How does small 12 volts battery get charged or trickle charged?

Discussion in 'Clarity' started by hanman, Oct 16, 2018.

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  1. hanman

    hanman Member


    I ask because I have a 2 weeks long trip away from my Clarity and knowing that the small 12 volts battery is a lead acid battery (meaning 3% discharge per day). I calculate almost about 42% discharge in 14 days.

    I left the car connected to the EVSE (120 volts one) and hoped for the best.

    I heard it being said once that the 12 volts battery gets only charged when the car is ON.

    Also I have had bad experience in the past with draining the 12 Volts battery while setting up the Android Auto software, in instrument mode not ON mode. The instrument panel and side screen ended up shutting down and when I tried to put car ON I got the multiple warnings that most people get. When I checked my small 12 volts battery it was at around 8 volts.

    So my question is: when/how ofter does the small 12 volts battery get charged? and do I need to hook up a trickle charger to it when I am gone on long trips?
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  3. petteyg359

    petteyg359 Well-Known Member

    That discharge assertion is ridiculous. I've left my CR-V sitting for over a month (100% discharge according to you) and the battery has been fine. Millions of people have left cars for two weeks unused while on vacation without battery problems.
  4. Force

    Force New Member

    I leave my cars sitting on airport for 3 weeks for international trip and starts fine. And this is on single digit temp.
  5. hanman

    hanman Member

    Okay I stand corrected, the self discharge rate of lead acid batteries is about 5% per month and not per day.

    So we are good for few weeks or few months, but my question remains, how does the 12 volts battery of the Clarity get charged? I know it gets charged from the 17 KWH propulsion battery, but does the car needs to be ON for that to happen?

    Screenshot 2018-10-16 21.14.20.png
  6. Sandroad

    Sandroad Well-Known Member

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  8. weave

    weave Active Member

    There's been some people who have witnessed a low 12 volt battery charging while the car is off. The theory is that it trickle charges from the high voltage battery, even if off -- but it will stop trickle charging if the high voltage battery gets too low. That would explain why so many 12 volt batteries are dead at dealers -- since their high voltage batteries don't get charged either.
    clarityowner12 likes this.
  9. hanman

    hanman Member

    Thanks weave, I love the theory and the conclusion.
  10. Atkinson

    Atkinson Active Member

    My Clarity seems to charge at intervals when driving, varying from 12.6v to 14.5v
    I haven't checked when charging the HV battery, but it must charge the 12v battery also at that time.
    No idea what happens when the car is off.
    I thought someone pulled documentation for this at some point.
  11. insightman

    insightman Well-Known Member Subscriber

    I just posted this on the dead battery thread, but it applies here, too:
    Poster @Hi.Ho.Silver used an inverter connected to his Clarity PHEV's 12-volt battery to power parts of his home after Hurricane Michael. @KentuckyKen then asked, "Did you have to turn the car on to have the 17kW hv battery keep the 12v battery full to do this..." and @Hi.Ho.Silver replied, "Yes, the car has to be on in the ready to drive mode to provide power to the 12v battery."
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  13. Vezz66

    Vezz66 Member

  14. Hoon

    Hoon Member

    Anyone knows when the 12V battery is charged? According to my dash-cam, it shows on starting from ignition ON it charges 13.8V, then drops to 12.5V level within couple minutes during a 10 minute drive. I just installed my dash-cam so I'm still trying to figure things out.
  15. insightman

    insightman Well-Known Member Subscriber

    AFAIK the DC-to-DC converter charges the 12-Volt battery from the HV battery only when the car is ON.
    Hoon likes this.
  16. As I remember it, the Ioniq does an interesting thing for 12V. They have a 12V battery within the housing of the traction battery that serves the function of 12V AGM batteries on most of the other cars. If it is accidentally drained (say, by leaving a map light on or leaving the headlights on) there's a button on the instrument panel that can be pushed to "jump start" the 12V section from the main battery via DC voltage converter.

    Does this all work as promised? I don't know. But the Ioniq does have a 12V battery--just in a different form.
  17. fotomoto

    fotomoto Active Member

    Anytime the car is in ON/drive mode (not accessory mode). It is continuously regulated by the dc-dc convertor using the HV battery and the ac-dc inverter that's under the hood as the power supply.

    I don't know for a fact on the Clarity design but on my other plug-in's I know the 12v is also charged/monitored during the HV battery charge session. I'd wager the Clarity is no different as the 12v has to be "hot" to open the HV battery contacts that isolate it from the rest of the car as a safety measure.
    Hoon likes this.
  18. sniwallof

    sniwallof Active Member

    While reading this thread, I realized that those of us with dash cams with voltage indications and parking mode can probably help to answer this question, when does Clarity maintain the 12 V battery?

    I noticed recently that after a couple of days of no driving, not plugged into L2, my cam was off by about day 3 (Thinkware F800PRO includes low voltage cut off; I set to 12.0V). On the other hand, I mostly leave L2 plugged in, and I don't recall parking mode ever going off before while plugged into L2 in the garage. It's motion sensitive and records walking by, however I rarely look at the videos anymore, just good to have, particularly for a parking lot hit and run.

    The 12V battery voltage shows on the recorded image frames, but there may be limits to usefulness. For example, not sure how to account for sitting in a parking lot on a sunny hot summer day. Any number of things, from 12V battery temperature to dashcam temperature (they can get hot), might change the voltage reading by a couple to few tenths in either direction.

    I think most blackvue installs add a low battery cut-off box, and also record 12V battery voltage on each image, not sure about other models. Any other parking mode installations out there that can comment on when the 12V battery voltage trickle charges and/or jumps to full charge voltage (>13V)?
    Last edited: Sep 3, 2019
  19. 2002

    2002 Well-Known Member

    I always assumed that the 12-volt gets charged in READY mode but not in ON mode, based on the charging indicator which appears whenever you are in ON mode.

    12-V charging indicator.png
  20. Hoon

    Hoon Member

    Doesn't that just mean that it's testing the 12V indicator light, just like any other ICE cars?
    And otherwise, light should stay off unless there's a problem with the 12V battery.
  21. 2002

    2002 Well-Known Member

    It stays on the entire time you are in ON mode, unlike the check engine light which goes off after a few seconds.

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