CNC grade converter
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  1. #1
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    Default CNC grade converter

    Does anyone know what is different about a CNC grade converter, compared to a regular rotary converter?

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    Quote Originally Posted by Bob-J-H View Post
    Does anyone know what is different about a CNC grade converter, compared to a regular rotary converter?
    Sanity check sez simply any RPC well-enough implemented and load-matched so as to not sag under load nor go unduly out of balance.

    RPC's are inherently clean sine-wave critters - can't build one any other way. With none of the switching artifacts of a VFD that might confuse a CNC critter's control electronics with fast-rising electrical spikes, just where IS "the beef"?

    Same place as "aircraft-grade" Aluminium. "Billet", any alloy. "Heavy duty" wotever, "Deluxe", or "Limited Edition", perhaps?

    How about one of PM's favourites: "hot water heater"?

    Useless device, Rotorua, New Zealand, at least. The water arrives already hot enough to cook food, why heat it?



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    If you really need to know I would call a place called Southern converter out of Texas. I bought a 30 HP set up and could not be happier. The guys name is Larry and he was very helpful in making sure I had the proper setup and size.

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    So you are saying Thermite, there is no difference, only hype.Thankyou Obstreperous but I am going to try to get my answere here. Anyone else?

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    They would indeed likely be intended to better hold up the generated leg. That's all that is really different about the generated leg vs the "pass-through". Might be a slightly different waveform in some motors. Not sure just what they might do, because the generated leg is inherently lower voltage than the straight-through legs if you use a regular motor as the idler..

    They might just oversize the idler motor, as many "heavy duty" ones seem to, that would help hold up (but still at the slightly lower-than-line voltage).

    They might have the motor wound to produce normal line voltage at the generated leg, that would be a few more turns in that set of coils. That way the voltage would inherently be at the normal line voltage at no load, instead of lower.

    They might do both, which would start at normal line volts, and then hold it up better under load.

    I suppose they might just print "CNC Grade" on the literature, but that would probably be discovered pretty soon..

    The big issue is having all three lines hold up so that the load is well distributed between the various rectifiers, and also so there is not a lot of "ripple voltage" on the rectified DC. CNC machines, especially older ones, seem to be relatively fussy about their incoming raw DC voltages.

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    As others have mentioned, I believe the key is getting away from the normal "1.5" idler:machine HP ratios and to something more stable when you do draw down on the generated leg. If it lends any reference, I believe my VMC has around a 30HP idler (Fadal VMC15 7.5HP spindle + 3 Drive axis). If you call that a total HP of 10, then I am close to a 3:1 idler/drive ratio.

    Naturally, this powers smaller machines with ease.


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