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Battery cable resistance
#91819 Wed Jan 19 2005 03:34 AM
Joined: Mar 2004
Posts: 745
M
mugsy Offline OP
Shop Shark
Anyone ever experienced voltage drop/resistance in battery cables from either being old or too thin a gauge or both? If so, what happened? How did you discover?
-David
Kustoms-and-Sleds


Tradin' up dimes for nickels...
'`'`'`'`'`'`
My \'65 Chevy C-20
Re: Battery cable resistance
#91820 Wed Jan 19 2005 08:42 PM
Joined: Oct 2001
Posts: 3,459
Extreme Gabster
I had the starter end of a 12V cable wear out and corrode on my Jeep. The cranking got slower and then intermittant. I found it when I saw it glowing one night after I started the Jeep. That was dangerous so I replaced the cable.

Too-small cables will get warm and slow down cranking speed fairly significantly. I like to use at least #2 cables for 12V and 2/0 or 4/0 cables for 6 volt, especially when the battery is mounted in the floor or trunk.

I am running 2/0 cables on my truck with 12V because I converted from 6 after I changed the cables, and the cranking speed is great. Of course, I am running a 6V starter, too, but the lights hardly dim when I am cranking.


Paint & Body Shop moderator
A lone amateur built the Ark. A large group of professionals built the Titanic.
Re: Battery cable resistance
#91821 Thu Jan 20 2005 03:19 AM
Joined: Oct 2003
Posts: 124
J
Member
The thinner the wire diameter, the higher the resistance - so you have a greater voltage drop.

The age of the wire is not really significant unless you have cracked insulation - the connectors are the places where you'll develop problems over time.

Going with the biggest guage wire possible, and keeping your cable clamps and connections clean is the right approach.

Re: Battery cable resistance
#91822 Thu Jan 20 2005 07:27 AM
Joined: Mar 2004
Posts: 745
M
mugsy Offline OP
Shop Shark
Yeah, that's pretty much what I'm thinkin'. Someone suggested to me that perhaps my cables were too thin and have too much resistance. Might be causing my hard start problem which I've still done nothing about.
I think my cables are about a 6 and my connections look clean. I'm not really buying the theory as slow cranking would be characteristic with voltage drop. She seems to crank fine, just randomly won't fire up.
Well, anyways, just wanted to run this by y'all.
-David


Tradin' up dimes for nickels...
'`'`'`'`'`'`
My \'65 Chevy C-20
Re: Battery cable resistance
#91823 Thu Jan 20 2005 03:42 PM
Joined: Feb 2000
Posts: 900
B
Shop Shark
I have to say some thing here. Although I believe I know what jgalt is trying to say, I belive he said it wrong.

Quote
Originally posted by jgalt_54-235:
The thinner the wire diameter, the higher the resistance - so you have a greater voltage drop.

Going with the biggest guage wire possible, and keeping your cable clamps and connections clean is the right approach.
The smaller the GAUGE of Wire the higher the resistance. You typically want the smaller wire strands within the larger gauge of wire. For example look at welding cable. Large gauge made up of many small wires.

Electricity flows on the outside of wire, not through it. Corrosion is one of the biggest problems. Corrosion on wires is like kinking a garden hose. It won't let the electricity flow.

Buy the largest gauge cables that you can. Then check the connections at each end. If you can flex the cable and see the bare strands of wire I would recommend sealing the Terminal end to the insulation with some shrink tubing.

Good luck


Brian Moore
1949 3100 5 window Deluxe
"Today is better than yesterday, but not as good as tomorrow"
Re: Battery cable resistance
#91824 Thu Jan 20 2005 10:59 PM
Joined: Oct 2001
Posts: 3,459
Extreme Gabster
Quote
Originally posted by Brian Moore:
I have to say some thing here. Although I believe I know what jgalt is trying to say, I belive he said it wrong.

[QUOTE]Originally posted by jgalt_54-235:
[qb]

Electricity flows on the outside of wire, not through it. Corrosion is one of the biggest problems. Corrosion on wires is like kinking a garden hose. It won't let the electricity flow.

Good luck
That's not quite correct. That is only true in AC current flow. It's called Skin Effect. In the DC case, the current uses the whole wire. Skin effect is still present in multi-strand conductors and it behaves exactly the same as in a solid conductor, the inner part of the conductor carries less current. It is due to how the electromagnetic field behaves.

Corrosion on the surface of a wire has no effect on its resistance. However, corrosion on the wire between the connectors and the wire is a problem.

The reason welding cables are made up of many strands is for flexibility and longevity. You will notice the same thing with the differance between extension cords and in-wall NM type wire. The extension cords are many strands and the wall wire is one solid piece. It is really easy to bend and extension cord but NM wiring is pretty stiff and will break if you do it too much.


Paint & Body Shop moderator
A lone amateur built the Ark. A large group of professionals built the Titanic.
Re: Battery cable resistance
#91825 Fri Jan 21 2005 01:58 AM
Joined: Oct 2003
Posts: 124
J
Member
Sorry for the confusing terminology. I meant the overall diameter of the cable, not the individual strands. 'Wire Gauge' would certainly been more clear.

The difference in starting from a '0' or '00' AWG cable to a 6 AWG was a jaw-dropper for me. Especially noticable when starting with the motor hot.

A tractor supply business is a good place to find the cable and connectors.

Re: Battery cable resistance
#91826 Fri Jan 21 2005 03:15 AM
Joined: Mar 2004
Posts: 745
M
mugsy Offline OP
Shop Shark
So jgalt, you went from a 6 gauge to 0 and cranking really improved?


Tradin' up dimes for nickels...
'`'`'`'`'`'`
My \'65 Chevy C-20
Re: Battery cable resistance
#91827 Fri Jan 21 2005 01:32 PM
Joined: Jan 2000
Posts: 1,609
T
Extreme Gabster
Large gauge building wire in the 2-0 to 4-0 range is made of 19 strands of soild wire about 10 gauge each.It's not very flexibe and can put a strain on battery terminals if not bent just so.It will work, but fine strand welding cable is better.
2-0 19 strand building wire is rated at 300 amps,600 volts in free air at 90 degrees Centigrade.This is for continious duty on power distribution ,not for 10 seconds of cranking on a engine starter.For short lengths, the conductor can take probably 100 percent overload.But with only 6 volts when cranking,a 10 percent voltage loss is a big deal.
Pay attention to the terminations on the cable, a large conductor is useless if the cable ends can't take the current.

Re: Battery cable resistance
#91828 Sat Jan 22 2005 08:20 PM
Joined: Jan 2001
Posts: 198
A
Member
2/0 welding cable is great on 6v systems, its very fine strands and bends very very easy, soldering the ends on is best, use rosen core solder and coat the outside of the wire with rosen flux (do not use acid will eat the wire),clamp the end in a vise pocket up, and heat till the solder melts inside, then fill 2/3 of the way, then insert the wire into the pocket slowly allowing the solder to wick up the wire. When the wire bottoms out remove heat and let cool. cover the connector to the wire with head shrink tubing.

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