Unlocking old C100 vfd


I have a CNCRP 4896 (Jan 2016) which has a GMT 2.2kW spindle and an LSElectric C100 VFD. My son bought me a rapidchange ATC magazine which requires the spindle speed to drop to 1000rpm. Easy to change I thought - I was wrong! I recently upgraded to Mach4 and found that Avid’s own screenset doesn’t allow a speed of less than 8000rpm.

Overcoming the screenset restictions wasn’t too hard - for anyone interested you need to modify the “dDefaultMinSpindleRPM” parameter under the [AvidCNC_Profile] group in the machine.ini file.

The hardest part I’ve found is that the actual spindle speed didn’t correspond to the commanded speed, particularly at low speeds.

For a commanded speed of 8000 the actual speed was 13128 (64% over!). Anything above that minimum, actual speed does converge on commanded speed until it matches at around 24000 rpm. Problem is that the difference between commanded and actual speed is non-linear.

I discovered that the LS C100 VFD can be programmed with a custom Volt in->freq profile, which should be able to compensate for the non-linear relationship.

However, CNCRP (now Avid of course) in their desire to stop anyone fiddling with the VFD have locked the VFD parameter.

Would anyone happen to know the numerical password for the C100? It’s needed to change parameter H95 - which is the locked/unlocked parameter.


I’m pretty certain we don’t do this with our existing VFDs. I don’t know the history here but I’d be surprised if we intentionally locked out settings.

A call to support might yield either the default settings for that VFD, or the password. Maybe you could reset it back to defaults?

Thanks. It’s definitely locked. Parameter H95 shows an “L”, also attempting to change any other parameter is rejected. This would have been originally set by CNCRP when I bought it, because I’ve never had reason to delve into the VFD until now.

I’ll try support and if that fails, I’ll have to resort to doing a hard reset. I’ve not had too much success with support so far.


The support team is really good, one thing that might be a bit hard on this particular issue is that this VFD may pre-date any of them working for us.

I wonder: does it also require a certain torque range at that speed?

I’ve not been able to try it out yet, but as far as I can tell the torquing up of the collet nut is mostly a factor of the spindle inertia and not so much the spindle torque. The spindle engages the thread at 1000rpm and keeps going for a time calculated to get the collet nut spinning, while it spins it hits spring loaded ball bearings that keep the collet in the holder and the whole process has a similar action to an impact wrench - it’s quite ingenious.