Drives that accept AC.

[Black Forest]

Which would you all prefer? A closed loop stepper system with an external power supply of 60v or a drive that accepts 220v AC directly? I lean towards the AC direct. Does the AC drive have an internal power supply. I can't imagine that it actually uses the AC electricity to the motor. The one advantage of the external power supply would be if the internal power supply on the drive fails then the whole drive must be replaced at a higher cost whereas the external power supply is inexpensive to replace. I want as trouble free a system as possible. These will get used with an Acorn board.

[suntravel]

If you want a trouble free system incl. the setup, stepper are the easy way (for small machines), best some with a documented wiring for Acorn.
But more important IMHO is how much torque at what rpm you will need and 2. how much money you can spend.
Kind of the power supply will result after this.

Regards

Uwe

[Black Forest]

These will be Nema 42 for a Klopp universal milling machine. I was going to put Delta servos on it but I can do it for half or less money If I go the closed loop stepper route. This machine doesn't get used often but I would like to convert it to CNC.

[suntravel]

Well i you get Delta servos for less than steppers with equal torque, it a no brainer even if you never use the full speed of the servos

Uwe

[Black Forest]

Well i you get Delta servos for less than steppers with equal torque, it a no brainer even if you never use the full speed of the servos

Uwe

I guess I wasn't clear in what I wrote. The nema 42 closed loop steppers will cost half as much if not more than the Deltas.

[tblough]

There are lots of online references that describe the pros and cons of stepper vs. servos. You should probably look at those and see if the stepper shortcomings will be an issue for you of if the money savings will outweigh them.

Servos will allow you to upgrade to a closed-loop control at a later date if you want to.

[ShawnM]

I recently have switched from steppers to servos on my customer's retrofits with Acorn and wont ever go back to any kind of stepper. The servos are more money up front but that's the only drawback I see. I love that they take 110v or 220 direct without extra hardware (power supplies) and wiring. Less components in the system means less components to troubleshoot or break. If you Google "stepper vs servo" you'll have plenty to read and watch to help with your decision.

[Muzzer]

To answer the OP, yes, the motors are driven from unisolated mains power. That's the same as a VFD and the motors are insulated accordingly. You would need an isolation transformer within the drive if you wanted to isolate the output from the input galvanically but you will find this isn't done.

I have several Yaskawa and Lichuan servos in my machines that run directly from 240Vac. Obviously it pays to avoid coolant and chips getting into unsealed connectors, to avoid tripping the GFCI / RCD.

[Black Forest]

Thank you for the replies. I will go with the AC drives and motors. Whether closed loop steppers or servos I haven't decided. This machine is in my home shop and not used very often. The conversion to CNC will be mostly electrical and motors as it already has ballscrews for each axis and is a very good quality machine. It already has DC brushed servo motors on each axis for powerfeeds. And it has Haidenhain glass scales on each axis but just yesterday the X axis scale started acting up. It might just need to be cleaned. The nema 42 size motors I can buy will bolt up with no modifications I hope. The X axis is direct drive to the ballscrew. The y and z are belt driven. The z axis will be done with the knee. I want to use the Acorn on this project.

[suntravel]

I will also need more power for my Z since i have a Servo for the spindle, because the 4Nm Stepper alarms while using larger drills.

I will get a 12Nm CL Stepper, brings 9Nm, and drops down to 2.5Nm at 700 rpm which is 1750mm/min.

A comparable 220V Servo has 750W 7Nm max. for short time, 2.39Nm continuous to 3000min-1 ( 7500 mm/min )

Cost is 164 to 489€

Only to have more torque for rapids, the stepper will be good for +3000 mm/min also, and that is more than i need for a small mill doing no jobs in series. And from 0-150rpm the stepper ist stronger than the servo.

Uwe

edit 559€ for a Servo, because needs a brake for Z....