Hooking 2 phase converters together for CNC, question.

[pgmrmike]

I know you can hook 2 regular converters in sequence for regular loads like engine lathes etc. But what about CNC applications? I have a American Rotary 25hp Converter that has been running my VMC, now I need one for a CNC Lathe. Can I just add another idler, start it separately and be good? Will the controls that smooth the current be able to handle the load? What about the capacitors etc? Since the second idler will be running off the current from the first, do I just replace ( appropriately sized for the new total load ) the wires and breaker going to the control box of the first converter and be good?

 

[Karl_T]

Yes you certainly can just add another idler to get more capacity, start it at leat a few seconds later. Biggest issue to watch here is wire sizing and fusing, this can get complicated.

The system will need additional capacitors. How many is best determined by trial and error. I suggest three voltmeters between each hot leg so you can easily watch what is going on. These are real cheap on eBay.

BIGGEST THING TO WATCH FOR on CNC equipment. make dang sure the "wild" leg does not go to the control. In nearly every case two hot wires go to the control transformer. Make sure this is the two single phase hot wires.

A suggestion for a shop with multiple machines: get a three phase load center. use it as a sub panel off the main single phase panel. Now you can go full size wire, up to two hundred amp if you need. if you are a scrounge, like me, these go for dirt cheap used. industry won't put in used equipment like this, no hobby market.

Put each and every three phase load on a circuit breaker with the proper wires sizes and breaker size. this includes the idler motors. Now you got an expandable system every time you buy another machine.

 

[Karl_T]

One more safety suggestion for CNC equipment on generated three phase.

Put a normally open relay with a 220 volt coil in your Estop circuit. Make sure one of the legs powering this relay is the "wild" leg. Now, if you loose the 3 phase generating circuit (or just have not turned it on yet) the machine goes into E-stop and will not run. But you still got the control running.

 

[pgmrmike]

Thank you for the reply. I will have to think about this for a bit. May not be worth the trouble if I have to add capacitors etc.