Auto electrical short

Discussion in 'Shop Talk' started by moopups, Oct 22, 2004.

  1. moopups

    moopups In Remembrance

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    My puddle jumper has the bad habit of draining the battery at night, the plan is to place my mini multi meter on the battery and pull fuses one at a time until I see a change. Is there a better way? What do you set the meter to indicate?
     
  2. Beeman

    Beeman Well-Known Member

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    You don't have a short, which would blow fuses, you have a parasitic load. An acceptable parasitic load is 30 milliamps measured in series between the negative battery cable and the negative post of the battery. The best way to measure this is with an auto ranging digital mutimeter. The best way is to have the meter hooke up between the two and also a bridge between the 2. The bridge allows all of the electrical circuits of the vehicle to power up, then you open the bridge and allow the current to flow thru the meter to get your reading. Be careful about turning anything on while only the ammeter is hooke up as they have a fuse inside and if the load exceeds the fused rating you will have to replace the fuse but if the fuse blows and you don't realize it you will get false readings.
    The bridge can be a jumper wire that you remove and leave the meter still hooked.
     

  3. moopups

    moopups In Remembrance

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    OK, then by pulling fuses it would show me what circuit is the bad one? Do I understand this correctly? Still need info of meter setting, plane 12 volt setting?
     
  4. Beeman

    Beeman Well-Known Member

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    AMPS not Volts is how you measure current, Fuses are rated in amps. You aren't measuring voltage you are needing to measure amperage so you will need a meter that will measure low amperage.
    Pulling fuses with the meter hooke in series showing current draw will show the drop in current flow when you pull a fuse for a circuit that is active. Now you might have something that is unfused drawing the battery. I have seen some alternators draw a battery down.
    Now I have no idea what vehicle we are working on so the methods I refer to are approved for vehicles with electronics. Now if we are working on something older we can get a little simpler. Disconnect the battry negative cable and hook up a test light in series between the battery and the negative cable. If the test light glows there is current flow. You can then pull fuses until the test light goes out. Remember that if you have the door open the dome light will show a currrent flow. Same goes for the glove box if the fuses are in there and it has a light.

    As I said the second method is for a simple vehicle, if used on a vehicle with electronics many times you will get a false glow from circuits powering up like the radio memory and other modules. No matter what vehicle try and prevent any arcing at the connection of the battery. A spark can cause a battery to explode and a voltage surge can damage electronics.
     
  5. moopups

    moopups In Remembrance

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    Its a '91 Isuzu Trooper, V6. I did replace the standard battery ternimals with aftermarket solid brass one, was told brass does not corrode, but did find thatbrass does corrode, even to the point that no currant was being transfered due to inside of the trenimal corrosion. What does this indicate?
     
  6. Beeman

    Beeman Well-Known Member

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    Not sure what you are asking. Many times corrosion will occur because of an overfilled battery out gassing and allowing the acid/water to contact the terminals.

    To stop corrosion clean the posts and the terminal thoroughly. When assembling coat everything with dielectric compound(silicon grease). The coating of grease will conduct electricity and yet keep out oxygen which is necessary for corrosion to occur. You can also just coat the terminals with grease or vaseline after assembly if you don't have dielectric compound. I have also seen people paint the terminals after assembly to seal them, I don't think it's as good but better than nothing.
     
  7. John Hill

    John Hill Grand Master

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    Hi Moopups, are we sure this is not a battery problem? A battery can have an internal short which will quickly drain one cell down. This looks like a 'flat' battery but all the other cells are still charged.

    When the engine is running the alternator will try to bring that battery up to charge which leads to overcharging of the good cells, they gas excessively which encourages corrosion of the terminals.

    Even a newish battery can get an internal short, depending on how it is made, caused by a bump or knock that distorts the plates or dislodges material into the bottom of the cell.
     
  8. moopups

    moopups In Remembrance

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    This is a possiability, I have smelled what appeard to be battery gas before when returning from a long drive and stopped to open the gate with it still running. Also just noticed that when I put the battery on the charger it goes from 10 volts to charged real fast. Like in 10 minutes or less. Does this fit the profile?
     
  9. John Hill

    John Hill Grand Master

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    Yes, I think I would be suspicious of that battery, 10v is pretty close to what it would read with one cell stuffed (to use the accepted technical term! :) ).

    If the battery voltage rises very quickly on charge that is an indication that the battery has very little capacity, which is the case if you are only charging one cell.
     
  10. mightybooboo

    mightybooboo Well-Known Member

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    2001 Jetta draws 100Ma at rest and thats normal.
    BooBoo
     
  11. moopups

    moopups In Remembrance

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    OK, changed batteries, now it is not bleeding down but it also is not right yet. Aparently the voltage regulator is stuck shut, the clip on battery meter shows that the currant stays a constant 14.5 volt charge reguardless of engine speed. Should not the meter show a return to 12 volts on occasion? When the resistance load switch is activated it does go down to 12 volts but not any other time.
     
  12. mightybooboo

    mightybooboo Well-Known Member

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    What you are saying makes sense,sounds like you may have cooked the old battery overcharging and you are on the right track(Im NO EXPERT)..Im a 3 out of 10 scale mechanic,know just enough to get me in trouble,LOL!On an older vehicle with charging problems I do like this.Take the Winnebago,a 1979 Dodge 440 dually for example.We just went thru and replaced the whole system,alt,belts,regulator,engine electronic module,cables,battery,coil,the whole schmear.Dont know it needed it all,but I do know all is up to snuff and now very dependable.Was little bucks(relatively) for the return of a charging/electrical system thats A-OK.Got the lifetime guarantees as this vehicle is a keeper.Now Im comfortable to replace individual components as needed,knowing the rest should all be working correctly.Kind of setting up a good baseline to start with.
    Yeah,not much finesse(like ZERO!),but it does work,and you get spare parts for repairs on road too in my case.
    Take care,
    BooBoo
     
  13. John Hill

    John Hill Grand Master

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    I think you are right on track. I do not think 14.5volts is too high with the engine running. A fully charged so-called 12 volt battery should show 13.8volts after you have stopped the engine and let it sit for 20 minutes or so (if I recall correctly). The alternator voltage has to be higher than the battery voltage for the charging current to flow.


    I found a site that might help you here. I have not read more than a couple of lines.

    My feeling is that you have solved the problem by changing the battery but keep a look out for signs of overcharging, for example gassing such and the terminals corroding. There is always the chance that overcharging caused one battery cell to fail that led to your other problems.
     
  14. mightybooboo

    mightybooboo Well-Known Member

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    I disagree,based on my home system of lead acid batteries 14.4 is an equalizing charge and boils the electrolyte,i can look in the cells and see them boil.A constant 14.5 seems wrong to me,that should just be a rapid boost charge at that rate,not a constant charge.It does a regular charge at 13.6,and 13.2 when charged fully.Though I could be wrong,maybe car and home sytems of lead acid batteries are different somehow with cars at a higher constant rate?
    I have an idea,pull the regulator and take it to autozone and they will test it,I believe Napa will too,for free.This link may or may not be helpful.Just some thoughts on this.Please let us know what happens with the problem down the line.
    www.bestconverter.com/chargewizard.html
    BooBoo
     
  15. John Hill

    John Hill Grand Master

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    My initial thought too was 14.5 is too high but I found that on a site somewhere, in fact that site said 14.7 as the high end of the acceptable range for charging.


    I have just checked four different maintenance manuals I have here which give the maximum voltage to be lowest 14.4 highest stated 14.7 but one very old manual (for an English Morris) gave a maximum of 16 volts!


    I also found some very interesting information of what temperature plays in all this. You need higher voltage to charge effectively if the temperature is cold. This was on a site concerning charger systems for boats where the comment was made that lower voltages are used in automative systems because the battery is in the rather warm environment of the engine bay.

    So, all things considered if you live in a hot climate or if the battery is in a particulary hot engine compartment then 14.7 may be a little high.


    Getting the regulator and alternator checked is good advice though, the vehicle does appear that it might have a history of overcharging evidenced by the corroding terminals.
     
  16. mightybooboo

    mightybooboo Well-Known Member

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    John,you are correct,looks like 13.6-14.6 is acceptable range in automotive charge system.This is pretty interesting stuff.
    Back to the regulator I cant find anywhere where it should be allowing 12 volts, curious to find if that regulator and alt. test OK.Thanks for the feedback
    Thanks for the education!
    This is a troubleshoot link.
    www.carcraft.com/howto/53318/index4.html
    BooBoo
    Found an Isuzu sight that said 14.5 is normal voltage
    www.off-road.com/isuzu/ppwelder.html