Traction Elevator counterweight overbalanced percentage

[Parachute]

Hello everyone,

If a geared traction machine has a machine data plate that says CWT percentage 40%. is there any other design / safety concerns if the unit is balanced at 45% but the motor amps is within the motor data plate when operating at full load / no load and all the functional tests work correctly?

 

[Baluncore]

Welcome to PF.

At first reading, it might seem to be OK, but there will always be safety concerns during operation. It is very hard to be sure when an engineer does not know what the machine does, and cannot inspect the equipment.

Is that CWT 45% a maximum or a minimum?

 

[Parachute]

Welcome to PF.

At first reading, it might seem to be OK, but there will always be safety concerns during operation. It is very hard to be sure when an engineer does not know what the machine does, and cannot inspect the equipment.

Is that CWT 45% a maximum or a minimum?

From what I usually see, geared traction units tend to have a counterweight somewhere in the 40–50% range. There’s also an application data plate on the motor (system design data), which I assume is meant to be followed since it reflects how the system was designed. With gearless units, the counterweight is typically around 45–50%, and most of the time it seems to be set right at 50%. My understanding is limited, but in the field we mainly make sure the functional safety tests meet code and that the motor isn’t being overloaded beyond the nameplate FLA. Outside of that, there doesn’t seem to be much specific direction in the elevator code, since counter weighting and overall balance appear to be left up to the design engineer.

 

[Baluncore]

What load variation, from minimum to maximum, is being lifted?
What load is the geared traction unit specified to lift?

 

[Parachute]

What load variation, from minimum to maximum, is being lifted?
What load is the geared traction unit specified to lift?

In BC canada, there are a lot of 2500 lb capacity units for regular passenger cars, if they need more of a freight style than 4500 lbs is common. I believe you can use geared or gearless for either application depending on what you need for speed and performance. the geared units here are common at 200-500 ft per min. and faster cars 500-1200 ft per min are typically gearless. this is from my experience in the field - other places could have different setup variations.

 

[Baluncore]

I expect that the 40% counterweight is a compromise between reducing the peak ±load on the motor, and increasing the rate of acceleration by reducing the total mass.