Chain Hoist Lift Time, Power, and Duty Cycle
How long a chain hoist takes to make its trim, how much power it draws doing it.
Example
You enter
- Lift height / trim (ft) 60
- Hoist speed (ft/min) 16
- Load per hoist (lb) 2000
- Duty-cycle fraction (0.40 = 40%) 0.4
- Rating period (min) 10
- Number of hoists 8
You get
- Lift time 3.75 min
- Hoisting (hp) 0.969697
- Allowed on-time per period 4.00 min
- Full lifts per period 1.07
No published worked example is on file for this calculation. It is checked against a hand-worked derivation of its method and an independent reference test.
Details, formula, and sources
ScopeHow long a chain hoist takes to make its trim, how much power it draws doing it, and how many times the rating allows that inside one period. The first line is the schedule, and it is the one nobody estimates correctly by eye: a hundred trusses that each take four minutes to fly is nearly seven hours of hoist time, and hoist speed varies by an order of magnitude across the hoists on a truck -- 16 ft/min for a standard motor, 32 or 64 for a high-speed one. The duty-cycle lines are the ones that surprise people. An electric chain hoist is rated for INTERMITTENT duty, and a common rating allows the motor to run 40% of a ten-minute period, four minutes on and six minutes off. Run it harder and the motor overheats, and the failure is not graceful. A one-ton hoist at 16 ft/min taking a 2,000 lb load up a 60 ft trim needs 60 / 16 = 3.75 min, draws 2,000 x 16 / 33,000 = 0.97 hoisting horsepower, and against a 40% duty over ten minutes has 4.0 minutes of allowed on-time -- 1.07 lifts per period, one lift and no margin. A show that needs the same rig in and out twice in a ten-minute window is asking the motor for more than its rating, and the answer is a faster hoist or a shorter trim, not a longer button press. Note that the hoisting horsepower is under one: chain hoist motors are small, and the number that sizes the distro is the INRUSH, not this steady figure. A planning screen; the hoist manufacturer's duty rating and load chart, ANSI E1.6, and the venue's qualified rigger govern.
Formula or tablelift_time_min = lift_height_ft / hoist_speed_fpm; hoisting_hp = load_lb x hoist_speed_fpm / 33000; allowed_on_time_min = duty_cycle x rating_period_min; lifts_per_period = allowed_on_time_min / lift_time_min.
Source and editionLift time from height and rated speed, hoisting horsepower from load x speed / 33,000, and intermittent-duty on-time from the motor's rated duty cycle over its rating period, by name; duty ratings and load charts are the hoist manufacturer's, and ANSI E1.6 entertainment hoist standards and the venue's qualified rigger govern. The distro is sized on inrush, not on this steady figure.
Free accessThe relations are public mechanics (33,000 ft-lb per minute per horsepower). The hoist speed, duty cycle, and rating period are read off the equipment the user has.
What governsEstimate. AHJ and licensed professional govern.
API field nameslift_height_ft, hoist_speed_fpm, load_lb, duty_cycle, rating_period_min, hoists, lift_time_min, hoisting_hp, allowed_on_time_min, lifts_per_period
- Horsepower 33,000 ft-lb per minute per horsepower; hoisting hp = load x speed / 33,000public mechanics
- Intermittent duty a common entertainment hoist rating is 40% over a 10-minute period; exceeding it overheats the motorhoist manufacturer duty ratings
- Distro sizing the feeder is sized on motor INRUSH, not on the steady hoisting horsepowerentertainment power practice