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Old 03-04-2014, 07:37 PM
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Battery cables

Hello All
Well I finished up the brakes and the fuel system today.So its on to the next phase.
I am installing the battery in the trunk ,due to lack of space under the hood. My question is ,Do I need to increase the wire gauge due to the long run from the truck up? I've read that some guys use welding cable. Is the fine wire in that better than the course wire in most real battery cables?
Thanks
Jeff

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Old 03-04-2014, 07:52 PM
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The use of welding cable goes back to when cars used six volt batteries and you needed a heavy cable to carry the current. If you are going a distance then go for the heaviest cable possible but a good connection is also very important.
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Old 03-04-2014, 08:23 PM
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X2. I like using a 1 or 2 gauge cable on a high compression small block and a 1 or 0 gauge cable on big blocks. Where weight is an issue you can go a size smaller cable with a quallity gear reduction starter. However if weight an money isn't an issue there it never hurts to go big.
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Old 03-05-2014, 12:21 PM
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A little electrical theory.
Lets start with the starter motor.
If you were to take a piece of wire the same length, and gauge as the wire in the windings of the starter motor, lay it in out in a big loop, without wrapping it up on pieces of iron, and hook that up to a battery, it would draw several hundreds amps, because it is basically a short circuit. But the wire is wound up in a motor.
Like most electric motors, the more voltage it gets, the faster it turns. Like all electric motors, the faster is turns, the less current it draws. This is because when an electric motor is turning, it is also generating a voltage opposing the voltage applied to it.
That is why the same length and gauge of wire in a starter is not a dead short, unless the engine is locked up.

Now, lets consider the cables. Every wire and cable has some resistance. Even battery cables. it is hard to accurately measur this resistance, because it is low, but it is there. The bigger the wire, the less resistance. The shorter the wire, the less resistance. Have you noticed that they put the battery under the hood, close to the starter motor? In most cases, they even put the battery on the same side of the engine that the starter motor is on. This is to keep the battery cables as short as possible.

One way to measure the resistance of a battery cable, or any other cable is to do a voltage drop test. Take a volt meter, put the positive lead on the positive battery post, and while the engine is cranking, put the negative lead of the volt meter on the battery cable connection on the starter. you should get a reading of less than .5 volts. Lets say it is .5 volts, that is an adequate measurement. (lower is better) Lets say for arguments sake the starter draws 200 amps when cranking. A little math tell me we are losing 100 watts in just the positive battery cable.
Now, lets put bigger cables between the starter, and battery. Lets measure the voltage drop again, and we get .2 volts. A little math again, and we are losing only 40 watts in the positive battery cable. A lot better.
But with the bigger cable, the starter turns faster, and draws less current, and the drop in voltage of the cable is even less. Less current, the voltage at the battery stays a little higher. Less current, the starter does not get as hot. A faster spinning starter, and the engine tends to start sooner.
And here is another benefit. If you have higher battery voltage when cranking, the ignition system also gets the higher voltage, and that also makes the engine tend to start sooner.

These are two new cables I made, they are about 2 feet long. I used 1/0 cable.

They are being used on a Datsun pickup with a 97 cubic inch engine.

Here is a lot more on electrical theory, andf voltage drops.
Voltage Drop Testing
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Old 03-05-2014, 12:55 PM
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Thank you Daniel, for your common sense post.
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Old 03-05-2014, 07:51 PM
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Quote:
Originally Posted by DanielC View Post
A little electrical theory.
Lets start with the starter motor.
If you were to take a piece of wire the same length, and gauge as the wire in the windings of the starter motor, lay it in out in a big loop, without wrapping it up on pieces of iron, and hook that up to a battery, it would draw several hundreds amps, because it is basically a short circuit. But the wire is wound up in a motor.
Like most electric motors, the more voltage it gets, the faster it turns. Like all electric motors, the faster is turns, the less current it draws. This is because when an electric motor is turning, it is also generating a voltage opposing the voltage applied to it.
That is why the same length and gauge of wire in a starter is not a dead short, unless the engine is locked up.

Now, lets consider the cables. Every wire and cable has some resistance. Even battery cables. it is hard to accurately measur this resistance, because it is low, but it is there. The bigger the wire, the less resistance. The shorter the wire, the less resistance. Have you noticed that they put the battery under the hood, close to the starter motor? In most cases, they even put the battery on the same side of the engine that the starter motor is on. This is to keep the battery cables as short as possible.

One way to measure the resistance of a battery cable, or any other cable is to do a voltage drop test. Take a volt meter, put the positive lead on the positive battery post, and while the engine is cranking, put the negative lead of the volt meter on the battery cable connection on the starter. you should get a reading of less than .5 volts. Lets say it is .5 volts, that is an adequate measurement. (lower is better) Lets say for arguments sake the starter draws 200 amps when cranking. A little math tell me we are losing 100 watts in just the positive battery cable.
Now, lets put bigger cables between the starter, and battery. Lets measure the voltage drop again, and we get .2 volts. A little math again, and we are losing only 40 watts in the positive battery cable. A lot better.
But with the bigger cable, the starter turns faster, and draws less current, and the drop in voltage of the cable is even less. Less current, the voltage at the battery stays a little higher. Less current, the starter does not get as hot. A faster spinning starter, and the engine tends to start sooner.
And here is another benefit. If you have higher battery voltage when cranking, the ignition system also gets the higher voltage, and that also makes the engine tend to start sooner.

These are two new cables I made, they are about 2 feet long. I used 1/0 cable.

They are being used on a Datsun pickup with a 97 cubic inch engine.

Here is a lot more on electrical theory, andf voltage drops.
Voltage Drop Testing
Ayuh,... Great post, 'n I read through yer link,....

I'm wonderin' whether anybody knows how the cable strand size plays into voltage drop,..??
Ya know, like battery cable, vs: weldin' leads,...
Course strands, vs: fine hair strands,..??

Donno's it's true, but one of my Mentors insisted finer strands carried better,...
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Old 03-05-2014, 08:06 PM
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My understanding, and I very well could be wrong is this. it does not matter with DC current, but with high frequency AC, it does. This is with radio type frequencies, not 60 cycle AC House current.

I made some cables about a year ago, for another project, and had a piece of welding cable. it is much more flexable. I also noticed when soldering the ends on to the automotive grade 1/0 cable, the insulation is easier to melt, than the welding cable, but I do not know about the long term effects of gasoline, oil and other under hood item on the welding cable insulation.

My personal opinion, if you relocate a battery some distance from the starter, you would need to go to even heavier gauge battery cables. I have not done this, but I possibily might also figure out a way to take the positive battery cable, and run it through a piece of PCV pipe as a insulation conduit, tucked inside a frame rail, for more protection.

You could probably check voltage drop with equal lengths, and gauge of "automotive battery cable" and welding cable, but I think you would need a fairly long piece to be able to measure the voltage drop differences, even witha fairly accurate high quality digital volt meter.
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Old 03-06-2014, 08:30 AM
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It was tought to me in school that the electrons travel along the surface of a stand of wire rather than the core, therefor the finer stands would be better. I don't know if this is true but that's what I've been tought. Welding cable are fine wire strands for flexablity for the most part.
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Old 03-06-2014, 08:55 AM
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I really do not know. I could easily see how people would think that, because it is pretty common knowlege, that if you are in a lightening storm, inside a car is a pretty safe place to be, as long as you stay inside the car, even if the car has a direct hit from a lightning bolt. This is not because the rubber tires insulate the car. It is because the metal skin of the car is a Farady cage. I think the thought is that when a car, or an airplane is struck by lightning, the excess electrons repel each other, and try to get as far away from each other, because like charges repel each other. So the electrons move to the outside of the conducting object.

Does the same effect happen in the core of a solid copper wire? I do not know. What happens if you have two, or many small copper wires, not insulated from each other, in a cable? Do the wires in the center of the cable bundle carry any electricity? Again, I do not know. If that were the case, it seems to me that cables would be hollow, or be wrapped around a non conductive core, or made from copper tubes, because why put expensive copper where it is not needed?

But all that is getting way into the weeds of electrical theory. In practice, the main advantage of welding cable is its flexability, compared to another cable of the same wire gauge, but with fewer strands. There may price advantages also.
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Old 03-06-2014, 09:17 AM
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Quote:
Originally Posted by tresi View Post
It was tought to me in school that the electrons travel along the surface of a stand of wire rather than the core, therefor the finer stands would be better. I don't know if this is true but that's what I've been tought. Welding cable are fine wire strands for flexablity for the most part.
Ayuh,.... That's exactly what Old Fred always said,....

Quote:
I made some cables about a year ago, for another project, and had a piece of welding cable. it is much more flexable. I also noticed when soldering the ends on to the automotive grade 1/0 cable, the insulation is easier to melt, than the welding cable, but I do not know about the long term effects of gasoline, oil and other under hood item on the welding cable insulation.
Weldin cable sheath is rubber, neoprene rubber,...
It'll hold up, longer, 'n better than the vinyl/ plastic coverin' used in automotive battery cables, by Far,...
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Old 03-06-2014, 10:09 AM
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I've had #4 cable on my turbo S-10 since 2002, but after all, it is only a low compression V6...

Russ
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