Repairs and upgrades for the charging system

Discussion in 'Electrical and Ignition' started by bohica2xo, Jul 18, 2011.

  1. bohica2xo

    bohica2xo Well-Known Member

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    It was time to start fixing the tired wiring in my 46 yr old Barracuda. Time, and a half finished engine swap before I bought it had taken their toll on the electrical system. Since I plan to upgrade the charging system to support more electrical loads, it was obvious I needed to start at the battery:

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    The original moulded cable from the starter was cut so short it barely reaches the junk terminal on the battery. Not only is this a poor job of installation, it is probably corroding in the clamp...

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    Yup. That sort of corrosion leads to hot conections, poor charging, dim lights...

    The bad news is that moulded cable is too short to re-terminate properly & still reach the battery. Since the OEM part will be hard to locate, and I want a larger gauge wire for the future 130 amp alternator - I will terminate it at a junction stud. Rather than use a single stud, I chose to use a MegaFuse for the rest of the system:

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    Crimping a battery cable requires a big crimper. There are much smaller hydraulic units around now, but the old lever type still does a great job.

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    The next item leaving was the wire from the bulkhead connector to the battery. The OEM wire was way to small for a big alternator. I went with a piece of 4 gauge welding cable:

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    The welding cable was routed over to the start relay, where the OE wire was. At the start relay, it was obvious the Fusible Link had been replaced with what looks like a piece of building wire. Lucky for me I have a bolt down connection for the link at the bulkhead connector:

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    I replaced the fuse link with an 8 gauge wire, for a couple of reasons. I now have an actual fuse, and I have installed a current shunt to take some of the load off of the OEM ammeter. The in dash gauge still functions, but does not move as violently when loads change. It will be able to give me a reading with a 130 amp alternator in the system - without starting a fire. Here is the shunt:

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    And here is the finished installation of the MegaFuse & Shunt:

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    The shunt also provides a place to connect high current accessories like electric fans or relay boxes. The terminals on the shunt are just like the ammeter - if the load is on the correct side it will show a discharge if the load is greater than the alternator output. A relay box for the headlights is in the near future for sure, but I need to clean up some other wiring first...

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    Yes, that really is the electric choke heater connected to the ballasted side of the coil circuit. No wonder it has a brand new ballast resistor on it. The terminal on the coil was so nice it needed it's own close up:

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    After I fixed all of that, I had a look at the terminal on the alternator output stud.

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    I was running out of time today, so I replaced the charge wire with a 4 gauge cable - but I still need to fix some other things in the harness on that side of the engine. I will take more pics when I get that cleaned up.

    B.
     
  2. 67Dart273

    67Dart273 Well-Known Member

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    I thought about going with an external shunt, but finally copied a mod posted on here--bought a Sunpro voltmeter, tore it apart, and mounted the old ammeter face over it. this is a SUPER simple mod in one afternoon.

    What are the shunt specs, and have you tested the shunt / ammeter combo to see what headlights, heater, etc register on the meter?
     
  3. bohica2xo

    bohica2xo Well-Known Member

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    Calibrated the shunt against a 130 amp load each way. Get full deflection of the OEM gauge @ 130 amps. Of course full fielding the 37 amp alternator on the vehicle right now gives about 15% needle deflection on the stock instrument - rather than full scale. Still shows charge & discharge, just not so violently now.

    The shunt could be made to take less (or more) of the load easily enough. I can do one that is 50% of full scale @ 37 amps.
     
  4. 67Dart273

    67Dart273 Well-Known Member

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    Thanks. I certainly thought about doing something like this, as well as a remote shunt/ more sensitive meter, but for now I'm happy with the voltmeter conversion
     
  5. nuttyprof

    nuttyprof FABO Gold Member FABO Gold Member

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    What is the shunt made of? How did you determine size?
     
  6. bohica2xo

    bohica2xo Well-Known Member

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    The shunt is 360 brass. Less conductive than copper.

    .035 thick, .490 wide, and .890 active length.

    I started wider and reduced the width for calibration.

    Ohm's law for parallel resistors will get you very close. The OEM ammeter is not terribly precise, I measured 3 different ones and got different readings.

    Obviously you will need a Wheatstone bridge to measure the very low resistance ammeter & shunt.

    B