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Battery always at 11.4 V; Static current draw 0.25 A... Normal?

Discussion in 'Technical Q&A' started by Mike328, Jan 21, 2004.

  1. Mike328

    Mike328 F1 Rookie
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    Oct 19, 2002
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    Mike
    A month or so before I last put up the car for winter work last December, I had been aware of a low battery condition that was making me worried.

    I've got an Optima red top, less than 1 year old. It's acting a little strange.

    Even though I've CONFIRMED 13.6 V to 13.8 V charging with my rebuild alternator, the battery when not being charged (low RPM or off) never really reads 12 V; it always reads 11.X V. Right now it reads 11.4 V after sitting for a month.

    One time after work, after I had the dome light on for a few hours and was starting it a few times, it went down to 10.X V and I had to trickle charge it, beause I found my FUEL PUMP would not PUMP correctly at 10.X V!

    I measured my static current draw with the car off, and I found 0.25 A, which at first sounded high but then I thought might be reasonable?

    I can think of the following items pulling current with the car off:
    1. Clock
    2. Keyless Entry -- must use some current to detect an active press of the "Open Doors" button on the remote?

    Is this reading (0.25 A static current draw) in line?

    The other symptom I'm having is that my alternator/generator/charging light just barely starts to go on at stop lights... Eventually the RPMs will get so low (with the low voltage?) the car stalls. The problem is exacerbated by putting on the brake (lights)!

    Sure does sound like I have a weak battery?

    --Mike
     
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  3. Ferrari_tech

    Ferrari_tech Formula 3

    Jul 28, 2003
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    Mike,

    0.25 amp draw is far too much, depending on your accessories (alarm, stereo, tracking system etc.) you should have somewhere between
    30-60 ma.



    MW
     
  4. 308GTS

    308GTS Formula 3

    Dec 27, 2001
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    TN
    Not meaning to interupt the thread but how do you measure static current draw? Thanks.
     
  5. Mike328

    Mike328 F1 Rookie
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    I promise to tell you if you promise to measure and post yours for reference :). LOL!

    Critical: Measuring voltage is a "parallel" operation, measuring amperage is a "series" or in-line operation.

    To measure current draw (amperage, in amps), you cannot just take a voltmeter and put it across the battery terminals like you do to measure voltage. This puts the voltmeter in parallel with the battery, and you may get a current draw reading but it will not be correct (you're getting something that can be shown with basic circuit mathematics, but it's not true current draw!).

    You have to put the voltmeter in SERIES with the battery.

    Remove the negative terminal clamp from the battery's negative terminal. 13mm, if I recall. Note: DON'T let the wrench hit the postive terminal when doing this, sparks will fly. I also don't recommend starting with the positive terminal, as you can easily make a connection with a ground in the car around that area (with the other end of the wrench!) and... yeah. Sparks will fly (shorting the battery).

    Make sure the CAR IS OFF. Don't turn it on during this operation. Few consumer voltmeters can handle the net amperage / current flow that a car draws across the battery, charging or not.

    The only reason we can do this is because we expect the current draw to be very low, lower than an amp or so. My voltmeter can handle 400ma (0.4 A) on the fused circuit and 10A on the unfused circuit. I used the unfused circuit.

    With the negative clamp OFF of the battery, put one lead on the negative clamp. Put the other lead on the negative battery terminal. It doesn't matter which one, you're concerned with the absolute value of the current draw and not the direction. Voila. Your voltmeter (now ammeter) is now in SERIES with the battery. Current is flowing ACROSS it, current which it can measure. Your voltmeter is now showing a reading. (Make sure it's measuring Amps, of course, not volts.)

    That's the reading you're interested in. That's where I'm getting 0.25 A... Yikes!

    P.S. You're not interrupting the thread. You've enriched it!
     
  6. Mike328

    Mike328 F1 Rookie
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    Hmm... Any ideas what could be drawing this? Could a short somewhere be causing the problem?

    Should I just start disconnecting fuses to isolate the circuit?
     
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  8. 308GTS

    308GTS Formula 3

    Dec 27, 2001
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    Ok, I will post mine. I know that when you have a short you should start pulling fuses. Then when the draw drops, look at the circuit and see what is on it. The try to disconnect the items individually. I am sure you already know this just trying to help. Cig. lighters are common to cause trouble and car alarms. Great Info, Very Descriptive, Thanks..

    Is there a reason to use the Negative side of the battery vs. the Positive? Just wondering.
     
  9. Ferrari_tech

    Ferrari_tech Formula 3

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    Mike

    Most common causes are glove box lights, boot and bonnet lights (if fitted). Keeping your meter connected, as you say, then remove one fuse at a time and see if the draw reduces, don't forget to remove fuses from aftermarket accessories as well.

    Also try removing the alternator wires and see if that makes any difference - I have in the past had problems with alternaters that have caused a draw on the battery.

    Normally if you have a short the the fuse will blow


    MW
     
  10. Mike328

    Mike328 F1 Rookie
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    No scientific reason. It's the same thing--current is flowing directionally across the ammeter/voltmeter.

    I found the positive side to in general be more troublesome to deal with just in terms of getting off, because of how easy it is to short it across the wrench whose other end is connected to a ground.

    As a rule I'll remove the negative terminal first, then you don't have to worry about the shorting issue. My guess is, this could be the expert consensus.

    A more competent wrench turner than me could probably do either one :). I'm just clumsy with a wrench I suppose. That said, next time I'll use my 13mm stub wrench!
     
  11. Mike328

    Mike328 F1 Rookie
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    Thanks, Malcom, for your helpful information--it's always appreciated... I intend to dive into this Friday through Sunday ;).
     
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  13. jselevan

    jselevan Formula 3

    Nov 2, 2003
    1,858
    Mike - thank you for this discussion. Ignition-off drain and how to measure this is always of interest. A few thoughts:

    First, you are absolutely correct in removing the ground terminal (negative) first, for exactly the reasons stated. When removing the nut on the positive terminal, it is very easy to touch the chassis with subsequent short circuit across your spanner.

    Second, it might be helpful for those less knowledgeable to use the term "multi-meter" when describing your measurement device. You refer to it as a voltmeter, but it can measure Ohms resistance, ampere current, and volts. Using the term voltmeter when measuring amperes may be misleading.

    Third, be VERY careful when suggesting that you do not want to place the multimeter across the battery terminals when measuring amperes. This will represent a short circuit. I quote your comment for clarity of my point:

    "To measure current draw (amperage, in amps), you cannot just take a voltmeter and put it across the battery terminals like you do to measure voltage. This puts the voltmeter in parallel with the battery, and you may get a current draw reading but it will not be correct (you're getting something that can be shown with basic circuit mathematics, but it's not true current draw!)."

    It sounds a though you are using a digital multimeter with current limiting features, but many will use an analog meter with no such current limiter. If they should place their multimeter (reading amperes) across the terminals, they will have a very hot gob of plastic gue to contend with. This is a direct short that will draw hundreds of amperes for the millisecond or so that it takes for the internal fuse to blow, or for the wires to melt.

    Fourth - I doubt that 250 milliamps represents a short. Electrical shorts are like being a little pregnant. They are either there or they are not, and a short will draw 10s of amperes for a few milliseconds, not 1/4 of an ampere.

    Fifth - If the clock draws 60 milliamps, think about what might make up the difference. A 2-watt bulb will draw (2 watts)/(12 volts) = 166 milliamps. This, with the 60 milliamps due to the clock, approaches your 250 milliamp measurement. A trunk, hood, glove compartment or other small bulb fits into this measurement. I have had experience in the 365 GTC/4 where the trunk light was not going off because the tab had been bent. Very difficult to chase this down, but that is what it was.

    Finally, 250 milliamps may not be an accurate number, depending on the quality of your multimeter. It could be less. I do not know what the factory specification is, but 250 milliamps is not unreasonable, and for a battery with 70 amp hour capability, this is negligable. There is clock current, memory-maintenance battery charging (radio stations), electronic ignition computer memory, etc. Malcom at Ferrari U.K. tech offers that 60 milliamps is more appropriate. And he is likely correct. As an engineer (read skeptic), I always like to see it in righting.

    Thanks for your thread.

    Jim S.
     
  14. Mitch Alsup

    Mitch Alsup F1 Veteran

    Nov 4, 2003
    7,677
    A properly charged good battery will hold 12.4 to 12.6 V under no/low load. A battery with 11.5 V and lower is in need of a full and complete recharge (NOW).

    I found the following after a search on the web for data on batteries. Aparently, the voltages one charges at are dependent upon the 'kind' of battery installed. In addition, the more maintance free a battery is, the higher the voltage regulator needs to be set to recharge the battery!

    http://www.landiss.com/battery.htm

    Here is a good deal of information

    http://www.optimabattery.freeserve.co.uk/batteryFAQ/dcfaq.htm
     
  15. Mark 328

    Mark 328 Formula Junior

    Nov 6, 2003
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    I do not have a strong electrical background, but I have been told that the diodes in the alternator might cause a slight draw. I was concerned with your 13.4-13.6 volt figure for charging. That is what my '87 328 is currently putting-out. I thought it should be closer to 14.5 volts, but I am glad to hear yours is a 13.6 too.
    In a previous car I had a voltage draw problem and I traced it to the wipers not being completly parked. I think about all you can do is to hook the multi meter and start pulling fuses. If you do not loose the draw then it is probably on a nonfused circuit like the starter or the alternator? I will try to check mine tonight.
    Mark
     
  16. AEHaas

    AEHaas Formula 3

    May 9, 2003
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    250mA is 1 Amp in 4 hours x 70 is about 23 days until full discharge. 250mAmps is way too much. I wound guess most cars draw 7 to 12 mA.

    aehaas
     
  17. jimangle

    jimangle Formula 3

    Nov 5, 2003
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    I just had this problem corrected on my 79 gts.
    I had a 2 amp draw. My alternator was trashed, no thanks to me for connecting the battery to the wrong terminals. My battery cables are reversed (red negative, black positive) so I wound up frying my alternator.
    What you have to do, is leave the amp meter hooked up to the battery, and start disconnecting fuses, and then you will see what your problem area is. But you won't find it that way if your alternator is drawing the volts. You'll have to disconnect it at the alt.
     
  18. Mitch Alsup

    Mitch Alsup F1 Veteran

    Nov 4, 2003
    7,677
    The data from the Optima Web site indicates that the battery charging voltage should/must be above 14.5V to properly charge the more maintance free batteries. Go read the pertinate data and educate yourself, but take it with the grain of salt that is applicable to a battery manufacture telling its customers about its products and others.

    In addition, after a full charge and letting the battery equilabrate for an hour after charging, the battery voltage should be 12.6V for a fully charged battery. A battery in the 11.5 range is almost completely discharged--a common failure mode if the voltage regulator is not putting out enough voltage.
     
  19. Mike328

    Mike328 F1 Rookie
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    (Sigh.) This is so frustrating. I agree, it sounds like the alternator is not putting out enough charge. But I've wired a voltmeter to the car (Switched voltage input) and it indicates 13.9V or so when charging (never over 14, though)...

    I (my mechanic) had the alternator rebuilt in February by a shop in Albuquerque. The labor pool in this area really sucks and you have no idea what you're getting. I wonder if the alternator continues to be problematic even after the rebuild...

    Mitch, when you say Optima says you need 14.5V, do you mean I should really believe that, or not immediately believe that because its coming from a battery manufacturer?
     
  20. jselevan

    jselevan Formula 3

    Nov 2, 2003
    1,858
    Mike - Mitch is spot on with the battery being the culprit. Your charging voltage is within spec at 13.6-13.8 volts, which is where most voltage regulators are set for older type batteries. It appears that your charging circuit is functioning correctly.

    It is more likely that the battery has a bad cell, and as the lead plates are in series, one of the six cells may be south for the winter (and beyond). That would explain the low ignition-off voltage.

    AEHass is correct in his calculation. My comment pertaining to 250 ma was to suggest that at that level, it is unlikely a short circuit. Diodes do have a leakage current, but unless the p-n junction is fried, this current will be in the few microampere range (for a high forward-current diode).

    I would check the battery.

    Jim S.
     
  21. Mike328

    Mike328 F1 Rookie
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    Let me make a confession.

    Probably like three times I've accidentally "shorted" the battery with the old spanner wrench across both terminals deal. Only for like a split second. I know, I'm an amateur, but it happened (and will never happen again with doing the negative terminal first and always using a stub wrench).

    Would this cause some of the problems?

    I mean, the damn thing less than a year old and under warranty. Maybe I need to walk in to autozone or pep boys or whereever the heck I got it and just plop it up on the counter?

    This of course after finding out what the heck is drawing 250ma.

    Also, at the present moment I *HAVE* removed the engine hood/lid cover, having disconnected all of the electrical spade connectors.

    --Mike
     
  22. BWS550

    BWS550 Wants to be a mod

    Apr 1, 2002
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    BRUCE WELLINGTON
    JUST CAME ACROSS THIS THREAD AND I SEE THERE ARE GREAT ANSWERS AND VERY WELL VERSED PEOPLE HERE..I APPLAUD THAT....

    MY SELF BEING IN THE BATTERY BUSINESS FOR 25 YRS, AND MY FAMILY BEING WITH EVEREADY ENERGIZER BATTERY CO. FOR ABOUT 85 YRS, AND NOT BEING AN ENGINEER....HERE IS MY ANSWERS WITHOUT THE TECHNICAL JARGEN.........

    A BATTERY THAT IS SUPPOSE TO BE 12 VOLTS, BOUGHT NEW AND FULLY CHARGED SHOULD READ ANYWHERE OVER 12 VOLTS, ANYWHERE OVER..SIMPLE AS THAT.

    SINCE THE CAR IS OFF AND THERE IS NO EXTREME LOAD ON THE BATTERY.THE READING SHOULD BE 12.1 VOLTS TO 13.8 VOLTS.

    IF YOU SAY A NEW BATTERY WAS JUST BOUGHT, PUT IN, AND FULLY CHARGED AND READS 11.8V OR EVEN LOWER: TWO ANSWERS ONLY:


    1- THERE IS SOMETHING ON IN THE CAR WITH MORE THAN 500 MAH OR 1 AMP OR MORE THAT IS DRAWING THE BATTERY AND YOU DONT KNOW IT.

    2- THE BATTERY IS DEFECTIVE AND I SERIOUSLY DOUBT IT




    GOOD LUCK,

    BRUCE

    OR
     
  23. Mike328

    Mike328 F1 Rookie
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    Hi Bruce! Thanks for chiming in.

    The battery was put in February 2003, and it's defintiely not brand new. As I mentioned above, I've shorted it a few times on accident (spanner wrench).

    Since it is under warrantly and I can probably just get a new one, I'm tempted to see how a new one does.

    --Mike
     
  24. KurtK328

    KurtK328 Formula Junior

    Mar 6, 2001
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    Kurt Kjelgaard
    I changed 3 BMW supplied batteries ("original BMW") on my 325 in 18 months.
    They lasted about 6 months each - electrical system on car in perfect condition - charging as it should.
    The batteries simply failed and were unable to keep charge.
    After changing to another brand - no problems.
    This is just to say that batteries can be unreliable things.
    You never know if a brand new battery will give you 6 years of service or 6 months.
    I suggest that you take your battery to the dealer - he can check if one of the cells has "collapsed".
    Try another one in the car and see how it works out.
    One battery guy told me once that a complete discharge, I mean complete as in leaving the lights on
    for a week, reduces battery life with up to one third.
    I don't know if this is correct, but it gave me something to think about.
    And, by the way, I don't think a quick shorting (you know, the type with sparks and an immediate
    reaction from the screwdriver operator to remove the thing) has any negative effects on the battery.
    Somebody correct me if I am wrong.
     
  25. 308GTS

    308GTS Formula 3

    Dec 27, 2001
    2,220
    TN
    I had an Optima too that went out early. In my experience they haven't been the toughest battery. So with the age of it and the few times you saw sparks it could do it. Take it to where you purchased it and have them test it. If it is bad then you saved yourself a lot of time.
     
  26. jselevan

    jselevan Formula 3

    Nov 2, 2003
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    Kurt - You are correct that the occasional short circuit is unlikely to harm the battery, HOWEVER, one must realize that for that instant several hundred amperes are flowing through the lead cells, and it is possible that heat or current density could do bad things for lead plates.

    Jim S.
     
  27. Mitch Alsup

    Mitch Alsup F1 Veteran

    Nov 4, 2003
    7,677
    A) I tend to think that your chargine system is operating as designed
    B) you have a battery that wants a higher voltage to get fully charged than is supplied by the alternator/Voltage regulator.

    This leave you with 2 options: 1) increase the voltage by diddling with tthe voltage regulator and use the current battery, 2) put in a lead acid battery that does not use calcium in the lead plates.

    I, personally, would believe what optima says, it is perfectly correlated with Yuasa motorcycle batteries (not maintance free). However, I offer no warrentee.
     
  28. Mike328

    Mike328 F1 Rookie
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    My thoughts were that MANY MANY folks used Optima Red Tops in their 308s! I'm sure they haven't fiddled with their VR...

    I think I'm going to post a poll to see what brand battery people are using.

    --Mike
     

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