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Larger CNC lathe on phase converter?

mmurray70

Stainless
Joined
Jan 11, 2003
Hi guys, my shop has a 125a single phase service. I have a 35hp phase converter running off a 100a breaker. Currently running a Fadal 4020 and Mazak quick turn 10 off this setup and its working well. Each machine has a 10hp continuous spindle. Im considering upgrading to a larger lathe but Im a little concerned about how much power I have available. I would like to try and get a machine with a 10" chuck, 3" bar capacity and seems like most lathes this size are 20-30hp and at least 30KVA. Seems like power requirements go through the roof on anything larger then a 8" chuck lathe.

I dont need this much performance. Im just a job shop doing small runs and want to be able to handle the occasional part that's a little too big for an 8" lathe. No need to do massive cuts on these parts, just want to be able to get them done and out the door. Do you guys think a larger machine could work with my setup if I make reasonable cuts? I would reduce the spindle ramp time as well. I've had a few machinery dealers suggest I should be fine, but obviously dont want to buy something I cant use. Any advice?
 
for as little as 15$ you can buy a kwh meter that will show you amps, volts, kwh, power factor, and watts.

100A AC Digital Power KWh Watt Meter Volt Amp Voltmeter Ammeter Open Close CT US 760970220593 | eBay

you will want two of them

one on the output of the third leg generated by your 35hp rpc, the other on the incoming leg. 4 of them would be better. one on the single phase input, 3 on the output.



A larger rpc will suck up more amps from your limited mains, but much of that can be offset by adding standard motor run capacitors to offset the reactive amps.

Also motors increase in efficiency with hp. If you can find a 40 hp or a 50hp rpc, you will likely get better power from it than you would by adding another 10hp to your existing 35hp motor. but if it is a lower efficiency, lower power factor motor, you won't get any improvement. you will need a watt meter to know which is better.


anyhow as it is, you don't really have any idea of how much power you need other than what you're getting billed for. you may be able to get away with adding another machine, or you may need better power to run 3 spindles at once.

the lathe's greatest power consumption may be accelerating the spindle as rapidly as it can, and you can probably very easily change such parameters. also the drives that run almost all major machines don't actually need 3 phase power. all they need is 340volts dc after the rectifier. so, by not having good quality power all you're doing is stressing out the rectifier and the dc filter capacitors. if you never run the machine beyond 50% full load, you could run it on single phase directly (though it almost certainly needs "3" phase, for all the other things such as coolant pumps, etc, that run from the line directly)

so, just get the data from your existing machines and keep an eye on the current being produced by the third leg of the rpc. if its a lot less than you thought and the voltages produced are good then you have the capacity to add another machine.
 
The lathe will most likely be replacing the old one so no need to run all 3 spindles. Would be nice if I could run the mill at the same time. Right now with both machines on and idling the total single phase load is around 30a. Starting spindle on the mill bumps it to 40-45a, starting the lathe is around 50-55a total. Settles back again once up to speed. I haven't checked it while actually cutting anything, but just ramping up the spindle is usually a pretty good load. May look into those meters.

Anybody have any idea what a machine this size will draw just sitting there idling along with the spindle running? Like how much I loose before it even starts to cut anything?

Some of the machines im looking at are a Doosan Puma 2600, Mazak QT250 or older QT20, Haas SL30, something around this size range anyway. Any brands I should avoid with questionable power? Maybe some are more likely then others to throw an alarm if manufactured leg drops?
 
Mr. Johansen,
You said, in your post here that the machine could probably be run on single phase, except for pumps and so on that need 3 phase.
Interesting.
I had the impression that these lathes used Inverters, or VFD's for the spindle drives and slide actuators, and I thought these needed to be fed with 3 phase power.
I have lots of experience using VFD's to generate 3 phase from single phase for manual machines.
I also had the impression the control systems were typically 120 volts or so single phase. Coolant pumps can easily run from a VFD.

So are you saying a smaller CNC machine could be run from single phase, with reduced cutting loads and spindle ramps ?

Thanks,
Bob
 
Any machine with a regenerative drive will probably need 3 phase and there is no way around it.
Older machines which will have brake resistors on the dc drives and spindle should not need 3 phase. All they care about is 340volts dc on the bus, how it gets there is immaterial. (200 volt machines will prefer to have a lower voltage.)
There is lots of talk across this forum about lowering the voltage on certain machines or older machines because the spindle drive will last longer. This is generally true, components wear out and capacitors age according to the 14th power of the applied voltage if you can believe that in extremes duty use. In normal use its probably more like the 5th power.

If the drives do not have active power factor correction: then they are just dumb rectifiers, and are electrically no different than any cheap vfd. for which you need a 50% derate on hp when operating on single phase otherwise the rectifiers will fail and possibly the capacitors will overheat and explode.

you may have to fool the spindle drives or the servo drives into thinking they have three phase available if the system was built with phase loss protection. If you can find the users manual for the drives, it will have all those details.


Much older cnc machines or robots which used 12 thyristors aka SCR's for their servo motor controls, do need 3 phase to operate. but at this point it is unlikely any of those machines are still around.


anyhow I cannot imagine there is any risk of running a modern cnc off of single phase power, provided you monitor the power consumption and pay attention to how much power it is drawing during rapids, and normal loads.


now obviously i'm not familiar with everything out there.

it is possible there are spindle and servo drives which have such minimal capacitance on the dc bus that they do need 3 phase. usually there is access to the dc bus of a servo drive because in many applications they all run off the same dc bus for all axis. you can go ahead and buy a bigger capacitor and install it.

usually cnc machines don't accelerate or decelerate all axis at the same time, which means that if the servo drives are all ganged together, you can definitely run them on single phase without derating, provided only one drive at a time is significantly loaded.


so anyhow if you can't find any manuals for the dc drives simply take the cover off and post a photo of the board, we can figure out what it needs from there.


for example, i bought some servo drives that have nearly no capacitance on the board and rely on an external dc supply.. now obviously, in such a case you can simply upgrade or replace the dc supply if you can't make the existing system work with single phase ac power.
 
Thanks for detailed thoughts here.
Not sure I understand everything you've written, but that doesn't really matter.
It' just interesting to know what's possible.
Thanks
Bob
 








 
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