So Nearly there - Mach3 and VFD Spindle Speed.

[davegrennan]

Hi Guys,

I just got a new Chinese 2.2kw spindle and huanyang vdf and its all set up and working beautifully. (almost). If I run the spindle manually (i.e PD002 = 0) then I can get the full 24000 rpms off the spindle. However when I run the spindle speed from mach3 all I can reach is 22,600 rpm and all the intermediate speeds are proportionally lower. Now you might be asking, we is he asking the question in the mach3 forum when it sounds like a vfd question. Well I tested the output from my BOB and at 100% all I get is 9.64V not the full 10v. This ties in with the 22600(ish) speed I see on the VFD, so I think the vdf is good.

The BOB is one of these;
http://www.ebay.co.uk/itm/5-Axis-CNC-Breakout-Board-MACH-3-For-Stepper-Driver-Controller-/301239616876?pt=LH_DefaultDomain_3&hash=item462347c56c

Its got the 0-10v output.

Maybe its just the cheapo BOB?

I suspect its something to do with the base frequency setting in mach3. I did some reading on this but I'm really none the wiser. If anyone has any advice on this, it would be genuinely appreciated.

Regards,

Dave.

[Clive S]

What Voltage are you feeding the BOB with? ..Clive

[JAZZCNC]

Have you set the pulley speeds.?

[davegrennan]

Hi Clive,

The BOB gets 24v from the main PSU. JAZZ, yes I set Pulley 1 to speed 0 - 24000 ratio 1. That was in the BOB documentation.

Regards,
Dave.

[JAZZCNC]

JAZZ, yes I set Pulley 1 to speed 0 - 24000 ratio 1. That was in the BOB documentation

When you say 9.64V at 100% you have entered 24000 rpm as the spindle speed in Mach havent you.? . . .. 100% is of the commanded speed not your VFD.!!

Try tweaking the pulley speeds and you should be able to dial it in.!

[davegrennan]

When you say 9.64V at 100% you have entered 24000 rpm as the spindle speed in Mach havent you.? . . .. 100% is of the commanded speed not your VFD.!!
Thanks Jazz. Yes definitely plugged in the speed:) Interesting thing I just discovered, when I put the multimeter on the 10v output while the spindle is running, thespeed goes up very close to 24000, 23700 to be precise. Once I remove the multimeter it drops back to 22608. So that would suggest to me the cheap chinese board is the likely culprit. I can live with that once I know that I'm not doing something stupid.

Cheers
Dave.

[Clive S]

Is it a cheapo meter you used as it is possible the meter loaded the circuit. .Clive

[davegrennan]

Hi Clive. Not a cheap meter but it it's quite old. I'll put the scope on out and have a look that way.

[davegrennan]

Well I put the scope on the 0-10v rail last night and immediately the RPMS shot up from the 23.6K to the full 24K RPM. I assume the scope is acting like a parallel resistor and effectively reducing the resistance across the vfd. Could be extra inductive resistance on the wires going from the BOB to the VFD? I'll replace that with quality shielded cable later and add a ferrite bead for good measure.

The scope didn't give me any further clues except the signal looked a little bit noisy. Might try a smoothing capacitor if the shielded cable doesn't help.

Cheers

Dave.

[Clive S]

Well the scope should not have loaded the circuit at all. I take it you have a separate daughter board on that BOB a small cap might help though. ..Clive

[davegrennan]

Ahh the sweet smell of success. Simply replacing the cable with shielded cable did the trick. I had to do a little bit of poking about with the pulley speed setting to get the intermediate values to fall into line, but now they all agree within around 20rpms. Thats good enough for me.

Thanks JAZZ and Clive for all your help.

BTW Clive there is no daughter board, the BOB has the PWM output directly on the board.

[Clive S]

Ok Well I don't think that I help much but Its good to bounce off people to get to the conclusion. Good luck ..Clive