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  1. #21
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    Quote Originally Posted by thermite View Post

    Page Three:

    "Just me", but "small shop", my 200 A residental service and neighbours sharing the transformer?

    I wouldn't try to do a 30 HP single-idler RPC even with a "pony motor" start.

    The 28 HP max "all active" one I have is one or two idlers more complicated than you need - partly because I have some really LIGHT loads at under 2 HP, each machine, total. Then ALSO machines with NO clutch, and others with very different loads, same power-cord.

    Your load is simpler? Break it up sanely. 2 could do yah, 3 at most.

    The goal is that your RPC IDLER starting load goes more easily managed as well as having the balls to START the load. It does not KNOW you will actally run it below 1/4 of its max power most days. Starting load "is what it is".

    With a multi-idler rig, yah do the hard work of the load startup, then drop one of the idlers off the line for running the machine-tool at - quite realistically - far lower loads than its maximum.

    Or leave it online for any period of use when more serious chip must be ripped. AND/OR .. there are to be a LOT of starts and stops. Andsatrts, again. My larger drillpress - with a foot-switch, yet - is one of those that drove all the "extra s**t" under this roof. "YMMV"

    It's a nuisance to do that for 10 HP RPC or less. Any genuine gain is in the higher loadings or squirrely variations in loadings. I just don't happen to have anything that is actually SIMPLE!

    I'm going to need to upgrade my rpc as well. Using the op's current example. Does he need a 30hp control box, and let's say three 10hp idlers? Or a 10hp control box that uses three 10hp idler motors?

    My guess is a 30hp controller. If desiring to start a 15hp load motor, do you start all 3 idlers at the same time, or bring idlers 2 and 3 on after idler one is up ?

    I do like this idea of multiple idlers, where you can run just one idler for most 1 to 3hp loads. Beats sucking down all that electricity for a single high hp idler. It was on my mind actually, as I didn't want to run so many amps on an idler for smaller machines.

    I'd downgrade a 15hp to 10hp in a machine for home shop though. If I'm buying idlers, I can buy a motor for the machine. Then use a 20hp rpc, with a 10hp and a 7.5hp idlers. Use the 7.5 for smaller machines 1-3hp. 10hp idler for machines with multiple motors. Use both together for 10hp machines.

  2. #22
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    Quote Originally Posted by texasgunsmith View Post
    I'm going to need to upgrade my rpc as well. Using the op's current example. Does he need a 30hp control box, and let's say three 10hp idlers? Or a 10hp control box that uses three 10hp idler motors?

    My guess is a 30hp controller. If desiring to start a 15hp load motor, do you start all 3 idlers at the same time, or bring idlers 2 and 3 on after idler one is up ?

    I do like this idea of multiple idlers, where you can run just one idler for most 1 to 3hp loads. Beats sucking down all that electricity for a single high hp idler. It was on my mind actually, as I didn't want to run so many amps on an idler for smaller machines.

    I'd downgrade a 15hp to 10hp in a machine for home shop though. If I'm buying idlers, I can buy a motor for the machine. Then use a 20hp rpc, with a 10hp and a 7.5hp idlers. Use the 7.5 for smaller machines 1-3hp. 10hp idler for machines with multiple motors. Use both together for 10hp machines.
    One absolutely does NEVER start them all at once, even if you will RUN them all for a spell!

    Nor even, necessarily, start them in the same digital demand meter sampling time-slot if yer a cheap bastid.

    Whole purpose of the excercise is to spread-out the starting load of the idlers as job ONE. Flexible sizing is just the desert course - job TWO.

    Soooo... I just use a single 10 HP-rated Phase Craft controller for the lot. Only the FIRST one is "started" in the conventional sense as an RPC controller views its world.

    The more important function is single-point normal shut-down AND.. "mag starter" AKA DROP OUT and STAY TF OUT until something with half a brain tells you it is safe to be "ON" again.. if there is a power interruption.

    Supplementary idlers dropped onto the line, later, look exactly like load motors at first. They "become" idlers for lack of power being extracted from their shafts. So, too, would a menagerie of ON but idle machine-tool motors. But that's a pain in the ass to manage or even remember whom is doing what, with which, and for whom. Also probable sanding belt or disk, grinding wheels, circular or bandsaw blades, etc.. whirling away looking for a careless blood-meal.

    The seldom-used 10 HP Brazilian-made Weg is the largest idler, so no larger need for the controller.

    Same 10 HP control/starter box kicks-off a 7.5, 5, or 3 HP "with vigor" but no harm.

    The run / balance caps are out on the idler motors, each one mounting "roughly" the appropriate ones for its rating as-if stand-alone.

    If any given idler is not actively selected? The run/balance caps on it are not in the circuit, EITHER.

    This because they often ARE "stand-alone", only one active - in the appropriate size - not running ganged unless needed to sort a hard to start, but easy to RUN load.

    AND THAT .. is why "most folks" only need the pilot-motor primary idler and ONLY ONE supplementary, idler, not three, nor even two.

    The only other "active" hardware besides the Phase Craft is ONE EACH stout contactor per-each idler motor .. and a panel of switches to select who gets to be run for initial start.

    Begin with the heaviest for the tasking about to be engaged in - add, then later remove, ANY of the sizes, later, depending on target RUNNING load - first and biggest idler included if appropriate.

    24 VAC control transformer, BTW. Off its own single-phase feed. Contactors are more common with that coil type, hence cheaper, and it needs to "be there" to execute commands, whether any Idler is yet running or is not asked to run. Run the OUTPUT (24 V secondary) through the "mag starter" Aux / sustaining contact, not the input. Got indicator lamps to light up, showing "READY" too.

    Switch the primary off? ALL fall down for the end of the day.

    Provide for this. Even if you run a "loop" with lighted e-stops in bathroom,den, kitchen, and bedroom.

    No joke.

    Lest forgetfullass leaves them running over a three-month holiday - as my underground soaker hose network was run all of one summer when I bypassed the timer "for one last good shot".. left it bypassed 24 hour running.. and headed for IAD and 3 months out of the country.

    Came back to the parked Dodge pickup bed full of pumpkins, back garden buried in thousands of cherry tomatoes hidden in a jungle of Chinese "Ong Choy" and silvery-haired "winter mellons!"

    Costs? Of the RPC. Not the vegetables.

    The "big bucks" were in really good idlers and their freakin' freight-in costs.

    All but the open, drip-proof rolled-steel casing Weg are HEAVY, cast Iron, finned, fan-over Reliance Duty Master / e-Master. I THINK my TOTAL with freight for the idlers is about $1,500-$1,800 for the four of them?

    The Phase-Craft was a bit under $300 bucks? It has been a few years on that and the first Weg.

    The Contactors about $30-$85 bucks.

    The caps were from Alpine HVAC, US made, high ripple rated, and in 4XX VAC, not 380 VAC. Website finds current costs.

    "New, Old Stock?" On the Idlers? The lightest two, the 10 HP Weg, and the 3 HP Reliance - were "Free Shipping".

    Weg was new, period, full-stop, and perfect.

    On the three older, heavier, Reliance, I had a cracked CI fan shroud on one, a dented drawn-steel fan shroud on another - both impellers just fine. Also had a bustid-off Zerk to repair. No big deal, any of that, as otherwise NEW ...vs messing with old, used, dirty, grubby, full of dog hair and MAYBE even burnt-up, motors.

    I'm good with a skosh of auto-body work for the price NRI et al wuz asking!



    If sparks are to be avoided?

    I use NOS Mercury-displacement contactors.. but do not recommend them for amateurs.

    Gigavac's are sealed, all around safer, and do not give a damn if the world happens to turn upside-down whilst you are taking a s**t.

    Mercury ones DO give a damn which end is UP! Are waaay cheaper than Gigavacs!
    but, but, but.. also have a serious-nasty possible failure mode. As said, not for amateurs. Don't try HG contactors at yer kitchen table! They are well-sealed, but that is not the same s beyond all possible dangers. The s**t is toxic. VERY!

    I just don't like s**t that wears out nor makes an arcy-sparky visible fuss pretending not to do. There are days.. when I have a lot of solvents wandering about in shop air, and "FAM" is not on my menu.

    Otherwise, most any "rated" contactor will do jest fine.
    That is why a "rating" exists.

    Some are just better than others.


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  4. #23
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    Perhaps you could call American rotary, I bet they could answer your ?s and perhaps surprize you with data you are searching for. I have two of their units, one running a bigger CNC machine,excellent products, I like you, never learned much aboot sparky stuff.
    Good Luck.
    Gw

  5. #24
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    Quote Originally Posted by Greg White View Post
    Perhaps you could call American rotary, I bet they could answer your ?s and perhaps surprize you with data you are searching for. I have two of their units, one running a bigger CNC machine,excellent products, I like you, never learned much aboot sparky stuff.
    Good Luck.
    Gw
    ISTR American and two (or more) other "major"makers' of ready-to-use commercial RPC even publish rather a lot of sound guidance for sizing to start various classes of loads, etc.

    In one PM thread, it was noted that a 'modular" approach comes in with some of the makers once they hit a certain size.

    Not the same as "supplementary idlers" (only..). Full scale independent RPC that are simply set up as two or more to automagically "sync' and share loads as teamed partners rather that a single, more massive, unit.

    That is also a method of reducing risk of single-points of failure.

    At least a portion - the most critical loads - can be supplied even if part of the teamed array has gone tits-up.

    "Put all your eggs in one basket, then WATCH that basket" is still the riskier route than a bit of inbuilt redundancy.

  6. #25
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    Quote Originally Posted by Greg White View Post
    Perhaps you could call American rotary, I bet they could answer your ?s and perhaps surprize you with data you are searching for. I have two of their units, one running a bigger CNC machine,excellent products, I like you, never learned much aboot sparky stuff.
    Good Luck.
    Gw
    Here yah go. More than a chart. Plug in yer own numbers:

    Sizing Chart - American Rotary

    Here's another source:

    Rotary Phase Converter Guide - Phase Converter Guides - Product Guides

    And another:

    Phase Converters >> Cedarberg

    Most makers (also) publish case studies and general technical information for planning:

    Ronk Notes - Technical Resources - Ronk Electrical


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