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Hot Rods Heavy Pos & Neg cables touching long distance ?

Discussion in 'The Hokey Ass Message Board' started by blazedogs, Jan 7, 2018.

  1. blazedogs
    Joined: Sep 22, 2014
    Posts: 463


    Running heavy insulated Pos & Neg bat cables from the trunk (battery in trunk). Seems I read this some time ago that these 2 Pos and Neg cables should not touch the entire length of the car. My intension is to run both wire together inside insulated cable clamps the entire distance. Is this a issue ?
    chryslerfan55 likes this.
  2. Joe H
    Joined: Feb 10, 2008
    Posts: 964

    Joe H

    Ever see jumper cables with both sides molded together? You will zero problems as long as the don't rub or scuff.
    loudbang and chryslerfan55 like this.
  3. blazedogs
    Joined: Sep 22, 2014
    Posts: 463


    Yup Joe Stands to reason... Old and had a brain fart.....
    loudbang likes this.
  4. Mr48chev
    Joined: Dec 28, 2007
    Posts: 27,897


    I don't see why it would make any difference. In some cases it could set up a slight magnetic field that might throw off navigation instruments at worst.
    loudbang likes this.

  5. squirrel
    Joined: Sep 23, 2004
    Posts: 47,142


    if they are not secure, and can vibrate or move around, they could wear off the insulation between them, and short, which is real bad.

    Jumper cables don't have this issue because the two wires are molded together.

    So secure the wires carefully, and keep them separated a bit, just for good measure.
  6. RmK57
    Joined: Dec 31, 2008
    Posts: 1,616


    Why do you have to run the negative cable all the way to the front? Cant you just ground it to the trunk floor.
    Ron Funkhouser, F&J, loudbang and 5 others like this.
  7. redlinetoys
    Joined: May 18, 2004
    Posts: 4,302

    from Midwest

    Run the ground to the frame. Then off the front frame to your block... you may need a jumper from the frame to body as well.

    Sent from my iPhone using H.A.M.B.
  8. You could put another layer of insulation around each conductor, like that spiral stuff, and then secure them so that there is no vibration.
    Truck64 likes this.
  9. I ran my ground cable from the battery ( behind the seat ) directly to the frame under the seat , then ran an o1 ground cable from the frame rail at the cowl over to the block. ( no need to run the ground the length of the vehicle ) From the block I ran an 02 gauge cable to a grounding block under the dash. I needed lots of good grounds with the fiberglass body. Never had a problem.
    loudbang, Elcohaulic and Poh like this.
  10. Dick Stevens
    Joined: Aug 7, 2012
    Posts: 2,989

    Dick Stevens

    It is best to run the ground cable just like OP plans, there is good reason why they don't make electrical wiring out of steel, it isn't a great conductor of electricity and the ground cable is a conductor!
    Mudgy likes this.
  11. I put a starter solenoid near the battery so the long, non circuit protected positive cable isn't hot at all times. You can bring all the vehicle wiring back to the trunk mounted solenoid instead of the starter motor cable post.
    Darryl Deir and Dick Stevens like this.
  12. Mike VV
    Joined: Sep 28, 2010
    Posts: 2,125

    Mike VV
    from SoCal

    And what to think about a few years down the road when grease, oil, road grime and...AGE take over the wire insulation. A starter that's had a hard life and requires a little more power to run..., a few extra cranks on the strater, heat in the system (wires !) and the deteriorated insulation fails, the main power wires short together...and boom...a fire results.

    My car...this would "never" happen, ALWAYS separate, (same thing with spark plug wires !).

  13. The likely hood of a (single) positive cable going to ground along it's route forward are just as high.
    Also no need to be alarmed by an insulated ground wire running right alongside a NON insulated ground (frame rail).
    If the ground wire is grounded, the ground wire is the same as the ground.
    Not the same as plug wires.
    AC, or a high voltage dc current that pulses then collapses, will create a magnetic field around the wire that can be detected, or make "noise" in nearby wires.
    A low voltage DC wire will not create the same effects. Even tho it can be detected by certain meters, it is not enough to be considered a disturbance like the ignition wires would be.
    Thats why its ok for harnesses to have many wires running alongside, but ignition wires rarely if ever run parallel.

    Last edited: Jan 7, 2018
    loudbang and Muldoon like this.
  15. RmK57
    Joined: Dec 31, 2008
    Posts: 1,616


    There are a ton of new cars with trunk mount batteries out there and I have yet to see one with a negative cable going to the front end of the vehicle. My neighbours Mercedes has a short negative cable going to the trunk floor and it seems to be pretty dependable.
  16. stanlow69
    Joined: Feb 21, 2010
    Posts: 4,885

    from red oak

    30 years ago, I ran a negative cable to my trunk along my frame to charge 2 extra marine battery`s. And a short ground cable to the frame. No problems.
    F&J and loudbang like this.
  17. I would ground the battery to the frame at the rear of the car. Ground the engine to the frame up front, and ground the body to the engine at the firewall. That covers all bases unless the body is fiberglass, then you need separate grounds for everything electrical.
    F&J and loudbang like this.
  18. Gene,
    I wonder if you don't understand the electrical system used in probably all automobiles? Please accept my apology if this is a bad assumption. The current flows from the battery to the component (like a headlight) being powered. After it accomplishes its task (lighting the headlight) the current returns to the battery through the frame of the automobile (ground). There is one short cable from the battery to the frame (ground). If the battery is in the trunk the short cable goes to the frame of the automobile in the trunk. The other post on the battery has many wires that go to each component.

    Charlie Stephens
    loudbang likes this.
  19. Is this really true? Has anyone used an ohmmeter and measured the difference between a copper wire and chassis ground? I would have guessed that a good quality copper wire has a lot less resistance than the the body of the car, especially if you measure at the starter, which draws the most current in the car.

    ...that's a guess, if someone has actual facts, please share.

    I've always routed a separate ground wire all the way to the starter, in the cars with the battery in the trunk (and a good quality ground wire between engine and chassis). Might be overkill, but on the other hand, it doesn't hurt anything.
    Dick Stevens, lothiandon1940 and F&J like this.
  20. F&J
    Joined: Apr 5, 2007
    Posts: 13,217


    Good question for this thread and needs to be pondered..

    I have memories burned in my brain from back in March 1970 when I first went to VW of America's Training center in NY... One thing is back then, VW had used 6 volts till the end of 1966, so the training center had a full testing procedure to diagnose those aging 6v VW's. The instructor showed how to use the ohmmeter to trace the resistance at each and every "assembled" or "Bolted together" connection, from the negative cable that was bolted to the body! ....then it traveled to the chassis floor pan, then through a ground strap at the trans nose, then he'd test the ohms even at potential places like engine-to-trans mating, starter bolts, etc! Each point in SALTY/rusty New England can cause the 6v LONNNG distance locations of the battery under rear seat, to ign switch, then all the way back to starter solenoid etc end up with a faint "click" on a cold morning!

    So to "assume" an possible answer to testing a long steel frame rail? Well, going by that instructors words... That "one piece" length of steel must? be superior?, or at least not inferior! to that of a large copper cable! When we have multiple points on a frame, or a body assembly, then the potential exists for resistance at each assembled joint.
    Darryl Deir, gas pumper and catdad49 like this.
  21. catdad49
    Joined: Sep 25, 2005
    Posts: 4,502


    Morning, Frank.
  22. 29moonshine
    Joined: Dec 30, 2006
    Posts: 1,301


    i always run the ground all the way to the motor. then ground it to the body in the trunk. and put a ground wire from the motor to the frame. may be over kill but my battery seem to last longer
    lothiandon1940 likes this.
  23. Frank. if I am reading your words of wisdom correctly, the steel frame/body is indeed a good conductor. The CONNECTIONS are/can be corroded, thereby losing ground.

    Glad you are still here!

    gas pumper likes this.
  24. BMWs with trunk mounted batteries have a high quality cable going right the way to the front. Worth harvesting from the breakers yard

    Sent from my SM-A520F using The H.A.M.B. mobile app
    lothiandon1940 likes this.
  25. I always ran the cables out the trunk floor using heavy wall grommets. The ground I would locate to the frame rail. Never had a problem even with stock cars, which were easier, just weld a stud on the roll cage.
  26. wsdad
    Joined: Dec 31, 2005
    Posts: 1,255


    Electricity acts differently in series than it does in parallel. If all those connections you mentioned were hooked up in series, then one broken link in the chain would break the whole chain and nothing would work.

    But they're hooked up in parallel, like a rope ladder. If one rung of a rope ladder is taken away, all the others are still ok to use.

    The starter is one rung on the rope ladder. The radio is another rung, the wiper motor is another rung, etc. If you remove the wiper motor rung, the radio and starter rungs are still attached and able to be used. The starter rung will still be attached to the ropes, even if you ship the wiper motor and radio to Antartica.

    The only way to stop the starter from getting electricity is to cut one of the "ropes" in two. The frame is one rope and the positive cable is the other.

    So long as you don't break the frame in two, you can attach or take away as many connections along the frame as you want. It just doesn't matter to the starter. If one of those connections gets rusty, the starter will still get all the electricity it wants.

    As far as being a better conductor, it can be argued that the cable is slightly better. But it's like arguing that twelve hundred dollars and one cent is better than having just twelve hundred dollars. The difference is just not enough to matter. It doesn't have to have "the best" when second best is so little difference. The starter will be happy with its twelve hundred dollars.

    If, however, the battery or starter has a rusty connection to the frame, then the starter won't get enough electricity because the battery, frame and starter are all in series with each other.

    If you did replace the frame with a cable, you'd still have to have a good connection to it, just like you would with the frame.

    The advantages of the frame is that it is already there and it's indestructible.

    That makes the long ground cable needlessly redundant.
    Last edited: Jan 8, 2018
  27. F&J
    Joined: Apr 5, 2007
    Posts: 13,217


    Ok Wsdad, I am getting ready to go do something right now, cannot read more of your post, ok? But that very good instructor was showing us the complexity of "combined? resistances, like a bit of bad connection at several or MORE points in that long trip through so many parts bolted together on an old VW bug! He simply stated, a tiny bit of corrosion, is not enough at just ONE point, but if a bunch are, then that 6v system won't start!

    So, what he really drilled into us, is that if we see ONE bad spot, that now DOES get the car to start after we clean it?, DO keep looking at ALL the others, as if one is corroded, more can be!, the VW car could/will fail next week or next month! Bye.. thanks, Frank
    Darryl Deir and gas pumper like this.
  28. Truck64
    Joined: Oct 18, 2015
    Posts: 4,230

    from Ioway

    For cables or wires carrying heavy current, measuring resistance isn't really possible. Or you'll hear guys say something "has good continuity." Well, sure. Even a single strand of braided cable will show "good continuity", and ohms resistance.

    Now, try to get it to carry 175 amperes @ 12 volts and see what happens.

    The only way to test then, is while the circuit is energized and under load using the voltage drop method. On the principle that electricity will always seek the path of least resistance the voltmeter probes are placed in parallel with the circuit under test. No need to get fancy or disconnect anything.

    The voltage lost in a circuit or connection will be displayed as a positive number on the voltmeter. This should not exceed 0.2 volts in ground circuits and 0.3 volts in positive side. Great method for testing headlight circuits, starter circuits, charging systems, heater blower etc.
  29. Boneyard51
    Joined: Dec 10, 2017
    Posts: 4,641


    You were advised to place a stater solenoid, near the battery, while this is not a bad idea, DO NOT use a starter solenoid, the are designed to only be excited for a few minutes at most. Purchase a “continuious duty” solenoid at the parts store, its twice as much, but will save you problems down the road if you chose to put a solenoid near the battery. Bones
  30. While steel is a poorer conductor compared to copper, it's more about cross-section of the conductor. Larger conductors will carry more current than a smaller one assuming the same material is used for both. Steel conducts at about 10% of copper with the same cross section, so if you increase the steel cross section by 10, you now have the same current capacity. As an example, if your frame is made of 2"x3"x.125" steel, each rail will have a cross section of one square inch. Times two for both rails, two square inches. This is the equivalent of 2500 MCM cable which in copper is good for over 2100 continuous amps in free air, more in short bursts. Keep in mind that any other metal parts attached to the frame can also add to its rating. I'll note that lead, commonly used for battery posts and clamps, is an even worse conductor than steel at only 7% of copper. In fact, once you get past the first 5 best conductor materials, conductivity falls off sharply; from 70% down to 30% or less.

    Those numbers may be hard to achieve; this represent drops of 1.5% and 2.5% respectively, the typical OEM or aftermarket harness can show more. GM allows up to 10% drop. I personally try for 3% on branch circuits, and a max of 5% as measured between the battery and the end point of the circuit. And voltage drops are additive; if you lose 1 volt between point A and point B in a circuit, and another volt between point B and point C, total drop is now two volts.
    Elcohaulic likes this.

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