Winch for a Land Rover

The winch should be rated in horsepower. You can convert horsepower to Watts by multiplying by 746 Watts per hp. (Electrical) power equals Volts times Amps,

P = V x I

and your Volts are twelve, so you can solve for Amps. Given the number of Amps drawn from the battery, you can decide how much voltage drop you want along the twelve foot cable between the battery and winch. The lower the voltage drop, the more torque you can get from the winch. You can use

V = I x R

to get the wire resistance necessary to achieve the desired voltage drop. In the equation, "V" is not twelve Volts, but the drop along the cable due to the current flowing through the cable resistance. So "V" might be 1 Volt, or maybe half a Volt. Once you have determined "R" from the calculated current and the desired voltage drop, you can divide it by twelve feet to get the ohms per foot, and then look up the gauge that gives you that value from:

http://www.tfcbooks.com/referenc/wiresize.htm

Hint: The table gives ohms per thousand feet, which is dimensionally the same as milliohms per foot. Your calculation will be in milliohms per foot, so just look for the number closest to what you calculated.

Example: Assume a 1 hp winch. That is 746 Watts. At 12 Volts, the winch will draw 62 Amps. You decide you want no more than one Volt drop along the cable. From

V = I x R,

you get

R = V/I = 1 Volt/62 Amps = 0.016 Ohm - 16 milliohms.

You need twelve feet of cable to give you 16 milliohms, so the resistance per foot is 1.33 milliohms per foot, which is the same as 1.33 Ohms per thousand feet. Per the url table, that is AWG 11 wire, much less than welding cable. Of course, if the winch is significantly higher power than my assumption, your numbers will come out differently. Also, and this is very important, you also get voltage drop in the return path, from the winch back to the battery. If you have solid structural vehicle metal as the ground between the winch and the battery, you can pretty much ignore the drop in the return leg, because you have all that metal. But if you need a wire return, you will have doubled the length of the wiring and hence the drop. If you have a wire return, you need half the resistance in each wire that you calculated for the single run of twelve feet. That takes you down three wire gauge sizes. In the case of the above example, you go from AWG 11 to AWG 8.

Hope that nails it for you. If you are unsure of any part, message back - this is easy, even if it doesn't look so at first glance.

Welcome.

If you already have heavy welding cable, and can terminate it properly for the respective lug sizes, then it will be fine. Websites sell winch hook-up cable sets, too.

My winch mounts in the hitch receiver, so I have plugs to allow it's removal. The wiring harness came in a kit.

BE SAFE!

Yes, use heavy duty welding cable that can take 300 amps starting current

I stand by my calculations and believe the idea of needing to size wire for 300 Amps starting current is fallacious. Not saying the numbers I came up with are precisely correct; just the methodology.

There are two reasons you don't need to size wire for a 300 Amp startup current.

1) The battery can't supply it. If you could draw 300 Amps from a lead acid battery through twelve feet of cable, with a 1 Volt drop, that would mean the total source resistance at the end of the cable was 3.3 milliohms. That is lower than the internal resistance of a lead acid battery alone.

2) The winch is geared with a huge step-down ratio. That is, for one revolution of the winch electric motor shaft, the winch barely turns the shaft on which the cable is coiled. That is how you get the huge mechanical advantage that allows a winch to pull a stalled vehicle out of a hole. It exerts huge force, at very low velocity.

EMC C has it correct and the only one to look further into your system. Your battery will not supply the power you require. The only reasonable thing you must do is this.

1. Upgrade your Alternator to a 125 AMP unit

2. Install a parallel battery system (Two Batteries) Both of which should be deep cell

The reason for this is: By the time you have used your winch, You may as well go ahead and pitch your tint, because your going no where.

thats very good now i already have a 100 amp alternator on it with a deep cell battery i always have the engine going when winching the winch is 12 thousand pounds pull 4 and a half h p motor i would of thought welding cable would of been well suited andno worries about things getting hot because of the lenth of cable the cable is 12 ml light strands together you dont get a voltage drop just to be safe what do you think well thanks very much

Hi Andrew,

4.5HP = 3.4kW = 280Amps from a nominal 12V battery (assumes you don't have an ex military24V model). That's a heck of a winch for a landy.

Use wire for both pos & Neg as your body is aluminium. If you can find it, look for the max acceptable voltage drop. Typically they are rated at 10V. So you can probably allow 1Volt drop over your cables so 50mm (1# AWG) cable will suffice. You might get away with 35mm (2 AWG) cable as I doubt you will use the full 5.5tons of pull. Your landy weighs in at 3.5tons (110 model) Without an anchor that pull will drag your landy along with wheels locked!

Make sure you use a fuse close to the battery (300A or winch makers reccomended capacity) and preferably an isolator switch, otherwise a simple rear-end shunt could cause a nasty fire or even an explosion.

Use the same thickness cable that is on the battery clamps, Done. We winch a Rubber Inflatable with 12 Scuba sets on board (about 2.5 metric ton). Also Start the landy when winching to compensate.

MY FRIEND INSTALLED A COMPONENT THAT USES A MODULE THAT U USE A EXTRA BATTERY WITH THIS MODULE THAT USED SEPERATE TO HANDLE THE WINCH.THE SUPPLIER IS IN THE U.S.A

I had a '69 MG once. The battery was in the trunk of the car (original location for battery was rusted out). I used standard battery cable wire from the trunk to the engine ((Nissan 4-cyl) (I also built a manifold and mounted a 1-barrel Ford carburetor off a straight 6-cyl to the Nissan)). I never had a problem starting the car. I also had a winch mounted to a boat trailer for pulling my boat out of the water. I used a standard #14 house wire for this with pinch clamps on the ends. I would open the hood of my truck and clamp the wire onto the battery terminals, pull the boat onto the trailer, un clamp and close the hood. Never had a problem here either.

Dear Land Rover Owner: My answer (not technically proven, but practically experienced)

If your have the Welding Cable Use it! ! ! My situation to back up my statement. I was covering a Micro Wave Site Trouble Call, where I had a 6 cylinder Diesel Generator with a 24 vdc starter inside, Failed due to a faulty Charger that Had destroyed the Battery. Outside about 100 ft from the Unit inside, I had a 28 vdc Battery (to heavy to carry that far), I took a coil of welding cable, connected the Battery to the unit outside to the Starter Inside, and it started the Inside Unit fine on three test starts. Good thing The Local Rural Power Feed failed, Making the make shift hook up, the Only Choice to Carry the Whole Site, for long enough to get a new standby battery delivered 75 miles, and installed, before dismantling the Welding Cable hook up. Cost did not enter this Picture, where it may in your case. Sr.Retired Troubleshooter.