Battery draining overnight

Electrical and Ignition

  1. Craig Burriss

    Craig Burriss Well-Known Member

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    Now that I’m starting to work on my car again, I’ve been trying to figure out why my battery will drain to nothing overnight if it’s left connected. I’ve noticed when the battery is disconnected, the ammeter rests perfectly in the middle of the gauge, but as soon as I connect the battery it will drop to here (see picture). This is with the key to the off position and everything turned off. Doesn’t this mean that something is drawing power from somewhere? I’ve been probing around with a test light trying to figure out what is doing it but can’t find anything. I’m thinking about just wiring in a battery kill switch somewhere.
    image.jpg
     
  2. toolmanmike

    toolmanmike FABO Staff Staff Member FABO Gold Member

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    Start pulling fuses one at a time until the draw goes away. That might help isolate it.
     
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    • brian6pac

      brian6pac Well-Known Member

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      That's a lot of current draw
       
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      • Craig Burriss

        Craig Burriss Well-Known Member

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        Just pulled every fuse and nothing has changed. I guess I’ll start unplugging everything else
         
      • Craig Burriss

        Craig Burriss Well-Known Member

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        Every fuse is pulled but my headlights still work. That can’t be right can it?
         
      • 65 Dartman

        65 Dartman FABO Gold Member FABO Gold Member

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        Headlight switch is not fused but has an internal circuit breaker. It is wired through the splice in the underdash harness coming from the ammeter - at least that’s the way it works on my 65
         
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        • RustyRatRod

          RustyRatRod 30 Degrees Outta Whack

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          Pull the big red hot wire off the alternator.
           
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          • Craig Burriss

            Craig Burriss Well-Known Member

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            After tearing my car to pieces and unplugging everything imaginable, that appears to have been the issue. But what does this mean? My alternator is basically brand new
             
          • RustyRatRod

            RustyRatRod 30 Degrees Outta Whack

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            New does in no way shape, form or fashion equate to good.
             
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            • Craig Burriss

              Craig Burriss Well-Known Member

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              So what you’re saying is I need an alternator
               
            • Craig Burriss

              Craig Burriss Well-Known Member

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              This is the alternator I have. Some people say that to use this I have to bypass the ammeter by moving both ammeter wires to a single post on the back of it, then just run an 8 gauge wire from the alternator to battery. I kind of wanted to keep to ammeter working but I’d rather not buy another alternator.
              Powermaster Retro Alternators 75191
               
            • RustyRatRod

              RustyRatRod 30 Degrees Outta Whack

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              The voltage regulator COULD be stuck. I would check that first. If it's not that.........
               
            • RustyRatRod

              RustyRatRod 30 Degrees Outta Whack

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              Rather than rely on "some people" I would call Powermaster and see how they say to wire it. Did it not come with deestruckshuns?
               
            • Craig Burriss

              Craig Burriss Well-Known Member

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              If it did they are long gone by now. When I said it was new I meant I bought it 3 years ago but have never driven the car with it. Calling them does sound like a good idea lol.
               
            • RustyRatRod

              RustyRatRod 30 Degrees Outta Whack

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              If it is supposed to bypass the ammeter, that might be an issue. I'm just bright enough on electrical to get me.....and whoever else in trouble. LOL
               
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              • Craig Burriss

                Craig Burriss Well-Known Member

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                So here is what I have done. I called Powermaster and talked to their tech guy Chris. He said to just run an 8 gauge wire directly from the alternator to the battery and not worry about the wire that I had going from the alt to the ammeter. I installed the 8 gauge wire, but instead of just capping off the ammeter wire, I connected both ends in the engine bay to the big post on the starter relay, and then connected both ends of the interior side to a single post on the ammeter. I hooked the battery up and everything seemed to work fine but I could see the battery was still draining with my multimeter. I disconnected the alternator and the battery stopped draining. I guess I’ll be sending it off for repairs now.
                 
              • Mattax

                Mattax Just the facts, ma'am FABO Gold Member

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                This is remained correct for most A-bodies and options until '75/'76. '76 moved some of the power distribution splices to the engine compartment side instead of using one main splice.

                It means the output stud is partially grounded.
                Need to look at the alternator to see how it managed to do that.
                Yes.
                Or fix that one.
                Exactly.
                Just this is year I bought a brand new AC Delco alternator supposedly to GM specs right down to the part number. (This was for my '85 AMC - just so you don't think this was Chevy application, LOL). Output stud came loose after a weekend in NY state - and fortunately I had just enough time to make it back to Phila in daylight. Opened it up and the insulator was misformed so the stud was cockeyed and therefore it was inevitable it would loosen up. Damn good thing it didn't short! Yes they took the return and exchanged it. Still totally BS. Never would have been accepted in real production.
                 
                Last edited: Oct 11, 2019
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                • Mattax

                  Mattax Just the facts, ma'am FABO Gold Member

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                  Sorry you had to discover that the hard way.
                  The ammeter was your friend here.
                  If you hadn't checked for a drain after making those mods, a lot worse damage could have occurred.
                  Its good you used your head. :)
                   
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                  • Mattax

                    Mattax Just the facts, ma'am FABO Gold Member

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                    That's a squareback or possibly a revised squareback alternator.
                    They are pretty easy to open up.
                    Before doing that, might want to see if the ohmeter will show continuity between the case and the output stud.
                    Then to open it up.
                    First remove the brushes.
                    upload_2019-10-11_17-44-55.png

                    Then flip it over and remove the three long case screws.
                    Seperate the two halves keeping the stator windings with the back (output stud).
                    upload_2019-3-20_21-50-52-png-png.png

                    The output stud should be completely insulated from the case.
                    If it is, then the battery drain must have been going back into the positve rectifiers.
                    One of the electronic guys can probably be more helpful about how that could happen.
                    As you can see it everthing can be removed and replaced easily except for the pulley and bearings.
                    (and yes I forgot to remove the brushes before disassembling that time. oops)
                     
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                    • Mattax

                      Mattax Just the facts, ma'am FABO Gold Member

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                      I think I follow what you did.
                      The one drawback (ignoring the loss of the ammeter) is the lack of protection from battery grounding.
                      While the fusible link from the battery feed/charge line is still there, the original alternator feed has no protection. Nor does the 8 gage wire. If the alternator's output circuit internally grounded, then the battery would feed as much current as it could down that 8 gage wire until something burned through. :eek:
                       
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                      • Mattax

                        Mattax Just the facts, ma'am FABO Gold Member

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                        Assuming there's no additional loads that will be draining the battery (like EFI fuel pumps, or electric fans), the optional '73 factory wiring is a ggod way to reduce the load through the bulkhead connectors.
                        You could leave the original alternator output wire in place if you wanted. It would just be a parallel path to the main splice.
                        You could also temporarily leave the original battery output/feed to the ammeter as long as you watch the current loads and make sure they don't stay above 15 to 20 amps for any length of time. Really that's the only issue with a high output alternator. It can charge at higher rate than the standard ones. it may not do it at idle (depends on how its made) but will definately be able to do it above idle.

                        upload_2019-10-11_18-16-32.png
                        Because two parallel fusible links defeats their purpose, it doesn't makes sense to have two parallel wires from the battery to the ammeter stud. That's why the battery feed line should be either what is shown above or the standard routing.
                         
                        Last edited: Oct 11, 2019
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                        • Craig Burriss

                          Craig Burriss Well-Known Member

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                          Thank you for all of the tips and info. It looks like I’ll be busy this weekend! I will keep updating with what I do. I’m keeping the battery disconnected until I figure it all out lol
                           
                          Last edited: Oct 11, 2019
                        • Dana67Dart

                          Dana67Dart Like a fine wine, only getting better with age! FABO Gold Member

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                          First thing I would do is remove the voltage regulator wire from the alternator and check for discharge.

                          My first thought was a bad or reversely installed diode in the alt.
                           
                        • skykeith

                          skykeith Well-Known Member

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                          The reason Powermaster wants you to run an 8 gage wire directly to the battery is because your ammeter and wiring was designed for 40 amps and the Powermaster alternator is claimed to put out 95. things could get ugly.
                          Diodes in an alternator can leak and cause a large current draw.
                           
                        • 67Dart273

                          67Dart273 FABO Gold Member FABO Gold Member

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                          He is full of shit, and I'm suprised an outfit that is allegedly that tech savvy would say something like that. THERE IS ONLY TWO THINGS that would cause a battery drain and it is:

                          1...IF the alternator is NOT a "one wire," then the VR circuit is wired wrong, as it likely must have a switched source for the field/ VR circuit

                          2...Whether the alternator is "one wire" or not, the other possibility is a problem (DEFECT) in the alternator, IE a bad diode, etc
                           
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