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Thread: Constant dead battery??

  1. #1
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    Constant dead battery??

    My battery light is usually always on, Very dimley and when I rev it comes on brighter.

    If I turn my car off for like 5 minutes and try start it up again, It usually cranks quite slow since the battery is nearly dead. Or if I turn it off for a couple of seconds with the headlights left on, The battery dies and I have to jump or push start.

    The battery is only about a month old (I had to replace it as my old one was too tall to fit in the front). I have only just started having the dieing battery the last couple of days. Latest things I have done to my car include adding a headunit and a water temp gauge. I wire the water temp gauge to the 12V ingnition that goes to the headunit to turn it on..

    I also measured battery voltage while the car was running, And it was ~13.5V. As soon as the car is switched off, The voltage is only at 12.2V.

    Time for a new alternator ? I bought a rebuilt one and it will be here in a couple days. But just wanted to know if anyone had more thoughts as to why it may be dieing so fast.


  2. #2
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    When running the voltage should be atleast 14V but before you go out and buy an alternator get a load light preferably an incandesent one because LED ones take very little current to light up and place it in series with the positive baterry lead (make sure the trunk light is off when doing this as well as every other electronic device). If the light lights up you have a draw and it's probably comming from your head unit. If there is no load then look into an alternator problem.
    "Screwed" by ESS Tuning

  3. #3
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    Well I have already bought a alternator, But it won't be here for a couple of days. And my old one has holes drilled in the fan blade things at the front that whine really loud when you rev... So I am pretty keen to get rid of it.

    But yeah I will try checking load. I guess I could use an ammeter? and check current being drawn from the battery while nothing is on. If I were to use my ammeter, What should the value be at? I assume either 0 or something low?


  4. #4
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    Quote Originally Posted by FrantiC View Post
    Well I have already bought a alternator, But it won't be here for a couple of days. And my old one has holes drilled in the fan blade things at the front that whine really loud when you rev... So I am pretty keen to get rid of it.

    But yeah I will try checking load. I guess I could use an ammeter? and check current being drawn from the battery while nothing is on. If I were to use my ammeter, What should the value be at? I assume either 0 or something low?
    Don't use an ammeter, you need a incandesent load light. Get one a autozone pep boys etc.

    You could use an ameter but it'll confuse you more then anything, a load light is quick and the bottom line with an incandesent load light is if the light lights up bright there's a draw and you know there's a problem. If you use an ameter you'll get a reading all the time becuase of systems in the car that are always on so you will never get a reading of 0V. Also you will need a pretty good ammeter to detect low amperage like that. I have a fluke one that I need for my aviation field but a radio shack one will not cut it.

    Just spend the $20 or less and get an incandesent load light.
    "Screwed" by ESS Tuning

  5. #5
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    Quote Originally Posted by FrantiC View Post
    my old one has holes drilled in the fan blade things at the front that whine really loud when you rev... So I am pretty keen to get rid of it.
    Those holes are to simulate the sound of a supercharger. You might notice a decrease in acceleration when removing this alternator.

  6. #6
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    Quote Originally Posted by barbierij View Post
    Those holes are to simulate the sound of a supercharger. You might notice a decrease in acceleration when removing this alternator.
    "Screwed" by ESS Tuning

  7. #7
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    Lol yeah thats what I heard they do..

    I tried checking with the ammeter and yeah it reads 0 so I guess it doesn't read low enough. I will have to get a load light tomorrow then.

    I have checked and nothing I know of is on, Except the digital clock which has always been on but dimmed. Is there anything other than the boot light that I could check as a known cause to drain the battery?


  8. #8
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    Quote Originally Posted by FrantiC View Post
    Lol yeah thats what I heard they do..

    I tried checking with the ammeter and yeah it reads 0 so I guess it doesn't read low enough. I will have to get a load light tomorrow then.

    I have checked and nothing I know of is on, Except the digital clock which has always been on but dimmed. Is there anything other than the boot light that I could check as a known cause to drain the battery?
    Radio that has to keep time and store stations.
    "Screwed" by ESS Tuning

  9. #9
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    Oh yeah true. I don't store stations, Only use CD..

    But another thing I forgot to add is last night when I was leaving my mates house when I was sitting in the car talking and letting the car warm up, I was giving it bit of a rev because we were talking about how I need to get my valves adjusted and blah blah, But every time I revved all the lights inside the car, and the headlights against the side of his house would all brighten up, then as the car revved down they would dim down again. They aren't dimed much, But they do get a noticable amount more brigther when I rev the engine.


  10. #10
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    Quote Originally Posted by FrantiC View Post
    Oh yeah true. I don't store stations, Only use CD..

    But another thing I forgot to add is last night when I was leaving my mates house when I was sitting in the car talking and letting the car warm up, I was giving it bit of a rev because we were talking about how I need to get my valves adjusted and blah blah, But every time I revved all the lights inside the car, and the headlights against the side of his house would all brighten up, then as the car revved down they would dim down again. They aren't dimed much, But they do get a noticable amount more brigther when I rev the engine.
    There's deffinately a drain on the system and the altenator can't kepp up with it. For example in my car I have a 600watt amp and when it hits hard the lights dim (I know I need a capacitor so it doesn't do that but I rarely use the system, I got it for free) but point here being that's a load or draw that the altenator can't keep up with so it draws extra from the batery hence needing a capacitor but my altenator's fine. You might need an altenator after all.
    "Screwed" by ESS Tuning

  11. #11
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    Definitely sounds like the alternator is on the way out. My e21 is getting another since mine went bad too

    Another way is to check for a drain in the system. Disconnect the negative cable and have the voltmeter in between and start pulling fuses. If you see a change when you pull the fuse then you know if you have a drain and where.

  12. #12
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    Quote Originally Posted by 1988 325ix View Post
    There's deffinately a drain on the system and the altenator can't kepp up with it. For example in my car I have a 600watt amp and when it hits hard the lights dim (I know I need a capacitor so it doesn't do that but I rarely use the system, I got it for free) but point here being that's a load or draw that the altenator can't keep up with so it draws extra from the batery hence needing a capacitor but my altenator's fine. You might need an altenator after all.
    Then it probably doesn't help I have a 500W amp AND a 1200W amp. But they worked fine in my old 325i, where this engine was out of and the headunit / speakers and amps. Only thing I changed was a new battery.

    Any thoughts as to why when I turn the car off from a running 13.5V it drops to 12.2V?


  13. #13
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    Quote Originally Posted by FrantiC View Post
    Then it probably doesn't help I have a 500W amp AND a 1200W amp. But they worked fine in my old 325i, where this engine was out of and the headunit / speakers and amps. Only thing I changed was a new battery.

    Any thoughts as to why when I turn the car off from a running 13.5V it drops to 12.2V?
    The amps only matter when they are runnign at full capacity.

    As far as voltage, the batery voltage should go up to around 15V-16V when running to keep the batery charged. That's normal. What I think is 13.5V is too low when the car is running.
    "Screwed" by ESS Tuning

  14. #14
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    The warning light in the cluster indicates that the alternator isn't producing enough output. That could be a failing alternator, loose alternator belt, a bad connection in the primary power circuits, or excessive load. A quick check is to measure the system voltage at idle (should be 13.5v or more) and at 2500rpm (should 14v or more).

    To check for excessive parasitic draw (the current drawn from the battery with the engine off) you need to measure the current drawn from the battery with a digital ammeter. That's best done by connecting the meter between the negative battery terminal and the negative cable. Normal parasitic draw is 30-60ma. If more that that is seen, one pulls one fuse at a time until the offending circuit is found. The most common cause of excessive parasitic draw is improperly installed aftermarket electronics.

    Although not usually a problem on an E30, with its lesser amount of electronics, later BMW's can spike 10a or more when the battery is connected. To avoid damage the the meter I power up the car via a jumper cable from the negative post to the negative cable, then connect the meter, and then remove the jumper cable for the current measurement.
    The car makes it possible, but the driver makes it happen.
    Jim Levie, Huntsville, AL

  15. #15
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    Yep it is at 13.5V at idle, But doesn't seem to increase when revving though.


  16. #16
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    In that case, the alternator isn't working correctly. It may be nothing more than worn brushes, which can be fixed by replacing the brushes or the regulator/brush assembly. Or you can replace the alternator.
    The car makes it possible, but the driver makes it happen.
    Jim Levie, Huntsville, AL

  17. #17
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    My replacement "rebuilt alternator" should be here tomorrow so I will just see how that goes. More interesting stuff though, Usually leaving the headunit playing for even 5 seconds used to kill the battery when the car wasnt running and it would not start again.

    But all day yesterday, last night and this morning the battery was on the charger. And today have had no problems at all. Even blasted my music for a good half an hour skating.. And then it started up perfectly fine afterwards. So I am thinking the alternator wasn't charging the battery up enough and replacing it should hopefully fix the issue. Fingers crossed..


  18. #18
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    Quote Originally Posted by FrantiC View Post
    My replacement "rebuilt alternator" should be here tomorrow so I will just see how that goes. More interesting stuff though, Usually leaving the headunit playing for even 5 seconds used to kill the battery when the car wasnt running and it would not start again.

    But all day yesterday, last night and this morning the battery was on the charger. And today have had no problems at all. Even blasted my music for a good half an hour skating.. And then it started up perfectly fine afterwards. So I am thinking the alternator wasn't charging the battery up enough and replacing it should hopefully fix the issue. Fingers crossed..
    Take a running voltage reading on the battery now just to see if it's up to the 15V-16V charging capacity.
    "Screwed" by ESS Tuning

  19. #19
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    The alternator should output no less than 13.7V and more than 14.2V. The voltage regulator is temperature compensated, so with typical temperatures the range should be 13.7 to 13.9V. The voltage should be slightly less at the battery terminals. If the battery is new and very discharged (e.g. reading 12.2V), the alternator output may be current limited, explaining a 13.5V reading. But after running for a 20 minutes the battery should slow its charge acceptance and the voltage should increase to 13.8V.

  20. #20
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    I have kind of a related probelm.....i think... my 328i died twice this week...AAA came and jumped me and told me the battery was good...and ran a check on the alt and that apparently came up good aswell.. yesterday it did it again out of nowhere it wouldnt turn over....i get click click click..... and then the rest of the power drains and nothing...try and jump it from another car ...not happening...AAA comes again in uses a power pack and it starts no problem....took my battery to pep boys and they tested it twice ...once on the reg machine and the second on the lil hot coil pack thing to try and overload the battery and nothing it comes out good both times....what could my problem be?? Thanks...

  21. #21
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    Quote Originally Posted by thejlevie View Post
    In that case, the alternator isn't working correctly. It may be nothing more than worn brushes, which can be fixed by replacing the brushes or the regulator/brush assembly. Or you can replace the alternator.
    It could also be faulty ground making it so the alternator wont charge. this was the case on my 318i. I scrubbed all the grounding points and cleaned them up, made sure they were all OK and fastened properly... took care of any issue I had.

    I know in the US most parts stores will test your alternator for free if you bring it in. Some stores you don't even have to bring the alternator in you can just bring your car and they plug it in to something!

  22. #22
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    Revival of my old thread huh..

    My issue was fixed with a rebuilt alternator.. Easy to swap out.


  23. #23
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    Constant Battery Drain

    86 325es -
    jsut read thru the 2005-08 posts on this subject and have a similar issue:

    Pulled Alternator and had tested - all good
    Voltage at battery is running 12.5-12.8 while running - seems quite low according to the threads...

    Battery is new - alternator is also new -

    reading same 12.5-12.8 at the power point under the hood -

    how can I check for good ground see if the alternator is putting out the correct voltage...

    the alternator bracket is showing some signs of 180k miles but the belt does not seem to be loosening - it is still tight..


    any thoughts ??? let me know...

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