VSO output pin rises and falls VERY slowly

math_indy

When I toggle the spindle button, the VSO output pin on my DDCSV2.1 rises and falls with a VERY slow exponential shape (not the linear ramp I expected).  Lowest VSO level is 0.1V and high is 10.4V.  The rise/fall time constant is about 8 seconds and it has this same VERY slow resonse whether rising or falling.  This behaviour is the same whether testing loaded with the VFD or disconnected from the VFD.  I'm measuring with an oscilloscope from VSO to the GND-O pin.  


I have tried changing parameters #224 and #433 but neither seems to affect this behaviour in any way.  


Is there a diagram of the DDCSV2.1's VSO output circuit?  I presume it comes from a DAC or perhaps PWM pin from microcontroller?

math_indy

Oh, that Facebook link is VERY helpful.  If capacitor C50 is 220uF (I see "22" marked on it) and R65 is 35K then that would explain why I see an 8 second time constant whether the VSO signal is rising or falling.  I will either remove that capacitor OR replace it with a smaller more appropriate value--maybe 22 uF or perhaps 2.2 uF.

THANK YOU YTLIU!  

math_indy

Nikolay81 Posted at 2018-9-29 02:30
I installed a capacitor of 16V 10μF. The spindle unwinding speed with this capacitor is the same as ...

I just tested mine and this modification worked but you have to remove C50 --AND-- set parameter #433 to a low number or zero.  To remove C50 I used a SMD hot-air tool and gently lifted C50 just as the solder melted.  Although you can remove it altogether I replaced C50 with 1uF so that PWM would still have some filtering.

The default value for parameter #433 is 1111 which, like C50, will also slow the ramp time.  The good part is that once C50 value is reduced you can now control spindle ramp time through the DDCSV2.1 parameters page.  Be aware that the VSO output is now closer to a PWM square wave so check to see if your VFD will work OK with that.  My VFD seems OK with the pure PWM signal but it was a little jumpy so this is why I made C50 1 uF.  I suspect my VFD has some of its own internal low pass filtering.

I was delighted to discover that the DDCSV2.1 back cover access to C50 can be removed without removing all of the control wiring--very helpful for for doing the modification easily.

TOM