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Thread: OT, Auto: Bubbles When Battery Is Charging

  1. #21
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    Quote Originally Posted by SLK001 View Post
    Test the alternator by starting the car, turning on as much electrical load as possible, then disconnecting the battery. If the car remains running, then the alternator is just fine. If the car immediately dies, then the alternator is bad.
    Really hope your joking --- you should at least add that face with the tongue sticking out you know so someone does not pop their regulator or worse yet ECU...

  2. #22
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    Well, that's my classic test for an alternator. But, as I said, I am not going to do the testing and repair myself. I just wanted to know why a battery would only bubble in one cell while being charged.

    So, there is an issue with disconnecting the battery while the engine is running? A little more on that, please. Are they putting fancy electronics in alternators now?

    The electrical load, after starting, is minimal. I have driven over 100 miles on the charge in the battery in past vehicles. Starting is the single biggest challenge for the battery: I have seen a starter motor draw over 500 Amps: the meter pegged HARD. 700 A, 800 A, 1000 A, more? I don't know but the wires were quite hot.

    Oh, and yes, with that bad alternator and a dying battery, I drove to the nearest open shop that I could find before shutting the engine down.



    Quote Originally Posted by SLK001 View Post
    Test the alternator by starting the car, turning on as much electrical load as possible, then disconnecting the battery. If the car remains running, then the alternator is just fine. If the car immediately dies, then the alternator is bad.
    Last edited by Paul Alciatore; 09-06-2019 at 05:27 PM.
    Paul A.

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  3. #23
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    Quote Originally Posted by A.K. Boomer View Post
    Really hope your joking --- you should at least add that face with the tongue sticking out you know so someone does not pop their regulator or worse yet ECU...
    Yes, totally agree, please do not disconnect your battery when the car is running. The battery is a huge filter that takes out out the AC ripple from the alternator's output. Without the battery there to do so you are taking a very expensive gamble that your alternator's output is clean. Not very likely , as a very compelling argument in favor of not doing this is that you will never find this as a suggested practice in any shop manual or diagnostic procedure that I've every seen.
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  4. #24
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    AFAIK newer vehicles (last 20 years or so) have electronic voltage regulators that can handle an open battery condition without damage. The alternator is three phase so the rectified waveform has only about 5% ripple, so the battery is not needed to smooth the DC output. The car's circuitry will have capacitors and surge suppression devices to protect against the usual fault conditions. A corroded or loose battery terminal is a fairly common occurrence, and usually causes no damage.

    Some discussion of this situation:
    https://forum.allaboutcircuits.com/t...rnator.118783/

    AIUI, an alternator generates a voltage which is proportional to field voltage and RPM. At idle (say, 600 RPM), the field is probably excited by pretty much the full battery voltage, and the output will be about 16 volts. At 3600 RPM, however, the rectified output voltage could be as high as 80 VDC, or perhaps even as much as 120 or so. If this is true, disconnecting the battery when the engine is idling will not create a huge voltage surge, and the electronic regulator is fast enough that it should adjust the field voltage to keep output within safe limits.

    The discussion above references the Lundell alternator, and posits that it is a constant current device. But that does not seem to be true, except in a limited sense. Traditional automotive alternators are inherently inefficient, typically around 50%, partly due to high internal impedance, which results in current limiting. This is partly due to iron losses which are prevalent at higher speed, which reduces the high voltage that would be produced by a more efficient device. This is an inherent safety factor, such that it can survive short circuit conditions, at least for a reasonable amount of time. More modern and higher power alternators, however, are more efficient, and thus may be able to supply a lot more current. Some technical info:

    https://electrical-engineering-porta...law-pole-rotor

    https://en.wikipedia.org/wiki/Alternator_(automotive)

    http://cdn.intechopen.com/pdfs/38166...lternators.pdf
    Last edited by PStechPaul; 09-06-2019 at 09:32 PM. Reason: link

  5. #25
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    Well, for better or worse, I am not going to disconnect the battery. The truck is 19 years old and just inside PSTechPaul's 20 year statement.

    Again, as I said, I am not going to troubleshoot or fix it. I have a good mechanic for that. I was only wondering about the bubbles in only one cell. By the way, I checked again today while it was on the charger and there were no bubbles at all. That may be more significant.
    Paul A.

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  6. #26
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    Quote Originally Posted by A.K. Boomer View Post
    Really hope your joking --- you should at least add that face with the tongue sticking out you know so someone does not pop their regulator or worse yet ECU...
    On the other hand, that is a great method for finding out how many processors your car has and how expensive they are.

  7. #27
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    It's never good practice and has actually been warned about in countless service manuals,

    the battery is not just a filter it's an amperage stabilizer, say the AC is on at the time of disconnect and the clutch was not activated then it kicks in - it's high amperage draw that all the little caps in the electrical system have virtually no buffer effect - therefor its a spike load that the regulator see's immediately and try's to "amp up" and compensate, then inevitably overshoots BIG TIME and has to keep trying to regain control --- again it's a very good way to pop a voltage regulator and if that happens and happens in the wrong way then you can toast your ECU immediately after,,,

    and as far as battery cables - if they just handled all the amperage it took to just start the car then there is obviously a connection good enough to run the charging system,

    bottom line - bad practice and in fact if you see a mechanic doing this as an electrical test for you car get his name date and time for future reference.

  8. #28
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    Quote Originally Posted by CarlByrns View Post
    On the other hand, that is a great method for finding out how many processors your car has and how expensive they are.
    totally agree.


    heck - certain alternator (with internal regulator) companies will not even honor their warranty if your just using the wrong sized battery - imagine what they would think with one disconnected...
    Last edited by A.K. Boomer; 09-06-2019 at 09:48 PM.

  9. #29
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    Quote Originally Posted by PStechPaul View Post
    AFAIK newer vehicles (last 20 years or so) have electronic voltage regulators that can handle an open battery condition without damage. The alternator is three phase so the rectified waveform has only about 5% ripple, so the battery is not needed to smooth the DC output. The car's circuitry will have capacitors and surge suppression devices to protect against the usual fault conditions. A corroded or loose battery terminal is a fairly common occurrence, and usually causes no damage.
    Paul I'll concede the fact that your knowledge of electronics is vastly superior to mine and in a perfect world you would be right, however my experience with automotive electrical systems leads me to believe that it is far from a perfect world.
    Hence my mention of the fact that you will never see the recommendation to disconnect the battery while the engine is running in any factory shop manual or as a professional diagnostic tool. You may have gotten away with this before cars were heavily endowed and dependent on sensitive electronic systems but it would be foolish to do so on anything produced in the last 25 years.

    You have way more confidence in automotive system circuit protection than I do. If you feel confident about your assertion that it is safe to do so be my guest and do so on your own vehicle a few times, take it for a drive around the block and let me know how you make out. Just too many variables in the equation for me to take that chance and I don't think you would either. Same reason I would not advise others to do so.

    A link to a small .pdf from Merceds on the subject below, I grabbed the first I found, many other links to AC ripple issues in automotive electrical systems, it bares mentioning that I have encountered AC ripple in just about anything I've checked it for, and that still functioned as intended. Toss in some leaky diodes and it's a safe bet to assume you are walking on thin ice. Automotive electrical systems are not as simple and robust to abuse as they were in the past.


    Too Much AC voltage in the DC Charging System Ripple Voltage

    What an alternator puts out, even after it is
    “rectified” by the diodes (that is, converted to
    DC), isn’t very pretty. Even a healthy alternator
    puts out some ripple. And it won’t produce AC
    readings on voltmeters that are nearly as accurate as a “pretty” sinusoidal waveform would.

    Specifications for the maximum permissible
    amount of ripple vary. In general, with older
    carbureted vehicles, anything under two volts
    peak-to-peak was okay; no sensitive electronics
    were aboard. On early fuel injected cars, generally under one volt peak-to-peak was acceptable.
    But on later models, nothing more than .5 V is
    acceptable. It’s typically when one or more
    diodes begin to break down, and allow current to
    flow in both directions, or neither, that AC ripple
    increases, and strange electrical problems begin.
    Remember, ripple propagates all the way through
    the vehicle's electrical system.
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  10. #30
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    I would not disconnect the alternator. A lot of auto parts stores will test the system for free, check if the battery is bulged or swollen this is a sure sign of a bad battery. I have turned the lights on and blown the horn and watched to see if the lights dimmed a lot. Bubbling in one cell would make me suspect a bad battery. I replaced the battery in my truck last year, OEM would have been its twelve d year.

    Jon

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