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Thread: Voltage Drop on Handbrake Release

  1. 10th December 2012, 11:48 AM #1
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    Exclamation Voltage Drop on Handbrake Release

    Hey Everyone,

    This is a weird one! I have noticed for a little while now while I am driving along that the voltage fluctuates and quite regularly drops to 12v or below (have a little cheap gauge with 4 lights giving me a range of voltages). I have always just assumed it was the gauge being dicky.

    I just installed a USI-160 Dual-Battery Isolator from Traxide and when I started testing it I noticed that when I released the handbrake that it would disconnect the batteries as the voltage dropped too low.

    I promptly rip the center console out to find nothing really out of the ordinary. I found a thread on here from a while back that mentioned it could be dirty earths, so I cleaned them all up. This "appeared" to fix the issue, in the driveway, but then I drove out and the issue reared its crazy little head again! Arrrggghhhh!!! Why couldn't it have been simple!!!

    I should mention, the previous owner seems to have been a bit of a douche and has crazy wiring all over the joint. I have been through most of it and either removed it or confirmed what it is for. Some of it I have had to redo. I don't think it is any of this causing the issue, but I am still playing\searching.

    Please any suggestions would be greatly appreciated, I am about to move to Perth and in doing so will have to drive about 4500 kms, I need to have the Dual-Battery System going so I can run the fridge.

    Please HELP!!
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  2. 10th December 2012, 12:22 PM #2
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    V8 or 300TDI?

    Is this while the engine is running? First thought is to make sure your alternator is working 100% otherwise you'll never get the required voltage for the battery separator to work correctly. Run the engine and check the voltage at the alternator, at first battery and at second battery. Should be over 14V at idle.
    - Justin

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  3. 10th December 2012, 01:05 PM #3
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    Make sure everything is running A1. This is a long, lonely trip , food and fuel prices are out of this world.From Border Village (SA & WA) no mobile phones work) for a long, long way.Then from Norseman to Coolgardie and then to Southern Cross it drops out again.I always take two Jerry Cans of fuel and have more than enough of drinking water.It is a monotonous journey so look out for white line fever,one straight stretch is 147 km long ,straight as a gun barrel ,don't travel at night,animals (big ones and little ones) are everywhere and its bloody hot during so air-con is a must.
    Have fun I've done it five times
    John.
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  4. 10th December 2012, 07:27 PM #4
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    Quote Originally Posted by Judo View Post
    V8 or 300TDI?

    Is this while the engine is running? First thought is to make sure your alternator is working 100% otherwise you'll never get the required voltage for the battery separator to work correctly. Run the engine and check the voltage at the alternator, at first battery and at second battery. Should be over 14V at idle.
    300TDI. Yep, with the motor running. Have tested the alternator, seems fine. It sits around 13.8v which is about normal. The issue isn't whether I get the voltage initially, I do, it is that after releasing the handbrake it drops to 12v or below which is not correct. I can't see any shorts\loads at or near the handbrake so I am a little lost at the moment.
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  5. 10th December 2012, 08:17 PM #5
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    Sounds to me like the movement of the engine on its mounts when you release the handbrake is affecting the engine/chassis (or body) earth link. The alternator is earthed to the engine, just about everything else to the chassis. Check the voltage between the engine and chassis with handbrake on and off and with engine running and a significant load such as headlights. If you do find a measurable voltage, it is easier to simply run an additional earth rather than to try and find the problem.

    John
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  6. 11th December 2012, 12:05 PM #6
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    All Sorted!

    All fixed. Thanks for the help guys. I was leaning towards it being an Earth issue from the beginning. All the tell tale signs where there.

    In the end I took it to Brendale Auto Electricians (Good, helpful bunch of blokes) to get them to chuck another earth cable in. After explaining the story I got the same odd look everyone has given me so far. A look of, your not all quite there are ya fella!?! He was, lets put it, mildly surprised I think when it worked.

    Yes, I know I could have done the job myself and I would have, but I am seriously running out of time and I just broke my big crimping tool so I couldn't make the cable up. They charged me bugger all for the job in the end and they squeezed me in among a HUGE amount of other jobs, so I am well and truly pleased.

    Again, thanks for the help, it kept me on the right track instead of going off some random tangent as I am well known for doing!
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