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Thread: Battery isolator issue

  1. #1
    Join Date
    Apr 2010
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    sydney
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    Battery isolator issue

    Hi guys, small battery isolator issue. I have a Redarc smart isolator in the car, 2011 2.7D D4. Recently replaced my starting battery after about 4 years. Around the same time, I got the sense the electrical system was a little off. Main thing I noticed was that when I started the fridge, which is connected to the second battery, the starting battery had a small voltage drop.

    I would leave the car overnight, so the batteries were definitely disconnected. They would read about 12.7-12.8V. Opening the car, main battery reads about 12.5. If i started the fridge, second battery would drop to 11.9 or so, but the main battery would drop to, say, 12.3. This implies there is some connection maybe? Is this correct? But I can't work out where it is. Only thing I notice is that when I put a continuity tester between the two positive battery leads, it will show continuity when it is connected up one way, but when I swap the leads around, there is no continuity. I don;t know what this means.

    Any ideas?
    Cheers
    Lucas

  2. #2
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    Hi Lucas and your auxiliary battery is not sounding too good if it drops to 11.9v with just a fridge as the load.


    Try starting you motor and let it idle for a minute or two and then measure the voltage at your auxiliary battery and cranking battery.


    Post up what you find.

  3. #3
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    Hi Tim

    I will check over the weekend, but the auxillary battery is actually pretty good, it will run the fridge for a couple of days. I think the voltmeter I have permanently attached has long wiring and with the fuses and connections it has a bit more voltage drop than normal.

    Cheers
    Lucas

  4. #4
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    As long as the wiring between the battery and the meter has nothing else connect or powered from it, it does not matter how long or how thin the wiring is.

    If you are powering other devices from the same wiring, then the readings can be way off, and not of much use for determining what is actually happening.

  5. #5
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    Jun 2013
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    When you say redarc smart isolator do you mean sbi12 or bcdc20 ? If it's an SBI there should be a light on when they are connected to each other.

    With these vehicles opening the doors starts all the ecms which does cause the battery voltage to lower a bit depending on age. My old battery would start the car fine but still drop.3v with a door open. I measured 30amps draw with my clamp meter.

    11.9 is low, if you don't have a good meter Jay car etc has them cheap, Check at the battery, at the lead poles, not the terminals, and make sure you have a good charge rate.

    You're aux might like a holiday in the charger for a weekend to get it back in good spirits
    If at first you do not succeed, maybe your just no good and should quit!

  6. #6
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    Also if it only does it when you first open the doors. A previous owner might have connected the second battery to a aux plug that was connected to the main battery. With the doors open it back feeds. Pull all your plugs out and make sure there are only two wires going to them.

    Where is your aux battery located
    If at first you do not succeed, maybe your just no good and should quit!

  7. #7
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    Tim, I'm not an expert on multimeters, but could the the positive continuity between positive battery terminals be due to the diodes in the Redarc isolator (it's an SBI212 by the way, not a DC-DC thing)? Do they let a but of current through?

  8. #8
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    Hi again Lucas, use the voltage measurements for doing any testing and this will allow you to easily find any potential problems


    Some basic tests are as follows and write notes of each test as this will make it easier to back check each test and see what it SHOULD read:-


    With the motor off, measure the voltage of both batteries, at their terminals.


    Start the motor and run it for a few minutes and the measure both batteries again.


    If the voltages are similar, continue on.




    Once the motor is running, you should then measure from the auxiliary battery’s positive ( + ) terminal to a GOOD earth point.


    This is done by placing the meter’s positive ( red ) probe on the battery’s positive ( + ) terminal and the meter’s negative (black ) probe on a good earth.


    Next, and this may sound a bit strange but follow as described.


    Placing the meter’s positive ( red ) probe on the battery’s negative ( - ) terminal and the meter’s negative (black ) probe on the same good earth.


    You should get a reading of no more than about 0.02v


    If you get a reading of 0.1 or more, then this indicates your auxiliary battery has a bad earth connection and is usually the cause of all your problems.


    See how you go.

  9. #9
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    Thanks Tim, I'll try tomorrow.

    I seem to remember that when i reverse polarity, it reads -12.6V, not the small amount you suggest.
    Cheers
    Lucas

  10. #10
    Join Date
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    Whyalla, South Australia
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    Quote Originally Posted by irondoc View Post
    Thanks Tim, I'll try tomorrow.

    I seem to remember that when i reverse polarity, it reads -12.6V, not the small amount you suggest.
    Cheers
    Lucas
    Please read again. Not reverse the polarity, the positioning of the probes.
    Cheers
    Tombie

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