Cap start cap run induction motor queries/problem

Discussion in 'General Electronics Chat' started by Danny D, Jan 3, 2013.

  1. Danny D

    Thread Starter New Member

    Jan 3, 2013
    4
    0
    :)

    Hi guys, im prob in wrong section,this is my first post.

    To the point,
    I bought an air compressor 200l tank, it was originally a three phase motor,
    It has a 5hp single phase capacitor start capacitor run motor now, the pump is a two stage pump, one head is larger then the other.

    Seems like it is powered with a 4squared 3core flex.

    The problem is while it is running all lights FLICKER, now they dim with any heavey load on start up so that is not the issue, it is the constant flicker that is bothering me.


    Im looking for potential causes, and fixes

    FAILING RUN CAP?.......what would be symptoms

    COULD THE CONSTANT LOAD! NO LOAD! LOAD! NO LOAD OF compression of the air, as in motor is under pressure on compression then eases up on intake etc etc
    constantly fluctuation up and down maybe?

    ELECTRIC PROVIDER HAS A TRANSFORMER LESS THEN QUARTER OF A KILOMETER SUPPLYING TEN HOUSES, IT IS OLD WIRING SO CABBLES TO HOUSE WOULD NOT BE AS LARGE AS MODERN BUILDS could this cause flickering as supply is just not there, i dont know, we have a 10kw power shower that runs sound but there is not load change so lights just stay a lil dimmer until it is turned off, by dim i only mean sleightly nothing major.

    I FEEL NEIGHBOURS MAY BE AFFECTED BY THIS ALSO! IE THE FLICKERING

    If it is the change in load can anything be put in place to smooth this or have a motor problem,

    I will run motor free from load and see how things go,

    What else can i check????
    Start cap
    Centrif switch
    Run cap
    Amps on start up
    Running amps

    Anyway sorry about all the shite talk but im just throwing anything that comes to mind
    which may contribute to this :)

    Thanks for your time
     
  2. Wendy

    Moderator

    Mar 24, 2008
    20,766
    2,536
    Welcome to AAC!

    I have moved your thread to a more appropriate forum. Good luck!
     
  3. crutschow

    Expert

    Mar 14, 2008
    13,046
    3,244
    It sounds like the large motor load is drawing enough amps to dim the lights due to wiring resistance. The light pulsations are due to the pulsating load of the compressor. If you can't run larger wire to the transformer or at least to your electrical box, then you might try a small pulley on the motor or a larger pulley on the compressor to reduce the load. Of course the compressor will operate slower but that may be an acceptable tradeoff.
     
    Danny D likes this.
  4. GetDeviceInfo

    Senior Member

    Jun 7, 2009
    1,571
    230
    Maybe try a different outlet, as the one you've choosen may be on the same branch circuit as the lights. For such motor loads, you should have a dedicated circuit with it's own breaker.
     
    Danny D likes this.
  5. Danny D

    Thread Starter New Member

    Jan 3, 2013
    4
    0
    Cheers guys,

    It is a seperate circuit it actually has a seperate line coming from main fuse, i got excited myself thinking that was the case but no joy, the pulleys is something i was thinking about,i was told a smaller motor will have the same effect as the larger one as it will be under more pressure! :rolleyes: so i can rule that out i think, i must try find a smaller set of pulleys for motor and check it


    My biggest concern was run cap was acting up, do you think i could rule that out as it runs very smooth and quite when operating?
     
  6. crutschow

    Expert

    Mar 14, 2008
    13,046
    3,244
    A smaller motor would still be driving the same load if the pulley sizes were the same, so it would still draw as much current (or overload and draw excess current if the motor is too small).

    If the motor seems to start and run normally, then I would think the run cap is OK.
     
    Danny D likes this.
  7. tinkerman

    Member

    Jul 22, 2012
    136
    34
    A go/no go test for the run cap:

    Attach a cheater cord to the terminals. Monentarily energize from a 120 volt line. Short the terminals. If you get a healthy spark the cap is good. Whatever you do, DON'T touch the terminals of the cap until you're certain it's discharged. Short those termnals more than once. It will bit hard.
     
    Last edited: Jan 4, 2013
  8. BReeves

    Member

    Nov 24, 2012
    412
    64
    Do not do this.. A cap across the power line will be a dead short, you ain't fast enough to get it disconnected before it blows something.
     
  9. PackratKing

    Well-Known Member

    Jul 13, 2008
    850
    215
    If originally designed w/ a three-phase motor, it will likely need at the very least a ten-horse cap start/run motor.
    Three-phase has enough torque on start, to get the ball rolling, where your motor may not. 2- stage is a heavy start-load.
    Another consideration, is a head-pressure unloader valve, operated by your pressure-limit switch. That is the contraption that bleeds air pressure from the head after achieving max set pressure, so your motor doesn't have to try to start around the pressure.
     
  10. tinkerman

    Member

    Jul 22, 2012
    136
    34

    Not so. Been doing it for years.
     
  11. BReeves

    Member

    Nov 24, 2012
    412
    64
    Maybe from a DC source but I wouldn't want to try it with AC. Can't imagine how you have been getting away without smoking something. Do motor run caps have a diode built in?
     
  12. tinkerman

    Member

    Jul 22, 2012
    136
    34
    No a diode would defeat it's purpose. They are designed for continuous use in series with the start winding. Start Caps are not continuous. They are short duration only and will blow if energized for more than a few seconds which often happens with a motor than can't start quickly enough. I've even measured amps on run caps with a clip on. They are tough units and don't often find a failed run cap. Start caps will fail as mentioned above and if you find one that is open chances are the foil under the cover (held in with a clip ring) is blown off. I've repaired those with a small screw if there is enough foil left.
     
  13. BReeves

    Member

    Nov 24, 2012
    412
    64
    OK I can understand having it in series with a motor winding but still can't buy connecting the terminals direct to house power using a cheater cord as stated. Something is going to smoke or at best the breaker will blow.
     
  14. Danny D

    Thread Starter New Member

    Jan 3, 2013
    4
    0
    ok controversial stuff ere :)


    thanks again for comments, but as i was saying it is not the starting i have issue with, it starts up handy enough, it has an unloader to bleed off for re-fill under load, its the constant flicker of the lights which bothered me while it is running.

    maybe smaller pulley on motor and a slower high torque motor???

    would that be of benefit to me?

    also i compared my fill times with other 200L (5HP&6HP) with same compressor cfm,locally, and mine fills 20% to 30% quicker, 140psi in under three minutes FROM TOTAL EMPTY, and when pressure drops it has tank topped up in under 30 seconds,COULD THIS MOTOR BE RUNNING TO QUICK? or is this standard?

    to many questions i think, but why not!
     
  15. tinkerman

    Member

    Jul 22, 2012
    136
    34
    First thing to do is check the current and voltage at the motor underload. Compare that to nameplate. Three phase motors have better starting torque than single phase but you say the unloader is working properly and since it starts and runs that shouldn't be contributing to your problem. The lights may dim initially but return to normal quickly. Then check size of wiring along the path and see if it's adequate. There may be other issues like poor neutral.
     
  16. crutschow

    Expert

    Mar 14, 2008
    13,046
    3,244
    What is the motor pulley diameter?
     
  17. Danny D

    Thread Starter New Member

    Jan 3, 2013
    4
    0
    ill find out tomorrow
     
Loading...