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[How do I?] 3-phase Rpc (and Machinery Attached To It)

Discussion in 'ELECTRICAL ISSUES - POWER YOUR MACHINES & SHOP' started by mmcgirr, Nov 14, 2016.

  1. mmcgirr

    mmcgirr United States H-M Supporter - Premium Content H-M Supporter-Premium

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    Greetings all,

    Apologies in advance for picture rotation. For some reason I cannot upload pictures the right way round (if anyone knows why, that'd be super).

    Anywho...

    Apart from the acquisition of 2 pieces of machinery ('57 bport and hardinge HLV lathe), I've also acquired a Leeson 15hp 3-phase 12 lead motor (which I plan on using as an RPC for the above, and whatever other 3ph machinery I acquire).

    However, I have many many questions about the RPC.

    The nameplates for the motors involved at first are attached. This one is for the RPC idler:

    20161114_120718.jpg

    This one for the bport:

    20161114_172721.jpg

    And this one for the hardinge:

    20161114_172912.jpg

    What I have a question about is the idler motor (I've clearly got more than enough headroom to run those two pieces of equipment).

    Question 1: is the idler a delta or wye motor? It seems to be a 12 lead motor, and I'd want / need to use the low-voltage connection type, but I can't figure out what kind of power it'll spit out.

    Question 2: what is the most basic way to get the sucker hooked up so I can fire up the motors on the equipment? I'm going to - eventually - stick a sub-panel in with proper disconnects and all that jazz, but I'd really like to get a 30A twistlock type of affair hooked up for the immediate future.

    Question 3: balancing legs - what would I need to do?

    I've researched the Fitch and other types of RPC, but I'm an electrical noob, so any guiding hands on how to get this squared away would be fantastic!

    Thanks much,
    Mike
    20161114_120718.jpg
    20161114_172721.jpg
    20161114_172912.jpg
     
  2. Keith Foor

    Keith Foor Active Member Active Member

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    220 pounds for a 15HP motor? Is it an explosion proof sealed motor? reason I ask is I have one that is and it's unbearable to start with capacitors. I have to spin it up with a drill motor and then hit the start button. can you post a picture of the full motor? I have a couple Leeson 15HP motors that are physically smaller than the 15 I have on the RPC and they cap start without issue. The RPC motor I have is as physically large as a newer style 100HP open air motor.
    Point is that you may need to get a 1/2 hp pony motor and get the thing turning if it's that heavy as opposed to starting it with capacitors.
     
  3. mmcgirr

    mmcgirr United States H-M Supporter - Premium Content H-M Supporter-Premium

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    I don't have a pic of the full motor (all I was interested in was the nameplate.

    However, it's a monster - it came off of an old orbiting screw 1000l mixing vessel.

    I was fully planning on using a 1ph pony to start it up, as I have a whole bunch of single phase motors and sheaves to select from at the shop for that specific purpose.


    The "nagging" questions I have are:

    1) What size breaker in my 1ph panel am I going to need?

    2) How many amps will the idler draw with no load
    2a) I see figures of like 30% of rated nameplate all over the web and so forth for generated leg full load amperage at idle, but I'm not sure.

    3) what size conductors should I be using initially - I'm thinking 10ga, but I've not consolidated all the voodoo from around the web into anything resembling intelligence at this point in time.

    There will be more to follow of course, but I want to "work it in stages". First part is to get the idler spinning and producing the wild leg. Second part is to hook up the motors and try things out (with a 30A twistlock that they already have), and then work on balancing and other fancy things later.

    Thanks!
    Mike

    P.S.: 254T frame dimensions indicate that it's about 13" tall (from foot to OD), with a 1 5/8" output shaft, and about 16" in axial length. Bearings spin absolutely perfectly on this thing (which is nice, not a lot of loss there I wager).
     
  4. Keith Foor

    Keith Foor Active Member Active Member

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    OK, while I get guff for this. I am running a 50 amp breaker to mine. I have never had issue with that. I would be looking at #8 wire and #6 if it's a long run to the panel.
    Now as far as running the motor without run capacitors, don't.

    I know there are a lot of 'professional' RPC's out there that don't have run caps, but they tend to have really high or low L3 voltages and that voltage tends to really dip under any significant load. It's better to do once and do it right. Now, if you are running a pony motor, keep in mind that the pony motor rpm and the idler rpm need to match and the drive needs to be one to one. I have seen a couple times where this was not followed and the pony motor would fail dramatically when the 3450 idler would come to speed on a geared down 1750 pony motor would hit 6000 rpm. Better to mention it and it not be an issue now than wait and tell you after.

    Run caps.
    10 uF per HP between L1 and L3 and 5 to 10 uF between L2 and L3.
    This does take a bit more tuning but is the most stable way of doing it and it draws the least power running with no load. My idle current is about 8 amps on the monster 15HP motor I have. And it don't sag. I have started 40 HP motors with my 15 HP RPC with no load and they always came right up. And the only time I ever lilfted the 50 amp breaker was when I was running a 3 phase 300 amp MIG welder full out with .062 wire running spray arc. I have zero issues running a Feeler precision lathe with a 5 hp motor, a Clausing lathe taking a heavy cut with a 5 HP motor and a 2 HP mill taking a heavy cut all at the same time. I even drug it over to a buddies shop that had a hard starting 10 HP 3 phase compressor that his 20 HP wouldn't start because the head dump didn't work right and it would fire it right up under a loaded head. His didn't have run caps, just a idler motor with a wild leg. It really makes a difference. That is also the difference in the RPC's that you will see advertised as CNC rated and the non-CNC rated RPC's one has the proper caps and the other don't.

    Another thing that is a necessity as far as I am concerned is it have an input AND output contactor. I see so many professional units that don't and I can't understand why. Here's the deal on that. If you only have an input contactor, the single phase 220 is routed to your gear directly. And with some designs will have 220 single phase applied to them all the time. This means that the control circuits are powered up and if you forget that the RPC is not running you are trying to start a 3 phase motor with a dead phase. It will not start, it's harder than hell on the motor and will draw silly amounts of current. Having an output contactor stops that. Now with needing a pony motor, you can still time everything off one start button. Have the start button close a contactor that controls the pony motor via a timer set the the time needed for the pony motor to get the idler motor up to speed. Once the timer drops it can energize the input power to the idler with the caps hard wired in. And the outputs can be connected directly to the motor. This is the ONLY way I would only have one contactor. If you were cap starting the motor I would say run 3 contactors. One for input one for output that had the run caps across it and one for the start caps that would drop out before the output contactor was engaged because that high value start caps across the L3 to L1 will have a high voltage (can be 300 volts) as the motor gets to speed. You don't what that getting out and into the control power of your machines. Also, the input contactor when properly wired will fail off if there is a power outage. Have heard of guys having their power go out for a couple hours and walk in the shop 3 days later and their RPC is sitting there running and eating up electricity. It's also a safety thing. A power failure should stop all your machines. On ones with control circuits, they do it themselves, but if you only have a drum switch or a single on off toggle, the power can fail and then the machine restart possibly while you have your hand in a place it shouldn't be with the machine running.

    That's my take on it. I build RPC's to finance my machine purchasing habits. I have built a number of them. I have never had a dissatisfied customer. Pricing is a bit higher on mine because of the extra contactors, but mine are CNC rated and don't burn up your equipment or allow you to feed power to your gear that's not 3 phase. And when mine are off, there is NO power getting to the connected equipment which is a safety thing.

    If you have questions, post them here. What I know isn't a secret. I read it on the web and share it with anyone willing to ask and learn. There is no black magic to an RPC. A good one requires you to put in some time to build it or a premium price to buy it. Others are easier to build, cheaper to buy but you get what you get.
     
    Last edited: Nov 14, 2016
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  5. mmcgirr

    mmcgirr United States H-M Supporter - Premium Content H-M Supporter-Premium

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    Thank you for the detailed information Keith. I have (and will likely have many more) questions for you - as long as you have the time and patience to humor me of course.

    Off we go:
    Bear in mind that I'm trying to do this with as much "found stuff" as possible, would having a pony motor that is say 3450 rpm, and knowing that the idler is 1730 rpm (per nameplate), could I gear it essentially 2:1 and call it good? I'm trying to expand my options, and I believe (though I'm not at the shop right now), that all the 110/240VAC motors we have are 3450 rpm jobs, hence I'd need reduction in there somewhere no?

    I don't really care how long it takes to spin it up (as long as it's around <=5mins). We may have some lovejoys at the shop for direct coupling, and we "might" have slower 1ph motors, but I'm just not sure (I'll have to dig around tomorrow and see.) Direct coupling brings to mind another question: once the pony has spun up the idler, is it advisable to mechanically de-couple it, or does it matter?

    So if I'm reading this correctly, for a 15hp idler, I should have 150uF bet. L1 and L3, and (averaged at 7.5uF) 112.5uF between L2 and L3? If so, are there any particular model numbers that fit this bill? I've looked at the surplus oil-filled jobbies online, and am having a hard time finding something in that range. Or, is it more of a hunt and peck / combine sort of affair (e.g. a few capacitors in parallel with one another across L1 and L3)?

    The control electronics I'm still getting my head wrapped around for the moment. I'm trying to understand the output of the idler and the input "requirements" first. However, I do understand what you're saying about the contactors and downstream / system protection. Thanks for that information.

    Again, thanks for your assistance, it's much appreciated. I'm going to get this monster back to my place tomorrow, along with a selection of smaller fiddly motors for ponies, and some sheaves from our stockpile and start taking better pictures of all this.

    Oh yes, one last question on the idler itself. It seems like (based on the only information I've been able to find online on the thing), that it's a delta-wound motor - does that matter for the application? (or am I wrong and it's a wye motor?) It's a 12 terminal motor from the nameplate, and L1, T1, T12, T7, and T8; L2, T2, T10, T8, T4; L3, T3, T11, T9, and T5 all connected, the only diagrams I've been able to find indicate that it's delta wound. (ex. http://www.wiringdiy.com/556509/12-lead-3-phase-motor-wiring-diagram.html) Though to be perfectly honest, I'm having a bear of a time wrapping my noodle around wye and delta, and why they matter, or what the complications are / may be in this particular application.

    Thanks!
    Mike
     
  6. Keith Foor

    Keith Foor Active Member Active Member

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    OK, the cap thing first.
    Caps add value when wired in parallel. So 3 50uF caps paralleled would be 150Uf. No you are not going to find an oil filled 150uF cap so parallel is the only way it happens. Remember that you need 300 volt or better rated caps.

    The gearing. If you have RPM differences in the motors, gear them so the RPM will match the rated rpm of the motor.
    If you have similar rated motors a lovejoy is fine. There is no need of mechanical disconnection. But, you will want a contactor to fully isolate the pony motor from the line so that there is no chance of induced voltage (motor acting as a generator) getting back into the electrical system.

    I will look into the motor winding thing. I an not specifically familiar with 12 wire motors.
     
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  7. mmcgirr

    mmcgirr United States H-M Supporter - Premium Content H-M Supporter-Premium

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    That's what I figured on both fronts, and thanks for looking into the motor wiring shenanigans. Appreciated.

    Mike
     
  8. Keith Foor

    Keith Foor Active Member Active Member

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    From everything I can find it should be ok to wire delta run low voltage and then use normally.
    That being said, I can't say what the cap values may be. I would start with the 10 per and 5-7.5 per HP as you would with a 9 wire motor and pay close attention to the 3rd leg voltages between it and L1 and L2. If the voltage is low you will need to increase the capacitor value between that leg and L3. If the voltage is high, then reduce the value. I would go in 1-2 uF hops to see how it goes. You may need to go find a surplus dealer and get a box of various used caps to work with. Just remember that they will all be metal can and 300 volts or better rated. You can't have a capacitor with a voltage rating that's too high. But if you are too low the caps will heat up and pop.

    Leading me to another very important part of any RPC. The metal capacitor cabinet or enclosure. You absolutely have to have your caps in a metal box of some sort. They do occasionally fail and when they do they typically explode. It is a memorable event, and if the cap is out in the open it can launch parts in all directions. It's a mess then, and can be a fire hazard. I just get some metal electrical box and typically will use hot glue to mount the caps. There are mounting brackets for them and they are a better option, but hot glue works.

    And as I said before, there is no black art to an RPC. If you understand basic industrial electricity and controls you can get one together with some internet searches and a bit of time. I would advise you to get a good (FLUKE) digital meter with a current clamp so you can monitor the input idle current and voltage. If done correctly as the voltage gets right leg to leg you will dip the idle current to it's lowest point. This is important for your electric bill and keeping the wife happy.

    I could go deeper into how that works but an understanding of LC tuned circuits would be needed for it to not all sound like I was speaking in Russian.
     
  9. mmcgirr

    mmcgirr United States H-M Supporter - Premium Content H-M Supporter-Premium

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    Thanks again Keith for your detailed information.

    I understand about the dangers of capacitors and ensuring they're enclosed properly.

    Not sure there's any way to truly keep the wife happy (apart from staying in my shop :) )

    This week has been a bear, so I won't be able to get the motor (and some other 3ph and single phase motors I've scored) home. However, once I do, I'll start cracking on this with fervor.

    Thanks Again!
    Mike
     

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