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80's vintage Bridgeport Interact Series 1 CNC mill converting single phase to 3 phase

eebj01

Plastic
Joined
Jan 19, 2016
I have this Bridgeport CNC mill. It is 3 phase 220v. I have single phase 220v.

Can I use a VFD solely as a phase converter to get the 3rd phase? I tried it with a VFD I was going to use for a standard mill but it keeps tripping a short circuit/current overload when the spindle tries to start. Is it too much of a current spike?

The machine powers up, control cabinet powers up, I can move the spindle up & down, move the X & Y axes. But, as soon as I go to start the spindle, instant trip.

The machine Is drawing less than half an amp & then the 2hp spindle motor tries to start which is rated at about 6.5 amps. I have no idea what the initial surge is.

Is there a setting I'm missing in the VFD or won't it run this CNC? The VFD is supposed to be good for up to 3hp.

Any help would be greatly appreciated
 
If it is the machine with the regular AC spindle drive motor then the spindle is the only important thing using 3 phase.
Also it needs air to release the brake
I would try wiring just the spindle to the inverter.
 
Your VFD is running the entire cabinet & motor.
What is the overload element that is tripping?
Shouldn't the VFD fault before a overload?

You can not use a soft start ramp on the entire cabinet.
Your cabinet probably has a contact closure to start the motor. VFD manuals have strict rules that make/breaks can't be done
with output terminals. The manuals I have seen say that damage can occur to output stage. In your situation you have a light
load in the cabinet and then shock the VFD with motor current by a contact closure. I'm not sure if a small idle current makes the
shock a less of a shock.

I would isolate the spindle motor to the VFD temporarily and see how it runs.
Provide VFD specs and cabinet nameplate numbers.
 
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If you're lucky, the VFD will accept a 5V signal from the control and spindle speed can be changed within the part program. If not, you're stuck with changing spindle speed manually and an RPC will work equally well.
 
If it is the machine with the regular AC spindle drive motor then the spindle is the only important thing using 3 phase.
Also it needs air to release the brake
I would try wiring just the spindle to the inverter.
I believe that's what I'm going to have to try. But, there is a ton of wiring/contactors/etc in the cabinet. I'm not sure what is wired to which legs of the incoming 3 phase. I would think it's distributed fairly evenly throughout which would mean changing a bunch of wiring around
 
Your VFD is running the entire cabinet & motor.
What is the overload element that is tripping?
Shouldn't the VFD fault before a overload?

You can not use a soft start ramp on the entire cabinet.
Your cabinet probably has a contact closure to start the motor. VFD manuals have strict rules that make/breaks can't be done
with output terminals. The manuals I have seen say that damage can occur to output stage. In your situation you have a light
load in the cabinet and then shock the VFD with motor current by a contact closure. I'm not sure if a small idle current makes the
shock a less of a shock.

I would isolate the spindle motor to the VFD temporarily and see how it runs.
Provide VFD specs and cabinet nameplate numbers.
It doesn't state what it is other than "short circuit/current overload." I have raised all of the overload protection parameters up north of 13 amps and it still does it. Even turning on the main power switch triggers the protection in the VFD sometimes. It only does that sometimes. It doesn't seem to like any sort of contacts closing. That initial power switch powers up the circuitry, the CRT monitor, etc. It must be too quick of a surge for it. I believe these VFD's are really just for starting a motor and isn't going to work for this application.

The VFD is just a cheap Amazon Chinese thing. I never used one before and figured I'd try a cheap one for my old mill just to see what they were about. It is a XCFDP 220V 2.2kw 3HP. The cabinet on the CNC lists:

Voltage 208
Phase 3
Frequency 60
Full load current (blank)
Spindle motor current (blank)
Control voltage 115
Fuse interrupt capacity 20
Schematic Diagram 215 275

The motor plate lists:

2 HP
208V 6.5 amps
220V 6.3 amps
Both @ 60 Hz
The motor is wired for low voltage not 480.

I don't mind abandoning the VFD on this machine if there is a better, simpler way.

thank you
 
I don't mind abandoning the VFD on this machine if there is a better, simpler way.

A rotary phase converter could be simpler, but let's try to get this VFD running for you first.

Even turning on the main power switch triggers the protection in the VFD sometimes. It only does that sometimes. It doesn't seem to like any sort of contacts closing. That initial power switch powers up the circuitry, the CRT monitor, etc. It must be too quick of a surge for it.

You've got that right. That's the inrush current to the main transformer. Setting the VFD overload protection as high as it will go might solve that problem.

Gustafson wrote:
It is my memory that for the varispeed ac spindle machines that the spindle is the only thing using the 3rd phase.

Yes, exactly.
 
I had always thought that VFDs didn't like any switches at the output. Maybe old knowledge since superseded.
These [AC spindle] interacts did not have speed available from the control, so it should be straightforward enough to wire the VFD as on with main power, then fire it from the spindle enable line. Now there is a pot on the front panel of the TNC that you might be able to use as a remote speed pot with a little work.
 
I have this Bridgeport CNC mill. It is 3 phase 220v. I have single phase 220v.

Can I use a VFD solely as a phase converter to get the 3rd phase? I tried it with a VFD I was going to use for a standard mill but it keeps tripping a short circuit/current overload when the spindle tries to start. Is it too much of a current spike?

The machine powers up, control cabinet powers up, I can move the spindle up & down, move the X & Y axes. But, as soon as I go to start the spindle, instant trip.

The machine Is drawing less than half an amp & then the 2hp spindle motor tries to start which is rated at about 6.5 amps. I have no idea what the initial surge is.

Is there a setting I'm missing in the VFD or won't it run this CNC? The VFD is supposed to be good for up to 3hp.

Any help would be greatly appreciated
You can do exactly what you suggest..... but not with that VFD. There are other ways,

Forget HP rating, the problem is current rating. If the spindle motor is rated at 6.5A, 2HP, then it is a regular induction motor, The inrush current will be around 40A or 50A at the start, The VFD cannot handle that, so it shuts down. That's the biggest reason why VFDs cannot generally use switches in the output, it just does not work.

Odds are that the rest of the machine will run fine on single phase. It may already do that, for controls, and servo positioners. You will want to verify that.

You need to separate out the spindle motor, and run just it with the VFD. Because the machine runs the motor start/ stop via CNC, it will be a more complicated conversion, the CNC needs to be interfaced to the VFD.

You can also likely use a much larger VFD, and simply produce 3 phase that way. It has to be a lot larger, with a current rating that can handle the starting surge. That can get expensive, but needs no change to the machine.

However, you can also just use an RPC and make no changes at all. I would suggest an RPC of no less than 3 HP, and probably 5 HP, just to avoid problems at the start, as well as giving you some opportunity to add other 3 phase machines as well..

The RPC will supply power that is basically just 3 phase, and the machine will be happy. The RPC will run other 3 phase machines as well, giving you more flexibility.
 
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At least with the smaller EX Trak machines the spindle was the only 3p item. I hooked the rest up to the appropriate voltage single phase, put my spindle on a VFD, and went from there. Mind you my spindle wasn’t computer controlled, so nothing complicated there. Not sure how this one is set up.
 
Yeah, Gustafson and JST are right about the VFD - dunno what I was thinking. Wasn't, obviously.

If eebj doesn't mind substituting a rotary phase converter for the VFD, that'd be simpler, could be cheaper. Wire it up to the machine the same way the VFD is. Best to have a line phase powering the control and drives, but that's a matter of rotating supply wires.
 








 
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