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  • #16
    This help Carl?

    Home, down in the valley behind the Red Angus
    Bad Decisions Make Good Stories​

    Location: British Columbia

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    • #17
      Yes Willy, it's the same one I found and it along with the text describing what #2 term does that helped me solve the problem. The text said that #2 wire should go to the (+) battery post to sense the actual battery voltage but it's not required, just desired. It was then that it all began to make sense.

      I found an online internal wiring diagram of the SI alternator and #2 does indeed go to ground through two resistors in series. From a tap between the two it senses a voltage for the regulator.

      I have a diode in that wire to stop reverse flow and it allows flow toward the #2 term and it is connected to the batt term. There in lies the problem. There is no way to put the diode to stop forward flow which is what it is doing and grounding through the resistors. What I can do is run that wire over to the stud on the coil that is fed by the ign switch. Since it is only sensing battery voltage it does not have to be hot all the time. I can eliminate that diode and maybe the other one as well because when the ign is off it's not hot. In fact I don't need a diode on either wire because when the switch is off nothing can back flow.

      EDIT: on second thought it could back flow through the primary winding of the coil so I will leave them in for good measure. One can't be to careful.

      Tonight I will rework the wiring to avoid the battery drain.
      Last edited by Carld; 09-21-2011, 06:01 PM.
      It's only ink and paper

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      • #18
        BINGO, fixed it. With both wires to the coil post there is no current drain and it charges as it should. I could have spliced both wires at the diodes and run one wire to the coil but this works fine.
        It's only ink and paper

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        • #19
          When installing diodes around charging circuits, it is essential to remember that diodes have a forward voltage drop of about 0.7 volts. Sure, they allow the current to flow in the forward direction only, but they do drop the voltage.
          Auto alternator regulators are set to keep the alternator's output voltage down to 13.8, which is the voltage at which a lead-acid battery can be charged all day without damage. Unfortunately that voltage is insufficient to fully charge the battery, which actually needs to get up to 14.4 volts or so if it is to be fully charged – but it can't be kept at that voltage for long, or it will be damaged.
          In other words, a car or truck battery is only ever about 2/3 charged, even when the vehicle's charging system is working perfectly with a new battery.
          Putting a diode in the circuit can mess things up quite significantly, by reducing either the output voltage if it's in that circuit, or the voltage the regulator is sensing. So think hard about the downstream effects before modifying the wiring.

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          • #20
            On this type alt. #1 term is a trigger voltage to turn the regulator on so it starts charging. #2 term senses the battery voltage to tell the alt to cut back when the battery voltage gets up to what the regulator is set to charge to.

            It has always charged at 20 to 30A after a start up and then gradually goes down to about 5A or less with day light driving. The only effect of a diode in the sensing circuit may be to keep the charge rate a little high because the sensing voltage may be about .7v low.

            I do a lot of start and stop with the Jeep and seldom drive more than 5 miles at a time. I think all the starting keeps the battery from getting a full charge.
            It's only ink and paper

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            • #21
              Carl, I have wired a lot of alts up over the yrs., and worked on a lot of others. Yours is the only one I have seen with a diode in the #2 sense wire, there is just no need for it. Although the #2 wire will work from the battery post, or the battery stud on the back of the alt., the ideal place is a remote junction block in the harness, or the hot side of the starter solenoid, that way while running it senses the needs of the whole system, not just battery voltage level. If you had to isolate #2 from constant voltage to cure your problem, you have a problem in the alternator.
              James

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              • #22
                The way the diode is installed the voltage can get to the regulator in the alt but when the engine is off it keeps any voltage from coming out of the alt into the vehicle wiring.

                I have been a mechanic for a long time, retired now, but I have never had this issue. On the other hand I worked on road tractors and you hardly ever see them again.

                When I first got this Jeep the battery would get low enough over night to make it hard to start. After doing a search I found the wiring diagram I posted in post #1 and put one diode in #1 line. I still had a slight discharge over night so I put the other diode in #2. It seemed to fix it but when I let the Jeep set for a few days the issue was back so it never really went away.

                That's when I posed the problem here and some statements led me to search for an internal wiring diagram for the alt. When I saw it and read the associated text I realized that instead of the #2 diode stopping reverse flow it allowed flow from the alt output stud to the internal resistors and then to ground as someone said may be happening.

                Then I decided to put the #2 wire on the coil post that is fed by the ignition sw. and was going to remove the diode. I got to thinking as I looked at the internal diagram and realized if there was any bleeding of voltage to the #2 sensor term it would also bleed into the coil primary but on the other hand it would also bleed into the resistor to the ground. So, for the time being I will leave it in but like you, I don't think I need it.

                Right now there is no current draw between the (+) battery post and the cable so I will call it cured. If there were something shorting to ground in the alt I would get a voltage between the cable and the post.
                It's only ink and paper

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                • #23
                  If that schematic is really correct, there is a bad error in the design....

                  D2 is connected to the base of TR2.... and there is no base -to-ground resistor shown.

                  it is common for zeners to have some leakage, there is a spec for it on any datasheet.

                  In this case, if there is leakage, TR2 can "steal" current from the base of TR1, just as if the voltage were higher than it is.... That can cause the battery to be always undercharged, which may cause it to have low capacity and act as if it has a bad leak, not to mention gradually sulphating up due to undercharging. With a resistor, teh leakage current will not end up as base current, and the problem is reduced or eliminated.

                  That will not be the problem here, most likely, unless the battery does have a low charge state, and the 32 mA is enough to drain it..... A clean start actually requires very little in terms of ampere-hours, so a battery can be pretty dead before it won't start the engine in warm weather.
                  CNC machines only go through the motions.

                  Ideas expressed may be mine, or from anyone else in the universe.
                  Not responsible for clerical errors. Or those made by lay people either.
                  Number formats and units may be chosen at random depending on what day it is.
                  I reserve the right to use a number system with any integer base without prior notice.
                  Generalizations are understood to be "often" true, but not true in every case.

                  Comment


                  • #24
                    Originally posted by J Tiers
                    If that schematic is really correct, there is a bad error in the design....

                    .............
                    The schematic is indeed correct.

                    Although I obtained this copy online for the sake of this being the easiest route, I do have several factory GM service manuals with the exact same illustration in them.
                    There are literally millions of these alternators in service since 1969.
                    The "error" was designed into this alternator by Delco-Remy's design team a long time ago and has not been changed for decades so it's effects must be minimal as the SI series alternator is probably one of the most universally used for a wide range of different OEM applications.
                    Home, down in the valley behind the Red Angus
                    Bad Decisions Make Good Stories​

                    Location: British Columbia

                    Comment


                    • #25
                      As I'm reading the diagram, pin 1 has no source of current when the switch is off. Pin 2 is a constant drain on the battery. If a diode added to the pin 2 wire were to stop current from the battery from flowing into the regulator, then it would also stop the regulator from receiving battery voltage to monitor the state of charge. The alternator would run 'full tilt'. If the diode were put in the other way, the battery voltage would have to rise an additional .7 volt before the regulator would begin tapering off the charge. The battery would get overcharged.

                      Taking the diagram to be correct, the current flowing into pin 2 must be very little, since otherwise batteries everywhere would be draining down and dying early. Assuming a 30 ma constant draw on the battery through the regulator, it would take 33 hours to use up 1 amp hour of battery capacity. Assuming a 50 A/H battery, technically it would take a little over 2 months of non-use for the battery to deplete. Most batteries in vehicles have higher capacity than that.

                      This suggests two things- the current flowing into pin 2 is probably less than 30 ma, and secondly if it's the drain from the alternator causing the battery charge to deplete, then the battery is shot or the rectifier bridge in the alternator is leaky and draining much more than 30 ma.

                      The field winding has no source of juice when the engine is not running except through the indicator light and the switch. There is no source of voltage to T2 unless the rectifier bridge is leaky, aside from a small current which may pass through the zener from pin 2. Only if the battery voltage is fairly high will any current normally flow through the zener. With the engine off, the battery voltage would drop off from the peak, essentially to the point where no current would be flowing through the zener. At any rate, current flowing into pin 2 is at a low level, unless the regulator is screwed. The current cannot increase in any way because of the transistors being in there. If some base current flows in TR2 it's of no consequence as there's no voltage coming in to the rest of the regulator circuitry for it to have any control over.

                      If there's nothing wrong in the alternator, it isn't causing the problem. What could be happening is that it's not producing enough charge to keep the battery up.Your battery could be sitting at 5% charge, and then a couple of days sitting would kill it. I've had a vehicle sit unused for a year or more, and still had enough charge to crank the engine, so the normal drain from the alternator must be pretty low- low enough as to be inconsequential under almost every circumstance.

                      Interesting though- if the alternator isn't putting out what it should, it could be because it's dirty inside. Enough dirt, add some moisture, and it could then be drawing more current that it normally would. I got brave one day and decided to hose out my alternator when I noticed that it was getting intermittent- I could see the brightness of the lights changing sort of randomly. I went to a car wash and basically blasted the inside of the alternator with soap, then again with rinse. I figured I had nothing to lose, since I'd be faced with replacing it anyway. That fixed it right up, and it was good for years. I did that again a few years later and got the same improvement. I did eventually have to repair it, not for bad bearings but because the slip rings were worn out. After getting over sticker price shock, I rebuilt the slip rings myself and used the standard bearings/brushes/rectifier kit. This is the original alternator in my Toyota with over 400,000 miles on it.
                      I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-

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                      • #26
                        Easy way to eliminate a lot of problems with a GM SI alternator, get yourself a self exciting regulator, one wire needed only. The #1 and #2 wires are not needed, I have used them many times, greatly simplifies the wiring.

                        Ed

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                        • #27
                          Originally posted by Willy
                          The schematic is indeed correct.


                          There are literally millions of these alternators in service since 1969.
                          The "error" was designed into this alternator by Delco-Remy's design team a long time ago and has not been changed for decades so it's effects must be minimal as the SI series alternator is probably one of the most universally used for a wide range of different OEM applications.
                          Wide use doesn't mean it's right....

                          If you carefully select diodes it works..... and it's that little bit cheaper than using the resistor, which would make Delco bean counters very happy.

                          However, it just may be (and probably is) true that a lot of cars with Delco alternators are charging less than others.


                          Since the average car alternator beats on the battery fairly hard by overcharging it, maybe the ones that have a "problem" work better.........
                          CNC machines only go through the motions.

                          Ideas expressed may be mine, or from anyone else in the universe.
                          Not responsible for clerical errors. Or those made by lay people either.
                          Number formats and units may be chosen at random depending on what day it is.
                          I reserve the right to use a number system with any integer base without prior notice.
                          Generalizations are understood to be "often" true, but not true in every case.

                          Comment


                          • #28
                            This just got interesting. I was hoping some one with more electrical knowledge than me would post how the alt reg works. I will have to read the last few posts several times to fully understand what was said.

                            Remember, this alt is on a 1951 CJ3A Jeep with NO accessories, only brake lights, parking lights, headlights, one dash light and the ign coil. The battery is a little over a year old and it turns the original 6v starter. The electrical system is converted to 12v and retains the 6v starter which is common practice for these Jeeps.

                            At some point in the future I may switch to a one wire Delco alt but for now it's run what I have for me. OH, and as of now there is no drain on the battery with #2 term wire run to the coil where the voltage gets turned off with the engine.
                            Last edited by Carld; 09-22-2011, 10:18 AM.
                            It's only ink and paper

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                            • #29
                              Just because your battery is a little over 1 year old is no reason to assume it's 100% good. I've seen batteries only weeks old that are weak, fully charge the battery and load test it, only way to be sure it's good. Even with a bad cell, and a recent charge from the alternator, it will probably quite easily turn that 6V starter.

                              Ed

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                              • #30
                                Originally posted by J Tiers
                                Wide use doesn't mean it's right....

                                If you carefully select diodes it works..... and it's that little bit cheaper than using the resistor, which would make Delco bean counters very happy.

                                However, it just may be (and probably is) true that a lot of cars with Delco alternators are charging less than others.


                                Since the average car alternator beats on the battery fairly hard by overcharging it, maybe the ones that have a "problem" work better.........
                                JT, I didn't mean to imply that you were fundamentally wrong.
                                And yes wide acceptance doesn't mean it's right, but after over 40 years of successful commercial application it does indicate that it is at least...good enough.
                                Home, down in the valley behind the Red Angus
                                Bad Decisions Make Good Stories​

                                Location: British Columbia

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