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What is causing this drain?

Discussion in 'Electronics' started by amwebby, Jan 5, 2008.

  1. amwebby

    amwebby Hardcore MB Enthusiast

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    Twice now over the holidays I've had to call out MobiloLife for a flat battery (new one year ago).

    Something is draining the battery but what? I have three possibilities:

    1. UHI Kit, retrofitted by myself with expert advice and the least likely as fitted for two months now.
    2. TV Tuner - as the car was pre-wired, with the exception of the amplifiers, unlikely as it should have been plug and play.
    3. Third party DVD/MP3 player. Most likely as just fitted, but by a professional installer. Unit goes off with ignition. One possibility was the USB input, a memory stick in there may have been draining when off but no light was showing from the stick when ignition off.
    Ideas please. I've disabled the DVD player until I can get it checked and I can see it is the most likely but why? If the unit powers down when the ignition is off there should be no drain, right?
     
  2. television

    television Hardcore MB Enthusiast

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    The max current allowable is 38m/a when the car is locked.

    This can only be checked by inserting an ammeter without breaking the circuit so that the path of the leak is not broken
     
  3. OP
    OP
    amwebby

    amwebby Hardcore MB Enthusiast

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    MobiloLife checked by some device that encircled the live feed from the battery. They said it should show no more that 0.08 amps. The closed the boot lock and locked the car to fool the car into thinking it was fully closed and shut down. It got down to about 0.18-0.20 after around 15 minutes.
     
    Last edited: Jan 5, 2008
  4. television

    television Hardcore MB Enthusiast

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    I hope you mean 0.018 -0.020 if not then something is drawing too much.

    The device they used was a clamp meter

    The figure of 0.080 is an outside max when they have problem cars but 0.038 is the correct max when perfect and locked
     
  5. OP
    OP
    amwebby

    amwebby Hardcore MB Enthusiast

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    They said about a quarter of an amp. So something is draining it.
     
    Last edited: Jan 5, 2008
  6. television

    television Hardcore MB Enthusiast

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    The Comand is one of the biggest reasons,it is quite simple to withdraw the fuse for this and pop an ammeter over the two contacts, this will cover all items on that circuit.

    Another is the OCP

    I have the Comand problem, so I modified the shut down circuit
     
  7. OP
    OP
    amwebby

    amwebby Hardcore MB Enthusiast

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    The MobiloLife technician mentioned COMAND as the most likely culprit. Why should it suddenly start doing this though, unless adding the TV caused it?
     
  8. Diesel Benz

    Diesel Benz Hardcore MB Enthusiast

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    I don't know anything about an SL but just happened to read about an incorrect relay installed on the additional fan, causing an additional current drain of 0.2 amps, this figure just goes with the figures measured from the car.

    I believe my clamp meter would be able to detect this current level without uninstalling the battery cable, would just need to remove the fuse for the additional fan.
     
  9. Diesel Benz

    Diesel Benz Hardcore MB Enthusiast

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    Again, don't know but there were several posts on other cars about the equipment on the CAN, the same one Comand would be using and any of those could cause Comand not going to sleep (of course an issue at the Comand unit itself too).

    But taking fuses out one by one should help diagnosing (although the one taken off might help the faulty one go to sleep).
     
  10. television

    television Hardcore MB Enthusiast

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    I think that this fan is the OCP one that affects the Comand
     
  11. Diesel Benz

    Diesel Benz Hardcore MB Enthusiast

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    Don't they have any SW update solution? If it is HW, I would expect a new device as it is a design flaw?
     
  12. Diesel Benz

    Diesel Benz Hardcore MB Enthusiast

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    I guess that fan could be an issue or the OCP panel itself but the document I was reading was really about the additional fan, covered by F42 to on the right fuse and relay box (I just happened to read about it, don't have any experience).
     
  13. OP
    OP
    amwebby

    amwebby Hardcore MB Enthusiast

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    That fits in with my theory, that the feed to the DVD unit is somehow at fault. I've withdrawn the power supply to the unit at the back but sadly I don't own a clamp meter.
     
  14. television

    television Hardcore MB Enthusiast

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    Up till recently there has been no one that would repair these things, but there are firms now that are starting to do work on them.

    MB have been quite happily taking a few grand for replacements.
     
  15. television

    television Hardcore MB Enthusiast

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    Before I modified mine the CD changer would keep trying to load until the battery cut off when it got down to 11.7 volt.

    CPC have a meter with a fuse plug on the leads, and you just plug this in in place of the fuse to get an instant read out of up to 20 amps, they cost about £6 + VAT.

    A clamp meter would cost around £300 to measure DC down to 20m/a
     
  16. OP
    OP
    amwebby

    amwebby Hardcore MB Enthusiast

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  17. television

    television Hardcore MB Enthusiast

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    www.cpc.co.uk part number IN04874 £6.95

    they have been on special offer.

    you could use a normal multi meter with if you have one with leads, part number IN04873
     
  18. OP
    OP
    amwebby

    amwebby Hardcore MB Enthusiast

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    Thanks Television. Now, where are the fuses?
     
  19. television

    television Hardcore MB Enthusiast

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  20. Diesel Benz

    Diesel Benz Hardcore MB Enthusiast

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    Just had another look at CL500 issues. There is a Comand SW update from 2004, perhaps this car is newer and then this update should not apply. Then there is a huge list of VINs for cars with a Comand unit where the only cure is to replace the unit. I assume you don't want to give the VIN but the list is also for Comand serial numbers. Could check, or send the document (unless you also have it).
     
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