I successfully built a working RPC
Close
Login to Your Account
Page 1 of 2 12 LastLast
Results 1 to 20 of 21
  1. #1
    Join Date
    Dec 2016
    Country
    TAIWAN, PROVINCE OF CHINA
    Posts
    264
    Post Thanks / Like
    Likes (Given)
    0
    Likes (Received)
    18

    Default I successfully built a working RPC

    So I just moved into a shop without 3 phase power. I asked the landlord about getting it and he said it would cost about 1200 dollars to do so. But since I only have about 3 machines (mill, bandsaw, and air compressor) that needs 3 phase, it's really not top priority. The landlord would pay the cost if I pay an extra 30 dollars a month in rent.

    So I bought a RPC from someone, but unfortunately the idler motor it contains is basically rusted shut (the spindle will not turn no matter what). The sucker weights a ton, and I don't really know how to fix a stuck motor, so I went to the seller and told him. He gave me a static phase converter and told me to try it out.

    So I did, and it turns out that it can get a motor spinning fairly easily, as long as there are no load. So I got the bright idea of hooking all my machines up to it, and using one machine's motor as the idler motor, I started that motor and everything else started working as though they are connected to 3 phase (albeit a bit slower start than grid level 3 phase power).

    The problem is the air compressor... it is 5HP but it draws quite a big load at startup. If the circuit can't put out the necessary inrush the motor wouldn't spin up at all. So what I did was buy another 5HP 3 phase motor. Start that with the static phase converter. Once that spins up, I would start the band saw (which has a 5HP motor as well). The two motor combined gave enough juice to start the compressor even with the high startup load... might not be as fast as grid level but it got the job done...

    I think I would want another 5HP motor for the simple fact that I really don't want to leave a bandsaw running unattended just so the air compressor can start up...

  2. #2
    Join Date
    Apr 2018
    Country
    UNITED STATES MINOR OUTLYING ISLANDS
    Posts
    9,839
    Post Thanks / Like
    Likes (Given)
    0
    Likes (Received)
    4730

    Default

    Quote Originally Posted by taiwanluthiers View Post
    what I did was buy another 5HP 3 phase motor. Start that with the static phase converter.
    All you had to do was put a rope around the shaft and pull it.

  3. #3
    Join Date
    Sep 2004
    Country
    UNITED STATES
    State/Province
    Wisconsin
    Posts
    289
    Post Thanks / Like
    Likes (Given)
    1
    Likes (Received)
    80

    Default

    Take the motor apart on the rpc you bought and replace the bearing on each end. It's an electric motor with no shaft sticking out. 4 screws or rods and the end bell pops off. You can then slide the rotor out and replace the bearings on the bench.

  4. Likes Janderso liked this post
  5. #4
    Join Date
    Apr 2004
    Location
    Modesto, CA USA
    Posts
    8,958
    Post Thanks / Like
    Likes (Given)
    0
    Likes (Received)
    1776

    Default

    A three phase motor is easy to take apart and put together. there are no extra moving parts, no centrifugal switch etc. Just three wires that connect to the fixed windings and a ground wire that is under a screw somewhere in the connection box. Removing both endbells and the rotor with bearings do not require you to touch any wiring.
    A quality motor may even have the bearing numbers, four digits, on the data plate. Often the two bearings are slightly different sizes.
    Bill D

    PS: Excellent English, by the way

  6. #5
    Join Date
    Sep 2011
    Country
    UNITED STATES
    State/Province
    Virginia
    Posts
    22,154
    Post Thanks / Like
    Likes (Given)
    7561
    Likes (Received)
    12736

    Default

    Fooks sake! Landlord arranges the service & wiring, you pay a flat thirty bucks a MONTH? That's but ONE DAY cost of my 5 packs a day of smokes.

    You lose no space, no sleep, have no hassle, and not even a demand charge top-up? Dollar a day fpr mains 3-Phase?

    Most 'ere would consider that heaven!

    Pay the freakin' thirty bucks and get yer azz back to doing something useful! Or at least more fun!

  7. Likes PackardV8, Janderso, JohnEvans liked this post
  8. #6
    Join Date
    Apr 2004
    Location
    Modesto, CA USA
    Posts
    8,958
    Post Thanks / Like
    Likes (Given)
    0
    Likes (Received)
    1776

    Default

    I was over 50 before I bought my first bearing splitter(seperator) to remove ball bearings. Should have bought one decades ago. For home shop type use you only need one or two sizes. Like one inch and two inch (30 and 60mm)will cover most you will ever see on a machine or motor. They are also useful when using a hydraulic press.
    I thought they were a gimmick until I used one.
    The trick is to buy one small enough it can get into tight spaces but still strong enough to have several tons of pull. This is a case where bigger is not always better
    Bill D.

    not recommendations, just pictures to see what I am talking about

    Amazon.com: DAYUAN 14pcs 5 ton Capacity Bearing Separator Puller Set 2" and 3" Splitters Remove Bearings Kit : Automotive

    How To Use A Bearing Separator - YouTube

  9. #7
    Join Date
    Jun 2006
    Location
    Spokane, WA
    Posts
    770
    Post Thanks / Like
    Likes (Given)
    6
    Likes (Received)
    231

    Default

    Quote Originally Posted by thermite View Post
    Fooks sake! Landlord arranges the service & wiring, you pay a flat thirty bucks a MONTH? That's but ONE DAY cost of my 5 packs a day of smokes.

    You lose no space, no sleep, have no hassle, and not even a demand charge top-up? Dollar a day fpr mains 3-Phase?

    Most 'ere would consider that heaven!

    Pay the freakin' thirty bucks and get yer azz back to doing something useful! Or at least more fun!
    X2 - trying to operate a 3-phase air compressor on a RPC seldom-to-never works. The RPC just doesn't like the high-demand startup draw time after time and the compressor motor doesn't like having to struggle up to speed on low supply.

    FWIW, I pay $21 a month for the meter fee for a storage building which goes a month without ever having the light turned on, much less powering up the air compressor.

    jack vines

  10. #8
    Join Date
    Apr 2018
    Country
    UNITED STATES MINOR OUTLYING ISLANDS
    Posts
    9,839
    Post Thanks / Like
    Likes (Given)
    0
    Likes (Received)
    4730

    Default

    Quote Originally Posted by Bill D View Post
    PS: Excellent English, by the way
    That's because he is a foreigner ...

  11. Likes Gordon Heaton, 3t3d liked this post
  12. #9
    Join Date
    Nov 2007
    Location
    marysville ohio
    Posts
    10,825
    Post Thanks / Like
    Likes (Given)
    3027
    Likes (Received)
    7485

    Default

    [QUOTE=taiwanluthiers;3818689]So I just moved into a shop without 3 phase power. I asked the landlord about getting it and he said it would cost about 1200 dollars to do so. But since I only have about 3 machines (mill, bandsaw, and air compressor) that needs 3 phase, it's really not top priority. The landlord would pay the cost if I pay an extra 30 dollars a month in rent.

    The local power co. will be happy to give me 400A of 3 phase for a small hook up fee. 18,000!!! I am 150' from the wire!

  13. #10
    Join Date
    Jul 2004
    Location
    Houston, TX USA
    Posts
    32,466
    Post Thanks / Like

    Default

    Quote Originally Posted by EmanuelGoldstein View Post
    All you had to do was put a rope around the shaft and pull it.

    Did that for years and years. Never any issues

  14. #11
    Join Date
    Nov 2007
    Location
    marysville ohio
    Posts
    10,825
    Post Thanks / Like
    Likes (Given)
    3027
    Likes (Received)
    7485

    Default

    Quote Originally Posted by johnoder View Post
    Did that for years and years. Never any issues
    On your air compressor?

  15. #12
    Join Date
    Dec 2016
    Country
    TAIWAN, PROVINCE OF CHINA
    Posts
    264
    Post Thanks / Like
    Likes (Given)
    0
    Likes (Received)
    18

    Default

    You mean the air compressor or the idler motor?

    I read you could just spin the motor by hand then apply power, but without the caps wouldn't the motor overheat because of voltage imbalance?

  16. #13
    Join Date
    Apr 2018
    Country
    UNITED STATES MINOR OUTLYING ISLANDS
    Posts
    9,839
    Post Thanks / Like
    Likes (Given)
    0
    Likes (Received)
    4730

    Default

    Quote Originally Posted by moonlight machine View Post
    On your air compressor?
    Hey, kids used to have to earn their keep. Dad had some painting to do !

  17. #14
    Join Date
    Dec 2016
    Country
    TAIWAN, PROVINCE OF CHINA
    Posts
    264
    Post Thanks / Like
    Likes (Given)
    0
    Likes (Received)
    18

    Default

    No idea who makes the motor or even what power it is. Name plate isn't there.

    In fact I tried hooking it up just to see if it would work (maybe an internal brake or something??), and it hummed for half a second then tripped the breaker. Plus I can see exposed copper in places within its wiring. So I wouldn't even rule out that the winding is screwed. The motor weights like 100kg or more. It took mechanical assistance for me and 1 other guy to get it into the shop.

    So part of the challenge is to get it apart and then figure out exactly what went wrong. That's assuming the winding isn't eaten through either, as it looks like this thing has been outside for probably 8 years or so.

  18. #15
    Join Date
    Aug 2014
    Location
    bainbridge island
    Posts
    1,489
    Post Thanks / Like
    Likes (Given)
    325
    Likes (Received)
    375

    Default

    in some places you have 3 phase power in the form of 2 phases of Y service but you don't know it.

    you can indeed hook up a 3 phase motor from line to line and line to netural, and you can delvelop about 2/3rds nameplate hp from the motor without over heating. but you have to find the hidden star point of the motor and connect it to your netural or ground. it will self start.


    in the case of the OP.. just pay the 1200 bucks and get your 3 phase. the landlord willing to amortuize the cost by only charging you an extra 30 a month is pocket change.

  19. #16
    Join Date
    Apr 2018
    Country
    UNITED STATES MINOR OUTLYING ISLANDS
    Posts
    9,839
    Post Thanks / Like
    Likes (Given)
    0
    Likes (Received)
    4730

    Default

    Quote Originally Posted by johansen View Post
    in some places you have 3 phase power in the form of 2 phases of Y service but you don't know it.
    I believe Taiwan is all 380v 50hz three phase, or 220v single phase.

    Agree, $30 a month is a no-brainer. Sha zi

    ^^^^ No, don't need caps, will run fine without.

  20. #17
    Join Date
    Dec 2016
    Country
    TAIWAN, PROVINCE OF CHINA
    Posts
    264
    Post Thanks / Like
    Likes (Given)
    0
    Likes (Received)
    18

    Default

    Taiwan uses 110v 60hz single phase for small appliance, and 240v for larger appliance.

    The three phase I have measured is 230v line to line. In fact to get 110 out of that you need a separate transformer.

  21. #18
    Join Date
    Dec 2016
    Country
    TAIWAN, PROVINCE OF CHINA
    Posts
    264
    Post Thanks / Like
    Likes (Given)
    0
    Likes (Received)
    18

    Default

    I bet this is what is going on, as when I measure the voltage between the two legs I am getting 230v, similar to what I get when I measured the leg to leg voltage back in my old shop (that has 3 phase service).

    When I measure single phase I get 249-250v when I measure line to line.

    My induction cooktop is also showing 230 volt too, as it displays line voltage when you shut it off.

    I guess I can try...

    Edit: For the voltage balance, it seems a little unbalanced, by about 30 volts. But when I start subsequent motors in the network the voltage became better and better balanced. With only the idler, it's 230 -260 -260, but with one other idler motor running it becomes 220 - 230 - 230. When all the motor in the network is running minus the air compressor, it's around 218 - 230 - 230.

    Tried connecting the motor just to the 2, and it just buzzes and not start (and draws a LOT of amps too). The static phase converter still has balance caps in it, and those run caps alone will start it.

  22. #19
    Join Date
    Dec 2016
    Country
    TAIWAN, PROVINCE OF CHINA
    Posts
    264
    Post Thanks / Like
    Likes (Given)
    0
    Likes (Received)
    18

    Default

    So I'm just going to give an update:

    2 5HP motor will start my 5HP compressor under load, but it's not always reliable, as one day it will start a bit slow but another day it will trip breakers. So I decided that I'm going to put a solenoid onto the unloader in order to no load start the compressor, as the start is just much easier and more reliable than trying to start them under load. As if I start the air compressor under no load it's no different than using the RPC to start another 5HP motor not connected to anything, and once it's up to speed it will pump.

    I asked the landlord about adding the 3 phase and he was really not wanting to do this. He said one of the biggest reason is that he's not sure how long I'd live there and felt if he spent the money to add 3 phase and I move out he'll be stuck with the bill, and that it wouldn't add any value to the property as he really doesn't want the property used as a factory. Then he said something about the electrical box MUST be outside, cannot be inside at all because a meter reader must be able to see it anytime (it's the guy the power company sends out to read the meter every 2 months). However the alley it's on is very narrow and he's afraid a truck can run into it causing power outage.

    I figure having a solenoid on the thing is good anyways as it would impart much less stress on the electrical system and the motor. Some of the higher HP compressors sold here uses solenoid to no load start the motor before it actually pumps, presumably to lessen the stress on the motor too. I can't imagine how much amps a 10HP or higher compressor will draw if it's trying to start under load, I suspect no electrical systems can handle it. Actually I had seen a 7.5HP compressor spin but not pump before, and the reason it wasn't pumping was because the solenoid was not closing.

  23. #20
    Join Date
    Sep 2011
    Country
    UNITED STATES
    State/Province
    Virginia
    Posts
    22,154
    Post Thanks / Like
    Likes (Given)
    7561
    Likes (Received)
    12736

    Default

    Quote Originally Posted by taiwanluthiers View Post
    I can't imagine how much amps a 10HP or higher compressor will draw
    Not your job to have to worry about it, but others have it covered.



    Lock & Dam at Charleroi, PA needed lots of compressed air for its repair.
    Powerco put in a special facility about 50 feet square back of very tall hurricane fencing just to run those.

    ISTR the line to that pad was 8800 VAC, and the transformer was taller than a man?

    Load was two air compressors. 500 HP motor on each. Bigger ones surely exist.

    Unloaders make good sense, any size. Yes, please, use them.


Tags for this Thread

Bookmarks

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •