest that would be great. The further I got into it I discovered it might not be an issue but I have some other weird things going on with the vfd that I need to get figured out before I could even know.

Has it been an issue with the other reports of the converter not reaching 10v?