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Phase converter question (For December)?

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  • Phase converter question (For December)?

    I picked up a 20HP rotary phase converter cheep like $300 cheep. The shop it came from got 3PH power and didn't need it any more. I also picked up a 25HP CNC lathe the next week. Now the rotary will start the CNC lathe and run it but I know it's not perfect and I'm not pushing the lathe hard either. When the lathe ramps up to higher speeds I do see the work light dim on the CNC. So on to the question.

    If I get another 15HP 3PH motor and wire it into the 3PH circuit threw a mag switch. Can I use the 25HP rotary converter to start the 15HP idler and then start the 25HP lathe? Having the addition of the 15HP idler running should make up for the under sized 20HP rotary. And I can still just run the 20HP rotary when I use the mill and smaller manual lathes. Or I'm I going to let the magic smoke out?

  • #2
    That does work. It will add idler capacity. Any motor that is not actually providing power will function as an idler.

    Many people find that a CNC wants a bit more RPC over what your total will be, but if it works, it works.

    I often see recommendations for more like 2x the CNC HP, when normally you might use 1.5x for a regular motor load. And some CNC apparently do not like RPCs at all.
    1601

    Keep eye on ball.
    Hashim Khan

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    • #3
      I'm given to understand that most CNC machines want "cleaner" power than a typical rotary can supply. It's not like the machine explodes the minute you switch it on, of course- it's a matter of various control boards and/or power supplies start having faults sooner than they might otherwise on native 3-phase.

      It's not cheap, but a Phase Perfect is generally the fix there- and as for 'cheap', the cost of a PP can seem cheap compared to trying to buy hard-to-find boards and controllers for older machines.

      Doc.
      Doc's Machine. (Probably not what you expect.)

      Comment


      • #4
        To be perfectly fair about it, the issue with an RPC as compared to a phase perfect is simple..... the RPC has more variation in the voltage of the generated leg than a Phase Perfect does. End of story.

        The voltage can be higher, in which case a poorly designed CNC (that seems to describe most of them, if the voltage limits quoted for them are to be taken seriously) may have a voltage go above a limit and damage something. The voltage may be low, in which case some voltage in he CNC may fall BELOW a limit and cause trouble some other way.

        According to the limits quoted by many people for a number of CNC units, they want some voltage, such as 220VAC, plus or minus nearly nothing, or they will urp and maybe die. This makes no sense at all. Any other device would be required to accept a minimum variation of +10% and - 10% from nominal without problems.

        I do not know why a CNC machine tool, which typically would operate in a factory environment of electrical noise and transients, should have such tight limits on AC voltage. But apparently they do, or at least some of them are claimed to. And this is tolerated for a factory device that may cost $40,000 to well over $100,000?

        It should be easily possible for the machines to tolerate a normal variation. I could not find an actual voltage tolerance range for Haas, for instance, when I went looking, but it would surprise me if it really was as tight as people say it is.
        Last edited by J Tiers; 11-30-2017, 11:22 PM.
        1601

        Keep eye on ball.
        Hashim Khan

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        • #5
          Ran into this recently. You either agree to the manf main voltage spec or they won't warranty it (new install)... and many machine will simply refuse to start up if it is outside. 2 x 60hp Phase Perfects, still needed a 45kva delta Y (nothing references neutral but they insist on a neutral to dump drive noise and regen energy, or no warranty) then boost to get back to 220 nominal. Frigg.
          Last edited by lakeside53; 12-01-2017, 12:21 AM.

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          • #6
            My Daewoo 240 must be extremely tolerant of voltage fluctuations. I have only had a message of low voltage once on start up. The lathe is set up for 208V and in the rotary there is a transformer correcting the incoming 220V. Maybe that’s how they (I’m) getting away with out any problems so far. This rotary was running a 15HP Daewoo Mill set up for 208V also. It ran the mill for 6 years with out any problems.

            The rotary is different than any other I have see. It only has run caps and the transformer in the control box. No relays or start caps. It has a Baldor motor with out an out put shaft on it.


            Sent from my iPhone using Tapatalk

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            • #7
              Originally posted by J Tiers View Post
              I could not find an actual voltage tolerance range for Haas, for instance, when I went looking, but it would surprise me if it really was as tight as people say it is.
              Per the Haas installation guide:
              For domestic (U.S.) CNC machine tool installations -- 208, 240 or 480 volts -- three phase power is required. This may be wye or delta type, 60 Hz. The power source must be grounded.
              A separate earth ground is required for power. Conduit type ground will not be sufficient.
              All phases must be balanced and voltages must be within ±10%.

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              • #8
                Originally posted by lbender View Post
                Per the Haas installation guide:
                For domestic (U.S.) CNC machine tool installations -- 208, 240 or 480 volts -- three phase power is required. This may be wye or delta type, 60 Hz. The power source must be grounded.
                A separate earth ground is required for power. Conduit type ground will not be sufficient.
                All phases must be balanced and voltages must be within ±10%.
                The grounding is "amusing", but no harm.... the 10% is a suitable tolerance, some of the Japanese units are said to quit if you get that far off.
                1601

                Keep eye on ball.
                Hashim Khan

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                • #9
                  With reference to the Haas quote. If the CNC will not run properly without an earth ground then it is wired wrong internally. There are no exceptions to this rule. I have been fighting this BS for more than thirty years.

                  Using an unloaded idler motor is an excellent idea. I once ran an entire chemical plant on single phase 480 for about 8 hours by cranking up the overload settings and cooling a few motors with water hoses.

                  The voltage sensitive part of a CNC is the control circuitry which is nearly always single phase. Be sure that the regenerated phase is not used for any control functions and you are likely to have no problems.

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                  • #10
                    Originally posted by garyhlucas View Post
                    ....

                    The voltage sensitive part of a CNC is the control circuitry which is nearly always single phase. ....
                    AND is almost guaranteed to have a well regulated power supply inside, if the designers had the slightest amount of good sense........
                    1601

                    Keep eye on ball.
                    Hashim Khan

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                    • #11
                      Good grief, don't these CNCs have regulated power supplies for the control circuitry? They (decent engineers) can build a supply that puts out 5 VDC, +/- 1% or any other DC Voltage you choose with any AC input from 90 to 250 VAC. And these power supplies cost between $50 and $250 or more depending on the current/power that they can supply. Heck, I could design and build one (with help from the chip maker's web sites, of course). Why wouldn't a $50,000 or $100,000 CNC device have a decent power supply. Any price differential would be a minor item in a machine in that price category. As for the motors, they certainly can stand substantial variations.

                      I don't understand.
                      Paul A.

                      Make it fit.
                      You can't win and there is a penalty for trying!

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                      • #12
                        Originally posted by Paul Alciatore View Post
                        Good grief, don't these CNCs have regulated power supplies for the control circuitry? ....

                        I don't understand.
                        Precisely. One wonders then why the crazy close tolerances that have been quoted by folks who say they have problems if those close tolerances are exceeded..... or if there is not a (pretty worthless) ground rod pounded right at the machine (potentially violating NEC requirements).......
                        1601

                        Keep eye on ball.
                        Hashim Khan

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