Please explain 12V system to me--how to keep battery charged while using accessories?

Discussion in 'Gen 4 Prius Technical Discussion' started by dpbsmith4, Sep 5, 2017.

  1. alanclarkeau

    alanclarkeau Senior Member

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    The OP hasn't responded to whether the car was in "P" or "N" (question by Elektroingenieur in Post #4). The answer to that could solve the problem if the car was in "N".
     
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  2. FuelMiser

    FuelMiser Senior Member

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    I don't believe the OP said the 12V when down while in READY mode. He said, "One morning, when we'd used the Prius to charge the battery several days in a row... as well as lazing in the car with the AC on during hot parts of the day... the car briefly flashed "12V low" and would not start." This could be interpreted as the car would not start after sitting overnight in OFF. He also says they had been using the 12V system to charge his CPAP battery as well as running the AC, and maybe had not been in READY long enough to fully restore the 12V before shutting off overnight.
     
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  3. dpbsmith4

    dpbsmith4 Junior Member

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    If FuelMiser will try the experiment with the Gen 4 I would be very grateful. Thanks very much to all who replied. Of the various things suggested, not being in READY mode when I thought I was sounds the most likely. I am happy to hear the consensus that it ought to work, i.e. the 12V is charged via DC-DC converter from the traction battery and charge should be maintained when the ICE is not running. Carrying a generator is not sensible, we are pretty cramped for room as things stand, and it seems like overkill given that the CPAP charger is, you know, maybe a 40W device if that. Because the car behaved fine on a camping trip last year, using it in the "idle-in-READY-for-hours" mode, and because there was not a hint of any problems after we got the jump, I'm guessing nothing is malfunctioning. And, yes, I'm now going to look for a suitable jumper battery to carry with us. We had one during the 11 years we had the Prius 2005 and used it once--I believe what happened was that a grandchild turned on the dome light, which apparently doesn't necessarily go out even when the car is shut off.
     
    #23 dpbsmith4, Sep 8, 2017
    Last edited: Sep 8, 2017
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  4. dpbsmith4

    dpbsmith4 Junior Member

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    1) As to whether the car was in P or N, I can't prove it but I am "sure" it was in P.

    2) My belief is that we sat in the car for a long time because of bad weather, listening to radio and so forth, shut off the car by pushing the power button before retiring for the night, and my wife discovered the "12V low" when trying to start it in the morning.
     
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  5. dpbsmith4

    dpbsmith4 Junior Member

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    Finally, if people would suggest some suitable way of monitoring the 12V, that would be very useful. I think there were two warning signs if only I'd paid attention to them: 1) Failure of my wife's iPad to charge via a USB charging adapter plugged into the 12V outlet in the console, and 2) Multiple, I mean six or seven beeps, which locking the car via the door handle. I know the second one sounds weird, but it was a symptom before the 12V battery itself actually failed on the 2005 Prius.
     
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  6. dpbsmith4

    dpbsmith4 Junior Member

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    Are there any interior lights that will stay on indefinitely when the car is turned off and all doors are closed and locked?
     
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  7. bisco

    bisco cookie crumbler

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    not sure about ben 4, but get 3, both the overhead light, if you turned it on manually.
     
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  8. alanclarkeau

    alanclarkeau Senior Member

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    I haven't tried them all, but the boot (trunk?) light turned off on mine after about 20-30 mins.
     
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  9. fotomoto

    fotomoto Senior Member

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    Details like this would have helped. Most likely operator error. BTDT
     
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  10. Elektroingenieur

    Elektroingenieur Senior Member

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    Yes to both. From the New Car Features:
    • The battery sensor (battery state sensor assembly) installed on the negative (-) auxiliary battery terminal calculates the current, voltage, battery temperature, SOC (battery charging percentage) and SOH (battery degradation percentage) and sends these signals to the hybrid vehicle control ECU via LIN communication.
    • To detect the current, a shunt resistor installed inside the battery sensor (battery state sensor assembly) is used to convert and calculate the voltage generated in the shunt resistor due to the battery charge and discharge current.
    • The auxiliary battery temperature is calculated from the resistance value of the thermistor built in the battery sensor (battery state sensor assembly).
     
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  11. ChapmanF

    ChapmanF Senior Member

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    Aha, that is new for Gen 4. So, Gen 4 enthusiasts installing inverters or other added loads would be well advised to be sure the tap is taken downstream of the battery state sensor assembly.

    -Chap
     
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  12. kithmo

    kithmo Couch Potato

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    On mine, all the interior lights go off 30 mins after switching off and locking the car, even if switched to the permanent on position. Don't ask me how I know :whistle:
     
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  13. ChapmanF

    ChapmanF Senior Member

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    I just looked again at the excerpt @Elektroingenieur posted, and saw that it says the battery state sensor assembly lives in the battery negative cable. So, any added load ought to be properly counted, as long as its ground return is to any body ground point, just not directly back to the battery − terminal.

    -Chap
     
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  14. Elektroingenieur

    Elektroingenieur Senior Member

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    That’s right. Here’s an annotated photo of the auxiliary (12-volt) battery on my 2016 Prius and some of the nearby connections:

    PriusBattery.jpg

    The sensor assembly is bolted to the negative terminal on the battery, and it has a threaded stud (labeled Engine Wire Connection in the photo) to which the No. 3 Engine Wire harness is attached. As @ChapmanF notes, an added load could be connected there or to any ground point, but not directly to the battery terminal, since a direct connection would bypass the current sensor.

    As seen in the photo, the No. 3 Engine Wire harness is connected to ground points DA and DF, but according to the Electrical Wiring Diagram (available by subscription to techinfo.toyota.com), within the harness, one wire from the battery is connected to ground point DA and another is connected to ground point DC, not shown. Connector C19 provides the sensor assembly with power and a LIN bus connection to the Hybrid Vehicle Control ECU.

    The Electrical Wiring Diagram divides the 12-volt battery and charging system among several System Circuit and Inner Circuit diagrams, which can be a bit tricky to follow, so I put together an unofficial schematic showing how it all goes together:

    PriusBatterySchematic.png
    The fusible link block assembly has the main fuses for the 12-volt electrical system. Here are two annotated photos of one I bought as a spare (part number 82620-47090, price ¥2,360):

    PriusFusibleLinkBlockAssembly.jpg
    The fusible links are not individually replaceable; if one blows, the entire assembly must be replaced.
     
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  15. DLC82SV

    DLC82SV Member

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  16. Mendel Leisk

    Mendel Leisk Senior Member

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    I remember soon after we got our 2010, walking through a parking lot, a chilly morning, on the way to my morning train commute, seeing cabbies "hibernating" in their idling Prius cabs, steam coming out of the exhausts. :cry::LOL:
     
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  17. DLC82SV

    DLC82SV Member

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  18. lextoy

    lextoy Active Member

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    Along the lines of dead battery needing to be recharged...is it safe to charge the 12v with an automatic charger or battery minder while the evse is plugged in and charging?? Or should I recharge the 12v only when the evse is disconnected. I have a ctek, batteryminder, and regular charger with auto mode.
     
  19. jerrymildred

    jerrymildred Senior Member

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    I don't think I'd put a charger on the 12V while the EVSE is plugged in, especially while the traction battery is charging. Beside, when the EVSE is powering the car's traction battery charger, it's also topping off the 12V battery. I haven't measured the voltage on my Prime yet, but I've read here that it doesn't charge the 12V as strongly as the PiP did. But it is charging both batteries.

    Back to the original subject, I had something happen one time (so far) with the Prime that might be related to the question about the 12V running down. I shut down the car, got out and closed the door, and it beeped at me. The MID said "Accessory." As far as I knew, it was off. But I got back in, made it ready and shut it off. No more beep. I have read that, if you're running a power window as you shut off the car, it will go to accessory mode rather than off. But I wasn't running any windows or anything else. Very odd, but perhaps that was the cause of the OP's trouble.
     
  20. Mendel Leisk

    Mendel Leisk Senior Member

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    I didn't see any cautions against this, looking in the Owner's Manual, page 587.
     
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