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Auxilary battery in car - need to know the name of device

Discussion in 'General Electronics Chat' started by Grossel, Jan 4, 2017.

  1. Grossel

    Grossel Member

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    Hi guys.

    I need to know the English term for a device that:
    • Connected to a car 12V outlet, a smaller battery, and an alarm system (dash-cam) - alarm system might be connected directly to smaller battery if charger is capable of charge the small battery while alarm system is powered from the small battery.
    • When voltage is applied from car battery, the smaller battery is charged.
    • When no voltage is applied from car battery, the small battery power the alarm system.
    Reason I ask I try to find one at eBay, but after several searches with different search phrases that only returns none of interest I give up :banghead:
    The boring fact is that I know I have seeing such one in a web store some months ago, but I never recalled it's exact name :arghh:

    All I find on eBay is those chargers that need 110 - 230 volts inputs, and I can't use that.

    Thanks
     
  2. MikeMl

    MikeMl Well-Known Member Most Helpful Member

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    A small 12V Sealed Lead Acid battery could be connected through a 3A Schottky power diode to a 12V automotive power port. My newer Subaru has power ports that are always live and others that are live only when the car is running.

    When the car is running, the power port will have about 14.3V to as high as 14.7V (depending on the age of the car) which will charge the SLA battery without overcharging it even with the forward drop of the diode.
     
  3. spec

    spec Well-Known Member Most Helpful Member

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    I will do a swap, the term in English is 'auxiliary battery', what is the equivalent term in Norwegian? :)

    spec
     
  4. dave

    Dave New Member

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  5. spec

    spec Well-Known Member Most Helpful Member

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    Why just a 3A Schottky diode Mike, wouldn't a 100A, say, Schottky diode give a much better performance?

    spec
     
  6. MikeMl

    MikeMl Well-Known Member Most Helpful Member

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    I have been using a 1N5822 to keep a 6Ah 12V SLA charged for about 10 years. The battery is in a 8000 lb car-hauler trailer to power the trailer's electric brakes in the event of a breakaway. 14.5V comes from the towing vehicle while its engine is running. The diode prevents the battery from discharging into other things when the towing vehicle is not running, or while the trailer is disconnected.

    I recently put a 100Ah auxiliary deep-cycle flooded battery into my Chev truck. It uses a high-current relay to isolate it from the truck's electrical system when the truck is not running. The aux. battery feeds pin 7 on the trailer connector, so it effectively becomes the third battery for the travel trailer that I tow with the truck. This would be the place to use your 100A Schottky in place of the 250A relay?
     
    Last edited: Jan 5, 2017
  7. Grossel

    Grossel Member

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    Thanks for answers. Well the norwegian term may be "reservebatteri" (depending of it actual use), and I have tried many kind of combination of "battery" "auxiliary" "car" "supply" in ebay search without finding anything usable.

    I may as well go buying a Schotty diode and a power button to solve this.

    [edit]
    One question - when I buy an auxiliary battery, I want to know its internal resistance or charge current so that I can estimate the maximum current that will flow through the diode. If possible I don't want to use an additional power resistor.
    Any sources to this?
    I will probably have to replace the main car battery anyway so I have to assume near zero internal resistance from the car, and also brand new auxiliary battery.
     
    Last edited: Jan 5, 2017
  8. spec

    spec Well-Known Member Most Helpful Member

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    Thanks. It seems that I should have said, 'dual battery system' or 'dual battery isolator'

    Here are some links I came across:
    http://www.fridge-and-solar.net/dual_bat.htm
    http://www.ebay.com.au/itm/ENERDRIV...DUAL-SENSING-CIRCUIT-VERY-SMART-/181653631902
    http://www.enerdrive.com.au/pdf-files/enerdrive/dual-battery-kit.pdf
    http://www.ebay.com.au/itm/12V-DUAL-BATTERY-ISOLATOR-DUAL-SENSING-CIRCUIT-ENERDRIVE-REDARC-COMPETITOR/291392450480?_trksid=p2047675.c100005.m1851&_trkparms=aid=222007&algo=SIC.MBE&ao=2&asc=39923&meid=3db74a1237574596b39995b0011c87b4&pid=100005&rk=1&rkt=6&sd=181653631902

    The auxilary battery internal resistance, for this type of calculation, is zero ohms
    That is correct. The main battery on your automobile will have a zero resistance, whatever its age, for the calculations you are talking about.

    The automobile alternator will also have a zero resistance up to a voltage of around 14.1V and up to the current limit of the alternator. Once either of these limits are reached the alternator will produce no more voltage and no more current.

    Alternator maximum current typically varies from 30A to 120A upwards, depending on the vehicle, type of engine, and country. Norway, being very cold in the winter, will require a high capacity battery and alternator.

    Diesel engine automobiles tend to have bigger batteries and higher current alternators to provide the starter motor with the high power required to crank a diesel engine.

    spec
     
    Last edited: Jan 5, 2017
  9. Grossel

    Grossel Member

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    Thanks a lot.

    "dual battery system" seems to be most appropriate solution, but one problem remains - I intend to use the cigarette outlet in the car - that is fused, so It would never work to parallel the auxiliary battery to main battery through cigarette outlet.

    I need to limit the current, so maybe I need go go back to the power diode and resistor solution.
     
  10. spec

    spec Well-Known Member Most Helpful Member

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    Can you describe exactly what you plan to do:
    (1) What is the fuse value for the cigarette lighter?
    (2) What A/H rating will the auxiliary battery be?
    (3) Will the auxiliary battery plug into the cigarette lighter socket?
    (4) Will the auxiliary battery be in the cabin of the vehicle?
    (5) How will the auxiliary battery provide power to the car when the alternator is not spinning?
    (6) What will the auxiliary battery be powering when the alternator is not spinning?
    (7) What is the maximum current that the auxiliary battery will be providing when the alternator is not spinning?

    Apologies for all the questions.:arghh:

    spec
     
  11. bwilliams60

    bwilliams60 Member

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  12. Grossel

    Grossel Member

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    Hi guys - I think I see what I need to do. I haven't checked the fuse rate and the battery is not being bought.
    The auxiliary battery is intended to drive a DOD LS460W, and I haven't yet decided by the battery AH ratings. I first need to figure out the dash-cam approx current consumption over a couple of days (numbers of movements detections will of course have a huge impact here)

    My problem is that the most easy solution that deals with diode and power resistor isn't good enough for me, wish more control.

    Therefore I spend some time at ebay and came down to the conclusion that I want to create a current limited circuit, beginning with a Panel Mount +/-100Amp AC/DC Current Sensor Module Board
    http://www.ebay.com/itm/Panel-Mount...or-Module-Board-based-on-ACS758-/371462981595

    And from there, I will try to design a simple pwm circuit that limit the current to say 5A. I also need to figure out if a lead acid battery can withstand any ripple current.
     
  13. tcmtech

    tcmtech Well-Known Member Most Helpful Member

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    You may want it but in your application it's totally unjustified making the endeavor little more than a complex waste of time and money to prevent nothing of consequence from happening. :rolleyes:

    Just factor in your wiring resistances plus diode drop between the alternator and the auxiliary battery and it's pretty obvious the peak currents and times they will last are largely inconsequential to the overall operation of they added battery circuit.

    I for one would have zero issues with wiring the 6 Ah battery circuit with 20 - 22 ga wire, a 3 - 5 amp Germanium diode and a 3 - 5 amp slow blow fuse. The inherent voltage drops in the wiring would easily compensate for any initial high current draws and even if they did not limit it well enough for long enough the fuse would take over and do it's job long before any problems occured.
     
  14. MikeMl

    MikeMl Well-Known Member Most Helpful Member

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    Likewise. In my two examples, if there was an in-rush issue, the added 6Ah SLA would blow the 3A diode; it hasn't. The 100Ah deep-cycle would have blown the 35A fuse built-into-the-vehicle which feeds the auxiliary battery; it hasn't.
     
    Last edited: Jan 7, 2017
  15. tcmtech

    tcmtech Well-Known Member Most Helpful Member

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    Having a fair grasp of electrical theory but poor understandings of applied electrical realty plus unrealistic expectations based on their theory that does not take into account small but important details of reality tends to be a common theme on these forums. :(

    That and worrying about unfounded 'what if's' that some basic rational sense, research and math would dispel as well. :banghead:
     
  16. spec

    spec Well-Known Member Most Helpful Member

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    Talking nonsense, making self serving arguments and trolling are also a common theme on these forums TCM.:arghh:

    I hope this is not going to be another thread that you kill!

    You will notice that I have made no comment about your cavalier attitude to design.

    Please behave.

    spec
     
    Last edited: Jan 8, 2017
  17. tcmtech

    tcmtech Well-Known Member Most Helpful Member

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    Did I touch someone's theory VS reality discrepancies nerve again? :rolleyes:

    If you don't want it to start then don't start it. :(

    Also, just because someone doesn't know the working details of something doesn't make the persons who do careless or wrong in why they do what they do for the reasons they do it. :facepalm:
     
    Last edited: Jan 9, 2017
  18. Grossel

    Grossel Member

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    tt - thank you for trying (too hard?) to give practical English lessons, but I'd hoped that the discussion would have involved forum members that - like me - have some interest in finding some justified balance between price of the project (parts) and quality (expected life time of fuses and batteries) of final product.

    For those of you that have visiting my home country in the winter - hunting for northern light, would know that we need to feed the small trolls to keep balance in the deep dark forests.
     
  19. tcmtech

    tcmtech Well-Known Member Most Helpful Member

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    What english lessons? I'm a life long English class flunky. :rolleyes:

    However if you don't want something read or replied to the obvious solution would be to not post it to begin with. :oops:
     

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