CORRECTLY SPECIFYING A CRANE:
The three most important factors that need to be known.
1. How much weight will be lifted?
2. How far out from the center of rotation is the load?
3. How often will the lift be made?
advertised maximum capacity is a statement of the maximum lift capacity of the
crane. Liftmoore does not recommend purchasing a crane for use at its maximum
lifting weight. A cranes capacity at a particular load radius is determined by
it's Moment Rating. Understanding this is essential to getting you the crane you
Rating is a mathematical equation determined by the WEIGHT times the LOAD
LOAD RADIUS: This is a
measurement from the center of the crane's rotation axis to the center of
the load on a horizontal plane.
WEIGHT: The amount of
weight to be lifted, includes all rigging used, including the travel block any
chains or slings and the hook.
Example of Moment Rating calculations:
A crane with a max lift capacity of 10,000 Lbs. with a 72,000 Ft. Lb. Moment
72,000 Ft.- Lbs. divided by 10,000
Lbs. equals 7.2 Ft. this is the Maximum load radius with this load.
At a 12 Ft. radius the maximum
load is 72,000 divided by 12 ft. equals 6,000 Lbs.
At a 20 Ft. radius the maximum load is 72,000 divided by
20 ft. equals 3,600 Lbs.
Note: the rapid
decline in capacity as the radius increases.
Always consider the size of the
object and that the crane is mounted on a truck. The distance to the edge of the
truck must be included in the load radius.
The above holds true no
matter the Manufacturer.
A cranes lifting capacity is based on it's
ROTATION: Many crane manufacturers claim to have 360 degree rotation, however, the rotation
may be limited at 375 or 400 degrees at which point the rotation will stop and
must be reversed. This limitation must be considered when positioning the truck
to perform the work at hand. Liftmoore cranes typically have unlimited rotation. There
is either an electric or electric/hydraulic swivel that allows this important
feature. As a result there is no limitation by mechanical or electrical stop on
the crane's rotation.
12V DC powered electric cranes have a limited duty
cycle as per S.A.E. J706 (section 6.2). These limitations are incurred because of Heat build
up in the Motors and the declining charge of the batteries. Exceeding the duty cycle constraints and over heating the
motor is the #1 cause of DC Motor failure. For longer duty cycles a Hydraulic
powered crane is required.
All 12V DC
powered cranes will benefit by having a battery as large as possible near the
crane. Motor and Solenoid life will be extended if an additional battery is
mounted near the crane. The two batteries under the hood of a diesel engine
truck are NOT adequate to power an electric crane. The DC voltage line loss
increases dramatically as the length of wire is increased and the voltage at the
crane can only be maintained with an additional battery near the crane. An
Auxiliary battery is required for cranes 3200 lbs and larger.
Turing off power to the crane will increase the life of it's
electrical components. Electrolysis causes corrosion which will reduce component
life and can cause intermittent electrical problems. All Liftmoore cranes are
supplied with a master disconnect switch or a Mecon quick disconnect for
disconnecting the crane from its electrical power source. A toggle switch is
provided to turn off the power on hydraulic cranes.