[sortafast]

So I have a tree 325j cnc knee mill. Currently it is at a shop with 3phase power. But I need to move it to my house where I have 1ph power. So I will need to convert the 1ph to 3ph to power said CNC mill. Currently I have a manual mill stuffed in my garage with a VFD to convert to 3ph and it works great. 2 questions: 1st, the cnc mill has its own VFD for spindle control (not phase conversion) so would stacking VFD's be a bad thing? And 2nd, would running a VFD for phase conversion F-up the electronics in the mill somehow? The mill only has the 3phase input cable and then there are transformers and what not inside to get the power for the computer controls as well as the servos, so they all draw power from a single source. If I retrofitted this machine it would be a non-issue as I would just run the 1ph-3ph VFD on the spindle and then power everything else using standard 110v, but the Delta 20 control runs good enough that doing a conversion and they ensuing headaches would not be worth it right now. Thoughts?

[keebler303]

You can't power non-motor loads with a VFD. For starters, they are full of electrical noise that the control would hate. It works on your manual mill because the motor is the only thing you need to power.

The easiest solution is to buy a RPC and just hook the machine up just how it has been. Another possibly less expensive route would be to dig into the electrics and figure out what actually needs 3 phase. Commonly (like on my bridgeport) there is a 3 phase transformer for the axis drives but each axis is only single phase. If this is the case, you could wire the axis drives and control to single phase power and then you only have to worry about the spindle motor. Depending on the VFD, it may or may not be capable of running on single phase. Most of the smaller ones can run on single phase but you'd have to check on your specific model.

If you ever plan to sell this machine, also consider that it may be harder to sell if you have hacked into the power wiring rather than just using an RPC and ;eaving the factory wiring intact.

I bought my RPC on craigslist for a fraction of new cost.

Good Luck
Matt

[sortafast]

I figured as much. Just wasn't sure if I could make it happen. It appears that there is a local guy that makes RPC's that aren't terribly priced. I just need to figure out how much it will cost to move my mill and what size RPC would work. I think I have the 3hp continuos 5hp max motor on the spindle.

[keebler303]

Just be careful that you connect the machine so that the "high leg" doesn't go to any neutral referenced loads (such as the control).

[mactec54]

It appears that there is a local guy that makes RPC's that aren't terribly priced.

You will have to have a CNC rated RPC, or you will have trouble with the control/drives Etc, check that the local guy is up to speed with that, or you will be wasting you money, Phase-Perfect is the best way to go if you need 3 phase power, but they cost much more than a RPC, but worth every sent

Look on the machine tag/label & see what total AMP the machine needs, then double that For your RPC & you will be about right

[keebler303]

You don't HAVE to have a CNC rated one, but it would be nice so you don't have to worry about it. I run my bridgeport CNC knee mill on a plain old Arco Roto-phase with no issues. As long as you are careful about where you put the high leg, you should be fine.

[kstrauss]

What do you mean by "high leg"?

[underthetire]

Or....
The only 2 things on the J325 that are 3 phase is the spindle drive and the coolant pump. So, if you don't use the factory coolant pump, and are handy, you can change the spindle drive to a single phase input with the typical 3 phase output. Probably not a bad idea to consider, since the vfd in your tree is old and are prone to failure anyway. The axis drives and control power all come off only 2 poles of the main breaker.

[keebler303]

What do you mean by "high leg"?

Phase Converters & Delta vs. Wye Configured Three-Phase Power - Phase Converter Information

Explained there better than I am able. Basically the third "generated" phase has 240V or so to neutral. If the application draws 120V from one leg of the three phase and neutral, you better make sure your don't connect this high leg to that phase. If you do, you will provide 240V to circuits designed for 120V. Sparks may fly.

Matt

[mflux_gamblej]

I run a 15HP spindle motor (CNC lathe / fanuc control) on a 20HP RPC and it gets dicey sometimes. Can't run both my mill and lathe simultaneously. Fanuc is 'finiky' but really it comes down to voltage stability. If I had more copper and bigger caps (i.e. 30HP or more rated RPC) life would be easier.

The lathe runs OK, but it is a pain that I can't run the CNC mill and the CNC lathe at the same time. My mill is a 10 HP spindle machine - Heidenhain control.


BTW, RPC is the only way to go. big power, real three phase, scalable, real-time, etc. You don't have to pay $$$. I bought a used motor (GE) and an RPC setup off of ebay. It works great. but it isn't a lie that a 2x rated RPC will make your CNC happy.

[skullworks]

Actually you should have more than double the RPC. I have a 3hp CNC and the starting loads are about double, but go into tapping mode now you are reversing the motor so the load is now about 4x peak. I have a 10hp CNC rated RPC and when I tap it sounds like that unit comes to almost a full stop for a tenth of a second.

We are tempted to look at nameplate specs and use those stead state values ignoring starting and reversing loads. Constant surface speed in a lathe can load just as bad.

[keebler303]

Most RPCs are sold by "running HP" but they are only rated to start a much smaller load. For example, mine is rated for "20 HP" total combined load. But it is only rated for starting a "7.5 HP motor". They are good for a bunch of small motors totally 20 HP but cannot support a single 20 HP motor. If you are doing a lot of "starting" such as rigid tapping or constant surface speed where you have sustained loads similar to "starting loads", you should up the size of your converter.

Matt

[Al_The_Man]

The only thing I have against the link is when using a 1ph to 3 ph convertor, any reference to neutral should not be made. particularly in a N.A. version as it does not conform to the standard 3ph reference to neutral as in a true Star or Delta supply, so often when someone builds or trouble shoots a VFD, they mention the voltage to neutral, which is meaningless in a VFD, especially from the generated leg.
Al.

[jknee2]

Or....
The only 2 things on the J325 that are 3 phase is the spindle drive and the coolant pump. So, if you don't use the factory coolant pump, and are handy, you can change the spindle drive to a single phase input with the typical 3 phase output. Probably not a bad idea to consider, since the vfd in your tree is old and are prone to failure anyway. The axis drives and control power all come off only 2 poles of the main breaker.

I totally agree, swap out the VFD to one that accepts single phase input and change the cooling pump to single phase. Change the power cord, a few simple wiring adjustments and you are up and running. A phase converter (add a phase) is just something else to fail.