# 25 ton bridge crane



## controlsparkie (May 23, 2012)

Hey Guys, 

We have a demag 25 ton crane at work that has a few issues.

North, south east and west all work, however....

Upon releasing the emergency stop the crane vibrates and makes a loud noise, almost like it wants to go up or down (or both) but cant. This happens without any of the buttons being pressed. 

Once again, the crane will run in all directions but up and down, keeping the e-stop released for more than a few moments will blow the fuses.

I cant get at our lift unitl tomorrow so the crane is out of service.

Any starting points when I can get up there?

Thanks

P.S. I normally do control work, so im going to dig up some drawings and start with the basics, (checking contacts, phasing, main line, etc) but if anyone has experience with this it would be appreciated


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## maddhatter (May 7, 2012)

contactor with welded shut contacts? 

depends how estop defeats the circuit..

got drawings?


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## JRaef (Mar 23, 2009)

maddhatter said:


> contactor with welded shut contacts?
> 
> depends how estop defeats the circuit..
> 
> got drawings?


I like it. As soon as the control power is applied the hoist motor is getting power, but because it is out of sequence, the mechanical safety brake is still engaged, which explains the shuddering and fuses blowing.


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## ScooterMcGavin (Jan 24, 2011)

JRaef probably hit the nail on the head. Our cranes release the brake as soon as you so much as flick the up/down lever. Once you stop there is about a 2-5 second time delay and then you will hear the brake engage again. Just as a side note we don't usually work on our cranes we always have a crane company come to work on them(mainly due to liability issues.)


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## vileislepore (Jan 25, 2013)

I experienced a similar problem more than once with our bridge cranes. Even now we have a problem that was caused by the hoist contactor welding itself shut too many times; to the point where now there is almost nothing left to the contacts. Were waiting for new contacts to arrive as we speak. How often does the crane company perform preventative maintenance on your cranes?


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## Pearce Services (Sep 9, 2012)

I have seen bridge rectifiers for DC brakes cause fuses to blow, is it a DC brake?

_________________________________________
Kevin


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