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Using the frame for part of the ground circuit for rear winch?

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knaffie

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Discussion starter · #1 ·
Putting in my rear winch soon and trying to save a few dollars of $$$ wiring. If I run the wire direct from battery to winch, I'm going to need something like 15' of wire just for the ground.

I'm thinking if I ground my battery to the frame with a short cable, then ground the winch to the frame with another short cable, the frame should be sufficient to carry that current from the front to the rear of the vehicle. I don't see any reason why the current would want to creep up through a factory ground strap or anything, as the resistance would be significantly more than up the 0 gauge wire.

Thoughts?
 
#3 ·
I've never seen anyone go back to the battery for the ground. As long as the battery is grounded to the frame you're good. For the winch "hot" are you coming to the starter or the alternator with a big hot from the battery? Why not take your HOT from there? Copper wire in big sizes is expensive, but its also heavy, so you can save some weight.
 
#4 ·
#5 ·
Last time I wired up my winch, I used a set of good jumper cables that the clamps were ruined. I went straight to the battery with both pos and neg. On those batteries that have side post and top post (like mine) you should not use the side post terminals for the winch hookup- they can't take the amperage draw. They're rated lower than the top posts. As far as the frame mounting- X2 on the serrated washers for biting into the frame.
 
#10 ·
doublej said:
suppose to go to the battery with both cables.
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This is not the case as long as your battery to chassis ground is good and the winch to chassis ground is good the frame is one HUGE ground plane, which is better than the resistance you pick up with the distance of your cables from the back of the vehicle to the battery.

My vehicle is wired with both batteries under the seats and the winch up front.
I ran 1/0 from each battery to the frame and a 2/0 to the winch for the positive cable. I ran a 1/0 from the winch to frame 6" from the winch. I have no voltage drop at the winch.
 
#12 ·
The problem with going to the frame is it's hard to check for corrosion at times. People tend to attach the wire in an spot that is out of the way which means it can be hard to see.

I like to get the amp calculator out and get the correct size wire (or at least not undersized) for the distance I need it and not worry about it. It's a few dollars more in wire, but when you have ~300 in batteries and 1-2000 in a winch it's cheap considering.
 
#13 ·
mj said:
weld a stainless bolt to the frame for the ground points
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That's what I did for all my grounds. Major ones are a 1/2" stainless bolt welded to the frame/cage threads out with a stainless nylock holding everything down. Batteries in the back, boat-switch on the trans tunnel, and a winch up front.

Just make sure you use big ass cables, unless you're running a tiny winch, voltage drop will be an issue. Mine is all 0000/4 welding cable, got it for free too
 
#15 ·
using a nylock is not a great idea. the nut could get hot, causing the plastic to melt out= loose connection.

happens on some of the newer cars i see (BMW), that should have a shouldered nut there instead. just saying what i see sometimes in that situation.
 
#16 ·
BigWoodyWag said:
I've never seen anyone go back to the battery for the ground. As long as the battery is grounded to the frame you're good. For the winch "hot" are you coming to the starter or the alternator with a big hot from the battery? Why not take your HOT from there? Copper wire in big sizes is expensive, but its also heavy, so you can save some weight.
Click to expand...
My battery is in the back and I have 2/0 cable going from the battery, through a Moroso battery switch on the dash, to the starter. You're saying I can run my front Warn 9000 from the starter? Will that melt my switch or starter soleniod?
 
#17 ·
chris demartini said:
My battery is in the back and I have 2/0 cable going from the battery, through a Moroso battery switch on the dash, to the starter. You're saying I can run my front Warn 9000 from the starter? Will that melt my switch or starter soleniod?
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A lot of starters get their power from a 4GA cable, at most a 2GA cable. So no, I wouldn't be dong that. The power cables for electric winches are already undersized for the job.

It's just opinion, but personally, I'll always run the copper cables straight back to the battery. Why? copper is many times more conductive than steel.

I would bet that if you sat down and did the resistivity math calculating for a voltage drop at 450A over the distance of your frame at steel's resistivity level you would find your car frame (assume 4x2x.125) isn't quite as adequate as you think it is with about 1.5 square inches of material. (4x.125x2+2x.125x2=1.5) This is also assuming the frame has no holes in it, which is a bad assumption.

You're typical buggy with 1.75x.120 tube would fare even worse at .4 square inches.(area of 1.75-area of 1.63 = .4) Of course, on a tube buggy the current will find more than one tube to go through so the math isn't that simple.

But the point is, once you account for the different resistivity levels of steel vs. copper, that frame connection for a ground to support a 450A potential load isn't as big as it looks.

Any electrical engineers here care to back me up or prove me wrong?
 
#18 · (Edited)
According to this chart: http://www.eddy-current.com/condres.htm

Annealed copper has roughly 30 times the electrical conductivity of high alloy steel.
Or conversely, steel has about 30 times more resistance than copper.


In high current/low voltage situations like winching, even very small resistances result in major power loss. Power dissipated in a resistance is equal to the current squared times the resistance (I^2 x R). As current goes up, power loss goes up exponentially.
For example, a VERY tiny resistance like .01 ohms with a mediocre 200 amps winch pull running through it wastes 400 watts and would create a 2 volt drop that would never make it to your winch. 300 amps would be 900 watts and 3 volts. 400a would be 1600w and 4 volts drop, etc. And that's just for a 1/100th ohm of resistance!

I^2 x R losses are why power companies transmit power across transmission lines at VERY high voltages and very low current, and it isn't changed over to safer and more useful low voltage/higher current until it gets fairly close to your house.

Yes, your frame works as a conductor. NO, its not the best way to do it for high current loads like a winch!
 
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#19 ·
I ran 2/0 for my front and rear winch + and - and I believe I paid ~4/ft that was when it was more $$ too, I think it's around $3.5ft now.

A highly flexible neoprene jacket surrounds fully annealed rope-stranded bare copper.

Used as a battery cable alternative because of its flexibility.

Heavy-duty welding cable is resistant to flame, oil, abrasions, tar and grease.

Temperature range is -50ºC to 105ºC.

Rated at 600 volts with a paper separator.

Meets or exceeds ASTMB-172 specifications and conforms to ICEA/NEMA welding cable requirements.
Click to expand...
It was very flexible, and I have enough scrap leftover to do more with too :D I used the same wire as the power lead to my alt fuse/block too, so I have a good amount of power available for lights, etc. My battery is mounted behind the rear seats, under the floor out of the way.

If everything was grounded to the frame should you worry when welding on your rig :confused:
 
#20 ·
Depends on how paranoid you are.

I weld on my jeep without even disconnecting the battery, but I keep the ground clamp close to where I am working. Ideally? Disconnect the battery and computer to be safe.

I run welding cable for all high current leads on our Jeeps as well. I also solder the joints and doublewall heat shrink them.
 
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