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  1. #1
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    Default Home Shop Phase Converter

    Hey Guys,

    I finally purchased a mill and lathe for my home shop and I have a few questions regarding phase converters.

    The lathe is 7.5 hp but has a clutch. Do I still need to buy a 15 hp rotary phase converter?

    The mill is 1.5 hp. If I purchase a 15hp phase converter will this be too large for the mill?

    Thanks for your input!!

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    You could probably get by with a 10 but price difference is small.

    have you looked at the RPC kits on eBay without the 3 phase motor? Then buy the motor locally. Great bang/buck.

    here's one listing
    15HP Rotary Phase Converter Quick Build Kit | eBay

    15 Hp phase converter control panel CONVERTER ROTARY RP15 | eBay

    15 HP Rotary Phase Converter Panel | eBay

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  4. #3
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    VFD for my 7.5 Monarch

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    I'll vouch for the diy rpc panels from the guy out of Yamhill, Or. I have his 20hp and 30hp panels running in parallel(when needing the power) and doing great.

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    Quote Originally Posted by Karl_T View Post
    You could probably get by with a 10 but price difference is small.

    have you looked at the RPC kits on eBay without the 3 phase motor? Then buy the motor locally. Great bang/buck.

    here's one listing
    15HP Rotary Phase Converter Quick Build Kit | eBay

    15 Hp phase converter control panel CONVERTER ROTARY RP15 | eBay

    15 HP Rotary Phase Converter Panel | eBay

    What's the advantage of an RPC over a VFD ?

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    Quote Originally Posted by crickets View Post
    What's the advantage of an RPC over a VFD ?
    Well, the OP asked about a RPC so answered his question.

    I put VFDs on almost all my machines - variable speed control. Even nice on a knee mill - don't have to adjust belting. I did NOT put it on a Leblond servo shift -machine already has variable speed.

    Upside of RPC - 3 phase machines ready to go as built and inexpensive.

    VFDs give variable speed and make machine plug into single phase if needed. Depending on machine can be quite a rewire job to get going.

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    Quote Originally Posted by crickets View Post
    What's the advantage of an RPC over a VFD ?
    Plus:

    - A decent RPC is about as bulletproof as a rock quarry.

    - One RPC can serve many loads, and each quite different, is easily paralleled or added-to, so not a lot of prior planning required.

    - No re-wiring needed to any of the powered loads.

    - Clean 'real' Sine-Wave power, with no nasty switching artifacts that can damage old pre "inverter duty" load motors or mess up your stereo or Pee Cee.

    Downside:

    - Bigger the RPC idler, the harder it is to START. Two or more smaller idlers, stagger-started or not even both/all always used can work.

    - Pushed hard, even an oversized RPC is only good for about 91% of continuous load-motor OEM nameplate power. Imperfect heat distribution, mostly, so we don't notice that for short bursts at full load.

    - No variable speed nor slow-ramp for the loads. None. Nada. Zero.

    VFD can do both variable speed/torque, slow-ramp start, even precise speed control, can carry a load motor OVER 100% of OEM nameplate, but ordinarily needs one VFD per EACH load, significant re-wiring, and has a shorter working life.

    RTFM. Most OEM makers ask for new capacitors at 7 to 12 years, even if they might run longer on average.

    Typical RPC might need a new start cap at that age or twice that, run/balance caps only at 20-plus years. It doesn't work them as hard as a VFD must do, especially when the VFD is forced to run de-rated off only a single-phase, not three-phase input supply.

    Used RPC are low-risk, easily restored even if imperfect. DIY is easy, used idler motor or new. Freight cost for heavy idler motors is a factor, though

    Used - or even "shelf stale" UNused old stock VFD - are a high risk dice-roll off capacitor age. New caps can cost more than a newer generation VFD, outright. Usually, they are replaced, seldom re-capped.

    It ain't religion. The costs are often nearly the same.

    The choice simply depends on the end-luser's specific balance of priorities, current, and future.

    "Some of each" is OK, too, after all.

    So long as you don't try to parallel them on the same load-side wire!

    Syncing three Diesels was once "Day Job" easy.

    But I don't mix the 3-Phase Diesel or my Phase-Perfect in EITHER! US DoD is no longer paying for my toys!


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    Quote Originally Posted by thermite View Post
    Plus:
    - Clean 'real' Sine-Wave power, with no nasty switching artifacts that can damage old pre "inverter duty" load motors or mess up your stereo or Pee Cee.
    Any chance you have a scope picture of that effect ?

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    Quote Originally Posted by crickets View Post
    Any chance you have a scope picture of that effect ?
    Ask and ye shall receive...(I seem to recall purple was the manufactured leg)



    The critter in question:



    How it was measured:


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    Quote Originally Posted by crickets View Post
    Any chance you have a scope picture of that effect ?
    Why would I need one? They are all over the 'net.

    VFD.

    Not just RPC.

    Also special camera shots as the VFD fast-rise generates corona discharge, peirces insulation, and "flutes" bearings by spark-erosion.

    "Sometimes" Not always.

    Google and ye shall find them.

    RPC don't do any of those bad juju things.
    At all.

    Acoustical noise?

    Well f**k's sake. "WIRE exists".

    RPC run just fine outdoors, other side of the house.. where the Diesel gen set lives, my stingy-about-conduit-trenching case.

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    - Bigger the RPC idler, the harder it is to START. Two or more smaller idlers, stagger-started or not even both/all always used can work.

    if using low voltage wire to 7,8 and 9 only or 1,2 and 3, jump 4,5 and 6. One or the other so motor starts at 1/2 HP rating. then when running use a contactor to connect the other 1/2.

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    In my opinion, a VFD on anything larger than 3 HP just doesn't make economical sense.
    Big dollars for a good quality (reliable) unit *that will run the motor at full power*

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    Quote Originally Posted by jim rozen View Post
    Ask and ye shall receive...(I seem to recall purple was the manufactured leg)



    The critter in question:



    How it was measured:

    wow those phases look beautiful. Within what %? You had to mess a lot with caps?

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    Quote Originally Posted by madmachinst View Post
    wow those phases look beautiful. Within what %? You had to mess a lot with caps?
    No capacitors were harmed in the making of that converter. It's totally, 100%, validated capacitor-free. Even the pony motor there is repulsion start, induction run.
    Key factor being the idler motor at 5 hp is very much larger than any of the load motors. The pony motor btw is 1/8 hp.

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    Per the OP questions...........

    The bigger the RPC the better, in general. With an RPC, the larger size just produces better power.

    With a VFD, a larger than needed one costs a lot more, and the overcurrent protection may not be able to be set to protect a much smaller motor.

    VFDs require much of the internal control system in the machine to be removed or disabled. An RPC is plug-and-play with zero change to the machine unless it needs a voltage conversion (which you'd have to do anyway).

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    Another question I know a motor repair guy ( real great guy next time I visit must bring 6 pack). He was concerned that he was always taught only use Wye connected motor for RPC. I am stuck with 50 hp delta. Am I looking forward to any problems? Otherwise he said that this idea over here in post #43 ( second drawing)

    3 phase starter circuit

    should work real fine. Come guys I need some more verification before I start buying the remaining parts. Please.

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    madmachinest. This current thread talks about delta or Y motors, as well as RPM and capacitors.

    Disadvantage/Problem with using a 1200 RPM, Wye wound imotor for an RPC idler motor

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    so basically I should have gotten a bigger motor. The only disadvantage I saw in Wye vs Delta is the heat dissipation according to that thread. If necessary could parallel another motor that fires up after start up would that alleviate that problem or not? All I am running on that 50 hp delta is a CNC Mazak ( lathe) SQT 18-MS Big spindle 20 hp con. 25 int. Other item is a retrofit V2XT CNC BP that I might add fuses for a third phase and step down transformer for UPS for computer. I'd go 3 phase w/ that so that I can decrease my amperage. Then the Bridgeport clone that is it for now. All this when I have 3 (POCO)wires running through my property. That CNC lathe is why I went with as big a converter as possible so I can keep it in balance and such.


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