min battery starting voltage

Interior and Electrical

  1. rhaegar77

    rhaegar77 Member

    Messages:
    10
    Likes Received:
    2
    Joined:
    Aug 25, 2017
    Location:
    United States
    im working on a little device that'll cut circuits that are using voltage while the car is off so theyre off before it drains the battery

    does anybody know what the min battery voltage is for the car to still start??
     
  2. Aspen500

    Aspen500 Well-Known Member

    Messages:
    3,145
    Likes Received:
    904
    Joined:
    Feb 14, 2015
    Location:
    Rib Mountain (Wausau) WI
    Depends on the engine, temperature, type of starter, etc but, generally the battery savers start shutting down non essential systems one by one around 11.5 volts (the factory ones on newer cars anyways). The static voltage isn't so much an issue as the voltage under load. What I mean is, you could have 13 volts static but have it drop to zero volts under load if the battery has no amperage capacity. You need at minimum of about 9.6 volts to start, and that's with the starter engaged. The lower voltage also will cause weaker ignition so even if the engine cranks, it may still not start. Maybe way more than you really wanted to know:D Keep it above 11 volts or so and you'll most likely be fine.
     
  3. BudW

    BudW Moderator Staff Member

    Messages:
    3,161
    Likes Received:
    864
    Joined:
    Mar 4, 2012
    Location:
    Oklahoma City
    With engine cranking, then yes, the 9.6 volt is the magic number – but generally at that point, the battery doesn’t have much power left in it and it goes downhill very quick at that point.

    Generally when I crank on a car and I hear the cranking speed start to noticeably slow down – it is time to stop and figure out what (else) is wrong.
    BudW
     
  4. Cordoba1

    Cordoba1 Well-Known Member

    Messages:
    388
    Likes Received:
    84
    Joined:
    Nov 22, 2011
    Location:
    Northern Illinois
    I'm a little curious what problem you're trying to solve. Even with parasitic drains, your battery shouldn't have any problems starting the car even after a few months. I have a Cordoba that stays in the garage in an un-heated garage in the winter. I have some parasitic drains from the radio, a memory-CB I have installed, and a satellite radio; but still can start the car without doing so for weeks.

    How long does it take before you're having trouble?

    Have you considered a simple battery cut-out switch?
     
  5. rhaegar77

    rhaegar77 Member

    Messages:
    10
    Likes Received:
    2
    Joined:
    Aug 25, 2017
    Location:
    United States
    is there any way to know how much the voltage will drop when the starter is cranking other than monitoring it every time you engage the starter?
    also, what difference does having electronic ignition have on the minimum voltage to start?
     
    Last edited: Aug 31, 2017
  6. rhaegar77

    rhaegar77 Member

    Messages:
    10
    Likes Received:
    2
    Joined:
    Aug 25, 2017
    Location:
    United States
    has anyone ever seen a voltage below 12.1v while the car is on?
     
  7. rhaegar77

    rhaegar77 Member

    Messages:
    10
    Likes Received:
    2
    Joined:
    Aug 25, 2017
    Location:
    United States
    basically, I'm super forgetful and have left the dome lights on so many times I have lost count at this point. Sometimes, its easy to find a jump, sometimes it's not. When my neighbor's mother had the same problem in her 85 Buick LeSabre and I helped jump her car, it became more of a thing I've been thinking about...just tired of being stranded
     
  8. BudW

    BudW Moderator Staff Member

    Messages:
    3,161
    Likes Received:
    864
    Joined:
    Mar 4, 2012
    Location:
    Oklahoma City
    When the car is running, the Alternator takes over from the battery (and charges the battery in the process).
    Depending on ambient temperature (temp at voltage regulator), the charging system voltage should be at:
    -30’C / -20’F = between 14.9-15.8 volts
    27’C / 80’F = 13.9-14.4 volts
    60’C / 140’F = 13.0-13.7 volts
    Above 60’C / above 140’F = less than 13.6 volts.


    The transistors inside of the ECU (electronic Control unit) has to have a min amount of voltage for transistors to do its thing. Below that voltage amount and nothing happens (as if the power was turned off).

    One of the nice things about today’s car, is it is hard to keep headlights on or dome light on, etc., for car turns off those items automatically.
    The bad news is – more things to break.

    Might want to invest in one of those small car battery jump boxes and keep in your trunk (or wherever).
    BudW
     
  9. Cordoba1

    Cordoba1 Well-Known Member

    Messages:
    388
    Likes Received:
    84
    Joined:
    Nov 22, 2011
    Location:
    Northern Illinois
  10. rhaegar77

    rhaegar77 Member

    Messages:
    10
    Likes Received:
    2
    Joined:
    Aug 25, 2017
    Location:
    United States
    Great info on the alternator voltages at temperature! Thanks for that!

    And I hear that, "more things to break", it's one of the reasons I dread power windows, I've replaced way too many window regulators in my day...

    Is there any way to know the minimum voltage for the ECU?

    Yeah, a jump box might be a thing, just annoying as they're mostly heavy and cumbersome to just have hanging out in the trunk.
     
  11. rhaegar77

    rhaegar77 Member

    Messages:
    10
    Likes Received:
    2
    Joined:
    Aug 25, 2017
    Location:
    United States
  12. BudW

    BudW Moderator Staff Member

    Messages:
    3,161
    Likes Received:
    864
    Joined:
    Mar 4, 2012
    Location:
    Oklahoma City
    Roughly about 9.6 volts.
    But at that voltage, the starter speed starts to go downhill very quick (not enough left in the battery).
    BudW
     
    Last edited: Sep 1, 2017
  13. Jonnyuma

    Jonnyuma Well-Known Member

    Messages:
    259
    Likes Received:
    62
    Joined:
    Nov 6, 2011
    Location:
    A Dirty Little Town in NW Oregon
    Piggybacking onto an older thread...
    I went to start my 79 Lebaron yesterday and it cranked until it didn't. I could tell it was draining the battery but I don't know why?
    Today I took the batt (a reman) to AutoZone for a charge, fully expecting to buy a new battery, but it tested @ 9.? V and took the charge just fine.
    I replaced the block and body ground w new cables and it started strong, Mopars love good grounds. Good as new, right... ?
    The good news was that I didn't have to buy a new battery. Bad news is: something else is wrong.
    Question: Do these alternators have an exciter-switch? Do they need to be brought up to a certain RPM to start charging? The Alt "gauge" shows no movement, but I don't trust it.
    I might drive it to work tonight w a cig lighter ammeter plugged-in to keep an eye on it but it's looking like either a parked drain, or a bad alternator/regulator...
    Any suggestions?
    IF I can find my multi-meter to test the charging voltage (buying a new one might be easier) which are the correct contacts to test output of the Alt?
    Those are pretty noob questions, but I haven't gone this deep w charging issues before... oddly, never had em before where an Alt test/replace didn't cover it.

    ETA: The car's voltmeter appears to be inop. Okay, I can deal w that later.
    I'm showing a charging rate of 14+ V at high idle, 13+ at low idle, it goes up or down depending on accessories being run (holy COW! Cold a/c... super spiff!)
    There HAS to be a drain somewhre... damn.
     
    Last edited: Apr 13, 2018
  14. BudW

    BudW Moderator Staff Member

    Messages:
    3,161
    Likes Received:
    864
    Joined:
    Mar 4, 2012
    Location:
    Oklahoma City
    Our cars did not come with a volt gauge, back then. They do on today’s cars – but not during the FMJ-body time frame.
    The Ammeter detects a current draw – and for most applications – doesn’t give most people good data.

    When car is at high idle, 14.4 volts is about right. The Voltage Regulator will charge according to the underhood temperature – for longer battery life (so charging voltage will be different when cold out (like say 30-) vs. hot out (110’, in the shade). Still, a voltage between 14 to 14.5 volts, at high idle, means the alternator is charging (voltage regulator is working, etc.).

    At normal idle, 13+ volts is common.

    The battery should between 12 to 13.2 volts when charged up (before cranking).

    The starter quits working at roughly 9 volts and ignition will not work below 9.5 volts (but your mileage may vary).

    Carbureted cars do have to have the throttle petal tapped (once) before cranking. That gives the engine a shot of gas plus resets the choke linkage. If you don’t tap the throttle – it will take longer for car to start up.
    It is not uncommon for people to forget this important step.


    There are not many things on our cars that can cause an engine off current drain.

    Before starting: I would do this first (before diagnosing any electrical problem):
    Find any underhood ground wire, remove its mounting bolt, take a wire brush and clean the dickens out of it, the bolt, as well as what it mounts to.
    Common ground locations to clean, are the battery terminals (both), the large bolt on engine cylinder head (to negative cable), the ground strap on rear of engine to fire wall (which engine side can be fun to clean), as well as on (or close to) the core support (the chassis part radiator attaches too) there is a ground screw on both sides of car, for headlights and other electrical items. If you trace the small negative battery cable – it will lead you to one ground source. The other side will be in the same basic area.

    The ground locations inside cabin or in trunk are not known to give that much trouble (but don’t rule them out).

    The only things I can think of that would draw power when car is off (key in hand) are: dome lamp, glove box lamp, trunk lamp, head/park lights, hazard lights, clock (analog or digital) and radio station memory (and your car might not have all of these options).

    Other components that have power when car is off (key in hand) would be: all of the lights mentioned above, stop lights, power door locks, cigar lighter, power antenna and source power for heated back glass (not for the control circuit, but power feed).

    There are several ways to check if one of the above items is causing a problem.
    The easiest one is "if you have a test light", is to disconnect the battery. Place the test light between the battery and battery terminal. If light is lit (but might be dim), then go to fuse panel and pull fuses for the above items, one at a time. The clock and dome light (if a door is open) will the test light to stay on. A person can pull clock fuse first and can push in the metal door ajar switch for testing purposes.
    Process of elimination and taking your time will find your problem.
    If test light does not light up, then you do not have a significant power draw.
    Note: the test light test version works for our cars - but doesn't work on newer cars, very well.
    BudW
     
    Jonnyuma likes this.
  15. Dr Lebaron

    Dr Lebaron Well-Known Member

    Messages:
    2,618
    Likes Received:
    545
    Joined:
    Aug 17, 2011
    Location:
    Islamic State In Canada
    Did you give it gas or just tried it EFI style-which won't work.
     
  16. Jonnyuma

    Jonnyuma Well-Known Member

    Messages:
    259
    Likes Received:
    62
    Joined:
    Nov 6, 2011
    Location:
    A Dirty Little Town in NW Oregon
    Carb'd stuff will get one press to the floor (set the choke) followed by a pump-shot and maybe another shallow, 1/4-travel press if it's been sitting for a day or two.
    The battery was weak when I first turned the key. As soon as I heard it I pretty much knew it wasn't going to start...
     
  17. Dr Lebaron

    Dr Lebaron Well-Known Member

    Messages:
    2,618
    Likes Received:
    545
    Joined:
    Aug 17, 2011
    Location:
    Islamic State In Canada
    I thought you where just cranking until the battery died.
     
  18. Jonnyuma

    Jonnyuma Well-Known Member

    Messages:
    259
    Likes Received:
    62
    Joined:
    Nov 6, 2011
    Location:
    A Dirty Little Town in NW Oregon
    Naaaww... well, sorta. I juiced it, turned the key, knew it wasn't going to fire but kept trying anyway. Since I've only had the car a few days I just wanted to see where it leads.

    I disco'd the battery Friday night when I got to work just to be sure it could get me home later this morning. I'll start some diagnosing later in the week when I get a day off.
    If there is a drain, it's gotta be big to take the battery down that fast... <2 days.
     
  19. BudW

    BudW Moderator Staff Member

    Messages:
    3,161
    Likes Received:
    864
    Joined:
    Mar 4, 2012
    Location:
    Oklahoma City
    Most car batteries will only last 2 to 4 years.
    If you are not sure how old your existing battery is, look for a white sticker on the side of the battery. It will say something like “B5”.
    The first letter is the month of battery build date: A=January, B=February, etc. and the number = last digit of year built: 5=2015.

    A sticker saying D8 would have been built on April 2018. Sometimes batteries will sit on the shelf for a while – so when you see a battery, you will at least know how old it is at first sight.

    Most people (and shops) have not been removing the dots on the top side of battery – which indicates when battery was sold – but same information will be on your receipt.


    On a different issue, the last decade or so, I have been taking my battery receipt, and insert it into a Ziploc bag. Then I stick the baggie, rolled up, and placed under the battery for future reference.
    Not sure if that is the best place to put it at – but hadn’t ran into any problems with using that method for many years.

    Almost everyplace I know of needs the actual receipt before they will exchange it. A 5 year battery warranty will still give you 1 year pro-rata if your battery expired after 4 years
    BudW