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Disconnect at 11.8V HOW? Please help!

  1. Jul 23, 2008 #1
    Hey guys,

    I am building an electric racecar for university and I'm stuck!. It has to be run on car batteries and it can only use one at a time... many people are just using an excellent battery with a great amp-hour rating... but I'd like to switch batteries halfway through...

    I want to disconnect a car battery when it reaches 11.8V and possibly using an adjustable voltmeter/detector?

    Please help, any advice would be great!

    Thank you!
    -Tom
     
  2. jcsd
  3. Jul 23, 2008 #2

    chroot

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    You're not going to build much of a race car with only one 12V battery at a time. A single 12V battery, even at 100 amperes of current, is only providing 1,200 watts of power. This is about the same amount of power generated by a lawnmower engine.

    - Warren
     
  4. Jul 24, 2008 #3
    There are plenty of battery voltage detector chips about.

    Maxim make a shedload.

    Combined with suitably zonky Power mosfets, then bob's yer uncle.
     
  5. Jul 24, 2008 #4

    berkeman

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    You Brits sure talk funny :rofl:
     
  6. Jul 25, 2008 #5
    We've had centuries to practice... :biggrin:

    Zonky, by the by, means "large" as in >100A Id(on).
     
  7. Jul 25, 2008 #6
    One way for a warning system would be to setup a diode with a resistor (or trim pot) combination that switches at 11.8V.
     
  8. Jul 25, 2008 #7

    stewartcs

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    What the heck does "then bob's your uncle" mean?

    CS
     
  9. Jul 25, 2008 #8

    mgb_phys

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    It means you're problems are solved

    Historical note:
    Robert Gascoyne-Cecil,was prime minister in the 1890 and was a big fan of nepotism - appointing his nephew as minister, so if Robert (bob) was your uncle you didn't have any problems getting a job.

    Interestingly neptosim is from the Italian for nephew and comes from Pope's giving appointments to their (cough) nephews (cough)
     
  10. Jul 25, 2008 #9

    stewartcs

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    Ah...Thanks.

    CS
     
  11. Jul 25, 2008 #10

    berkeman

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  12. Jul 25, 2008 #11

    Redbelly98

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    Do I understand that both batteries will be in the car at all times, and you want a circuit that electrically switches over to battery #2 when battery #1 reaches 11.8V?

    If this is for a contest, how will you convince the judges that only one battery is being used at a time?
     
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