Swamp Yankee
Addicted to ArboristSite
OK, as promised here's some basic info on winches. Let's just say this is chapter one. Depending upon response, questions, and how onery I am after writing this more may follow.
Please before you beat me senseless read the following:
The information given here applies only to electric 12 and 24 volt winches built for consumer, off road & light duty use. Winches electric and hydraulic built for commercial applications fall under different guidelines that may be addressed in a different thread. (See previous paragraph)
How is a winch rated? I'll bet I could ask 20 different people and get 20 different answers.
It all starts with the drum and wire rope, not the motor or gearbox. Get into that later. The output of the gearbox is torque and is a fixed maximum value measured in lb-inches. (Load in lbs multiplied by the radius at which the load is applied) In essence its the same principle as a lever and fulcrum just applied radially.
Let's say the output torque to the drum, regardless of the motor hp, and gearbox ratio and efficiency, and bearing losses is 2000 lb-inches. If the drum diameter is 1-1/2 inches and the wire rope diameter is 3/16 inches, the effective radius of the load is (1-1/2 + 3/16) / 2 or 27/32 (.843 inches). It is assumed the load is applied at the center of the wire rope. Dividing 2000 lb inches by .843 inches says in theory the winch should pull a load of 2372 lbs on the first layer aka bare drum. If the same wire rope was put on a 2-1/2 inch dia drum and we do the math the same gearbox output will only allow a load of 1488 lbs. We'll use this information later if you haven't hit the back button yet. (By the way this rule applies to all winches commercial and consumer.)
Winch line pull is rated on the bare drum or first layer. So if a winch is rated at 2000 lbs that's what it will pull on the first layer. As layers increase or the cable builds up on one side of the drum the line pull drops. (It's our old friend the radius coming back to haunt.) There are specific formulas for calculating line pull loss as the layers increase but let's just say a line pull loss of 10 percent per layer is a good rule of thumb.
Ok enough with the theory lets talk specifics. The rated line pull of a winch used to be defined as, the weight the winch could dead lift for 1 foot with a constant 12 volt, (24 Volt in some systems), on the first layer with 5 wraps of wire rope on the drum. Five wraps were used as the wire rope anchor on all these winches is not intended to or required to hold the rated load.
There's a couple of flaws in this application. First in a mobile application, depending upon the battery, connections, lead wires, and system temperature you'll never maintain a 12 volt input. Second during this test the manufacturer may use equipment other than that supplied as standard to the consumer to test. (oh and they won't tell you) Things like 2 gauge wire instead of 10, solenoids with gold contacts, ambient temp of 30 degrees etc are often implemented. This doesn't apply to any one manufacturer they all have their own test set-ups. I would love to get my hands on some of the Chinese stuff and run a few experiments.
All this means is once installed a winch sold with a 3000 lb line pull probably will never get there. Oh it may show a load of 3000 lbs on a load cell put it isn't going to get a ton and a half off the ground.
Ok so we now know the load capacity of a winch is not exactly what it says it may be. A lot of people believe the winch rating is the load the winch will pull for it's entire wire rope length. Nope not true. Another rule of thumb, take the winch rating divide it by 5 and that's probably about the load it will pull for the full length of the wire rope. If you have a winch rated at 8000 lbs with 100 feet of wire rope, it will probably pull 1600 lbs the full length. The biggest thing you buy when you spend the money for a winch with a larger line pull rating is on time.
Consumer winches are not required to meet any standards for strength, though they do exist. Keep this in mind when thinking about a winch and what you'll be using it for. Winches are designed and intended for pulling not lifting. Never use a winch for lifting unless the manufacturer specifically rates it for crane or hoisting applications.
Ok, I'm shot. If there is any additional interest I'd be willing to give some info on winch features, gearboxes, motors, brakes, mounting etc. None of which will make much sense until the winch rating concept is grasped. Give me your feedback, send PM's, or just tell me I'm full of it and go dry up.
Take Care
Please before you beat me senseless read the following:
The information given here applies only to electric 12 and 24 volt winches built for consumer, off road & light duty use. Winches electric and hydraulic built for commercial applications fall under different guidelines that may be addressed in a different thread. (See previous paragraph)
How is a winch rated? I'll bet I could ask 20 different people and get 20 different answers.
It all starts with the drum and wire rope, not the motor or gearbox. Get into that later. The output of the gearbox is torque and is a fixed maximum value measured in lb-inches. (Load in lbs multiplied by the radius at which the load is applied) In essence its the same principle as a lever and fulcrum just applied radially.
Let's say the output torque to the drum, regardless of the motor hp, and gearbox ratio and efficiency, and bearing losses is 2000 lb-inches. If the drum diameter is 1-1/2 inches and the wire rope diameter is 3/16 inches, the effective radius of the load is (1-1/2 + 3/16) / 2 or 27/32 (.843 inches). It is assumed the load is applied at the center of the wire rope. Dividing 2000 lb inches by .843 inches says in theory the winch should pull a load of 2372 lbs on the first layer aka bare drum. If the same wire rope was put on a 2-1/2 inch dia drum and we do the math the same gearbox output will only allow a load of 1488 lbs. We'll use this information later if you haven't hit the back button yet. (By the way this rule applies to all winches commercial and consumer.)
Winch line pull is rated on the bare drum or first layer. So if a winch is rated at 2000 lbs that's what it will pull on the first layer. As layers increase or the cable builds up on one side of the drum the line pull drops. (It's our old friend the radius coming back to haunt.) There are specific formulas for calculating line pull loss as the layers increase but let's just say a line pull loss of 10 percent per layer is a good rule of thumb.
Ok enough with the theory lets talk specifics. The rated line pull of a winch used to be defined as, the weight the winch could dead lift for 1 foot with a constant 12 volt, (24 Volt in some systems), on the first layer with 5 wraps of wire rope on the drum. Five wraps were used as the wire rope anchor on all these winches is not intended to or required to hold the rated load.
There's a couple of flaws in this application. First in a mobile application, depending upon the battery, connections, lead wires, and system temperature you'll never maintain a 12 volt input. Second during this test the manufacturer may use equipment other than that supplied as standard to the consumer to test. (oh and they won't tell you) Things like 2 gauge wire instead of 10, solenoids with gold contacts, ambient temp of 30 degrees etc are often implemented. This doesn't apply to any one manufacturer they all have their own test set-ups. I would love to get my hands on some of the Chinese stuff and run a few experiments.
All this means is once installed a winch sold with a 3000 lb line pull probably will never get there. Oh it may show a load of 3000 lbs on a load cell put it isn't going to get a ton and a half off the ground.
Ok so we now know the load capacity of a winch is not exactly what it says it may be. A lot of people believe the winch rating is the load the winch will pull for it's entire wire rope length. Nope not true. Another rule of thumb, take the winch rating divide it by 5 and that's probably about the load it will pull for the full length of the wire rope. If you have a winch rated at 8000 lbs with 100 feet of wire rope, it will probably pull 1600 lbs the full length. The biggest thing you buy when you spend the money for a winch with a larger line pull rating is on time.
Consumer winches are not required to meet any standards for strength, though they do exist. Keep this in mind when thinking about a winch and what you'll be using it for. Winches are designed and intended for pulling not lifting. Never use a winch for lifting unless the manufacturer specifically rates it for crane or hoisting applications.
Ok, I'm shot. If there is any additional interest I'd be willing to give some info on winch features, gearboxes, motors, brakes, mounting etc. None of which will make much sense until the winch rating concept is grasped. Give me your feedback, send PM's, or just tell me I'm full of it and go dry up.
Take Care
That little winch got me out of many of jams and raised and lowered my snow plow too many times to count.
