Hoist Motor

as a rigger, you better contact the manufacture reguardles of the warrenty status. these guys will bend over backwards to fix the problem.. the last thing they want is being sued for personal injury.

Stop using the equipment immediately, and get the manufacturer in, same day, to assess the problem and make repairs.

I'd send the manufacturer an email, I'd also include the email address of a industrial accident attorney in the address line. I have a feeling you'll be quickly contacted by both.

fredski, would be interested in joining club? most people know us as the out laws

oh great

1%er

you have been showing your true colors around the forum the past few days

why are you here?

Yes, very dangerous and must be rectified immediately, if not sooner.

Where are you located ?

i have helped a steel plant in India select and install crane control (a 300-ton hot-metal crane, no less) in the days of conventional control ... the electromagnetic brakes (primary and backup) would slam closed a full 5 feet before the limit switch was hit. The power would be cut off to the motor 1 second after the brakes clamped. There is freewheeling delay effect in DC electromagnets, this was eliminated by using massive DC contactors with series blow-out coils.

This was 35 years ago. You mean the new technology has made things more risky? Well well, one lives and learns.

[immediately if not sooner] has always been my line. did i trin you?

Shridhar,

You are right, it is D.C brake which is culprit. There is residual magnetism in the D.C coil which holds the brake disc from engaging. We had solved this problem by installing a air break contactor in brake coil circuit which cuts off the supply in D.C coil when brake is engaged.

Thanks.

Could be, but as Tornado says, we need the full schematic and lots more information.

The slow DC did cause a small issue in an old steel plant in the east, and i was glad that i was lucky enough to trace it to the freewheeling effect. As you did, i used two heavy duty contactors with series-blow-out coils and solved the problem (my company made the contactors too, happily ) It would have given rise to a high surge voltage, but thankfully, it did not damage anything, the MOV had not been invented perhaps, and what is more, none of us knew it anyway

Who designed the control system?

too much info. a simple answer is always better. short, sweet and to the point.

Hope you realize you're within a blayswidth of making yourself quite unpopular.

You should also learn to punctuate correctly^[1], if you want to be taken seriously.

Edit:

[1] or maybe get your shift key fixed.

Have to agree. (GA)

If, on reaching the top limit, it didn't allow some 'down slip', the thing would lockup and/or break something, and/or be 'unrecoverable'.

But 1 second is far too long and speaks of wear and/or poor practice - like using the safety as a 'height set' routinely at maximum load, and/or messing with the settings to 'make it all faster'.

The top ultimate limit is not designed with separate brake control (as in VFD) in mind so this should be used as a safety line otherwise, immediately applying the brake, of course.

In the event, there shouldn't be any significant drop if controlled correctly.

BTW I supply VFD to crane hoists amongst other applications.

Hi

The braking actuation with a delay setting is normal feature, but the delay depends on the speed setting on the drive. The S curve of the drive and motor optimisation may be checked. The setting provided can be programmed to reduce the delay and optimised. check out the time delay on present setting and decrease the delay depending on the S curve optimisation.

all the best

gsk

A full control schematic might help.

This is mainly a maintenance problem on the brake assembly.

If the Hoist was not a vsd type, the same thing will be there. How does the hoist stop at any height? You just disconnect the power to the motor and the brakes come automatically before any momentum is accquired to the extend that it will overload the brakes!

With a vsd drive, you can have the luxury of slowing down to a standstil almost before the brake is applied ( DC Brake and then a mechanical type).

If you are having a down slip it means that the brakes need servicing and re-adjusting.

I worked as a designer for a hoist company for several years. A typical hoist will only have a single upper limit switch. This is standard in the hoist industry. The way that the machine MUST function. is that when ever the motor is not running for any reason the motor brake must be applied. VSD are eqiped or they should be with several monitoring functions. Should there be a problem detected the brake relay will be de-energized.

There is no provision in any code pertaining to any hoist weather personnel rated or other wise that permits the free fall in any condition under normal operating conditions. This includes running into the limit switches.

The only time a free fall condition is permitted is during a "drop test" this test is performed to test the performance of the emergency braking system in a personnel rated hoist. A non personnel rated hoist in not required to have emergency braking in most areas,

a long winded answer to your question.

Stop using the hoist NOW! lock it out. Contact the manufacturer.

If this hoist new (less than a year old) and you do not get an immediate response, let them know that you intend to contact OSHA or your local safety organization.

If it is more than a year old, have an AUTHORIZED service agent look at it.

In any case you have a defective piece of equipment that could cause injury or death.

before I get all sorts of nasty grams... after 1 year the manufacturer is going to blame the customer for any problems. Having an AUTHORIZED agent look at it will eliminate un-necessary chaos.

Thank you ,This has been like this for many years.There are two upper limits,one to stop and other a emergency stop, before you reach the ultimate stop which kills the 3 phase.The free fall happens about 3 times a year.(when both these limits fail).This is a fully automatic crane.(no operator error).

Is it known how and why are these limits are failing? (Contrary to post 24, I like the idea of more than one limit, especially if the second gives a signal that the first has failed.)

If not the aforementioned schematic, a complete operational description would be useful. Perhaps design, maintenance, and testing should all be reviewed, even with a formal hazard analysis.

There is no contrary about it, however I agree that two switches are better than one. talk to the standards dept. at ANSI. I worked for years to get this rule changes to no avail. every hoist I designed had two upper limit switches. The differences between the function of the switches is that the lower (stop) switch would slow the hoist to a controlled stop whereas the upper switch (emergency stop) would stop the hoist right now.

OK with that said it is a known issue that the "brake relay" contacts will weld themselves together. During an annual inspection (required for all hoist used in the workplace) the relay be replaced, along with the varistor.

If YOU are not a licensed certified hoist technician and when there is an accident YOU will be held responsible and face criminal charges. Believe me this happens far more often than one would think.

GET PROFESSIONAL HELP NOW PLEASE!!!!

GA welding/sticking contacts would do it.

It sounds as if the VFD is carrying out a normal stopping sequence stop at the top ultimate since the brake is applied but only after losing control because of the open circuiting of the motor by this limit.

So, the hoist is missing the usual stop limit, hits the ultimate, open circuits the motor but the VFD starts its ramp to stop (controlled stop) and normal brake control output sequence BUT IS NOT CONNECTED TO THE MOTOR NOW. It doesn't sound as if an overspeed comes in (or maybe, why doesn't it? - but we don't know how far it drops before the motor brake(s) are applied and what speed it reaches - pretty fast, pretty quickly would be my guess)

This is wrong in several ways from a control perspective and I too would strongly recommend to get some clear professional advice to get this rectified before further use.

I'm rather concerned about your description of one of the switches as an "emergency stop".

An Emergency Stop (such as those with big red mushroom heads on a yellow circle:

) should be exactly that. It should stop all movement in the shortest possible time. It should be regularly tested. That you've said failure "... happens about 3 times a year ..." is very disturbing. Maybe it's just incorrect terminology; I hope so.

Even if this isn't an "Emergency Stop" switch (in the true sense), the fact that both switches fail frequently suggests a serious design fault. Have the switches failed, or just not been actuated correctly?

Echoing others, a full system schematic would be very useful.

The term "emergency stop" is what it is commonly called in the industry. technically it is the final upper limit. ad it MUST function as you describe. There is a major problem with this hoist.

Eltech, out of interest is the brake DC?

yes its dc, brake output from the drive which is 100m away to a relay, brake works of the relay which is fed ac then to a rectifier in the motor terminal. contacts on the ac and dc are open to close the brakes

hi all

In general practice, the hoist in EOT has a gravity limit switch and rotary limit switch, which is double check point with all over emergency stop for all motions. Hope this is a general practice in crane manufacturing.

with regards

gsk

Hi Eltech, the problem is that you are disconnecting the VSD from the Motor.

When the limit is reached you should use the VSD to Ramp the motor to a stop, but right now you are letting the motor coast to a stop by disconnecting the VSD.

The VSD should have an emergency stop function (This is also Called an Enable function) The is what you need to interrupt when the hoist gets to its linits.

I hope this is of help, it would also help is i knew what vsd you are using.

Best Regards

Joe