Denford Novamill Mach3 conversion

[JohnHaine]

OK, I've sort of been inspired by this thread to work out a simple circuit to interface the PWM from a BoB to a non-mains-isolated speed controller such as the Sprint or KE type thyristor units. This circuit does not need an auxiliary power supply, it runs from the 10v available from the controller itself. It uses an ST Micro dual "rail-to-rail" op amp to hopefully get the full 10V control range. It isn't tested yet but offered just as an example, but I think it should work.

I've just noticed an error in my labelling - on the input side the pin labelled "0V BoB" should go to the output you have selected for the PWM speed control, not the 0V rail!

On the controller side, it looks like for the Sprint box that Miller has, +10 V comes from terminal 1; the control input ("0-10V to controller") goes to terminal 2; and 0V is on terminal 4.

This could easily be made on a small piece of strip board, but take care with the IC2 connections as there will be mains voltages on pins 5 and 4 so make sure they are well isolated from 1 and 2.

I suggest configuring Mach for about 25 Hz PWM base frequency. One problem you may find is that the low speed end where the machine may not start until the speed is turned up a bit from zero; or may run very slowly even though set to zero. It's quite complicated to replicate the function of the "min speed" pot in the controller.

I do need to get round to adding speed control from Mach to my Novamill, so this should get tested sometime! But any questions or feedback welcome.

John.