Quick question on the MAD by pass.

Discussion in 'Electrical and Ignition' started by frederick_76, Jun 3, 2018.

  1. frederick_76

    frederick_76 FABO Gold Member FABO Gold Member

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    With the alt being hooked directly to starter relay, is that also by passing the voltage regulator? Do I need an internally regulated alt? Thanks.
     
  2. 67Dart273

    67Dart273 Well-Known Member

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    No You still need the VR as is. In fact the Mad or / other bypass SOLVES part of the VR problem with voltage drop. You want the power supply to the VR (the ign terminal) which is ALSO the "sense" terminal to be as close to battery voltage as possible. This applies to the VR case/ ground as well

    A side note: I don't really care for "one wire" alternators partly for the same reason............in them the "sense" terminal IS the alternator output post. This means that voltage drop along the charge wire will affect the system, unless the charge wire is oversized
     
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    • billccm

      billccm Member

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      Just did this on my road runner. Eliminated a 1.3Vdrop. Best $12 and 15 minutes ever spent.
      Agree on the regulator comments, but the one wire alternator is very reliable. I'm still keeping the separate regulator for now.
       
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      • frederick_76

        frederick_76 FABO Gold Member FABO Gold Member

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        What size wire are you running from the alt the the starter relay?
         
      • billccm

        billccm Member

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        I used SAE 8 awg wire from the alternator to a 4 inch 12 awg fusible link. Soldered all ring terminals and connections. Heat shrinked all connections.
        Under dash I soldered the ammeter wires together and heat shrinked.
        Chineseium under dash voltmeter tied to my back up light switch source.
        Drove around this weekend with my DMM monitoring the voltage at the cig lighter. Very good at 14.7V after start up and settles to 13.8 in about ten minutes.
         
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        • billccm

          billccm Member

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          I have part numbers if interested.
           
        • 67Dart273

          67Dart273 Well-Known Member

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          You may know this but the VR is temperature compensated. The shop manual details this
           
        • frederick_76

          frederick_76 FABO Gold Member FABO Gold Member

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          Ok, thanks for the info. That's should do it.
           
        • jbc426

          jbc426 Well-Known Member

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          As stated above, your stock voltage regulator will work by controlling the field inputs of your alternator.

          For what it's worth, and for those wanting significantly higher amperage at idle to run heavy electrical loads such as any combination of electric fans, big fuel pumps, high power stereos and A/C. I use a slightly modified version of the Madd wiring theory, and installed a CS144 alternator that has a heavy duty bridge rectifier, rewound stator and heavy duty voltage rectifier. It puts out around 130 amps at idle and just over 200 at a fast idle if needed.

          I use a 2 gauge feed and an "1" gauge ground. A separate ground for the alternator is very important especially with higher output amperages. 70 lbs Odyssey battery in the trunk.

          The AC Delco CS 144 alternator is a pretty easy bolt on upgrade when following the MAD theory to keep the high amperage circuits out of the cabin. I use a 12v distribution lug and relays to feed any high amp loads from under the hood.

          CS 144's can be had with either remote voltage sensing, output terminal voltage sensing or self-exciting set-up. They do make significantly higher output versions, but I don't need that much power.

          Here's the link to a good source for these alternators.

          USA Built High Output Alternator, Upgrades, Parts, Kits
           
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          • frederick_76

            frederick_76 FABO Gold Member FABO Gold Member

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            Got it done today after work, everything looks good.
             
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            • BillGrissom

              BillGrissom Well-Known Member

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              For others, wiring "ALT out" to "big stud" on Starter Relay is the same electrically as wiring straight to BAT+. You will notice there is a thick wire from there to BAT+, so you are simply leveraging that existing wire. That wire is thick because it carries the starter current. I recall this is true in early A's and may not apply to 1970's cars or some trucks.