[Zapnologica]

Hello,

I am buys building a cnc for my self.

I have reached the stage where I want to mount the spindle, But before i can do that i need to build the spindle control circuit.

I am using linux cnc with a break out board. So i have Spindle PWM and Spindle ON / OFF.


I have a relay and some proto-board. I know how tyo hook up the on and off relay. But i am not sure hwo to do PWM with 220v AC as I have only done it with DC.

What is the procedure? Do I just pop a NPN transistor on the negative cable and then PWM that transistor?

I am using a dremel 300 for my spindle for now.
its rated at 125w 230- 240v ac


Thanks

[Al_The_Man]

Why not use a Triac controller, if you have a dremel it should be a Universal motor, if so you can also run it off of DC.
With Universal motors it is usually necessary to have feedback of some kind, simple tach etc.
Al.

[Torchhead]

Hello,

I am buys building a cnc for my self.

I have reached the stage where I want to mount the spindle, But before i can do that i need to build the spindle control circuit.

I am using linux cnc with a break out board. So i have Spindle PWM and Spindle ON / OFF.


I have a relay and some proto-board. I know how tyo hook up the on and off relay. But i am not sure hwo to do PWM with 220v AC as I have only done it with DC.

What is the procedure? Do I just pop a NPN transistor on the negative cable and then PWM that transistor?

I am using a dremel 300 for my spindle for now.
its rated at 125w 230- 240v ac


Thanks

PWM to AC speed control can be tricky. You first need to convert the PWM to a varying DC control voltage and then use that to control the motor speed. You cannot drive a triac with PWM or even varying DC. You have to have a phase control circuit. You also have to worry about not mixing the AC control side with the low voltage logic side and burning up your controller. Typically you opto isolate the PWM (which is the main reason it is PWM to start with) because it will drive a digital signal through an opto isolator whereas analog will not.

A universal motor like on a conventional router or Dremel will slow down if you lower the voltage BUT it also lowers the torque as well. With no feedback you find that lowering it very much just makes the motor so weak it won't cut. There are various methods of getting feedback (reversve EMF is one) but the only really good way is to have a sensor on the moor shaft and a feedback loop to the controller to instantly adjust the voltage if the RPM starts to drop. That is not an easy thing to design nor is it low cost. You could turn 220VAC to DC (about 300 to 350VDC) then use a high voltage FET and PWM that BUT isolation is essential as the High voltage side is referenced to AC neutral (maybe) and a component failure will destroy everything downstream! You also have to deal with inductive kickback and spikes that can kill power FET's or IGBT's.

CAUTION: There are lethal voltages here and if you have no experience with power electronics and high voltage circuits stay away from it.


My advice: If you want a real variable speed spindle do it with a 3Phase AC motor and a VFD that has a control voltage (0-10VDC) input. You will get good torque across a much wider RPM range and better speed regulation. Trying to make a cheap router into a variable speed spindle will be disappointing.

TOMcaudle
www.CandCNC.com
Old Power Design Engineer with the burn marks to prove it

[Al_The_Man]

Motorola designed an IC specifically for this, including simple tach F.B., TDA1085 spec sheet is on the Motorola site.
Al.

[Dylwad]

What about controlling a hobby servo with the pwm that changes the built in speed control on the dremel?

Sent from tapatalk

[vegipete]

I think the neatest one I saw was done by replacing the variable resistor speed control from whatever tool it was with a CdS photo sensor. The PWM signal was applied to an LED shining on the photo sensor. Alas no feedback, but certainly an interesting opto-isolation technique.