My first RPC 5-10HP is Fitch still the design to use? I have parts galore to build it
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    Default My first RPC 5-10HP is Fitch still the design to use? I have parts galore to build it

    My son and I just landed our keeper lathe, a Cincinnati 13x48 Hydrashift with a 3HP motor. I have a VFD but don't want to use it with this lathe as it needs to be connected directly to the motor, so I want to build 5-10HP RPC. I have been reading and studying for days, to me it looks like the Fitch 1998 design would be best for my needs. I have everything except the damn motor, going out this week to find one, everything else is laid out on the tailgate. I don't currently have any other 3 phase requirements, but who knows, maybe a milling machine will find it's way into our shop one day.

    So is this still the "go to" design? Cost is no object as I have pretty much everything except the motor.

    Thanks!
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    Quote Originally Posted by kilohertz View Post
    My son and I just landed our keeper lathe, a Cincinnati 13x48 Hydrashift with a 3HP motor. I have a VFD but don't want to use it with this lathe as it needs to be connected directly to the motor, so I want to build 5-10HP RPC. I have been reading and studying for days, to me it looks like the Fitch 1998 design would be best for my needs. I have everything except the damn motor, going out this week to find one, everything else is laid out on the tailgate. I don't currently have any other 3 phase requirements, but who knows, maybe a milling machine will find it's way into our shop one day.

    So is this still the "go to" design? Cost is no object as I have pretty much everything except the motor.

    Thanks!
    I probably had enough relays and capacitors in the Hell box to build six to ten RPC's. Among other quirks, I hoard Mercury-Displacement contactors and Crydom SSR's.

    As with rather a lot of PM'ers, "other demands" on time, etc. so I just bought mine from Jim Gorman, "Phase Craft". He has retired now, no longer builds them. I didn't even bother to see which "design tribe" he based his units on. They JFW.

    Jim's the guy to ask, if he dasn't mind the bother vs fishing or wotever.

    That said, when one selected a Phase Craft, the selection criteria included pole-count, eg: idler motor "base" RPM. He optimized for that characteristic as well as for HP. That may be a part of WHY his units "JFW".

    Ergo I bought my idler motor (a brand-new Weg, Brasil, 10 HP Open Drip Proof case style) FIRST. ISTR it was about $384, shipping included.

    I just yesterday ordered a 27 KVA Delta-in, Wye-out transformer for it. It will be gaining a 5 HP supplementary idler, arranged so I have a 5 HP, 10 HP, or 15 HP idler "array" line side of the one transformer. My max starting load is a 7 HP, unloaded spindle, but no clutch. Two like that, actually. My max running load is likely to be 3 HP., average running load mebbe 1 to 2 HP.

    Find the idler motor first.

    Give a thought to the "supplementary" idler concept. You may be able to reduce the need of diddling balance caps, still have the stones for starting and/or running heavy loads.. or operating lighter ones with less idler noise and fewer wasted ergs.

    The Delta-Wye transformer is simply because I DETEST corner-grounded or high-leg Delta existing "outside of its box".

    2CW
    Last edited by thermite; 09-04-2018 at 10:22 AM.

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    RPC designs are all about the same thing..... The differences are basically in the starting system, and sometimes in the issue of run capacitors etc. (and build quality, of course) The difference between idler motors is usually not a big deal, although there are exceptions.

    It makes more sense in many cases to just buy one, than to build it, assuming you are going to do something complex, with starting and so forth. Depending on your cost per hour for your time, it really is not that expensive even to buy the whole thing, idler and control, in one piece. That also generally gets you a UL mark, which your electrical inspector and OSHA will like

    Fitch is as good as any other shop built variety, since they all work the same way. Once they are started, all RPCs differ only in details, and even the start method is fairly standard. The Fitch design has a decent set of directions to guide you, so that is an advantage to a person of limited experience.

    The advantage of complete units is that they usually are UL, optimized already, they take no fiddling, just wire up and use. Some may be made to avoid the voltage issues by adjustment of the windings in the motor, or other means, which is superior to fiddling with balance capacitors, but that is not a big deal when just running motors with them. For running a CNC, it may be a different matter..

    You can also buy the controls, and add your own idler. That can work just as well, but some of the folks making the boxes are not as good as others. And a generic control often does not work as well as one that is designed, made, and optimized for a specific, known, idler motor.

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    Okay I have 2 motors now, both really nice motors, premium energy saving, deluxe blah blah blah, a Toshiba 5 HP and a Teco 10HP, plus I found a very cool power factor capacitor box, containing about 26, 61uF 360VAC oil filled caps. The deal is I need to fix the motor donors (lumber yard owner's) RPC in trade for the motors and parts I got, no problem, I have all the parts to do it now.

    So this week as time permits I will start assembling my RPC, start with the 5HP motor and see if that drives our 3HP motor on the Cinci, then rebuild the 15HP RPC.

    More later.

    Cheers
    Attached Thumbnails Attached Thumbnails img_5474.jpg   img_5470.jpg   img_5473.jpg  

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    Hey guys, where can I find this "Fitch" design RPC? Is it just a set of plans online, accessible to anyone? Thanks so much.

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    Thanks SAF

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    A couple of days working on the tailgate and I have a perfectly running 5HP RPC, the Fitch design and tuning procedure worked perfect. I ended up with 50uF Cp, 35uf Cs, and 14uf Cpf, a contactor for 500uF start caps and a big contactor for the main supply. I built it into a 60A fused switch box, I removed the big fuse blocks to make room for the components, it all fits perfectly and looks cool. All hard wired with #10, magnetic latching of the main contactor, momentary start/stop switches from an old broadcast transmitter (pays to be a "collector") and rather than a potential relay or time delay relay, I chose to just use the push button, hold it for 2 seconds until the idler comes up to speed and release.
    Ended up with voltages of Vab 240, Vbc 254, Vac 254, line current of .6A and Icn of 6.9A. seems to me to be as close to correct as I could get.


    A few pics...now need to confirm it's operation with our 3HP lathe.

    Cheers
    Attached Thumbnails Attached Thumbnails img_5500.jpg   img_5506.jpg   img_5507.jpg   img_5499.jpg  

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    Quote Originally Posted by kilohertz View Post
    A couple of days working on the tailgate and I have a perfectly running 5HP RPC, the Fitch design and tuning procedure worked perfect. I ended up with 50uF Cp, 35uf Cs, and 14uf Cpf, a contactor for 500uF start caps and a big contactor for the main supply. I built it into a 60A fused switch box, I removed the big fuse blocks to make room for the components, it all fits perfectly and looks cool. All hard wired with #10, magnetic latching of the main contactor, momentary start/stop switches from an old broadcast transmitter (pays to be a "collector") and rather than a potential relay or time delay relay, I chose to just use the push button, hold it for 2 seconds until the idler comes up to speed and release.
    Ended up with voltages of Vab 240, Vbc 254, Vac 254, line current of .6A and Icn of 6.9A. seems to me to be as close to correct as I could get.


    A few pics...now need to confirm it's operation with our 3HP lathe.

    Cheers
    LOL! Shades of Terry Matthew's key krew at Kanata! Ingenious lot, and fast-movers! Must be the short "growing season", eh?

    Only a Canadian redneck "ingineer" could start with a beater pickup, moldy plywood, rust piles, and gardening rakes and produce a neat-as-a-pin "product".

    South 48, we'd need Bondo, RTV and/or hot-melt glue, zip-ties, "duck" tape, and "too much" beer to argue it over for two months on PM!!!

    Good on yah for the "lean, mean, and hungry" approach!


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    Quote Originally Posted by kilohertz View Post
    A few pics...now need to confirm it's operation with our 3HP lathe.
    Cheers
    Nicely built. If the lathe is at all hard starting you could consider going with the 10 hp motor.
    The larger the idler is in relation to the load motor, the less finicky it will be regarding tuning.

    I noticed the Fitch instructions were dated '98. Has anyone heard anything from him in the
    recent past?

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    Quote Originally Posted by thermite View Post
    LOL! Shades of Terry Matthew's key krew at Kanata! Ingenious lot, and fast-movers! Must be the short "growing season", eh?

    Only a Canadian redneck "ingineer" could start with a beater pickup, moldy plywood, rust piles, and gardening rakes and produce a neat-as-a-pin "product".

    South 48, we'd need Bondo, RTV and/or hot-melt glue, zip-ties, "duck" tape, and "too much" beer to argue it over for two months on PM!!!

    Good on yah for the "lean, mean, and hungry" approach!

    Thanks! Well, classically trained in electronics and electrical, I only push dirt now 'cause it pays better, 3 dozers, 3 Bobcats, excavator and a dump truck. That pickup has been my workbench for years, which is why I am finally building a shop this fall. I am so tired of working outside on the gravel driveway. I'm also a ham and have been collecting all things electrical for years, had all of this stuff in stock, just had to assemble it into something resembling an RPC.

    Thanks for the compliments.

    Cheers

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    Quote Originally Posted by jim rozen View Post
    Nicely built. If the lathe is at all hard starting you could consider going with the 10 hp motor.
    The larger the idler is in relation to the load motor, the less finicky it will be regarding tuning.

    I noticed the Fitch instructions were dated '98. Has anyone heard anything from him in the
    recent past?
    Hi Jim,

    Thank you! I don't think our Cincinnati lathe will be a hard start, the motor powers up unloaded, just the little hydraulic pump that shifts gears, then when the spindle is engaged, it uses a clutch so I can control the engagement load on the motor by easing it in.

    I too was wondering where Fitch was, haven't seen any activity from him in a long time, hope he is well.

    Cheers

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    Quote Originally Posted by kilohertz View Post
    Thanks! Well, classically trained in electronics and electrical, I only push dirt now 'cause it pays better, 3 dozers, 3 Bobcats, excavator and a dump truck. That pickup has been my workbench for years, which is why I am finally building a shop this fall. I am so tired of working outside on the gravel driveway. I'm also a ham and have been collecting all things electrical for years, had all of this stuff in stock, just had to assemble it into something resembling an RPC.

    Thanks for the compliments.

    Cheers
    Dunno where it has gotten to, but one of the three of Doug MacArthur's comms team I knew, Manila => Australia => Manila, then setting up the broadcast of the surrender signing, Tokyo Bay, "K4TJ" had hauled around a monster vacuum capacitor for ages. I photographed it when we wrote "The Electronics Bench Manual", early 1970's and haven't seen it since.

    He ran a a pair of salvaged Marconi wotsits on his SSB rig. Simply mounted them upside-down in the rack rather than correct the Russian-pattern power switches designed by that notorious chekist agent provocateur, Colonel Ivan Ivanovich Upizoff to hamstring British progress in things electrical. He needn't have bothered, actually. It will be a while, yet before they take up either challenge in Blighty. Progress. Or proper application of electricity.

    I actually had the sitting CEO of L.M. Ericsson personally apologize to me on behalf, as he put is, of "Himself and all <some huge number> of Ericsson staff, worldwide." for a Telco International "Gateway" Switch'es WEIRD faux pas.

    He was able to chuckle over it only because it had helped him get his job. His PREDECESSOR had bought the silly bugger from an English firm.


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    Quote Originally Posted by jim rozen View Post
    Nicely built. If the lathe is at all hard starting you could consider going with the 10 hp motor.
    The larger the idler is in relation to the load motor, the less finicky it will be regarding tuning.

    I noticed the Fitch instructions were dated '98. Has anyone heard anything from him in the
    recent past?
    Fitch (ex Rocketdyne => Boeing, IIRC, and whip-smart for-damned-sure) announced a retirement to PA quite a while back. 20 years have passed now. He may have as well.

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    Quote Originally Posted by thermite View Post
    Fitch (ex Rocketdyne => Boeing, IIRC, and whip-smart for-damned-sure) announced a retirement to PA quite a while back. 20 years have passed now. He may have as well.
    This seems to be happening more and more these days, you look somebody up and then find out exactly why
    one has not heard from them in a while......

    ;(

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    Quote Originally Posted by jim rozen View Post
    This seems to be happening more and more these days, you look somebody up and then find out exactly why
    one has not heard from them in a while......

    ;(
    "these days?"

    Jim.... I dunno about EARLY man, but my family alone has an unbroken record of dying with a certain degree of regularity - "on the record" - for one HELLUVA long time. We just tend to be slothful as to getting it done, is all.

    Lemme know, you find some other option, willyah?

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    More and more these days, to ME. Could be a sign of my advancing age.
    As you say, the does beat the alternatives.

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    Quote Originally Posted by jim rozen View Post
    More and more these days, to ME. Could be a sign of my advancing age.
    As you say, the does beat the alternatives.
    Yeah.. that passage of time.. I recall the first time - age 39 - I reported to a person younger than I was. An uber-over-acheiver of a Vee Pee who was also female.

    And older mate just chuckled:

    "The age thing just happens, you live long enough."

    "The gender thing is just a sign of the times."


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    Hi guys,

    I finally just about finished the shop this spring, and just moved in the lathes. I am now able to make full tests on my RPC and did so today, with not as great results as the "bench test" I did last fall.

    You can scroll to the top to see what I have done so far, with the values as I indicated, I am getting 209, 215 and 237 across the Vbc Vac and Vab. I fiddled with the cap values some and am now getting 225, 225 and 237 loaded, unloaded it's 264, 262 and 237. I think this is acceptable, could you please let me know if this is okay? The other thing I noticed today is that my big lathe, the Cinci hydrashift, it's motor is actually a 3HP 208 3 phase, not 230/460 like I thought. Could this be a problem? The Icn on the idler is 11A, (FLA on motor is 12.6) and no load Iline is 6A, a big jump from 1A with the old cap values. I am only using test clips for the extra caps, there is about 2-4A thru each one, so I will try again tomorrow with some proper 12GA wire and also try to better tune the input cap to reduce Iline.

    I now have a concern about my little Hercules lathes, they are only .55KW, tiny little motors, do you think I will need a separate RPC for them? I don't want to have to fiddle with cap values for the little machines as well. Maybe the voltage will drop down just fine. They are being repaired right now (restored) so a tryout is difficult. Would just going to the 10HP idler eliminate some of this fiddley adjustment. I would like to just have one RPC for all my 3 ph stuff.

    Thanks for all the help.

    Cheers

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    you don't mention what voltage the .55KW motors are but if they are 208 then i would fix that issue by wiring up some buck boost transformers to drop the voltage, they won't be enough of a load to pull the 264 volts delivered down to a level that won't overheat them. if they are 240v motors then its not a problem

    this is one method to connect the transformers to get 120/208 from a 240v rpc.. but because there is no delta winding in the 16:120v transformers the neutral is useless and unbalanced loads will cause problems. https://i.imgur.com/9UtkTZj.jpg


    regarding your main 208 volt lathe.. you can instead use a single 16/32:120/240 buck boost transformer to drop the voltage from your single phase supply line to 208 instead of 240, but directly connect the third phase to the generated leg from the rpc. so the rpc sees 240 volts but your lathe sees 208 plus the generated leg. you might not need any balancing capacitors.

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