Denford Novamill Mach3 conversion

**JohnHaine** · 18-10-2014

I think you're being a bit categorical here Irving! You can't rely on a limited slew rate to do the smoothing for you. And your comment on ground referencing isn't helpful because by definition "signal ground" is what the control inputs are referenced to! The question is, can the 0v on the controller be safely connected to the signal reference on the vfd?

The Novamill does not use a vfd since the motor is a dc permanent magnet type and the original controller I think is thyristor based. There may or may not be isolation between the trigger circuit and the speed control circuitry, on the KB Electronics one I have there isn't.

Miller, I suggest that you ask the question on the Denford forum, denfordata.co.uk .

**Miller** · 18-10-2014

Thanks, so it's not as easy as it looks then. I have couple more diagram, one for the spindle driver and another one where it shows the breaker board's own 5V supply used to form an analog signal. Can we draw some definitive conclusions over the above issues?

Breakout board's own analog signal.

Sprint 400 spindle driver schematics below, pot goes on terminals 1/2/3 on the left.

**EddyCurrent** · 18-10-2014

Duff drawing removed, please ignore

**Miller** · 18-10-2014

Great stuff EddyCurrent! I also need a power supply and that's pretty much the hardware done with. The motors are 1.5A for X and Y, and respectively 3A for Z axis. They are all rated at 30VDC, which I take it it's the max voltage?

Anyway, what is the optimum voltage to feed the stepper drivers? I can get a a nice deal on a quality 24-28V 10A power supply.

**JAZZCNC** · 18-10-2014

No I think Eddy's wrong.

You want to connect to the PWM+10V(pin3) and 0V(gnd) to (Pin2) the 10K resistor is just showing the POT resistance. You are controllong the 0 to 10V signal from PWM on the BOB so don't need it.
But Like John said best check if the Spindle controller 0 is floating or at mains potential.? Putting to Gnd on the BOB could fry it.?

Edit: correction to pins

**EddyCurrent** · 18-10-2014

Originally Posted by JAZZCNC

No I think Eddy's wrong.

needs a 3rd opinion now.

found this in mean time, it uses 5v with resistor but same idea with 10v, also I'm sure everyone realised that in my earlier post I purposely left out run signals etc.

**irving2008** · 18-10-2014

Originally Posted by JohnHaine

I think you're being a bit categorical here Irving! You can't rely on a limited slew rate to do the smoothing for you. And your comment on ground referencing isn't helpful because by definition "signal ground" is what the control inputs are referenced to! The question is, can the 0v on the controller be safely connected to the signal reference on the vfd?

John, not categorical but maybe I'll accept I was being too generic. I hadn't read whole thread, but was responding to specific posts. I can rely on VFD not needing external capacitor cos it works for me and many others. Most VFD have internal low pass filters anyway.
And the diagram posted by the OP shows a VFD.

However, it now transpires that's all irrelevant to the OPs requirements.

I agree with Eddy, to show COM as 'chassis' but have it at some unspecified high voltage is wrong in my book.

**JohnHaine** · 19-10-2014

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.

**Miller** · 19-10-2014

No worries Eddy, and thanks everybody especially John. The circuit looks easy enough, I should be able to test it sometimes next week.

Alternatively, I have found an off the shelf converter from Axiomatic:

http://www.axiomatic.com/TDAX13020X.pdf

But I have a feeling it's going to be much more expensive than the diy version John proposed, so not really an option.

On another note, can somebody confirm a 24-28v 10A power supply would do, and what voltage do you feed to stepper drivers?

**JohnHaine** · 19-10-2014

Hello Miller,

Let me know if it works and any questions.

On the PSU, the one I use in my Novamill conversion is similar to the 36V one here: but I got mine direct from China via ebay for rather less money IIRC. Look for topengineer1989 as the seller. I use the common 2M542 drivers. 36 volts is fine to drive the steppers assuming the drivers are rated up to 40 or 50 volts. I think I have set the X and Y currents to just less than 2A and the Z probably 3 but could check those.

John.