RPC- Ready made, panel, or kit?
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    Default RPC- Ready made, panel, or kit?

    I've decided to get an RPC to run my home shop. Right now, I just have a 1 hp mill and a 1 hp surface grinder, but I might get a bigger lathe some day, so I want a 10 hp RPC to handle up to 5 hp. My choices are to buy a ready-made unit for a bit over $800, buy a panel for $300, plus a 10 hp 3 ph motor, or buy a 'kit' for $125, plus the motor. There's an auction coming up with a number of 3 ph motors, and they usually go pretty cheap. If I get lucky, I could get a motor for about $100.

    Being retired, money is always a big factor. I'm one old guy, so would only run one machine at a time, doing hobby stuff, and maybe a little paying work, but nothing serious. I have the mill on a VFD, and don't much care for it. I'd rather fire up an RPC when I'm going to do some work, and have it run the entire shop without having to mess with it.

    Is there any big advantage to a ready-made rig over the other options? Is a panel better than a kit? The old machines I use aren't very fussy about having clean power like a CNC would be. I have the time to build an RPC, and have above-average electrical skills. I just need to know if I should bid on a motor in this upcoming auction.

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    I think the cheapest way given the horsepower you need is to run everything off individual VFDs. I guess there's some question of the tradeoff in wiring costs that might impact it as well, but I doubt that will be very significant for a max 5 HP machine.

    What exactly are you having to mess with that's bothering you about the mill VFD? If you don't want take advantage of the VFD's frequency control, just set it to 60 Hertz and use the machine as you would on standard three phase power.

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    Any more than a 5hp RPC motor given your requirements is a waste. You probably can get by with a 2-3hp RPC motor.

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    Quote Originally Posted by rons View Post
    Any more than a 5hp RPC motor given your requirements is a waste. You probably can get by with a 2-3hp RPC motor.
    If he gets a lathe with a 5hp motor, he is going to need a 10hp rpc at minimum, and you know how shops go, machines get added to it. As far as multiple vfd's being cheaper than 1 rpc, yah maybe if buying the cheapo chinese units, but replacing them every few years adds up. I'm no fan of the noise generated by an rpc, but I'll take it over the high pitched whine of a vfd that makes your ears bleed.

    MushCreek, if you are comfortable building one you can source the components on ebay rather inexpensively, want cheaper find a scrap yard and scrounge the parts, you might even find a motor there too. Take a volt meter with you and ohm the windings before purchase.

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    Default RPC- Ready made, panel, or kit?

    A VFD on a mill is pretty sweet. Whatís not to like about it? Is it a Reeves drive? Are you still using it vice using the VFD?
    The VFD is nice for power tapping , just turn the switch from forward to reverse and done!

    Edit- I have a 10hp American Rotary phase converter that runs my 5hp gear head lathe and my 3 phase VFD mill. It works very well, but is fairly loud and puts out noticeable heat.


    Sent from my iPhone using Tapatalk Pro

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    Quote Originally Posted by dalmatiangirl61 View Post
    If he gets a lathe with a 5hp motor, he is going to need a 10hp rpc at minimum, and you know how shops go, machines get added to it. As far as multiple vfd's being cheaper than 1 rpc, yah maybe if buying the cheapo chinese units, but replacing them every few years adds up. I'm no fan of the noise generated by an rpc, but I'll take it over the high pitched whine of a vfd that makes your ears bleed.
    He's buying used parts for an RPC; he can find used, high quality VFDs that will probably outlast his uses given this is a home shop. A quality 5 HP VFD can be had for under $500 new, if necessary. Good quality 1 HP VFDs are <$200. Compare to $1,500 for a 10 HP RPC, I don't see how the math works in the RPCs favor. Now if he were running a CNC machine he'd have no choice, but it doesn't sound like that's happening.

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    Admittedly I'm biased in favor of a rpc for its simplicity and longevity. But $1500 for a 10hp rpc is overpriced quite a bit for someone capable of doing it themselves. I'm thinking $500 tops and that's buying a ready made panel and supplying the motor yourself.

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    You'll spend $500 on a panel and shipping alone...and VFDs are also cheaper used. The caps in both are the weak points, at the end of the day. For home hobbyist use, I'd be surprised if either presented an issue in a time period that OP would care about.

    That said, you can lead a horse to water but you can't make him drink. If OP wants an RPC, buying a panel and a used motor is a lot cheaper than buying the whole kit new. I don't know how much (if any, realistically) can be saved on building the panel himself; I wouldn't personally trust used caps, and punching holes in sheet metal is not my idea of a good time and likely won't be cost effective for him.

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    Quote Originally Posted by dalmatiangirl61 View Post
    If he gets a lathe with a 5hp motor, he is going to need a 10hp rpc at minimum, and you know how shops go, machines get added to it. As far as multiple vfd's being cheaper than 1 rpc, yah maybe if buying the cheapo chinese units, but replacing them every few years adds up. I'm no fan of the noise generated by an rpc, but I'll take it over the high pitched whine of a vfd that makes your ears bleed.

    MushCreek, if you are comfortable building one you can source the components on ebay rather inexpensively, want cheaper find a scrap yard and scrounge the parts, you might even find a motor there too. Take a volt meter with you and ohm the windings before purchase.
    A bigger lathe just means "bigger", not 5Hp. Then the words "might get" are in there. Then there is the interpretation that 5Hp means a combined number from all machines running at the same time
    As well as the interpretation that "handle up to 5Hp" is for only one machine.

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    Quote Originally Posted by rons View Post
    A bigger lathe just means "bigger", not 5Hp.
    From the OP "so I want a 10 hp RPC to handle up to 5 hp", its what he wants. And "I have the time to build an RPC, and have above-average electrical skills"

    With a little scrounging he can get the parts to build one for $100 or so, and run just about any machine he wants.

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    How do you power tap with a VFD? Mine takes a while to stop and reverse; true three phase power is instantaneous. That, and I'd have to buy a VFD for each piece of equipment. Right now, I have three 3 ph motors in the shop. It starts to add up, especially if I get a bigger machine. I could get by with a 5 hp RPC right now, but don't want to be painted into a corner if a deal comes along on a bigger machine. I could have gotten a good deal on a lathe at an auction, but it was 7.5 hp. I could even envision a CNC bed mill, which usually run at least 5 hp.

    My thought right now is that it would be worth a few extra bucks to buy a ready-made panel, and a used 10 hp motor. Some places will even tune it for you if you give the specs on the motor. I guess I'll see what kind of $$$ the ones at the auction go for.

    Not sure where you're getting your pricing. A 10 hp RPC is $830 on ebay; the panel is $275 or so. That's for an American made RPC.

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    Quote Originally Posted by Hodge View Post
    Admittedly I'm biased in favor of a rpc for its simplicity and longevity. But $1500 for a 10hp rpc is overpriced quite a bit for someone capable of doing it themselves. I'm thinking $500 tops and that's buying a ready made panel and supplying the motor yourself.
    About $700 or so, "free shipping" having been included on the 10 HP Weg (Brazil, not China), brand-new idler motor.

    My control box is from Phase-Craft, but jim has since quite making them and retired,

    Used motor? Anywhere from sub-$50 to ABOVE new prices is ASKED. That's why I kept looking until i found a good price on brand-new WITH shipping included. Scout for that FIRST, because it can drive the decision off the back of its cost.

    5HP, 7.5 HP, 10 HP - AND ...one can add a "supplementary idler", later, same control box, with minimal extra spend.

    VFD's - the cheaper ones most of all - can be hard on older motors. Those built before "inverter duty" design and labeling came into use to survive truant VFD's. If-even...

    Two Cents... one RPC, two Phase-Perfect, one 3-P capable diesel gen set.. and NO VFD still in active use worth. .

    I use Dinosaur Current with KB-Penta drives (180 VDC motors), or Parker-SSD DC drives (230 VDC and above motors) where I need variable speed.

    DC Drives don't need new capacitors every few years. They didn't have them to begin with.


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    Thermite, I've got you beat! I bought 2 20hp Phase a matic rpc's on online auction for $400, +$200 to ship to my door, then flipped 1 for $600, and kept the other, so net cost $0

    MushCreek, auction may or may not be the place to buy a motor, all depends on who shows up. If there are any scrap yards in your area that will let you pick, go check them out, you'd be amazed at what companies will scrap. If its a good/busy yard you should be able to find everything you need, might take a week or two of strolling, but it can be done cheap cheap.

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    Quote Originally Posted by rons View Post
    A bigger lathe just means "bigger", not 5Hp.
    Well.. no .. it might be 7, 10, 12, 15 HP or even 50 HP.

    Doesn't have to be all that "big";

    - My 14 X 30 lathe is only 7 HP, but the hydraulics AND the juice pump add another chunk..

    - My drill press is only 7 HP. That, too has a juice pump.

    - The rather modest Quartet mill has 5 HP horizontal spindle, 1 3/4 HP vertical - not used at the same time, but the 3/4 HP knee power and a 1/2 HP juice pump ARE used with either spindle, just not all STARTED at once, or even a 10 HP RPC would be challenged.

    Some among us try hard to NOT cut "dry" as well. The Kasto saw has a juice pump as well as its main motor.

    Total power budget can add up, even for one-person use. Multiple motors are common.

    VFD count, if I used those? Near-as-dammit essential they be dedicated. Every one of those machines would also have to have control circuits rewired. I'd need to pay for, then fiddle-with, then maintain a veritable platoon of VFD, plus as many filters, (all my motors are old).

    Most would be sitting idle while just 2 or 3 were at work.

    Phase-Perfect or RPC expect to share multiple loads. No rewiring of the machines at all. Little or no spend on filters. Fewer capacitors to replace at intervals.

    Don't judge the rest of the world by your little Hardinge at what? 2 HP? Or a usually 2 HP if not less, BirdPort mill.

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    Quote Originally Posted by MushCreek View Post

    Being retired, money is always a big factor. I'm one old guy, so would only run one machine at a time, doing hobby stuff, and maybe a little paying work, but nothing serious. I have the mill on a VFD, and don't much care for it. I'd rather fire up an RPC when I'm going to do some work, and have it run the entire shop without having to mess with it.

    Is there any big advantage to a ready-made rig over the other options? Is a panel better than a kit? The old machines I use aren't very fussy about having clean power like a CNC would be. I have the time to build an RPC, and have above-average electrical skills. I just need to know if I should bid on a motor in this upcoming auction.
    Thermite is all ready to come out to the garage and make an evaluation and take notes. He has nothing better to do. The ideal time would be during his next banishment from this forum.

    All he needs is a wheelchair ramp, pack of quick change diapers, and a carton of cigarettes.

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    False alarm. All of the motors went for way more than I was willing to spend on a used, untested motor. Then there's the exorbitant 'buyer's premium' that have become the norm at auctions. This place charges 18%, with that plus the sales tax adds 25% to the cost of an item! Auction houses have gotten so greedy. They used to be satisfied with the sales commission; then they started that buyer's premium BS.

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    I wouldnít give up too easily. The motors pop up on Craigslist fairly often and fairly cheap.

    Iím running a CNC machine on my RPC, so my requirements were a little different, but Iíll echo what a lot of folks have said: go with the premade panel. Iíve made a few RPCs with the help of an electrician, and it was still a hassle. And we had access to boxes, conduit, fancy contacts for starting the single phase motor used to spin up the idler, etc. We didnít even balance the legs with capacitors. It looked great, but the hardware would have cost WAY more than I paid for an American Rotary panel, and that was for a 15 HP. Itís also stupid easy to build with the instructions that come with the panel.

    Iím also an advocate for a VFD on a Bridgeport. We have 3-phase at work, and they still use one for similar speed adjustment reasons mentioned above.

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    If I were to do it today I would use a VFD. Back in the day I had 2 cave man 5 hp rotary converters, Big motor, lovejoy, small motor, momentary switch, 3 phase breaker. Ran ~18 hp worth of machines with as many as 3 guys running them. For 6 years. No problems. I think the couplings were the only things I actually paid for.

    You need to size the converter motor for the largest load, not the total load. Especially if you are working by yourself oversizing is a waste of money and electricity

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    Quote Originally Posted by MushCreek View Post
    How do you power tap with a VFD? Mine takes a while to stop and reverse; true three phase power is instantaneous. That, and I'd have to buy a VFD for each piece of equipment. Right now, I have three 3 ph motors in the shop. It starts to add up, especially if I get a bigger machine. I could get by with a 5 hp RPC right now, but don't want to be painted into a corner if a deal comes along on a bigger machine. I could have gotten a good deal on a lathe at an auction, but it was 7.5 hp. I could even envision a CNC bed mill, which usually run at least 5 hp.
    If you set your deceleration / acceleration parameters on the VFD appropriately you can make it stop as quickly as it can without needing a braking resistor. These are usually in units of seconds.

    Usually the defaults are a fairly long period for each. If thereís not much inertia in the machine you can probably shorten it a lot.

    On my surface grinder on VFD I set a long acceleration time. On the mill my times are much shorter. I need to play with the lathe settings because Iíd like it to stop faster (and for e-stop to free-spin so the footbrake doesnít fight the decel on the VFD).

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    Brandenberger beat me to it. My Fadal spindle uses a VFD to rigid tap all day long -- granted because it's CNC I had to get an RPC to run the whole thing.

    Quote Originally Posted by MushCreek View Post
    False alarm. All of the motors went for way more than I was willing to spend on a used, untested motor. Then there's the exorbitant 'buyer's premium' that have become the norm at auctions. This place charges 18%, with that plus the sales tax adds 25% to the cost of an item! Auction houses have gotten so greedy. They used to be satisfied with the sales commission; then they started that buyer's premium BS.
    Check Ebay. I've bought countless motors through Ebay, shipping isn't very expensive compared to pay fractional amounts of new. This one comes out to less than $350 including shipping and NJ sales tax: 10 hp baldor electric motor 1760 rpm 230/460 volt 3 phase, | eBay


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