Results 1 to 10 of 10
  1. #1
    Dave K2's Avatar
    Dave K2 is offline Hot Rolled
    Join Date
    Apr 2007
    Location
    Hertfordshire, England
    Posts
    914

    Post

    Hi all, i am in the middle of setting up a new workshop and this time i am fitting an RPC to save altering my machinery.

    I have a 2.2kw rotary and intending to drive the following, only one at a time though.

    2hp BP Mill,
    3hp Colchester lathe,
    1.5hp Boxford lathe.

    I dry tested the rotary and as expected, the voltages were unbalanced. What i need to know is, if i am alternately driving 3 machines with differing loads, i expect the best balance to be on the 3hp load as it is rated for that size. With the smaller motors, is it worth adding some local balancing caps at each machine to help balance or is it just not that important?

    Thanks in advance
    Dave

  2. #2
    toolnut is offline Stainless
    Join Date
    Aug 2005
    Location
    Kingsport, TN
    Posts
    1,173

    Post

    With a RPC size so close to the loads, I would simply balance the RPC at idle such that the two generated phases are no more tha +5% above the incoming line voltages. It should work very well at this point. If you need more starting capability you can add caps to increase the generated voltages some but do not go above +10% of the incoming line. You have a very easy situation and it is similar to mine. I have the same machines and am using a 5 hp(3.7 KW) idler, 30 amp RPC which performs beautifully with these machines. I can run two of them at the same time.
    Bruce Norton
    Kingsport, Tn

  3. #3
    Dave K2's Avatar
    Dave K2 is offline Hot Rolled
    Join Date
    Apr 2007
    Location
    Hertfordshire, England
    Posts
    914

    Post

    Thanks for that. This particular RPC is designed to supply a 400% start boost which enables it to run its rated load, its made by Boost Technologies and contains a large idler, a transformer to give the 415v from 240v a bank of caps and a little black box which aparently is their secret!

    Would i balance voltages from phase to phase or phase to neutral?

    Dave

  4. #4
    peterh5322's Avatar
    peterh5322 is online now Diamond
    Join Date
    Dec 2002
    Location
    Monterey Bay, California
    Posts
    10,111

    Post

    "Would i balance voltages from phase to phase or phase to neutral?"

    Phase to phase.

    Neutral is never used in an RPC system, as the RPC itself is 69 volts above neutral when it is putting out a 138 Y system, which is equivalent to a 240 ∆ system.

    Or, to use "per unit" notation, which allows one specification to apply to any actual line voltage, the input line is either 0.5 + 0.5 or it is 1.0 "per unit", the Y system is 0.578 "per unit", and the Y point floats at 0.289 "per unit".

    0.578 + 0.289 = 0.867.

    Recall that the "usual" specification is 0.866, but I always use 0.867, as 0.867 is divisible by 3 without remainder, while 0.866, which is actually an irrational number, is not.

    Multiply any "per unit" number by the line voltage, and you get the actual voltage at or between the two terminals.

  5. #5
    toolnut is offline Stainless
    Join Date
    Aug 2005
    Location
    Kingsport, TN
    Posts
    1,173

    Post

    Dave,

    I would first just use the RPC as it is. Sounds like it is a very well made device and I suspect it will operate your machines just fine.

  6. #6
    Dave K2's Avatar
    Dave K2 is offline Hot Rolled
    Join Date
    Apr 2007
    Location
    Hertfordshire, England
    Posts
    914

    Post

    Ok, its up and running, got all 3 machines running right direction first time!

    Double checked to ensure no control circuits were on the generated leg.

    Voltages under 3hp load were
    A-B = 366
    B-C = 375
    A-C = 413

    Assuming B is the false leg.

    All motors come up to speed nearly instantly and all seems to be ok, I'll leave well alone for a while

    Thanks for assistance.

    Dave

  7. #7
    Join Date
    Jul 2007
    Location
    NE Wisconsin
    Posts
    13

    Post

    I just have one question what voltage is that motor oringally connected at 240 or 480 volts ??

    if you have motor connected at 240 volts with the RPC and you say you are at

    " Voltages under 3hp load were
    A-B = 366 B-C = 375 A-C = 413 "

    then the voltage is too high it can burn up the windings

    but if connected on 480 volts it is too low and it will draw more current and can overheat the motor as well

    if lightly loaded motor you may be ok for while but if you start to hear the koncking noise that will indacted either single phasing or open phase conenction also if your current is really unbalnced it will do the same thing as well

    Merci , Marc

    opps, sorry i did miss the OP is from England sorry i missread it

    with 400 volts 50 HZ system i did read it you are petty close ther as long it dont knock or make a moaning noise you are fine there

    { edit to add quick info ,, sorry about that }

  8. #8
    peterh5322's Avatar
    peterh5322 is online now Diamond
    Join Date
    Dec 2002
    Location
    Monterey Bay, California
    Posts
    10,111

    Post

    With A-C being 413, it is most likely a 240Y415 system.

  9. #9
    Dave K2's Avatar
    Dave K2 is offline Hot Rolled
    Join Date
    Apr 2007
    Location
    Hertfordshire, England
    Posts
    914

    Post

    Yes, it's a 240v in, 415v out converter which explains the A-C being 413v-very close to required voltage.

    Our supply currently measures 242v which is a bit odd as we're supposed to be 230v now !

    There are no unusual noises and each motor will come upto speed very quickly, i was just a bit worried about the lower B phase voltage - dont want to risk toasting any motors.

    Dave

  10. #10
    peterh5322's Avatar
    peterh5322 is online now Diamond
    Join Date
    Dec 2002
    Location
    Monterey Bay, California
    Posts
    10,111

    Post

    "Our supply currently measures 242v which is a bit odd as we're supposed to be 230v now !"

    Just as the EU countries "harmonized" on 230/400, supposedly replacing 220/380 and 240/415, that harmonization was in name only.

    A similar situation exists in the U.S., where we supposedly "harmonized" on the metric system, yet most customary units are still English engineering units.

    To answer your concerns in re: low B-phase voltage, increase the A-B and C-B capacitor values.

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
  •