Latching Relay Adjustment?

Discussion in 'Shop Talk' started by Jena, Jan 18, 2005.

  1. Jena

    Jena Well-Known Member

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    My bunk feeder has an automatic brush. It's not working. According to my manuals, the problem is the "mechanical latching relay" which needs to be cleaned, lubed and adjusted.

    I found the relay they are talking about and I'm sure I can handle the cleaning and lube, but how the heck to you adjust this thing?

    Thanks

    Jena
     
  2. herefordman

    herefordman Well-Known Member

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    Do you know what kind of relay it is ?
    Some have an adjusting screw under the cover, and some others require just bending the arm the spring is attached to to get the gap right, understand though if you mess with it and it locks on, you will burn out the motor or whatever its running.
    If its easily replaceable get a new one, and if your not sure if thats the problem, try another one from a different panel location in the same spot.
     

  3. John Hill

    John Hill Grand Master

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    A latching relay sounds like something that would be made by a specialised manufacturer so examine it for a name and or part number. Do a Google search on these and see what turns up, it may be a long shot but you may get all the information you need.
     
  4. cowboy joe

    cowboy joe Hired Hand

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    Jena,

    Herefordman is correct. Latching relays sometimes have adjusting screws to set the pressure of the contacts. Cleaning the contacts (via burnishing (preferred or with extra extra fine sandpaper or emory) may leave a small gap in the two sets of contacts due to material removal or distortion of the arms from bending. You will want to adjust the set screw or carefully bend the arms to allow the contacts to just touch. The arms should bend slightly but not too much...just enough to allow the contacts to seat against each other. You will be able to judge if they are set right by watching the relay operate...too little pressure will allow arcing which will burn the contacts...too much and the arms will distort permanently. Hope this helps.
     
  5. Jena

    Jena Well-Known Member

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    Thanks. The relay is what tells the motor to switch from forward to backward motion. The explanations given make sense, since the brush continually goes forward only and won't switch. It I flip the switch to reverse, there's some arcing, so I would take that to mean the contacts are too "loose".

    I'll give fixing it a shot, but if I ruin the thing, I won't be any worse off than I am now and I can by-pass it to save the motor, as I have been. Is this something I can take to an electrical supply house and find a replacement? If not, I know the silo guy can get me one and mail it to me. He's mailed me parts before.

    Jena
     
  6. herefordman

    herefordman Well-Known Member

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    Been thinking of this, are you sure your book doesn't acually mean clean and lubricate the mechanical trigger that the brush hits at the end of its travel ?
    This is sometimes also called a mechanical relay, as it sounds like the electrical relay is arcing its probably functioning.
    Usually conveyers etc, have a metal trigger somewhere that trips an electronic switch called a proximity switch, and it either stops or reverses, whichever its required to do.
    See if you can find anything like that on the bunk itself, if you find a switch push it in and out, if you don't hear, or feel a click the switch is shot.
    Sometimes the proximity switch looks like a square head box with a wire coming out of it, and when a piece of metal passes the square head, it senses the steel and trips the relay, look for a little one inch square metal tab on the conveyer chain somewhere, and follow that in its travel until you find the switch.
    Any industrial electrical supplier should be able to get any of these switches.
    good luck.
     
  7. rambler

    rambler Well-Known Member Supporter

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    A brand name would help at this point. :)

    --->Paul
     
  8. Jena

    Jena Well-Known Member

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    Herefordman....I know what you are talking about and that is not what the book was talking about. On my bunk they are called limit switches. They are activated with the brush goes by and knocks them sideways.

    I took the control panel apart, found the relay. It all looked pretty pristine (it was in a sealed metal box). There was one small cobweb thing in there, which I blew out. I didn't mess with it otherwise because it looked in good shape.

    I put it all back together and it works like a charm.

    Easy fix, but thanks for the help. Always better to quit when you're ahead!

    Jena
     
  9. agmantoo

    agmantoo agmantoo Supporter

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    Jena, I am reiterating what I think you already know. The operation of the bunk system electrical arrangment is as follows as I understand it. The brush travels and at near the end of the travel the limit switch is activated. This in turn activates the latching relay which latches and reverses the motor direction and continues to remain latched until the brush nears the end of travel in the opposite direction. At this end, the other limit switch is activated and the latching relay is released from the latched condition causing the motor to switch directions again. If it were not for the latching feature the device would cease to operate after the limit switch is activated and the brush ceases to have the limit switch activated. I would check the limit switches to see that they are being tripped by the brush each time. You may need to adjust them. PS... how are the fingers in this cold weather
     
  10. Jena

    Jena Well-Known Member

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    That's about how it works. The limit switches are working fine. It must have been that little cobweb in there, though I can't imagine it. Maybe I knocked some other stuff off the relay taking it apart...

    The fingers are not happy. Slow working. Unscrew something, go warm up my hand. Unscrew something else, go warm up my hand.....oh well...it's supposed to get better after a year or two.

    Jena