Larger CNC lathe on phase converter?
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  1. #1
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    Default Larger CNC lathe on phase converter?

    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?

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    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.

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    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?


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