Electric Trolley Hoist TRANSFORMER? HELP?

Discussion in 'The Projects Forum' started by Ben_C, Jul 9, 2013.

  1. Ben_C

    Thread Starter Active Member

    Oct 19, 2010
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    I'm really stuck with an electronic hoist at work. It's an electric trolley hoist and is held onto a steel girder for moving backwards forwards etc...

    What happened was the pendant control panel wire got caught in between the hook and the hoist motor cover (cut off switch control broke off a while back so no limit) and shredded the wires so control from the pedant stopped working.

    A workmate (fellow electronic engineer student) had cut the wire down to after the shredded part and rewired it back into place. Now, I dont know where he's gone wrong, He states the time delay fuse T1.25L250V internally kept blowing. So this was replaced with a T1.6A250V but still kept blowing.

    I came up with the idea that the motor was drawing a lot of current as it would "think" that there is too much load on as the hook was jammed right up to the motor cover. I took the hook off and magically the fuse stopped blowing but non of the pendant controls work on the input, it just wont move at all.

    It's a 415V supply and the transformer drops the voltage to 24V, I've placed a multimeter on the input to the Transformer and its giving ~415V. When I place the + probe to the "24V" output of the transformer I'm getting around 235V :confused:

    WHY?

    Logic tells me as it's stated on the Transformer that it should be 24V output not x10 that.

    nothing is working at all, no contactors are flicking over or anything. My diagnosis is that the transformer has broke down, is it just a simple case of getting a new transformer?

    It's a 2000KG 3 phase hoist which operates with a 415V input. It has an electric trolley to move back and forth on the girder and has a motor for pulling items up and down. I would assume the control pendant would only (should only) need 24V due to health and safety etc.. but again a multimeter test on the terminals show a similar reading to what the output of the transformer is showing ~235V



    PLEASE HELP. :(
     
  2. Dodgydave

    AAC Fanatic!

    Jun 22, 2012
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    Your meter needs to be on AC, not, DC, either its wired wrong, or the transformer has gone, the fuse is rated at 1.25A , 230V, so it will blow.
     
  3. Ben_C

    Thread Starter Active Member

    Oct 19, 2010
    65
    4
    The only wires changed apparently were the Control pendant, these have numbers and all match correctly. The T1.6A was the closest value I could get from Maplin and don't see how that can not make anything work. They're not blowing anymore thankfully.. So it just all point's towards transformer..
    What about the motor ? Could that have been damaged? Is that possible? I might just go and but a new transformer but dont want to waste money if it's not that..


    and thanks for the reply :D
     
  4. Ben_C

    Thread Starter Active Member

    Oct 19, 2010
    65
    4
    Just to be sure, when checking the output voltage of the transformer I was connecting the neutral of the DMM to the input neutral of the 415V supply.. This should show at 24V and is not the reason I was getting 235V right?
     
  5. Dodgydave

    AAC Fanatic!

    Jun 22, 2012
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    745
    Wrong you measure the output on the transformer windings, to measure the input put your meter on the supply side, phase to phase or Neutral, if your getting 24AC on the secondary then it must be the motor.
     
  6. strantor

    AAC Fanatic!

    Oct 3, 2010
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    Not sure about the laws in the UK (or here in the US for that matter) but I used to work in maintenance in a plant and I (nor anyone else) was not allowed to service the cranes. That had to be done by outside licensed crane techs. That may have just been company policy but I strongly suspect it was law.

    Anyway, I suspect that the 235v you were measuring was due to improper measurement. Your input fuse was blown, correct? Does it have an output fuse? Open the pendant and verify there is voltage across the switches (be careful not to pinch the wires when you put it back together). If yes, verify that your contractors are getting voltage across their coils when a friend presses the buttons. Are there fuses/breakers/thermal overloads for the motors and on the main input? I bet there are, check those. Is the thing still mechanically jammed, despite you removing the hook? Did your friend do a shoddy job rewiring? Check for continuity between conductors in the pendant cable and to grpund (dont let NC switches fool you!)
     
  7. Ben_C

    Thread Starter Active Member

    Oct 19, 2010
    65
    4
    Continuity is there on the pendant yes.. its just there is no contact flicks as i heard when it was working.. nothing happens at all infact when buttons are pressed on the pendant.
     
  8. strantor

    AAC Fanatic!

    Oct 3, 2010
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    Did you check any of those Other things I listed?

    There should NOT be continuity between conductors in the pendant cable, unless there are NC buttons in it,
     
  9. Ben_C

    Thread Starter Active Member

    Oct 19, 2010
    65
    4
    Sorry by nc you mean not connected? Im deffo getting continuity from checking return/source, would that mean the motors gone? Theres two glass fuses on the board non of these have blown and are getting power. Its not jammed i can manually move the chain up/down by rotating the motor... you're a brilliant guy for helping thanks alit. Meant to be picking a transformer up tomorrow but just want to make sure it is that before i pay any money.
     
  10. strantor

    AAC Fanatic!

    Oct 3, 2010
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    Hah?

    By NC I mean normally closed. I am referring to the pushbuttons on the pendant when I say that. I am prompting you to check for continuity between the wires of the control pendant. Each wire has its own function and there should not be any continuity between any of them unless there are Normally Closed pushbuttons in the pendant. This only one of many things I suggested you check.
     
  11. strantor

    AAC Fanatic!

    Oct 3, 2010
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    Have you re checked the output of the transformer, measuring from the 2 output taps?
     
  12. Ben_C

    Thread Starter Active Member

    Oct 19, 2010
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    Ive got it working ! :D

    Well, partly. No power was there due to a faulty transformer. I replaced it today and when I switched the power on instant contact noise and i can move it back and forth on the girder now.

    The problem is when im pressing up/down the motor sounds like its turning but the chain isnt moving.. theres a ring on the outside with two wires going into it.. is that the brake? When i remove it it does move the chain up and down, when i depress the button once it just keeps going for about a meters worth of chain and then slows to a stop...? When the ring with the wires is on though it wont move at all just makes a noise like theres power there but just not going up or down..?

    Motor gone? Or dodgy wiring ie brake is always on?
     
  13. Ben_C

    Thread Starter Active Member

    Oct 19, 2010
    65
    4
    I got it working thanks guys, I tightened the brake on too hard :p thanks for your help Strantor
     
    strantor likes this.
  14. strantor

    AAC Fanatic!

    Oct 3, 2010
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    Hi Ben, sorry for not replying to your last post. I have been busy doing my own machine troubleshooting. Thank you for the feedback. It's good to hear when something turns out well.
     
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