Why ground to the battery? (1 Viewer)

[Blade 80LC]

What is the advantage to running the ground back to the battery? Some older winches just ground through the mounting bolts to the frame. Is there a particularly good reason they stopped? You know. Assuming that at the battery side of things, you have a really good heavy gauge ground to the frame.

Particularly for a rear mounted winch. Heavy gauge wire is pricey.

 

[e9999]

well, for one thing you'd have a high current going through the frame which could possibly do weird things and more connections in between that can go wrong.

 

[canman]

Good question. I think part of if it had to with voltage drop. For large current draw, it is important to reduce voltage drop as much as possible, because DC motors compensate just by drawing more current = downward spiral. Also, that current has to get back to the batter somehow, and if the negative cable back to the battery is of insufficient size, your back to first scenario = possible fire.

 

[shelfboy1]

on all my vehicles with rear mounted winches under a heavy load the engine would stall and sometimes the ground would do wierd things like go to ground through the plow controls .since i have used the extra wire no problems .i got used welding cable at an auction for mine

 

[george_tlc]

V = IR (where in this case V is the voltage drop due to the resistance of all the wires/connections and I is the winch current draw)

cheers,
george.

 

[Blade 80LC]

V = IR (where in this case V is the voltage drop due to the resistance of all the wires/connections and I is the winch current draw)

cheers,
george.

I think some units on that formula would help. If the winch is pulling 200 amps, and resistance through the frame is half an ohm, would the voltage drop be 100?

 

[george_tlc]

Yep... 1/2 ohm would mean at 24A you would drop 12V

Your wiring better have a LOT less resistance than 1/2 ohm for powering the winch.

So, the summary is that with ONLY 12V (ok, let's be generous and say 14.4V with alternator running) any resistance (chassis, washers, bolts, nuts, rust) will have a major impact to voltage drop when we're talking 100's of amps. So, big gauge wires and as short a path as possible between the battery and the winch.

cheers,
george.

 

[Blade 80LC]

Yep... 1/2 ohm would mean at 24A you would drop 12V

Your wiring better have a LOT less resistance than 1/2 ohm for powering the winch.

So, the summary is that with ONLY 12V (ok, let's be generous and say 14.4V with alternator running) any resistance (chassis, washers, bolts, nuts, rust) will have a major impact to voltage drop when we're talking 100's of amps. So, big gauge wires and as short a path as possible between the battery and the winch.

cheers,
george.

Then V=IR may very well be the answer to my question, why not just improve my ground cable from battery to the frame! I haven't compared the resistance in my frame to a run of copper wire. I would not be surprised to see it was a fraction of an ohm greater than zero. I don't do much electrical work. On a Harbor Freight multimeter, I've generally considered 0.1 ohm and 0.0 ohm to be the same number. For a high current load, that may not be acceptable.

 

[george_tlc]

HF meters are junk for low resistance measurements (and many other measurements). 2 wire measurements are hopeless for low resistance measurements. For practical purposes your typical meter is not suited for low resistance measurements. See a trend here?

Even 0.1 ohms at 100A is a 10V drop.

The issue with chassis grounding is the quality of the connection. Consider the chassis is painted. Bolt holes have dirt/rust/grime. Steel/iron is a poor conductor of electricity compared to copper. Of course you have (depending on where) more thickness of steel/iron. Without taking into account all the variables you really have no idea what the resistance will be. Cable on the other hand is predictable, you know the gauge and therefore you can look up a table of gauge/length versus resistance. With cable you have one lug at the battery and one lug at the winch and nothing but copper cable between.

Just one example you can search the web for -> http://www.powerstream.com/Wire_Size.htm

Anyhow, unless there's a really good reason, I would suggest you run a dedicated ground wire from your winch to your battery. 2/0 gauge is not a bad idea. Remember your winch can get up into the 400A range when close to a stall when pulling your butt heavy 80 out of a serious stuck...

cheers,
george.

 

[shelfboy1]

why worry about it just do it the way you want and let us know how it works for you might save some folks some money if they dont have to run the extra wire.