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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

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.

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.

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

I have to say some thing here. Although I believe I know what jgalt is trying to say, I belive he said it wrong.

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

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.

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.

So jgalt, you went from a 6 gauge to 0 and cranking really improved?

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.

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.

Lots of good info about wire here.

The way I test battery cables is to measure the voltage drop across the cable.

Put the plus lead on the positve terminal of the battery and the minus lead on the power stud on the starter. Assuming a fully charged battery, when the motor is cranking the meter should read at least 9 volts if everything is happy.

If its lower you need to check pieces of the circuit to find the problem. Think of the electrical circuit as a loop made up of connections to each part of the circuit and going from the positive post on the battery to the negative post.

Keeping the plus lead closest to the postive post on the battery check the voltage drop across each connection. Start with the plus lead on the battery post itself, and the negative lead on the connected connected to the plus terminal at the battery.

With the meter connected check the voltage drop. Its been years since I read what values you are looking for, but my rule of thumb for the starter circuit is that any drop of 1-volt or more is probably an issue.

If the voltage drop is between the battery and the connecter on the cable, you may be able to clean things and make it work better. If the voltage drop is in the cable itself, either the cable is too small, or its too corroded to work.

I generally start by measuring across several things to narrow down where the problem is, and then measure each piece within a segment to identify the specific issue.