maintaining 12v Batt while using Techstream

Discussion in 'Gen 2 Prius Technical Discussion' started by RC-Pilot232, Jul 9, 2017.

  1. ChapmanF

    ChapmanF Senior Member

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    No, it was one of the "food truck has 20 hamburgers, 7 customers buy hot dogs, how many hamburgers are left" questions.

    -Chap
     
  2. Mendel Leisk

    Mendel Leisk Lapsed Cargo Cultist

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    Wait, don't rush me...
     
  3. KokomoKid

    KokomoKid Junior Member

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    If you want the battery to last a long time, you should maintain it at around 12.8 volts. Techstream will probably work with the battery discharged to 9 volts, but if you do that very much, you will greatly decrease the life of the battery.

    Posted via the PriusChat mobile app.
     
  4. edthefox5

    edthefox5 Senior Member

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    Nope. All chargers and maintainers will charge to 13.8. Thats a full battery. That's why the charging voltage from the Inverter is 14 volts and not 12.8
    12.8 volts is not fully charged and maintaining it to 12.8 is very poor practice.
     
  5. ChapmanF

    ChapmanF Senior Member

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    That would be the correct answer in any thread that was about "maintenance charging" as the term is commonly used.

    Understanding what this thread is about requires a look at the original post, which is about a different question (even though the word 'maintain' is in it). In this thread, the question is "I'm going to have the car in ACC or ON for some extended period (probably in the many-minutes-to-few-hours range), what voltage supplied to the 12 volt battery will prevent it discharging during that time." (In fact, the original original question was "... so the HV battery won't discharge" which turns out to be a non-issue in ACC or ON, so this is the only question that's left.)

    The right answer to this question, already given more than once upthread, is "anything at or above the battery's own open-circuit voltage," or around 12.8. If you can supply that consistently, there will not be current flow out of the battery, which meets the original poster's requirements. (But, as also pointed out upthread, a power source with at least several amps of output capacity will be needed to sustain that.)

    True, that would not be the right answer to "what voltage should a maintenance charger put out?" but that would be a different question for a different thread. (And a typical maintenance charger, while putting out a higher nominal voltage, would generally be incapable of the amps needed to hold up even 12.8 under the conditions asked about here.)

    -Chap
     
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  6. KokomoKid

    KokomoKid Junior Member

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  7. KokomoKid

    KokomoKid Junior Member

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  8. edthefox5

    edthefox5 Senior Member

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    Excellent thank you.
     
  9. 05PreeUs

    05PreeUs Member

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    The REASON 12.8 will not work for maintaining is there is such a thing as voltage drop and internal resistance of a battery.

    These create three distinctly different, yet inter-related problems for "maintaining" 12.8V.
    1) You cannot charge a (full @ 12.8V) battery WITH any 12.8v source (charger, other battery, etc), because the voltages are EQUAL, no charge can flow.

    2) #1 is compounded by the internal resistance of the battery you want to maintain OR charge. Resistance means you need supply voltage to be GREATER than that of what you are trying to charge, or the resistance will prevent current flow.

    3) Voltage drop occurs in EVERY circuit and the amount is a function of the circuit and amps you are trying to pass (V = IR, or as I prefer V = CR). Therefore, if you try to put 13.8V thru a PAIR of wires having 1 ohm of resistance EACH @ 0.5A to maintain or charge a battery that measures 12.8V at rest; you will only actually apply 12.8v to the battery terminals :(

    Not even *so called* "smart chargers" are designed, or smart enough to measure the voltage applied AT THE BATTERY terminals, which is coincidentally, the ONLY place it matters :/
     
  10. Fred_H

    Fred_H Misoversimplifier

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    I maintain that maintaining 12.8 Volts is not sufficient to maintain a battery.
     
  11. dolj

    dolj Senior Member

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    And yet again, this post is not about maintaining the 12 V battery, but rather trying to prevent the HV battery from being drained while using Techstream. Yes, really, that was the question.

    Asked and answered.
     
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