Winch not starting under load

[startermotor]

Our company uses a three phase winch with electrical ratings of 400v @ 35A per phase under full load
When the winch starts gradually in connection to the weight it pulls, it works, but if I stop the winch with the weight suspended and try and start the winch,it won't move.
Do you think it is something to do with a soft start, like starting in delta and then to star.
We have been assured the winch is man enough for the job.
This is a £20,000 pound winch, I can't believe it can't start with a load attached to the winching cable.
Any comments would be gratefullty recieved.

Thanks

 

[itsmoked]

What do you mean it can't be started? What exactly happens? Fuses blow? Breakers trip? Drives trip? Cables melt?

This thing really has a soft-start running it??

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[BobM3]

Voltage drop due to high starting amps?

 

[LionelHutz]

Apply full-voltage to the motor. If the winch doesn't move then the winch can not handle the load or the voltage is dropping so much the motor can not develop enough torque for the load.

Just don't apply full-voltage for very long. If it doesn't move within 3 or 4 seconds it's not moving.

 

[edison123]

Check the brakes. They are probably solenoid & spring operated and they come into play when you stop the winch. When you start again, may be they are not released due to loss of supply to the solenoid.

* Women are like the police. They can have all the evidence in the world and yet they still want a confession - Chris Rock *

 

[MikeHalloran]

A generic soft-start control won't deal well with the asymmetry caused by the load, and won't know how to coordinate the brake. There are specialized 'not so soft start going up' controls developed especially for hoists; I hope you are using one of them.



Mike Halloran
Pembroke Pines, FL, USA

 

[startermotor]

Thanks guys for your input.
To answer Keith's question the winch tries to pull the load, but it seems like there is not enough torque and therefore it does not move.
The fuses and overload protection are fine when the winch does not move.
The winch works with a solenoid brake system, as edison pointed out.
There is no down control on the box, only an up control.
The down is controled by the brake.
In regards to the brake, it is disengaging fine, and everything is ok there.
The strange thing is that when I start with the winch cable slack and gradually take up the slack the winch pulls the load all the up with no problem.
It is only when I stop half way, by engaging the brake, does the problem occur.
The solenoid releases the brake and the load just stays suspended half way neither going up or down.
I can here the motor trying to work, but it just wont pull the load.
I have to let the load all the way down and winch right to the top without stopping.
We have been in contact with the german company who makes this winch, and are awaiting their answer.

Thanks guys for the help I think Mike Halloran is correct in what he has stated.
Thanks Mike, it seems that from what I can hear from our guys who have been talking to the manufactures, that this is where the fault lies.
I don't know for sure yet, but I think the wiring to this "up control starter" is wrong, and needs to be looked at.

Thanks again everyone

Jason

 

[MikeHalloran]

Find a local overhead crane manufacturer, and ask them to send out a hoist control technician to diagnose the problem for you. The fast diagnosis will offset the high rate demanded.

Crane and hoist controls are mostly similar to each other, even across manufacturers, but they look weird and unnecessarily complex to your average control technician. They include a lot of interlocks, each added because of an unfortunate outcome... which you don't want to repeat.





Mike Halloran
Pembroke Pines, FL, USA

 

[itsmoked]

And also, it should be noted that cost has zero to do with what any particular winch can do. Though I do understand and have fallen victim to that particular form of logic myself.

Please do keep us informed of further developments as then we can confirm or correct our knowledge.

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[LionelHutz]

I should point out that a good VFD combined with an encoder should be capable of starting the winch.

Most inductions motors have a much higher breakdown torque (the torque when the motor stalls once at speed) compared to the starting torque they are capable of producing. So, it's much harder to stall the motor once it's running compared to it's starting capability.

When the motor is running at speed before the load is applied the winch is probably capable of about 2x the pulling force compared to the force it can generate when you try to start under load.

 

[trevorm]

If I understand correctly, a soft starter was mentioned.
If this is a soft starter that works on the reduced voltage principle, the torque will be seriously affected.
Torque is directly proportional to the square of the voltage. Reducing voltage to start will reduce the torque available.
I agree with LionelHutz, a VFD is the correct animal for a hoisting application. Good ones even have Direct Torque Control.

 

[RobWard]

One thought: is this a freely suspended load (i.e you have a hoist, rather than a winch) or is it running on rails/rollers/wheels etc or even just being dragged along something?

You'd have to take into account stiction in the system in that case.

"I love deadlines. I love the whooshing noise they make as they go past." Douglas Adams

 

[waross]

Good point RobWard.
I have seen several winches used to pull lumber out of dry kilns. They have to start with some slack in the winch line. If you stop the winch, you had to pull some slack to get it going again.
And on hoisting applications, I once saw a unique arrangement on an elevator type material hoist. As the carriage was lowered to the bottom of the tower a fixed pulley encountered a bight in the lifting line. The lifting line mechanical advantage within 4 feet of the ground was 4:1 and above that the bight lifted off the fixed pulley and the MA transformed to 2:1.
If this hoist was stopped in the wrong place when loaded it had to be returned to the ground to take advantage of the 4:1 MA before it could be raised again.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[itsmoked]

Ah Bill, that's a cool design! Very clever. I like it.

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com