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Automobile Jumper cables

Discussion in 'Electrical Engineering' started by Chief McGee, May 6, 2005.

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  1. Chief McGee

    Chief McGee Guest

    I pull a backhoe on a trailer behind a 1-ton GMC truck. Sometimes when it
    is cold I need to "jump off" the backhoe from the truck's two batteries
    while it is loaded on the trailer. Since the jumper cables are too short to
    reach the tractor from the front of the truck, I would like to run two
    permanent cables to the back bumper of the truck . Then I could hook
    regular jumper cables from the tractor to the terminals on the back bumper.
    Question is: What type and size cable should I run? Would 4/0 copper
    "entrance" cable do? This is stiffer than welding leads, therefore, harder
    to work with. But if it gives me more cranking amps it would be worth the
    trouble. Does a 4/0 copper with a few thick strands carry more CRANKING
    amps then a 4/0 with many finer strands? Is welding lead the best wire
    to make
    jumper cables? What size? Thanks, Chief
  2. At DC, I don't think there is a measureable difference between the two cable
    types. They make heavy guage cables with large plugs on them for winch
    applications. This is so you can use one winch on your vehicle by moving it
    from the front to the back. I would look at that type of cable and then add
    a compatible plug to the end of a set of jumper cables.

    Charles Perry P.E.
  3. SQLit

    SQLit Guest

    I know that back hoes can be a bit hard to start on cold mornings. I
    challenge you that 4/0 is needed. I would think that #4 maybe less sized
    conductors would be all that you would need.

    Your might consider a inverter and a battery warmer. Smaller wire for sure.
    You would need less than 1500 watts.

    The biggest concern would be the routing and protection of the cable from
    the front to the back of your truck.
  4. Dwayne

    Dwayne Guest

    AWG is a standard that relates to current carrying capacity of the wire.
    All current values are for continous draw.
    The calculator at the bottom can be used to determine the voltage at the
    backhoe batteries (the box labeled "voltage at load end of circuit").
    Welding wire is usually the cheapest solution.

  5. Guest

    Here's how I'd go about solving this...

    First, make sure the charging system on the backhoe is in good order.
    It may not be keeping the battery fully charged. Make sure the top
    and case of the battery is clean. You might also see if there is a
    key-off drain on the backhoe battery. If there is, find it and fix it,
    or install a battery cutoff switch in the negative cable of the backhoe
    battery. After you drive the backhoe up onto the trailer and shut it
    down, flip the cutoff switch and your battery is guaranteed to be
    disconnected from everything on the backhoe so it won't discharge.
    Just remember to flip the switch again before you fire it up.

    Second, if the backhoe battery is fully charged and it's still hard to
    start (old engine, it's cold out, etc), you might try warming up the
    battery, as has been suggested. You can test this theory with a plain
    old drop light / trouble light. Some morning when you don't have to
    go anywhere, put the light near the battery (under is best) on the
    backhoe and leave it plugged in for an hour or so. Then try starting
    the backhoe. If it starts up, you can either warm up the battery
    before you leave the house, or install a heater on the backhoe.
    There are battery heaters available that work off of 120 V, but then
    you need an inverter to get the 120 V. If you have a long enough drive
    from the house to the job, or can go out and plug in a connector some
    time before you leave, you might install a 12 V heater on the backhoe.

    Buy a couple of double-contact automotive bulb sockets and mount them
    under the battery on the backhoe such that the shells are grounded to
    the frame. Put an 1157 (35 W) or 2357 (37 W) bulb in each socket. Wire
    all four wires together and to a piece of 14 gauge or better wire.
    Also connect a piece of 14 gauge or better wire to the backhoe frame.
    Run these wires to a 2-wire connector on some handy place on the
    outside of the backhoe. Run two more 14 gauge wires from the trailer
    connector to the mating 2-wire connector. At the trailer connector,
    connect the hot wire to a separate contact - don't hook it to the
    running lights as the new bulbs probably draw too much for the running
    light circuit. Hooking the ground wire to the existing ground wire
    in the trailer connector is probably OK, as long as you upgrade the
    ground wire on the truck side of the connector to at least 14 gauge
    as well. On the truck side, run a 14 gauge hot wire from the new
    contact to the battery, and put in a 15 A fuse at the battery. Now,
    whenever the trailer connector and the 2-wire connector are both
    plugged in, the backhoe battery is getting heated. You probably
    don't want to leave this plugged in overnight as it would drain the
    truck battery too much. But plugging it in an hour or two before
    you leave should be fine.

    Third, running permanent cables is also a valid option. Tow trucks
    often have cables that come in two parts. There is a short part
    (three or four feet long) with lugs on the ends of the cables for
    attaching to the battery. The other end has a two-pole "Anderson"
    high-current DC connector, which gets mounted to the truck grille.
    The long part of the cable (ten feet or more) has jumper clamps on
    one end and the mating Anderson connector on the other end. The only
    problem with this scheme is that the short end of the cable is probably
    too short to reach the back of your truck.

    Welding cable is probably a better choice than entrance cable, since
    it's more flexible and therefore better able to withstand the vibration
    of an automotive application.

    What I'd do is to buy a chunk of #2 or #4 welding cable a little bit
    longer than the truck, some copper lugs to suit that cable, an
    Anderson connector and the terminals for it, a length of split
    corrugated tubing as long as the welding cable, a set of jumper
    cables long enough to go from the bumper of the truck to the backhoe,
    and some miscellaneous zip ties, mounting screws, etc.

    First, cut the clamps off of one end of the jumper cables, and put the
    Anderson connector terminals on the cables. You can solder them on (use
    rosin-core solder and a propane torch; they're too big for a soldering
    iron) or crimp them on - trade beer (or whatever) for use of the crimp
    tool with an electrician friend, or possibly rent one.

    Next, figure out where on the bumper you're going to mount the other
    Anderson connector, and cut a piece of welding cable long enough to go
    from there to one of the frame rails on the truck. Put the Anderson
    terminal on one end and a lug on the other end. Put the corrugated
    tubing over the cable. Use an existing hole in the frame or drill a
    new one. Use sandpaper to get the area around the hole down to bare
    metal, then bolt the lug to the frame. Use a lock washer or Nylock
    nut on the other side - don't use a sheet metal screw or lag screw.
    Spray-paint the completed connection to cover up any remaining bare
    metal. Plug the terminal into the Anderson connector and bolt the
    Anderson connector to the bumper. Use the zip ties to dress the wire
    up out of the way.

    Up front, locate another hole in the frame rail near the battery, and
    prepare it the same way (bare metal). Install a cable from here to
    the negative terminal of the battery - you can either make one out
    of lugs and welding cable, or buy a ready-made "switch to starter"
    cable at the auto parts store. (Yes, the battery is grounded to the
    frame already, but this is typically through a #10 or so wire that
    will melt if you try to jump the backhoe with it.) Use more corrugated
    tubing over this cable.

    In the back, attach the Anderson terminal to the long piece of welding
    cable. Put the corrugated tubing over the cable. Plug the terminal
    into the connector, and then route the tubing+cable to the front of
    the truck. Avoid moving parts and anything that gets hot. Get the
    thing secured to the frame or body at least every 12 inches. At the
    front, crimp a lug on the cable and attach it to the positive terminal
    of the battery.

    You may want to make a cover for the Anderson connector on the bumper
    so it doesn't get mud and water in it. You might be able to find a
    vinyl tube cap that will stretch over the end. Or, instead of bolting
    the connector to the bumper, get a small plastic toolbox and bolt that
    to the truck. Cut a slot in the side of the toolbox for the cables.
    When you're not using it, put the connector in the toolbox and latch
    the lid.

    To use the rig, make sure the jumper clamps aren't touching and then
    plug in the Anderson connector on the jumper cables to the one on the
    truck bumper. Connect the positive clamp to the backhoe battery and
    the negative one to the backhoe frame, and start it. To disconnect,
    unhook the negative clamp first, then the positive, then the Anderson

    You can probably get all of this except the Anderson connector at your
    local electrical supply house. You can get the Anderson connector and
    terminals here:
    You probably want the 175 amp kind. If you do decide to go with
    thicker wire, you can go with the 350 amp ones.

    Good luck!

    Matt Roberds
  6. Dick Alvarez

    Dick Alvarez Guest

    <<I would like to run two permanent cables to the back bumper of
    the truck I would like to run two permanent cables to the back bumper
    of the truck.>>

    Be extremely careful to protect the cables mechanically throughout
    their length, and to protect the terminals against accidental
    contact. If a piece of metal accidentally shorts out cables that
    big, powered from a big battery, the cables can melt and throw molten
    metal, and the battery can explode, spraying sulfuric acid in all

    Starting-fluid may help. It is available from truck supply
    stores, in pressurized spray-cans. Be careful with it, as it is
    highly flammable, and the pressure is high inside the cans.

    Dick Alvarez
    alvarez at alumni dot caltech dot edu
  7. robert grant

    robert grant Guest

    Im from the UK so dont know what a backhoe is. I would suggest checking the
    charging system , is battery AMP/HOUR capacity low ,or quite simply charge
    the battery from the vehicle system as done in caravan trailers.
    news:[email protected]_s22>
  8. calhoun

    calhoun Guest

    This is the best solution. I did the same thing. Truck, with 7 pin trailer
    plug, already has a full time hot feed. Just get a batterybox and deep cycle
    battery. Mount on trailer tongue and hook up to hot feed. You will always
    have a charged battery on the trailer. That with a can of starting fluid and
    I could always start my massy ferg 50C. even at 10 degrees.
  9. ehsjr

    ehsjr Guest

  10. Jimmie

    Jimmie Guest

    Instead of running a circuit for jumping the backhoe. Consider just running
    a couple of small wires to keep the batteries warm. I would think you would
    need nothing more than 10 guage to do this. A few minutes of chagre time
    before cranking should be all it needs to get the batteries up to temp. If
    this will not take care of your needs it means the backhoe batteries and/or
    charging system is kaput..
  11. w_tom

    w_tom Guest

    Sidebar: since anti-freeze is only rated to -40 degree F,
    then what is used in Alaska for -50F and -70F?
  12. Jimmie

    Jimmie Guest

    O yeah if you decide to do this remember to disconnect it before starting
    the backhoe or you will burn up the wires. 10 GUAGE WIRES MAKES LOUSY JUMPER
    CABLES.. Actually I think your problem is a bad battery or charging system
    on the backhoe.
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