Crane Question

Simple: an outstanding deferred maintenance issue.

A telephone call to the equipment manufacturer can often provide a useful pointer to the cause and is highly recommended.

If local Technicians cannot solve the problem, then a call-out visit by the manufacturer's Service Technician may be overdue.

As cranes are strongly in the focus of safety, do not delay in making the call.

Good answer!!

If it’s a slipring motor on the hoist check the resistance banks.

Could be any number of things depending on the type of drive system incorporated...It sounds like the motor is failing to engage and the secondary brake is kicking in...

https://www.thefabricator.com/article/safety/six-dangerous-misconceptions-about-crane-safety

It seems to me that the spring between the lifting motor and the brake is relaxing when the brake is applied.

A rider to that answer, though: <...want to hoist the weight higher the crane will start to lower it...> the Original Poster has withheld from the forum whether the crane motors down on selecting motoring up or whether it runs down freely before motoring up. Wrong-way motoring would suggest a control problem rather than a brake problem.

GA, though.

When the crane is in "hoist" mode, the brakes would not be engaged as that would be counter productive to the brakes and the motor.

it is obvious to me that the brakes can hold the load but it is beyond the power of the motor.

I ASSUME the crane is very old and operates on DC. If this is the case it is common to have to lower heavy loads on first point up. That is brake released but motor TRYING to go up but overloaded. Since you are only at about half of capacity of crane (not a heavy load) this probably indicates an electrical problem causing first point up to be too weak. I would suspect one of the resistors has changed value (possibly poor connection, loose or corroded). Or it could indicate motor deterioration (shorted turns in field or armature or worn brushes). Ignore this if it is an AC crane or not very old.