WAS CNC mill - now 3phase help

Ok... now I'm in a slight bind.

I have a mill to arrive Monday. It isn't rated in HP, because the entire system is 3-phase. The spindle is run off a built-in VFD and allows programmable spindle speeds.

But... I can only find references to 3-phase rotary converters listed in HP, and no references for how resistive and inductive loads other than motors affect them.

The mill will draw as much a 60-amps inrush at 230V.

So... What size idler motor do I need for a 3-phase converter to run it?

HELP!

LLoyd

Reply to
Lloyd E. Sponenburgh
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"Lloyd E. Sponenburgh" fired this volley in news:Xns9B87D01C423E8lloydspmindspringcom@216.168.3.70:

By the by... I've just sort of joshed-around and figured if it draws

60 amps, I should use a motor with a full-load amperage of about 60 amps.

That works out to 25-30HP. Is that right thinking?

LLoyd

Reply to
Lloyd E. Sponenburgh

The listing says 2hp spindle motor. I know that there are feed motors, too, but it's hard to see where the 60 amps comes from. You could Google the model & see it there's an online manual (or wait for your manual on Monday). I'd guess that you'll not be using more than 5hp & a

10hp idler would work.

Bob

Reply to
Bob Engelhardt

If you don't have to use it immediately, I'd suggest waiting until it arrives and examining it. My CNC mill was 3 phase just because it was designed to run from one power source. My mill was wired for 460VAC 3ph and a transformer was connected to run the CNC controls from 120VAC single phase. The only thing that needed 3 phase was the spindle. There are VFD's that will give you 3 phase output from single phase in. It would be very likely that you could run your mill from single phase if the VFD is rated for single phase.

Also, I wouldn't size the continuous supply for the inrush current. The inrush current is high most likely due to capacitors that charge in the VFD and motor drives. Normal circuit breakers will allow high inrush currents. Like another poster said, if your rotary phase converter can handle 5HP that should be enough. I would recommend you to examine the circuit first though. If your motion control drives are single phase you might want to isolate that from the 3 phase spindle drive.

When I get around to doing the EMC2 conversion on my mill, I plan to make the whole thing run off of 230VAC single phase or 3 phase. Right now my spindle doesn't use a VFD, just a motor starter.

RogerN

Reply to
RogerN

You problably know this but make sure the control transformer is not across the derived phase.

Wes

Reply to
Wes

I have been running a Bridgeport CNC Series I with a BOSS 6 controller, using a 3hp idler motor in a homemade phase converter. The spindle on my machine is 2HP. The BOSS controller is fed from one of the unconverted 110 volt line legs.

Russ

Reply to
R

That's what I was suspecting, the 3 phase is really only needed for the spindle and the CNC controls are powered from single phase. If the original spindle drive won't handle single phase input, then I would swap it out for a drive that will such as this Hitachi for $202:

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That way the entire mill could run on 220-240VAC single phase. My experience with the drives is that they handle the power factor problems in running motors also. My CNC lathe has a 7.5HP drive and I use a 10HP Hitachi drive. At idle my drive delivers ~13-15A to the motor while only using 5A from the single phase supply. For those who understand you don't get 15A 3 phase from 5A single phase, it's a power factor thing. The motor side is delivering apparent power while the single phase side is using true power, or at least that's how I understand it.

RogerN

Reply to
RogerN

R fired this volley in news:eCJ7l.2806$BC4.1051 @nwrddc02.gnilink.net:

controller,

THAT's what I wanted to know. Thanks. I figured the electronics were really running single-phase, but three-phase enters the cabinet, and I don't have the unit here to inspect, yet.

LLoyd

Reply to
Lloyd E. Sponenburgh

Ayup..lots of supposition, but no facts yet

Post some pictures of the drive cabinet up close and personal

Gunner

"Upon Roosevelt's death in 1945, H. L. Mencken predicted in his diary that Roosevelt would be remembered as a great president, "maybe even alongside Washington and Lincoln," opining that Roosevelt "had every quality that morons esteem in their heroes.""

Reply to
Gunner Asch

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Not for the BOSS-3 through BOSS-6. Those run each axis's stepper motor from a *big* three phase power transformer -- one phase per axis, with a Mag-Amp (saturable reactor) changing the voltage to the stepper motors from a lower voltage (about 40-60 VDC IIRC) when just holding position or during very slow steps, up to about 80VDC when running at the maximum step rate.

Those stepper motors draw quite a bit of current, and the current to charge up the power supply capacitors.

This means that you will either have to run the stepper motor drivers from three phase, or re-wire to run from single phase (involving replacing the big three-phase transformer with three transformers of appropriate size and voltage, or one much larger transformer, again with appropriate output voltage.) I don't know what the total current would be running all three in parallel from a single 240V line. The computer drops to almost nothing by comparison.

Oh yes -- be *very* careful to balance the rotary converter properly. Since each axis derives power from a different phase, and there is no regulation (other than the mag-amp to take the voltage to maximum or minimum), and the transistors driving the steppers are pretty close to their maximum voltage rating, an unbalanced rotary converter will result in popping power transistors like popcorn -- and these particular ones are hard to find these days, I believe.

Good Luck, DoN.

Reply to
DoN. Nichols

Don sez: "Whole bunch of good advice . . . ." Second all what Don said. Also, remember to make your RPC from an idler motor that is at least 1-1/2 x the max rated HP of the load. There's some good articles on RPCs in

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Follow the advice in those articles and don't skimp on the required amount of balancing capacitance. Remember there are 2 sets of balance caps, 1 "series" set in each led and another across the input line to minimize overall current draw.

[ ... ]

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Not for the BOSS-3 through BOSS-6. Those run each axis's stepper motor from a *big* three phase power transformer -- one phase per axis, with a Mag-Amp (saturable reactor) changing the voltage to the stepper motors from a lower voltage (about 40-60 VDC IIRC) when just holding position or during very slow steps, up to about 80VDC when running at the maximum step rate.

Those stepper motors draw quite a bit of current, and the current to charge up the power supply capacitors.

This means that you will either have to run the stepper motor drivers from three phase, or re-wire to run from single phase (involving replacing the big three-phase transformer with three transformers of appropriate size and voltage, or one much larger transformer, again with appropriate output voltage.) I don't know what the total current would be running all three in parallel from a single 240V line. The computer drops to almost nothing by comparison.

Oh yes -- be *very* careful to balance the rotary converter properly. Since each axis derives power from a different phase, and there is no regulation (other than the mag-amp to take the voltage to maximum or minimum), and the transistors driving the steppers are pretty close to their maximum voltage rating, an unbalanced rotary converter will result in popping power transistors like popcorn -- and these particular ones are hard to find these days, I believe.

Good Luck, DoN.

Reply to
Robert Swinney

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