Centroid M40 Wiring and VFD Question.

[RookeeCNC]

Just wondering if some of the cnc expert can help me out. I bought a CNC knee mill with an M40 Centroid control. The machine was powered by 230 three phase from the shop of the previous owner. I have the mill in my garage now and don't have any three phase power. I was thinking of buying an AutomationDirect VFD GS2-023PO which is a 3 HP 220 single phase coming in and three phase out.
I followed the three phase wiring going into the cabinet and the three phase wires goes to three fuses, to an E stop contactor, to a spindle reversing contactor, to a spindle overload protector and then to the spindle motor.
The three phase wires after the E stop splits to another three wires to a coolant contactor and then to the flood coolant pump.
Also, the three phase wire going into the E stop, L2 and L3 have extra wires. The extra wire coming from L2 and L3 goes to Transformer T1 and T2 to power up the control.

Question:
I was thinking of splitting the wires going into the cabinet.
L2 and L3 wires going to the transformers, I was going to connect to separate 220 VAC power that I already have in the garage.

I was going to buy a VFD and connect the three wires L1/L2/L3 to power up the spindle and the flood pump.
Will the VFD mess anything up because it is not connected directly to the spindle motor because the VFD power has to pass thru the E stop/Spindle contactor/Reversing contactor/overload protector then to the motor?

Do I need another small VFD to power up the coolant pump?

Any suggestion on how the best way to modify the wiring on the mill?

Thanks in advance for your help!

RookeeCNC

[Dennis Storzek]

DON'T do it! VFD's do not like being disconnected under load, and operating the reversing contactor will likely blow the VFD.

I've just gone through this, putting an AC Tech VFD on the spindle of a Series I BOSS 6 that had been previously retrofitted with the older Centroid M15 control. My situation was a bit different, as I have real three phase power, and was only using the VFD for speed control, but here are some things that may be useful to you:

The only thing on my machine that was still three phase after the M15 conversion was the spindle motor; everything else was 120V powered off a control transformer wired between L1 and L3. The M15 control had come with it's own 120V line cord and had it's own self contained control transformers for the voltages it needed. The line cord COULD have been wired to the existing control transformer, but wasn't; the guy who did the conversion just plugged it into a wall outlet. The M15 control had its own reversing contactor and overload relay; three phase just entered from the existing fused disconnect and was wired through the reversing and overload relay to the spindle motor. See if you can identify the source of all your control power circuits and combine them on L1 and L2 of the single phase line you have.

Most VFDs have a reversing function and overload capacity built in. Mine did, and I simply used it to replace the reversing contactor / overload relay. The contactor was a modern modular DIN rail mount affair, which I disassembled and salvaged a single contactor to switch the three phase to the VFD. In your case you would use it to disconnect the single phase power to the VFD. It is powered through the E-stop contactor, so when the E-stop is pushed the VFD powers down.

The original reverse set-up had a pair of little 5VDC relays on a circuit board that switched the 24VAC power to the coils of the reversing contactors, one output per coil. I removed all the 24V wiring from these, and used them to switch 12VDC from the VFD's internal control power supply back to the FWD and REV inputs.

The original overload relay had a set of auxiliary contacts that opened the coil circuit of the E-stop contactor, thereby stopping everything if the spindle motor stopped. This wouldn't work with the VFD, as there is no manual reset. I instead used one of the VFD outputs programmed to "output on fault" to drive a relay that opens the Z+ limit switch circuit. Not exactly elegant, but the M15 control had no other provision for input to make it pause. As it is, if the VFD faults, table motion stops and I get a "Z+ Limit" error message, but the VFD display is flashing FAULT, so it's pretty obvious what the problem is. Cycling the E-stop resets the VFD and clears the limit, without losing the place in the program.

I used a set of dry contacts provided on the VFD to power the Bijur oilier, so it only runs when the spindle is running, If other provisions can be made for the lube pump, these contacts could be used in lieu of the separate relay to open the limit switch on fault.

I hate to raid membership from one forum for another, but I found a lot more expertise about specific VFD applications on the Practical Machinist web site here:

Transformers, Phase Converters and VFD

Dennis

[9 1/2]

A Leeson VFD I used (on a prevous machine) had seperate Logic / analogue inputs for Estop and brake and well as reverse. I used these to connect an Estop and a Reverse contactor.

Your idea of seperating the 120 volt components seems logical and one that I too am waiting to complete.
which VFD were you considering using?
I'm currently using an Hitachi but fell the Leeson, that I previously used, was a better unit. easier set up, connection and better features. Just my opinion however.