VFD and 3 Phase vs DC.

[Dougal]

So what are the pros and cons of a VFD vs DC motor and drive?

3 phase motors and cheap and plentiful, VFD's are a good price and come with logic inputs.
Just considering future options.

[Dougal]

Anyone with an opinion or idea?

[LeeWay]

When I did my mill and lathe, there was an abundance of viable DC motors and controllers that would work great. Cheaper than the VFD alternatives. I didn't need anything large either.
DC motors are now a little more scarce. Some say it's because they generate power as well and they are being scarfed up for wind turbine projects.

Today if I needed another, I would go with VFD and AC motor. They are reasonably priced now too. It seems they were a little more costly when I was looking.

[Al_The_Man]

Pros and cons? alot depends on availability and what you spindle features you expect.
For example, if using a DC servo motor, these often come with tach feedback, this gives you precise control that only a VFD with PWG or encoder on the motor will give you.
Surplus DC motors and SCR controllers can also be obtained cheap.
Both VFD and DC SCR controllers usually have +-10volts input.
If you use Mach, this means a PWM to analogue converter.
If you get a 4 quadrant DC drive, you get +- analogue control and dynamic braking.
Modern CNC machines typically have a VFD style drive to induction type 3 ph motor, but have a pulse wheel feedback from motor to drive together with dynamic braking for precise control.
Al.

[Dougal]

Thanks guys.

I was looking at future upgrades of my lathe and mill. My lathe is single phase AC and I noticed several people have upgraded them to DC for variable speed. But for me a Telemecanique (or similar) VFD is a far cheaper and more versatile solution.

Small 3 phase motors are also cheaper and available in a bigger range of power and speed ratings than DC motors here.
I just wanted to make sure I wasn't missing anything important.

[Al_The_Man]

Originally Posted by Dougal But for me a Telemecanique (or similar) VFD is a far cheaper and more versatile solution. .

I have used the Telemecanique Altivar series, so far they have done a nice job.
Al.