delta ras-12 vfd vs static converter

[cody michael]

I just got a ras-12 and it's 3 phase, i am trying to decide between a vfd and a static converter, vfd are about 115$ static converter closer to 50$ is the vfd worth it?

[David Kumm]

Get the vfd. More choices for options that you don't need but you will get full power vs the 1/2 to 2/3 from a static. You can always use the vfd for other machines if the need arises. Dave

[Malcolm McLeod]

Depends on how you want to use the RAS. If you stick to cross-/miter-cuts, the static converter is probably better deal.

If you use the RAS like my father did his (everything from sawing and drilling to a dovetail bit), then the VFD can allow you to drive the motor at any speed up to 400Hz (~6.5X rated speed). Dad would have killed for one (in 1966)!

FWIW, speed of 400Hz is not something I'd recommend for extended use - - kind of hard on the bearings. But short sprints are well within most tools abilities.

[Mike Heidrick]

A static a bit bigger can easily take a used ideler 3ph motor (bought from CL) and service a few tools. Best to balance it with run caps but it sure would work just fine. I am not a fan of servicing multiple tools with one VFD.

[Bruce Page]

A properly sized static converter will typically give you 60-80% of full power. I run a static converter for my 2hp milling machine and my 5hp engine lathe. I have not had any problems with it in 20+ years and have never stalled either machine. Sure, I would I rather have a rotary or VFD, but at the time this was all I could afford and now it's not worth the trouble to change out.

[Mike Schuch]

Get a VFD!

I have used static converters in the past, have a 10 hp rotary phase converter and MUCH prefer my VFD's. Rotary phase converters were great before VFD's got so cheap. I still use my 10hp RPC to power my 7.5 hp Redstar turret arm radial arm saw (The grandpa of your saw!) because a VFD that size is still expensive. For everything else I use VFD's including my 5hp RAS.

Great saw by the way, the turret arm saws are my favorite by far!

You can add a big power resistor to most VFD's so the VFD will act as a motor break. Kind of a neat feature!

[Malcolm McLeod]

Get a VFD!
... can add a big power resistor to most VFD's so the VFD will act as a motor break. Kind of a neat feature!

All VFDs I've ever worked with will dynamically brake a load if selected in configuration. Simple version is that the motor becomes a generator and the VFD becomes a resistor to dissipate the energy.

The problem arises when the load has particularly high stored inertial energy (think BIG flywheel). It can feed some energy back into the supply line, causing problems with other systems (motors), or just too much heat for the VFD to dissipate. So, it overheats and quits. Solution is larger external resistors that dissipate this excess heat, or cheap way is just to use a less aggressive deceleration time.

I think adding resistors is probably over-kill for most wood-working applications with 5hp or smaller motors. A bandsaw (>20") or a very large bowl blank on lathe, with very aggressive brake times (2sec or less), might be only exceptions. And if you're trying to brake these to a stop in 2sec, I suspect your power grid is the least of your problems.