Denford Novamill Mach3 conversion

[irving2008]

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]

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]

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]

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.

[Miller]

Yes, that's the seller I bought the BOB from. It came as a complete package with 3 x 2M542 drivers. Still in the post but should be getting it quite soon.

The motors are rated 1.5A and 3A at 30V, so I will keep about same amp rating and feed 36V then.

What I had in mind for power supply is this. It shouldn't make more than £30 posted and looks nice quality and DIN mounted, but if it's less than ideal because of the lower voltage, I'll go for the 36V as you suggested.

Just to confirm, your circuit has 2 x 470K and 3 x 47K resistor. I have selected this for C1, and this for C2, and this for the op amp.

[EddyCurrent]

I had to get up at 4:30 am this morning to get rid of my duff drawing, couldn't sleep knowing it was there

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.

John, it looks to me like the input to the drive is terminal 3, terminal 2 goes to a pot for 'minimum speed' which creates a potential divider along with the external pot to give an offset from zero.

[JohnHaine]

Oops! Eddycurrent, you're quite right, terminal 3. Terminal 2 is not connected.

Miller, the eletrolytic you selected is a surface mount type, is that what you wanted? The other one is leaded. Maplin is a good place for miscellaneous components. Well, the 36 V works fine for me, lower voltages may work but the drives are fine with 36. That's the package I bought too of the BoB and drivers.

John.

[Miller]

Miller, the eletrolytic you selected is a surface mount type, is that what you wanted?

John.

It was the only option for a 10V 10uF. The closest through-hole I can find is 16V.

[EddyCurrent]

This is a good place for components too;

http://www.rapidonline.com/Electroni...tic-Capacitors

[JohnHaine]

The voltage rating isn't critical, 16 V is fine, leaded much easier to solder.