Winch Power Draw Calculator for Campers

This calculates voltage drop, battery drain and amp draw of your winch configuration. It turns a potentially stressful recovery situation into a set of numbers. Simply plug in your cable spec, winch model and estimated load, and let the calculator do the work. Now you know what your electricals is capable of during a time of need.

One additional overlooked variable in any recovery is the rope layer on the drum. As the drum becomes near empty, the winch will pull slower, not simply because the speed decreases but also because it’s a leverage issue. The effective radius of the drum change as the rope spools up onto higher layers. This results in a different gear ratio which means the motor must spin faster at the same line pull. Thus the current draw increase dramatically for the same hook load. This geometry is one reason why the calculator factors in the layer derating. It reveals how much more the system is stressed when pulling from the top of drum. This has important electrical effects that cannot be ignored.

Know Your Winch Limits

Though batteries seem like unlimited sources of energy, they’re not. They have limits, especially on chemistry. When your winch pulls three hundred amps from a standard starting battery, it use up what’s left in just a few seconds. At this point, an alternator can’t rescue you. Alternators typically supply about fifty or one-hundred amps to help recharge your battery. That’s hardly enough for a major tug. Your battery can only do so much; it has to replenish itself before attempting another large pull.

When the calculator show a large percent of your amp-hours being burned during use, you should stop. Allow battery to refill before proceeding. If you don’t let the battery recover, you risk a dead battery at the worst possible moment.

The other key element here is cable voltage drop. Thicker gauge cable cost more money and is harder to run, so many folks just get minimum recommendation for their setup. Keep in mind length plays a role in this equation. Two-gauge cable used on a 6′ run is not going to behave like that same 2 gauge on a 10′ run. Voltage gets consumed along the way as it faces resistance which will be cumulative by the time it hits the motor. Lower voltage mean the motor has to pull more amps to create the same amount of torque. It becomes a feedback loop of poor performance and heat. Your amp draws will increase. No matter what battery you have, there is no way to fix that kind of inefficiency if you are experiencing too much voltage drop. The chart below show how various sizes perform at varying loads.

For trail use, maybe the most applicable output from the calculator is duty cycle. Winches aren’t meant to be run continuously; they’re made for brief spurts. Burning out motor windings by pushing a hot winch harder trying to save a few seconds wont get you anywhere. Depending on thermal load and how long you pulled, it will tell you when it’s time to cool down. That’s based off the physics of cooling down. If you don’t heed this recommendation, you risk melting solenoids or burning out motor windings.

There’s no single “winch”, it’s really an electrical chain that has bottlenecks all along the way. That’s where this tool comes into play; which link is your weak point? The weak points are load, heat, and voltage. What do those numbers mean? Why don’t you know yet? Why are you still guessing? When you do, you can pull confidently and be sure knowing why.

Know before you engage. You should of known before a dead battery on a line at the worst time. Do the math.