battery ground fault protection

Discussion in 'Automotive Electronics' started by SaravanaA, Jan 12, 2016.

  1. SaravanaA

    Thread Starter New Member

    Dec 30, 2015
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    hai
    any idesa to design ground fault protection for battery pack in automotive field......have any method ???
    please help me
     
  2. tcmtech

    Well-Known Member

    Nov 4, 2013
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    Fuse.
     
  3. crutschow

    Expert

    Mar 14, 2008
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    Exactly what fault are you concerned about and what exactly are you trying to protect?
     
  4. SaravanaA

    Thread Starter New Member

    Dec 30, 2015
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    Battery ground fault that means how to do earth leakage of battery?
     
  5. DickCappels

    Moderator

    Aug 21, 2008
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    A more clear description of what you want is still needed; you are asking about something that might not yet exist except in your mind, hence the need for a clear description of what you want.

    What battery, the automobile battery?

    By "earth" are you referring to the automobile chassis?

    By "ground fault" are you referring to when current flows through the ground rather than a current return wire?

    The above are pertinent questions that will help define your request. Please provide any other information that might help.
     
  6. SaravanaA

    Thread Starter New Member

    Dec 30, 2015
    15
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    ya its automotive field....i have no idea about how to design earth leakage protection that means in case occur some insulation fault in battery chassis that current would be leakage to earth ..how is it do it...what are the method????...what are dc earth leakage method???
     
  7. #12

    Expert

    Nov 30, 2010
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    At first glance, one might think some current flow from a +12V wire to chassis is a fault, but that current will still return to the battery ground terminal through the body grounds, therefore it can't be detected unless all body grounds are isolated into a single circuit and all proper loads have a return wire to the battery. If all proper loads have a ground wire and the entire body is isolated from them, you can measure current from the body grounds.

    I thought about the engine needing grounds and thought, the starter is easy enough to provide 2 wires for, right after you get a custom built starter that HAS 2 wires instead of using the engine block for ground. The ignition system already uses a transformer to isolate the engine block from the battery ground. This seems achievable if you build the whole vehicle yourself.

    I had a 1948 Ford that discharged its battery through leakage current. I just unplugged the headlights and continued until all the wires were removed, then I replaced all of the wiring. That fixed the problem. I was a rather proud 16 year old after rewiring a whole truck with no schematic! I don't think you can do that with modern cars, unless you have weeks to do it and several hundred dollars for connectors and other parts. So, I guess you will be building cars from the ground up.
     
    Last edited: Jan 13, 2016
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  8. tcmtech

    Well-Known Member

    Nov 4, 2013
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    In a vehicle that uses what is essentially a one wire with common frame ground return design it would be almost impossible to do leakage testing without having every single live line disconnected from its end point be it a switch, relay, control module, security feature, or remote controlled function.

    By far the most common cause of vehicle batteries going dead is not from bad wiring leaking current but the necessary power drains created by the many small computers and electrical control systems that need to have a constant live feed to them for their memory or other functions even when the key is off.

    Most every vehicle built in the last 40 years that uses anything electronic in one or more of its systems has a constant power drain that can be anywhere from a few milliamps to over 200 milliamps which when given that over the years the average battery amp hour capacity of most vehicles has been reduced while their parasitic but necessary power drains to keep memory alive has grown substantially.
     
    BR-549 and JohnInTX like this.
  9. crutschow

    Expert

    Mar 14, 2008
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    What is the smallest leakage current you want to detect?
     
  10. profbuxton

    Member

    Feb 21, 2014
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    Is the battery pack isolated from "ground", chassis" or is one terminal of battery connected to auto frame.?
     
  11. BR-549

    Well-Known Member

    Sep 22, 2013
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    I'm still not sure I understand the question.

    The first post....ground fault protection.

    The second....earth leakage of battery.

    The third.......insulation fault in battery chassis that current would be leakage to earth.

    A ground fault is a ground short, if I remember right. As already stated a fuse takes care of that.

    If you want to measure standby current draw on a garaged car, an ammeter will tell you that.

    Battery leakage does not go to ground. It's across the terminals. Most only notice it in cold weather.

    I would hate the task of measuring it. One would probably have to redesign the battery to allow internal current detectors.

    Or if you have the time, self life can give you an approximation.

    But I doubt that is what you are asking.

    Are you trying to monitor the state of discharge, or try to prevent all discharge?
     
  12. #12

    Expert

    Nov 30, 2010
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    I agree. That 1948 Ford pick-up truck I re-wired was a very rare exception.
     
  13. WBahn

    Moderator

    Mar 31, 2012
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    I also agree. It is far more common for a component to fail in such a way that it produces a constant current draw than for it to be from bad wiring. I've got a truck that the battery goes dead in a matter of hours (sometimes) and I think I've narrowed it down to a failing fuel pump in the front tank. It's gonna cost ~$500 to get it fixed. Fortunately I was having some work done (installing a used lift gate) that mandated some wiring work anyway and so I had a pair of battery isolators installed that allow me to separately switch main power to the truck and auxiliary power to the gate and winch. Works beautifully and I can let the truck sit for months without the battery draining. Fortunately the truck is old enough that I don't have critical items, such as some of the modern computers and radios, that give fits if they lose power.
     
  14. slackguy

    Member

    Feb 11, 2016
    29
    1
    i agree with what dick said

    the most important thing in using probes or tracing issues is to know what is serving as ground (12v? 5v? 0v?) (there are say 20 computers in a car, there is a compputer that deals in steering multiple voltages around per request that has et alia relays, under dash)

    but gfi is an old concept so you can order a part once you know at what rating it must operate
     
  15. slackguy

    Member

    Feb 11, 2016
    29
    1
    you should limit the current to be within the rating of the battery, since you cannot konw for sure if a short to ground is "heavy use" or "a poorly connected short"

    if current is limited that action might shut down the battery or keep it out of use until cooled
     
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