Playing with RPC idler / motor wiring / amps questions
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  1. #1
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    Default Playing with RPC idler / motor wiring / amps questions

    I have an old Monarch with a 15 horse motor. To this point I've been running it with an old 10 horse VFD that was given to me. This VFD is designed specifically for converting single phase to three phase. It starts my lathe motor just fine and will run most of the gears in the lathe except the top two or three speeds. I am planning a RPC build to power the shop so I can add more three phase equipment down the road with less hassle. Because I'm worried about the inrush issues of starting a 25-30 hp rotary deal, my plan is to run a dual idler setup. I'm going to cap start the first 15 horse motor and use that to start the second 15 horse idler. I'm not afraid of the added complexity and I have basically unlimited access to used components. Is this a dumb idea right from the start? I've read a bunch but haven't seen anybody specifically build a dual idler setup this way. I know guys will start other equipment on the line to add potential, but never a dual idler. I know I could pony start a 25 or 30 horse too and that may be an option if my dual idler doesn't pan out or if you guys think its a horrible idea.

    The real reason for this post: The first idler I acquired for the idler is a 15 horse marathon that had an input bearing going out. I brought it home and put new bearings in it. Last night, just for fun, I wired my 10 horse VFD up to it just so that I could hear it run and see how loud it would be in my shop. It's a typical 9 lead motor and I had it wired for low voltage. The drive did this really funny sounding two-step start up when I first fired the idler. I immediately shut it off and double checked everything. Started it again and same thing. Two-step start up. I checked the RPM of the motor with a tach and it's spinning about 1800 rpm like it should. Then I noticed that the readout on my VFD was showing 10 amps just idling this 15 horse motor. My 15 horse lathe motor idles at like 2 or 3 amps with four belts on it. At his point I was getting a little confused. I took the motor out of service before putting bearings on it and it was a functional motor. It spins plenty freely by hand. Why the high idle amps? So at this point I wired the motor for high voltage just out of curiosity. The drive started it fine again, still with the two step thing going on, only this time idle amps were down to 2-3 just like the old motor in my Monarch. I'm 99% sure I wired the motor in my Monarch correctly for low voltage. It's a real nightmare to double check because of how tight it is in there. I never really checked now that I think of it what the drive outputs for voltage. I just assumed 220 in so about 220 out. I can't imagine the monarch would run as good as it does on low voltage if I've had it wired wrong this whole time. Any thoughts?? I'll check the drive when I get home to see what it outputs for voltage. I would be really surprised if it wasn't 220.

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    Quote Originally Posted by Baitshop View Post
    .. my plan is to run a dual idler setup. I'm going to cap start the first 15 horse motor and use that to start the second 15 horse idler.
    That can work. Or the supplementary idler can be smaller than the primary, and there can be more than one supplementary idler.

    .. still with the two step thing going on,
    Whatever else is in play, that sounds like the VFD is doing a normal "ramping up".

    Very useful built-in feature for starting. Crucial, even, whenever a load motor is heavier than the VFD's rating.

    Also usually adjustable off one or more parameter settings as to by how much and over what period of time. That said, your one sounds as if it is already doing the right thing.

    As you have plenty of hardware, you may want to add leads for permanent test points or even built-in meters. Safely protected, of course.

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    Thank you for the reply and all of that makes sense. What I can't understand is why the drive doesn't ramp up this way when starting the 15 horse on the lathe. The two motors were manufactured some 50 years apart, but I'm not sure what that would have to do with anything. I also can't figure out why the lathe motor would be idling at 1/3 the amps. I did verify last night that the drive is outputting around 248 volts, so both motors should be wired for low voltage. I'm going to try and get the doghouse cover off of the lathe motor today to verify how I have it wired. I hope I have it wired wrong. That would at least make some sense.

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    Quote Originally Posted by Baitshop View Post
    Thank you for the reply and all of that makes sense. What I can't understand is why the drive doesn't ramp up this way when starting the 15 horse on the lathe. The two motors were manufactured some 50 years apart, but I'm not sure what that would have to do with anything. I also can't figure out why the lathe motor would be idling at 1/3 the amps. I did verify last night that the drive is outputting around 248 volts, so both motors should be wired for low voltage. I'm going to try and get the doghouse cover off of the lathe motor today to verify how I have it wired. I hope I have it wired wrong. That would at least make some sense.
    You could spend a whole lot of time educating yourself on just how very, very different electric motors can be and how that affects their starting and running characteristics. I don't mean "QC" fail" nor production variations. I mean different internal design and implementation.

    That's a feature, not a bug.

    The type of motor, pole-count, slip curves, stability, compensation, etc - basically what sort of "service" it was designed for - matter greatly.

    Condition of bearings & c. matters. A motor's "design" age does not matter so much, as the engineering and manufacture of all this stuff has been reasonably stable for longer than most of us have been alive.

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    Regarding multiple idler RPC, I think it is a good idea. My RPC consists of three 7.5 horse idlers. The first one is capacitor start and the rest are started directly. Additional run capacitors are wired directly to the additional idlers in an attempt to keep it roughly in balance.

    I have a bunch of other things like phase loss detection and current and voltage meters. There are many ways to use up those used components that you have available.

    I do not like the noise of the RPC so all the idlers sit in a dog house outside the shop.


    By having multiple idlers I can try to minimize my power consumption wasted in the idlers and try to match the required power with the load, ie one running for the bandsaw and two for either lathe or mill and all three for the welders.

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    Is this a dumb idea right from the start?
    It's a good one.

    I once worked in a shop where the second idler ran an injection molding machine. It ran fine, even without extra caps for the second idler.

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    15 HP motor full load amps, per NEMA tables (usually close but a tad over) is 42A.

    Motors commonly idle at 30 to 50% of full load, (but at a low power factor, so small actual power). Your 10A is not out of line for a 15 HP motor. The 2 or 3 A is way low, presumably due to the wiring for HV.


    https://www.safecoelectric.com/image...%20430.250.pdf

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    Quote Originally Posted by Bill Simmons View Post
    Regarding multiple idler RPC, I think it is a good idea. My RPC consists of three 7.5 horse idlers. The first one is capacitor start and the rest are started directly. Additional run capacitors are wired directly to the additional idlers in an attempt to keep it roughly in balance.

    I have a bunch of other things like phase loss detection and current and voltage meters. There are many ways to use up those used components that you have available.

    I do not like the noise of the RPC so all the idlers sit in a dog house outside the shop.


    By having multiple idlers I can try to minimize my power consumption wasted in the idlers and try to match the required power with the load, ie one running for the bandsaw and two for either lathe or mill and all three for the welders.
    I like your thinking.

    Here's another case for RPC flexibility:

    I have a "Combo" mill (USMT Quartet) with four 3-P motors, only one of them with any form of clutch:

    - the fractional HP juice-pump I could replace with 1-P, and may do.

    - the traverse - 3/4 HP does have clutches, does not start loaded-up.

    - vertical spindle is just under 2 HP. No clutch.

    - Horizontal spindle is 5 HP, directly into a rather stiff Reeves drive, R/A gearbox, then Gilmer belts. No clutch, and the spindle even has a stabilizing flywheel to spin-up as well.

    "The plan" is to START (whichever) motors off the 10 HP idler. If using only the vertical spindle, bring the 5 HP idler online, then drop the original 10 HP idler OFF. Max total load with spindle, traverse, and juice-pump active is still sub 3 HP.

    Different deal, 7 HP drillpress, or 7 HP lathe. Both have high-drag drivetrains. PIV-Werner Reimers ++, or Variator ++.

    - Begin by firing-up the 10 HP idler, add the 5 HP idler, start the chosen machine, then drop-off the 5 HP for ordinary running. Leave BOTH 10 HP + 5 HP online only for really, really rare uber-heavy working.

    Just TWO idlers worth, but lots of flexibility. OTOH, I also have two Phase-Perfect, and some Dee Cee powered machines. so...

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    Thank you all for the replies. It turns out that I am more of an idiot as time passes. I rebuilt the motor for this lathe. I know the thing was most likely 480 from where it came from. Somehow I put that motor back together and stuffed it back into it's "inaccessible to wiring home" without having looked at the data plate and rewiring the thing to match my residential low voltage. Pretty disappointed in myself to be honest. Figured I better own up to it in case it helps someone else searching about the same thing. Also, the 10 horse drive will now start the lathe in any gear no problem, unlike before when it wouldn't spin the top two gears without abusing the clutch to get it going. D-U-M dumb. Anyhow, I managed to remove that motor even though the door is partially blocked by my beer fridge, fix the wiring, and reinstall it with one arm. I ruptured the distal biceps tendon in my right arm a month ago so I've been in a fixed brace since then. At least I get credit for will power. Thanks again everybody.

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    Quote Originally Posted by Baitshop View Post
    Thank you all for the replies. It turns out that I am more of an idiot as time passes.
    You are MEANT to take a number on that and wait yer turn...like the rest of us.

    Sorry to hear you were distal-whipped by a beer fridge with bisexual tendoncies, but them's the breaks when you get to playing with idlers.

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    So when paralleling two idlers is rotation the only thing that you have to worry about? Ie: both idlers rotating same way?


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