Incorrect RPM on VFD then what's selected in DWC

dhusolo

I was able to get the PWM convertor working from this thread. Since then I've upgraded to a Duet 3 MB6HC, now I can now control my VFD through DWC. However the RPMs shown on the VFD are different than what is selected in DWC.

M950 R0 C"vfd+out7" Q3000 L5999:24001                   ; create spindle #0 connected to vfd pin and 24k rpm at full PWM
M563 P1 S"Spindle" R0                                ; create tool #1 with spindle 0
M568 P1 F0                                  ; set initial tool #0 active and standby temperatures to 0C
T1                                          ; select tool 1
M3 T1 S0
M5

RPM set in DWC on the left and RPM shown on the VFD on the right.
7000 = 6000
8000 = 6384
9000 = 7752
10000 = 9100
11000 = 10465
12000 = 11830
13000 = 13200
14000 = 14550
15000 = 15930
16000 = 17300
17000 = 18650
18000 = 19990
19000 = 21310
20000 = 22465
21000 = 23570
22000 = 24000

Alijambo73

I have a similar issue. I noticed that when I disconnect the pwm to analog converter the vfd out output is 4.85v when set to 24000 rpm but when connected to the converter it drops to 3.9v and the output from the converter is only 9v.

My config.g is
M453
M950 R0 C"vfd" Q2000 L0:1 K0:24000
M563 P1 S"Spindle" R0 F0

I had the same result with the M950 line as M950 R0 C"vfd" Q2000 L0:24000

Im using a HY 115V, 1.5KW VFD. Any idea on what would be causing the voltage drop when connected to the converter? I double checked to make sure the jumper was on 5V.

dc42

@Alijambo73 ignore the voltage drop at the Duet Laser/VFD output. It's caused by the series resistor that provides some protection to the output. The peak voltage level at that pin doesn't matter as long as it's high enough to drive the opto isolator on the converter. The converter output depends on the PWM of the input, not the input voltage.

To get the RPMs to match more closely, either adjust the potentiometer on the converter that controls the output voltage at 100% PWM, or adjust the line in config.g that defines the RPM at full PWM.

hurzhurz

I made the experience that those widespread PWM converters are not very good.
The output is not very linear and also depends on the supply voltage and PWM frequency. I also had trouble to get 10V output with 12V supply voltage.

Maybe have a look at the alternative one I mentioned here: https://forum.duet3d.com/topic/34506/alternative-pwm-to-0-10v-converter-for-spindle-control

Alijambo73

@dc42 I did try to adjust the potentiometer but the highest i could could get to was 9.11V.

Should I use the "M950 R0 C"vfd" Q2000 L0:1 K0:24000" or "M950 R0 C"vfd" Q2000 L0:24000" and wich value should I adjust?

Alijambo73

@Alijambo73 I switched the pwm converter to a 24V power supply and switched to using out2 then played with it until I got to the point that it can reach 24,000 rpm and when set to 12,000 rpm I'm getting 12,500. I ended up adjusting the hz to 400 to acheive this.

M950 R0 C"out2" Q400 L0:24000 K0:1

I would love to get it dialed in more if anyone has any suggestions.