Abnormal Contactor Wiring.

Discussion in 'The Projects Forum' started by Homebody, May 29, 2011.

  1. Homebody

    Thread Starter New Member

    May 29, 2011
    7
    0
    I recently purchased a lathe that after wiring it up it did not run. I found that the coil on a contactor had sort of melted which also made it so that I could not even operate it manually/push it in by hand. There are two other contactors, a forward contactor and a reverse contactor, so I am not sure what this one is for, but it has power to it at all times and is pulled in. The only way to stop it is to use the main disconnect on the machine. Could this be why it was burned out in the first place? I can see from the footprints inside the panel, that the contactor is not the same as what was there at some previous time. I understand that this is not enough information, but before I spend hours of studying to try to teach myself, I am wondering if this is normal in some applications. I cant see that a machine should have an energized contactor at all times nor does it seem right to have to shut the main disconnect off when not in use. I have been looking for a schematic for this machine for several months and have not been able to come up with one so I guess this is going to be a learning experiance.
    After replacing the contactor (Allen Bradley 100-C09) the machine runs fine and all of the controls work as they should.
     
  2. Kermit2

    AAC Fanatic!

    Feb 5, 2010
    3,765
    925
    If you have the model name and number then perhaps www.homemodelenginemachinist.com can help you if you post the question and data there? They have lots of members who not only have small home shops but work with many different types of industrial size equipment too. It sounds like a 'master' power relay, and would be the one that controls any safety interlocks the machine might have.
     
  3. Pencil

    Active Member

    Dec 8, 2009
    271
    38
    Does the machine have an E-stop button? (Emergency stop a.k.a the
    big red button.)

    If it does this relay may "drop out" (denergize) when it is pushed.

    The E-stop circuit should be normally closed with all the buttons/limits wired
    in series.

    Just one idea. There are other possibilities.
     
  4. Homebody

    Thread Starter New Member

    May 29, 2011
    7
    0
    Thanks Kermit2 for the suggestion! I will go to that site as soon as I leave here.

    Pencil, Yes it does have a red stop button as well as an emergency foot pedal stop.
    I did check the botton stop and it is normally closed. I have not checked anything out with the foot pedal but it does work as it should.
    The fact that the contactor is energized at all times is what makes me question the wiring. Last night after reading some about contactors and starting circuits I looked at the contactor again. I replaced the old contactor with another one just like it. At that time I saw that it was rated at 25 amps and the motor full load amps is 21.6 so I assumed this was ok. Last night I noticed on the side of the contactor that it is rated at 3HP at 230 volts and 2 HP at 120 volts. The machine has a two speed motor and is rated at 3 HP and 7.5 HP. Now I am wondering if not only the machine may be wired wrong over the years, and the contactor may be wrong as well.
     
  5. Homebody

    Thread Starter New Member

    May 29, 2011
    7
    0
    The machine also has a jog button and a lever that has forward/reverse/off positions.
     
  6. williamj

    Active Member

    Sep 3, 2009
    180
    32
    Homebody,

    At times, due to excessive arching, contacts on relays and contactors (as well as switches and push buttons) will actually "weld" together thus maintainning current flow, from your discription it sounds like one of your control relays, contactors, selector switches or push buttons has done just that.

    Disconnect the machine and check each relay, contactor, slelctor switch and pushbutton for proper opperation and each coil for continuity. Replace anything that doesn't function properly.

    If you are interested I can work up a simple ladder diagram which will show the current flow and maybe give you a better understanding of what is happening.

    good luck,

    williamj
     
  7. PatM

    Active Member

    Dec 31, 2010
    81
    72
    The contactor seems to be too small.
    If the contacts are rated at 3HP at 230 volts and 2 HP at 120 volts,and you are controlling a motor that uses a higher current (7.5 HP and 3 HP), the contacts will eventually fail.
     
  8. #12

    Expert

    Nov 30, 2010
    16,247
    6,744
    In post #4 you said a constantly on contactor makes you suspect the wiring is wrong. I just want to sharpen the point on this: There are situations where this is the right way to do it.

    Kermit and Pencil said this but your answers seem to indicate you might have missed it. Having a constantly on contactor in a machine like this does not necessarily mean the wiring is fouled. Fail-safe circuits use this principle, and fail-safe is a good thing with machinery that can eat body parts.

    ps, Pat is right about the load rating. If that motor ever goes into 7.5 horsepower mode a 3Hp contactor will be at risk of welding shut.
     
  9. Pencil

    Active Member

    Dec 8, 2009
    271
    38
    An Emergency Stop button will be generally red with a large mushroom top.
    Another requirement (I believe) is that cannot return to its normal operating
    position without some sort of intervention. (Example: button locks when pushed and has to be turned in order to unlock.)

    A plain red stop button is not necessarily an E-Stop.

    The foot stop sounds right for a manual lathe.

    When the foot stop is activated does the relay in question de-energize?
    Does another relay de-energize?

    On a manual lathe there are not many safety features. Make sure they all
    work properly. I gaurantee you will need to stop that thing in a hurry someday for one reason or another. This applies to the spindle brake as well.
     
  10. Kingsparks

    Member

    May 17, 2011
    118
    5
    On my lathe, a manual Grizzly 10" X 22", there is a relay, contactor energized all the time the STOP button is out. Power is removed completely only when the big, red mushroom top STOP button is depressed.

    Pencil is right too, you have to turn it to the right and pull to disengage, that is, restart the machine. My manual recommends always stopping the lathe with this button then turn the run switch off. It also has a third switch PB, which has to be pressed to start the lathe. If you don't use the stop button the lathe will run with just the run switch turned on. Not a good idea in my opinion. All set up to prevent inadvertent actuation of that dangerous critter. :eek:
     
  11. Homebody

    Thread Starter New Member

    May 29, 2011
    7
    0
    Thanks for all your responses. Sorry I misse the suggestion that the machine could be performing as designed. Maybe I will just need to shut of the main disconnect when not in use.
    I will check all the other switches etc though and weather or not the contactor opens when I hit the foot controlled e-stop. The red buttin is just a small square push button that is normally closed and goes back to the closed position when I let off the button.
    William j, if you are willing to draw something up that would be great! Even if the machine is wired correctly it would be a good learning tool.
    After I get a better handle on how it all works I will need to figure out what the right contactor should be and change it.
    I am still hopeing to find a schematic on the Home Model Engine Machinist site, but if I dont it was deffinitly worth the try. Its a great web site with alot of information.
    Thanks again!
     
  12. Homebody

    Thread Starter New Member

    May 29, 2011
    7
    0
    I forgot to ask this,,,, I am confused at why the contactor is rated at only 3HP at 230 volts but at the same time rated at 25 amps. The machines 3hp/7.5 hp motor is rated at 21.6 full load amps. So on one hand it seems that the contactor would be large enough, but not when going by the rated HP. The contactor is an Allen Bradley Cat# 100-C09 Ser. A
     
  13. franzschluter

    Active Member

    Jun 1, 2009
    95
    0
    You should change for a higher rating. I got this old surface grinder. For moving table back and forth, it has 3 relays. 1 always being powered. Sometimes they weld on... So despite the limit switch /proximity sensor the table bangs to one end every blue moon. What I did was removed the contacts and changed the height gap of the contacts and a slightly stronger spring. This made the contactor louder but now it doesn't weld or lag. What you want is a fast acting contactor.. Sometimes the spring inside gets hot hence the spring elasticity is reduced therefore making bad arcs sometimes. This could lead to a weld. A faster switch is the solution for a longer life and reliability. A stronger spring or magnet will also result in better contacts. Bad contacts could also cause unnecessary heat

    And its normal to find contactors permanently energized when the machine is "on". All of my workshop machines work that way. Once E-button or main switch is flipped or pressed. Power goes out at the mains.

    Regards
    Franz
     
  14. Laird Scooby

    New Member

    May 31, 2011
    11
    0
    Hi there, i've just joined this forum after finding it by accident but i can help a bit with some of your queries. To be honest i've only read certain details in the thread so if i say something that's already been said, my apologies!

    First of all, it's common practice to have a Control contactor (the one that's on all the time) in machine tool wiring. This is so that when you hit the Start button, things like the slurry pump (for delivering coolant to the tool/work), lighting, CNC or similar control are all started and working before the main motor starts the chuck. Therefore it's my belief this lathe is wired correctly.

    Secondly, there will be many different ratings on the contactor you've got there. The one that is for 25A is quite likely for when it's used in a DC application or for AC heating where the load is purely resistive. The one you need to take notice of will be the HP/kW rating at the specified voltage. On the basis it's a 3HP contactor (2.2kW approx) at 415/380Vac, check the rating plate on the motor. As long as the motor takes less than this you should be fine with it as the other circuits powered by it take a negligible amount.

    Lastly (for now), it's always good workshop practice to shut off the main isolator when you've finished using the lathe (or any other machine tool) so if you're already in this habit, that's a good thing!
     
  15. shortbus

    AAC Fanatic!

    Sep 30, 2009
    4,000
    1,512
    The main reason for the extra contactor is safety. If there is a sudden short power outage, it will shut down the whole machine. Without that if the forward/reverse lever is still engaged the spindle will start to turn when power is restored.

    All industrial rated machine tools and manufacturing equipment that I've ever been around is wired this way.
     
  16. CDRIVE

    Senior Member

    Jul 1, 2008
    2,223
    99
    Just for clarification, magnetic contactors are simply large latching relay circuits. The main feature and benefit of them is for protection from power outages. The idea is to prevent the machine from automatically restarting when power is restored.
     
  17. CDRIVE

    Senior Member

    Jul 1, 2008
    2,223
    99
    Oops, we doubled!
     
  18. shortbus

    AAC Fanatic!

    Sep 30, 2009
    4,000
    1,512
    CDrive- the forward/reverse contactors don't use the latching contacts in the contactor, they use the F/R lever to hold them in(on a lathe or mill).
     
  19. CDRIVE

    Senior Member

    Jul 1, 2008
    2,223
    99
    Yeah, they usually use a Furnace or Drum switch (the old machines that I have do) but I thought we were talking about his magnetic contactor.
     
  20. shortbus

    AAC Fanatic!

    Sep 30, 2009
    4,000
    1,512
    @ Cdrive- From the O/P first post "There are two other contactors, a forward contactor and a reverse contactor, so I am not sure what this one is for, but it has power to it at all times and is pulled in"

    My two old lathes one from the '30s or '40s, and one from the '50s have that type drum switch, but my new one from the 1990s has the three contactor style.
     
Loading...