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Exciter wire voltages 900 1992

Just installed a new alternator. I'm curious about the voltages on he exciter wire off the alternator.

With key out of ignition, it measures 0 volts (Good thing).
With key on position 2, it measures 1-2 volts, very little.
With engine running, it measures 15.5 volts, yet voltage on positive alternator terminal is only 12.6 volts. Voltage at battery terminals also measures 12.6 volts. Why such difference in voltage between exciter terminal and alternator plus terminal?





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    Exciter wire voltages 200 1981

    Sounds to me that your not using the same reference for all the measurements. I would take all measurements using the battery negative terminal as ground. You may want to take a few measurements of other "ground" points with respect to the battery also.





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      Exciter wire voltages 200 1981

      All the ground connections test well. I can use negative battery terminal, any part of chassis, or even any part of the engine. It makes negligible difference.
      My question remains, why am I getting 15-16 volts on he exciter wire, on alternator, with engine running, while I'm only getting 13 volts on the positive alternator output terminal that feeds the battery?

      Alternator is Bosch, rebuilt and guaranteed. I also had a new regulator/brush/diode module which I swapped with no difference.
      I'm having the same issue with old and new alternator. I'm starting to think they are not the problem. I'm starting to suspect instrument cluster or ignition lock.





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        Exciter wire voltages 200 1981

        You mentioned:
        "why am I getting 15-16 volts on he exciter wire, on alternator, with engine running, while I'm only getting 13 volts on the positive alternator output terminal that feeds the battery"

        My answer:
        Could be the alt is CHARGING the batt while you're taking voltage measurement. The exciter terminal doesn't connect to any heavy load so you get the full voltage ie. 15-16volts. Let the engine continue to run idling for 1 hour or take a short 1/2 hour drive to charge the batt. When done, read back the voltage on batt terminal on alternator. You should get a much closer reading between batt and exciter terminals. If nothing changed then you can bet one of the diodes in your new alternator has malfunctioned.

        The most overlooked rule while doing alt voltage measurement is to use a good batt. This has been mentioned in Bosch alt manual.





        Amarin.





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        Exciter wire voltages 200 1981

        Hi,

        Ok Tim I think you are obsessed with this “exciting” issue of a thing. (:-)

        We as a non technical group don’t get into this but Art Benstein does here!

        https://www.brickboard.com/RWD/volvo/1385648/220/240/260/280/link_good_wiring_diagram_observation.html

        I put this on here so you can see the dash, switch, battery, firewall connector... the whole she bang!
        If you so dare or need to, go ahead and study this to trouble shoot things.
        Like you said, the other end of that exciting wire is entertaining us!
        (:-)
        Now to most of of us, it looks like some strange Artist work! But it’s just Art, trying to help us in the 240 section.

        You have raised up some good thoughts especially the part of how am I getting more volts that the battery has! We both know there is no step up transformers here, so why?

        Well, some how you have picked up on the AC side of things going on inside the alternators windings. His diagram shows the back feed circuit to the regulator and how it’s the middleman over to the rotors slip rings.

        There is actually more voltage being generated in the windings because as the voltage/ current pluses pass through a diode, the voltage drops across the diode. So there needs to be more!
        This is Very similar to a resistor and it’s about .7 of a volt drop.

        An open or shorted diode will pass no voltage or will show voltage with no drop from its input!
        It is an actual method of tracking or troubleshooting a circuit for damage. Especially, if a transistor has failed in electronics. Some look for gain but it’s not in voltage but signal gain.
        That is, if you have the right kind of voltmeter, called an oscilloscope. It shows peak to peak volts in AC.
        A regular voltmeter use a Root Mean Square readings for AC readings.
        This Gets me, that it is the same math as a sine for a 45 degree angle ... .70746. I have that memorized!
        30 degrees is .5. Machines move with right angle coordination within a Cartesian space.
        Electronics will always elude me as my last frontier! So many wonders, so little time!

        So, that supposedly wild high reading depends on the ground point like John says. He is Mr. numbers in the thread! (-:)1982Dl*****.
        We both think it is how you are reading things and we are not there to see it.

        Going back to Arts diagram you can plot out the three windings and corresponding outputs through diodes.
        He shows the two points on the regulator set off to the lower left corner to how it becomes the middleman.
        Now Art can explain this better than I can, but just maybe, the regulator diodes are leaking through excessive voltage and raising those voltage readings.
        It should not be higher than the charging system voltage but only slightly less. The light bulb has to create a voltage drop as it is a resistance.

        These reported findings, from you, are throwing everyone a curve!
        In electronics, Sometimes, this could be called a floating ground issue between pluses?
        A term that I have not understood either!

        I personally have never bother to check the exciter wire but I would only look for voltage coming through from the dash to ground only! Only off the end of the wire.
        Not connected to the regulator side of the circuit on the alternator D+! When you are connected you are messing around with a voltage producer!
        I have no experience, but you do!
        Normal DC volts can be as high as 16 volts written on alternators.
        I have read where people claim 45 volts! How they can get that, I don’t know and you don’t want to see that. It can blow out light bulbs.


        Have you ever checked the alternator housing back to the battery negative post with your voltmeter?
        When in parallel you should get 0.000 on the meter. Same with the positive side. You are allowed up to 0.020 millivolts of discrepancy. Above a 0.2 is serious.
        Any higher then you start having resistances almost exponentially. This reading can cause and is a sign! It’s a voltage drop someplace in a whole circuit between test points.
        You want to eliminate stray incomplete groundings for sure.

        Remember, I said the regulator looks for TENTHS of a volt variations and makes current adjustments accordingly.
        The connections/continuity of voltages thing can not be over emphasized!
        This check is done with something on in the car or with the car running and having a current flow in-or out of the cable will do!

        You are looking for a high resistance in any battery cables or connecting wire on either side.
        In electronics the circuits are tiny and so is the tricks it does with very little power.
        A car alternator is big stuff but the same principles apply.

        Anyway, I think you will get the puzzle figured out and even might understand, it eventually, better than most of us! No kidding!
        Answers are always on the end of questions and in the back textbooks, but they just don’t fall out when you shake the book! Getting an answer to quickly is cheating yourself!

        Head scratching is allowed on the BrickBoard, so we all learn!
        Interesting that John is like me, on the 240’s, as it has gotten slow over there!

        Phil





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          Exciter wire voltages 200 1981

          Thanks!
          Just when I thought you were detail oriented, I see the charging system drawing by Art. Amazing... it must have taken him hours. I assume Art did this years ago before smart phones of digital cameras. People on this board continue to amaze me.
          I'll get to the bottom of this, I'm sure. I appreciate good challenge. I'm retired...so time is on my side.





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    Exciter wire voltages 900 1992

    Hi,

    I don’t usually answer any questions on the 900’s because I have never owned one or worked on one. Since this is an alternator and a alternator is a alternator! Maybe I got a chance?

    The statement about checking the voltage on the exciter wire, it seems that you are asking, What should the voltage be on the exciter wire if is disconnected from the alternator?
    It will be very low!
    I’ll explain as best I can.

    If it’s disconnected the alternator, the alternator does not get a tickle of current to get thing up and going!
    So, it will put out no voltage rise or have actual current to raise the voltage above the resting voltage of the battery. It needs about one-volt above the system voltage for current to flow towards and into the battery.
    As the car is running, the battery is getting drained down to the 12.65V surface charge or lower if allowed to keep going.

    The exciter wire gets its power through the “red battery light” under normal operation.
    This voltage is considerably lower because the bulb acts as a current/ load dropping resistance.
    Only a few volts and a low amount of current flows to the regulator. From there it goes into the rotor to create a magnetic field. The magnetic lines of force cuts through the many turns of windings and out pops electrons!
    This only starts the output and from here it gets greater.

    The regulator then starts watching the systems B+ voltage on its output windings and related diodes.
    It is comparing or watching for a few tenths of a volt rise and ups the ante with more current.
    There are two set limits of “roughly” 13.2 to 14.2-.6 volts. Variances are allowed for ambient temperatures but the idea is to be holding the pushing power of 1.0 to 1.5V and the getting the current flow to hold it there!
    No matter what sudden but “normal” withdrawals happen.
    Jump starting is not normal. If the two systems can get closer equalized, say, with passage of some time hooked up, before drawing on the circuits, it is safely done to both of the systems to suppress surges on diodes.

    When voltage is lower, it self feeds some of its own current, being produced, back in towards the rotor.
    It then becomes a “self regulated” charging system.
    Some models of newer alternators are slang called “one wire” because it’s all internally controlled.
    I haven’t seen or used one but in my younger days the early hot car roadsters used them for their simplicity. A solid housing mount makes the ground wire nonexistent, right there!

    Anyhow, The output now opposes the voltage coming from the dash to ground that’s through the regulator,
    The idiot light will now glow dim and then goes completely out!
    You have seen it hundreds of times!
    It does not take much of an output to do this, because the voltage is so low it’s easily overcome!
    The light bulb arrangement was explained before.
    This is why it is a false indicator that the alternator is all OK or hunky-dori!

    Remember tenths of a volt count big time here on current output.
    There has to be good connections to get the best readings, in tenths of a volt, to that regulator.
    He is the middle man! Just like in food prices, he truly affects things!

    A dash mounted voltmeter is the best indicator, to watch that middle man work on the system!
    A flickering of headlights helps wake you up to look at the voltmeter but a “scanning habit” is best as you don’t see, them headlights, in the daylight very well!
    A real good airplane pilot develops this scanning habit in order to survive!
    He is always looking for a possible place to land on his route too! Because #### happens everywhere!

    If your belts get too loose the voltmeter wiggles or sits parked tilted and consequently lower than usual.
    The red idiot does nothing until it’s real bad! Maybe in like, the alternator is about to fall off, bad!
    Remember that, it’s a rubber bushing mounted unit and that is not better than sliced bread!

    The whole ticket is to be an “overseer” of the middleman’s whole system by using the voltmeter!
    If you don’t have an in-dash meter, then when checking oil, flop a handheld digital voltmeter on there!
    Look for a steady hold on the voltages held between this two readings above. A battery in a good charged condition, the tenth numbers are the best heads up to worn brushes or corrosion.

    Hope this helps you understand how it works and how maintenance pays out dividends with no tow bills.
    I like that you are pondering and asking questions, for better insight!

    Insight is what grows in between the foresight and hindsight of a human!

    IMHO
    Phil





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      Exciter wire voltages 900 1992

      Dear Phil, firstly, huge thanks for such detailed explanation. I really appreciate it. Yes, I am very curious person, always asking "why" or "what if" questions. I don't care for status quo. When I measured exciter wire voltage I did it with wire connected to the alternator, not disconnected. It appeared odd that voltage on it would be so high with engine running. I expected high voltage to be on battery feeding connector, but that isn't the case. Like the two connectors are reversed on alternator side, but they obviously are not, as they are physically different and impossible to swap.
      I essentially have new alternator (bench tested good) that isn't outputting enough voltage. Ground connections have all been tested, cleaned, tightened and retested.
      I cleaned and tested all the fuses. I also cleaned and tightened battery terminals. Battery is good, it holds the charge well. There is no power loss over days of not running. But the alternator only puts out around 13 volts at idle with accessories turned off. If I turn on the lights and fan, voltage drops below 12 volts. Alternator can not keep up. The battery icon light bulb on instrument panel is not burnt.





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        Exciter wire voltages 900 1992

        Hi Tim,

        I’m a little confused with the posts. You had higher voltages in the first one and now you are to low with a load applied.
        This means to me, like you said, curious, that current flow out of the alternator is not correct.
        It’s acting like one diode or two are not working at full capacity.
        You see the alternator puts out three waves of pluses in one rotation. That’s why they are more efficient than the old DC generators before 1965.
        You could short an output into the regulator or from the stator windings.

        You said you “essentially” have a new alternator? I don’t relate to essentially. Is it off a scrapyard car, a rebuilt one from a parts house or what?
        Bench testing is only as good as the person testing it with good connections.

        Are you sure that housing of the alternator is grounded with a wire to the engine? Remember Volvo uses those rubber mounts! You are not the first person to find a faulty wire down there.
        Of course, I assume that the 900’s still use rubber mounts? I not up on the 900’s.

        On used or rebuilt alternators there can be a snafu using either! Rebuilds are not always completely refurbished or assembled with due diligence!
        If the rotor brushes or the slip rings on the rotor are not conducting current into the rotor the magnetic field will not get stronger and therefore less current output.
        In other words, the middleman, the regulator & brush pack can not deliver the goods!

        I suggest you pull the alternator off the car because something is not right and you are going to have to do it anyways!
        If you remove the regulator & brush pack, you can verify their condition. The regulator is held in by two screws. It’s a straight forward job to inspect it’s contact spring and brush lengths. The brushes must slip freely in their spring loaded holders.
        You can look into the hole and observe the slips rings for wear. If the brushes are short or a deep groove can be felt with your finger in the slip rings, there is a problem!

        Checking diodes are more difficult as they are on a heat sink plate but can be replaced individually.
        If need be, by automotive electrical shop. Most people get another alternator, especially, if there are signs of wear as mentioned above. Just use a reputable shop!

        I wish I knew what we are dealing with, you know, like a warranty?
        You can rebuild it yourself, as that is how people in the business, get started in the business!
        This way, you know what you have in a good reliable alternator!
        This is a recently changed site that you can learn a lot from and they have god part descriptions and prices the last I knew. Some people on the Board have used them in years past!

        https://www.aspwholesale.com/search.html?search%5Bkeywords%5D=Bosch&_a=category

        Let’s see what you have and we will come out on the other side, more knowledgeable!
        If it’s hot or cold outside it’s a good bench project tearing these things down.

        Phil





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