Battery draining

Discussion in 'E9 Projects and Restorations' started by mr bump, Feb 11, 2019.

  1. mr bump

    mr bump Active Member

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    Got a bit of a pain........when I leave the battery connected on my 72 e9 cs, the car seems to drain it's power and over a period of a week, the battery is completely flat. I purchased a brand new battery, and it's done it to that too. Im leaving nothing electrical wise on, no central locking, no alarm led flashing, the trunk/boot light goes out as it should, so does the interior light so What could be the problem?
     
  2. bluecoupe30!

    bluecoupe30! Active Member Site Donor $

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    does your dashboard clock work?
     
  3. stphers

    stphers Active Member

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    First thing to do is to figure out how much is drawing on the battery. If a new battery went flat in a week, it looks like a fairly large draw. One quick thing to do is disconnect the + lead on the battery and remove all the fuses and put a test lamp between the + cable and the post of the battery, see if the light comes on and how bright it is. Removing the fuses eliminates a lot of items. If your light stays on, start checking the alt ( again disconnect and see if the light goes out ) If the light does not come on with all the fuses out, put one fuse in at a time and see if the test light comes on. This is just a matter of trial and error. Ign switch, lights, wipers , all of these things could cause a draw. Remove the interior , trunk and hood bulbs to make sure that it isn't one of those. Get a good wiring diagram Good luck


    Clock probably won't be enough to draw the battery down, that would take a least a month to do. Do you have a sound system in the car? a lot of times . they continue to draw after the key is off. Don't leave the key in the ignition ( some do when the car is in a secured garage )
     
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  4. Mike Goble

    Mike Goble Active Member

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    Is your glove box light on? You can put a test light in series with your battery cable and start removing fuses to more closely locate the leak. You can also put a disconnect on your main battery lead to keep it from draining until you figure it out.

    [​IMG]
     
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  5. bluecoupe30!

    bluecoupe30! Active Member Site Donor $

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    Come to think of it, it did take a month to weaken my battery (when the clock was still working). That, combined with a marginal battery, often resulted in a failure to start. I disconnect battery now, whenever car sits.
     
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  6. E9Wayne

    E9Wayne Member Site Donor

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    Wow, I had a similar problem years ago and it wasn't the obvious culprits. SF don eventually talked me through this and it wound up being that the load shedding relay was not closing. Mine was installed above the fuse box and was warm, even when my car was off. I removed it and problem was solved. I did replace this relay a few months later but I don't think it does much on our cars...
     
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  7. adawil2002

    adawil2002 Well-Known Member Site Donor $$

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    I disconnect the battery if the car is sitting more than 2-3 days.
     
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  8. m5bb

    m5bb Well-Known Member Site Donor $

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    This is my best guess.
    A friends 74 would do this. Took a while to figure it out. Removed relay like Wayne.
     
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  9. teahead

    teahead aka "Rob" Site Donor

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    Remove negative wire from battery and put a circuit tester in series with it and measure amps.

    See if you get anything more than say, 60mA and start pulling fuses to see if it drops.
     
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  10. mr bump

    mr bump Active Member

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    Thank you so much chaps, I've orderd a set of quick release clamps (Thank you keshav), and I shall carry out all the above on Saturday.
    Thanks again.:)
     
  11. m5bb

    m5bb Well-Known Member Site Donor $

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    IIRC that relay I mentioned above is not fused. It's on all the time. It should show up in your test.
    Good luck.
     
  12. Cornishman

    Cornishman Member Site Donor

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    If the doors are not fully closed the electric windows stay live on a phase 2 csi. Not sure if the others are the same. This caught me out when the car was new to me. Resulted in a flat battery. Clearly the same result if the door switches play up. You may wonder why I leave the doors open. If the car is wet after a wash or shower I dry it then leave it in the garage overnight with doors, bonnet and boot all open to dry better.

    I also disconnect the battery pretty whenever the car is in the garage.
     
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  13. Peter Coomaraswamy

    Peter Coomaraswamy Well-Known Member Site Donor $

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    The load shedding relay may be ONE of the things causing the problem and the bloody clock could be the other. The relay is a VERY easy fix and that helped, but the clock was still draining my battery so I disconnected the hot from the clock and have not had a problem since. It also works out that the clock is 100% accurate twice a day :)

    I stored Sam's sienna e9 for 6 months and it started up without a jump, so there can be multiple gremlins to track down which will help you become an Electrical Engineer if yo wish to go that route.

    Good luck :)
     
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  14. HB Chris

    HB Chris Well-Known Member Site Donor $

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    And I can park the coupe for two months and it starts every time, and the clock keeps perfect time too! I never use a battery tender either.
     
  15. Stevehose

    Stevehose Well-Known Member Site Donor $

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    Ditto. Except my clock loses 3 min per week. I love setting it to correct time as part of pre-flight checklist.

     
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  16. gwittman

    gwittman Member

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    I have found when my clock is working, the battery does not drain fast. When the clock is not working, the battery drains faster. My theory is; the mechanism that rewinds the spring is in the rewind mode and continues to draw current. However, I am sure there are other ways the clock could stop working that would not continue to draw current.

    That relay sounds like it is something to check on though.
     
  17. bavbob

    bavbob Well-Known Member Site Donor

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    Did you check voltage when car is running to ensure alternator is functioning?
     
  18. mr bump

    mr bump Active Member

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    That's on my investigative list for this weekend.
     
  19. mr bump

    mr bump Active Member

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    No, it's never worked since I bought the car.
     

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