Finding bad grounds...

Discussion in 'Electrical Systems' started by branbell, Dec 10, 2017.

  1. SRGN

    SRGN Veteran Member

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    Feb 20, 2009
    Central NJ
    With no radio installed that's too much. I'm guessing switched power and constant power inputs are transposed at the digital dash or switched power input isn't switching off at the digital dash. Again, unplug the alternator first to see if it changes. Make sure the meter is zeroed properly as well. Some clamp meters pick up electrical noise from nearby sources.
     
  2. branbell

    branbell Veteran Member

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    Jun 6, 2011
    Myrtle Beach, SC
    I appreciate the advice! I'm going to take a look at it again tonight.
     
  3. APEowner

    APEowner Veteran Member

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    Dec 9, 2013
    Albuquerque, NM
    I think SRGN is on to something with the digital dash and I agree with unplugging the alternator. Also, if you have them check the trunk light, glove box light and under-hood light.
     
  4. Jim Streib

    Jim Streib https://www.flickr.com/photos/121766713@N04/albums

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    Saint Louis, MO USA
    I have been doing car audio systems going back into the late 70's and ideally one would like to see 0.00A draw off of the battery and while this doesn't happen a lot with the installation of newer electronics such as digital radio's, engine computers, and such, the most I like to see is 0.02A. My feeling is when you get above this number and the car is not driven regularly, the battery gets drained too much to where even if it does start it does harm to the battery.

    I have had situations with some car that when I have measured initial current draw off of the battery, the number is high in the neighborhood of 0.10A but then after a few minutes, this high amount then drops down to a more acceptable level such as 0.02A. The situation I had with this was an original vehicle with engine management computers that at first drew a lot of power but then backed down on their demands and then this lower amount was acceptable.

    You said you have a Dakota Digital dash and I also have one but it is one of the first ones they made and on it, they have a 12V terminal on the control module but this model was designed to where one could wire this 12V terminal to a voltage but the design of it allowed the 12V terminal to be wired to an accessory 12V with no ill affects to how it performed. I did look at a newer offering from Dakota Digital with the VHX series and the control module shows a constant power (battery 12V) as well as an accessory power connection and I have to wonder why this is necessary and then wonder, could you have thee two connections reversed ?. On mine with the accessory 12V as the only power to it, the odometer has always retained it's memory of things such as the overall vehicle mileage and the last trip mileage and sometimes the battery has either been dead or disconnected for years.

    I think what you need to do is disconnect any aftermarket things powered off of the car to where you have a 0.00A current draw and then bring things back online one by one and measure each increase or non-increase with each connection. Eventually, you should see what is inline or excessive. If you still have anything above 0.00A with all of the aftermarket equipment disconnected, then you have to start looking at alternator issues, trunk/under hood light issues, vanity mirror light issues, glove box light issues, dome light issues, and so on.

    Jim
     
  5. branbell

    branbell Veteran Member

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    Jun 6, 2011
    Myrtle Beach, SC
    You all are a bucket of knowledge...all this is advice is great...

    I do have one other question...my battery was dead again this morning...can I hook up my battery charger and still test all these options while it's charging? Or should I wait until the battery is fully charged again?
     
  6. SRGN

    SRGN Veteran Member

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    Feb 20, 2009
    Central NJ
    Clamp meter may pick up the charging amperage. Stupid question, but if you charge the battery out of the car does it maintain charge while not connected to anything?
     
  7. McCune

    McCune Veteran Member

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    Aug 22, 2015
    st.george utah
  8. Jim Streib

    Jim Streib https://www.flickr.com/photos/121766713@N04/albums

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    Apr 6, 2004
    Saint Louis, MO USA
    If it was me, I would be disconnecting the battery when you are not trying to figure out the problem. My opinion is normal batteries do not like being drained dead and to me they never come back to how they were before. I believe and have seen this is if a normal car starting battery starts off being 100% but then is drained dead and recharged, it now does not return to this 100% but now is 99%. Drain it dead again, recharge it, drain it dead again, recharge it, and the percentage keeps dropping and dropping.

    Another reason to disconnect the battery until you find the issue is you may have an issue that could cause a fire and I've seen too many cars or car collections going up in smoke and then possibly also taking out the building they are housed in.

    Like SRGN suggested is disconnect the battery and charge it, then let it sit a while and take a voltage measurement with it not connected to anything and write this number down. Now a few hours later, take another measurement and write this number down. Still leave it disconnected and then maybe a day later, take yet another measurement. If the battery voltage over a day or two after being charged up continues to drop and drop, then the battery is shot. It may get to a point that the voltage stabilizes and this could be good but it depends on what that voltage is. If you do some online searches for "automobile battery state of charge" there are voltage readings that give you an idea if the battery is 100%, 90%, 75%, and so on.

    Jim
     
  9. McCune

    McCune Veteran Member

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    Aug 22, 2015
    st.george utah
    12.6 is a fully charged battery and 12.0 is a dead battery that need to be recharged.
     
  10. SRGN

    SRGN Veteran Member

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    Feb 20, 2009
    Central NJ
    They are available at lower cost, just not from snap on. We have the snap on one at the shop, its not sensitive enough to see a temperature delta on a low current component vs background temperature.
     

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