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  • Electrical conductivity questions:

    I'm thinking of making some custom battery-cable clamps. What's the best material to use?

    The battery is an automotive, an Exide Orbital, which is a "sealed cell" copy of the Optima, which supposedly doesn't vent acid fumes to cause corrosion.

    Doesn't lead have a pretty poor conductivity? Why do they still use it, other than due to sheer corporate inertia?

    Anyway, I'm thinking of making some custom cable ends out of copper. I have some surplus blocks about the right size, and I propose to simply drill the side, insert the stranded cable, and solder it in place.

    Is there any reason the soldered connection wouldn't be as good as a mechanical clamp, swage or setscrew type connection?

    How much power have I lost running sixteen feet of 00 cable from the starter to the trunk?

    Doc's Machine. (Probably not what you expect.)

  • #2 Should have what you want w/out much hassel.

    I have saw them made out of copper, just terminal ends crimped on. Never had a problem mounting battery in the trunk... I did have this camaro w/no subframe connectors that would not crank all the time, I took a ground to the transmission and all was well. It'd pull one front wheel then not crank the next time. I sure wrinkled that old body.

    David Cofer, Of:
    Tunnel Hill, North Georgia


    • #3
      Brass terminals are common at boat shops,they work good,but one word of caution,the bolts they use are brass plated steel crap,pitch the bolts in the trash and replace with a stainless or galvanized bolt/nut.

      As to the lead thing,since the plates in the battery are lead,so are the posts,mainly because the acid doesn't attack the lead.The terminals can be nearly anything,but the lead is prefered due to corrosion and formability,those brass terminals do take a lot more wrench work to tighten.

      I have seen the factory strap connectors last a long time too,the ones where its just a strip of copper plated steel pinched on with a bolt.

      [This message has been edited by wierdscience (edited 09-06-2004).]
      I just need one more tool,just one!


      • #4
        24K gold would work real well.
        Try to make a living, not a killing. -- Utah Phillips
        Don't believe everything you know. -- Bumper sticker
        Everybody is ignorant, only on different subjects. -- Will Rogers
        There are lots of people who mistake their imagination for their memory. - Josh Billings
        Law of Logical Argument - Anything is possible if you don't know what you are talking about.
        Don't own anything you have to feed or paint. - Hood River Blackie


        • #5
          I'm pretty sure Sterling silver would conduct the best, but since you have to consider all the other component materials in the great chain of conductivity, I would think it would just be wasting silver if the wiring is copper.



          • #6
            ZINOM has it, the best conductor is silver. Gold isn't all that good a conductor but is used on terminals because it doesn't ever corrode. It is known as a noble metal, same as platinum.
            Free software for calculating bolt circles and similar: Click Here


            • #7
              You don't want to use the lead cause of resistance, ok don't solder the wire ends into place either then. Mechanical connection will work great.

              You see all that pimp gold colored connectors in "pimp-boys" cause it attracts the simple buyer.

              I like the copper idea, you could always spray all the outer surfaces with clear lacquer to keep it from turning green (I like the green).

              On my car I used 0000 welding wire to put the batt in the trunk. JR
              My old yahoo group. Bridgeport Mill Group



              • #8
                As for the conductivity of the clamps, that is a secondary concern as long as a fairly good conductor is used. The resistance in a set of cables will primarily be in the cables themselves, because they are longer and in the connections including the connection made when they are clamped on the battery terminal(s), auto body, or other attachment point. In this respect, you would want a material that resists corrosion so the connection does not deteriorate. I suspect this is one reason why lead is commonly used.

                You also want a material that will have a minimum chemical or electro-galvanic reaction with the battery terminals, which are lead and the wire itself, which is likely copper.



                Of course you need good mechanical strength to allow a firm clamp to be established and maintained on the battery terminal. I believe many commercial terminals have a steel core with lead cladding.

                Solder connections are very good in terms of resistance. Welded might be a little better, I don’t know. However, a properly made crimp connection will also be excellent as it should be made with sufficient pressure to cause both the terminal and the wire to cold flow and also to cause spot welding at a number of small points within the crimped area. Stretching a properly made crimp connection to the point of mechanical failure should cause the wire itself to tear apart, leaving broken-off pieces of most or all of the strands in the terminal. If the wire pulls out, the crimp was not very good. Any crimp tool can and SHOULD be tested in this manner.

                The above applies to a new joint. However a number of factors will cause a joint to age. In automotive service these include temperature, vibration, battery acid, oil, and other chemicals. A soldered joint will likely be most susceptible to vibration, which will cause metal fatigue in the wire just beyond the area where the solder wicked to. A proper strain relief would help here. A crimped joint will allow the various chemicals, including battery acid, to penetrate between the strands, inside the joint area where it can attack the small spot welds that are the basis of a low resistance joint. Grease or other corrosion prevention substances can help here. I really would not count on a manufacturer's claim of a "sealed" battery to prevent acid from getting out and on nearby connections.

                2/0 cable has a resistance of approximately 0.1 Ohm per 1000 feet. 32 feet (16’ X 2) will have a resistance of 32 X 0.1 / 1000 = 0.0032 Ohms. The total voltage drop will be given by V = IR and the power lost will be P = I^2 X R. So, these numbers will vary with the current being drawn. A starter can draw 500 to 1000 Amps. Using 750 Amps, P = 750 X 750 X 0.0032 = 1800 Watts. That’s as much as a toaster, iron, or window AC uses. And the voltage drop, which might be even more significant, would be about 2.5 volts. I would use a larger wire size. 4/0 would give you a 40 % reduction in that figure and 1250 kcmil would cut it to 10% of that figure or about 180 watts. The voltage drops would also be less. Of course, other electrical devices in a vehicle use a lot less current and can be run with smaller wire so it depends on what is being run.

                The manufacturers of battery cables and clamps have thought all of these problems out. I do not think you will go far wrong if you properly apply commercially available products. In any case, please keep all of your installation well separated from the fuel tank and any area where fuel fumes can accumulate. Think NO BOOM!

                Paul A.
                Paul A.
                SE Texas

                Make it fit.
                You can't win and there is a penalty for trying!


                • #9
                  Make the terminals from copper, as you were going to do. Drill the hole for the wire and strip the end of the wire, just before you want to make the connection. Smash the junction together for a mechanically tight grip, then solder, using electronic solder. Don't use the acid stuff. Heat the junction until it will melt the solder, and watch it wick into the joint. If possible, watch it wick until it's 'saturated' the junction. Let cool and clean with acetone, that's it. Paint on some tool-kote, or similar, to cover all but the area that makes contact, and where the bolt head will be. That will be mechanically sound, electrically the lowest resistance joint, and offer the most resistance to corrosion. If you want to get fancy, use two colors of tool-kote, red and black, to identify the leads at both ends, since the wire itself will only be black.

                  It's true that the most resistance will be in the length of wire, but if a poor contact develops at a junction, that point will quickly become the highest resistance, concentrating heat there when high currents are drawn.
                  The copper junction will also help the connection to the lead terminals last longer by draining heat away down the wire. Brass is not as good at that, though a close second. I'm ignoring silver, since that might mean some of your wife's spoons might go missing, and you wouldn't want to try explaining what you used them for.
                  I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-


                  • #10
                    And one more thing... Don't forget that the "holes" should be tapered just like the posts. Also, the Positive post is larger than the Negative post.

                    Unless, of course, you have a side terminal battery. Then the standards are all different.


                    • #11
                      One more thing from someone who has done several. If it is a street car, use rubber grommets around the holes the cables pass through, grief will follow otherwise.

                      David Cofer, Of:
                      Tunnel Hill, North Georgia


                      • #12
                        Grommets? Heck yeah, otherwise be quick with the wrench and practice removin the batt. cable cause the fire won't stop till you do. JR
                        My old yahoo group. Bridgeport Mill Group



                        • #13
                          I use copper house wire on vehicles,usually #2 or #4,bend it to fit with a tubing bender.

                          On boats I use copper tubing on insulated posts.

                          I find the heaveir sections carry the same current if not more and the corrosion problem isn't nearly so bad.

                          When a fine strand batt or welding lead gets a little green started in it,it goes down hill from there.
                          I just need one more tool,just one!


                          • #14
                            Most of the points I can think of are covered.

                            Bronze battery clamps have been used in marine applications for 70 years.

                            Copper against lead is a strong galvanic couple. If you pair a copper terminal and a lead battery post in a corrosive environment you can expect problems with corrosion. "Sealed" batteries somehow still grow white corrosion on neglected battery connections.

                            Just be sure the terminals are liberally coated with a corrosion preventive including a liberal application to the mating surfaces at assembly. Siloo makes a good product for this application.

                            A slug of sacrifical metal should be bonded to each terminal for galvanic protection. Zinc is traditional and readily available.

                            [This message has been edited by Forrest Addy (edited 09-06-2004).]


                            • #15
                              Incidentally, if you look at the stock starter cables, they are way undersized.

                              Done because they are cheaper that way, and they weigh less. The time of use is so short that normally they won't heat significantly. And the voltage drop is accepted.

                              In colder weather, conductivity is better, and that is when you need the high currents.

                              And if you can get 1000A from any auto battery in starter service, you will be the very first.


                              Keep eye on ball.
                              Hashim Khan