Centroid Community CNC Support Forum

I tried the capacitor method again and turns out that it works, i first connected the capacitor on vfd side and now on acorn side, I thought everything was hooked up correctly with the capacitor but turns out it was not, instantly the voltage was 0v and now gives me 100% spindle speed at 10v

Everything works fine now!! So your recommendation where good!!

Thanks for all the support guys!

Glenn

Add the capacitor across the analog pair, as Tom suggested above.

cncsnw wrote: ↑Sat Aug 28, 2021 2:24 pm Add the capacitor across the analog pair, as Tom suggested above.

I'm happy to hear that this solved the problem but can anyone explain WHY this worked?

What's the principal here? Is it a noise issue, impedance matching issue?

It's hard to learn new things and apply them to future problems if all we are told is "just do it". Why are we doing it?

Obviously Tom has seen this issue before and knew what to do, but please explain what is going on here!

Dave C.

As I understand it, some VFDs' ADC inputs react with Centroid's DAC output, to cause a resonance or oscillation. If you look at the "incorrect" analog signal with an oscilloscope, you may see a significant sine wave there, rather than a steady DC voltage.

The capacitor shunts that high-frequency oscillation.

Here is a scope view of the analog signal between an Allin1DC unit and an old Saftronics (Yaskawa) PC3 inverter, with what should have been a steady 2.0VDC analog command. At eng199's suggestion, I added the snubber circuit shown here (two 0.1uF capacitors and a 10-Ohm resistor). With that snubber circuit in place, the same analog command looked like this (same scope settings).

Incredible!

Thanks for the explanation and the diagrams.

Never to old to learn something new!

Dave C.