Does the inverter charge the 12V battery when the ICE is off ?

Discussion in 'Gen 3 Prius Technical Discussion' started by Jon Hagen, Mar 6, 2012.

  1. Jon Hagen

    Jon Hagen Active Member

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    The thread below about short (3-5 years) life of the 12V battery got me wondering. Does the inverter maintain constant charge to the 12V battery by using power from the traction battery, or does it quit charging the 12V battery when the ICE is off ?

    Slow speed or city driving where the ICE starts / stops often, would cycle the 12V battery constantly if not charged when the ICE is off, especially if lights and cabin blower are on.

    I get from posts on this site that the 12V battery is an AGM deep cycle type, still, cycle it enough times and it will wear out.

    If the system works as I suspect, that little deep cycle battery may live a harder life than a starting battery in a conventional car with a constant running engine that supplies all electrical needs until you turn it off and need to restart.

    Anyone measured voltage on the 12V system with the ICE on / off to see if the voltage increases to around 14V when the ICE is on ?
     
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  2. bear4

    bear4 Junior Member

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    The 12 V system is charged by HV battery every time the car is in Ready mode regardless of ICE running or not
     
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  3. direstraits71

    direstraits71 Member

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  4. David Beale

    David Beale Senior Member

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    As stated above, the Prius system puts 13.8V (GII) or 14.3V (GIII) on the 12 Volt "buss") continuously when in "ready". There is no "charge control" that I'm aware of in the GII. Haven't monitored the buss voltage in the GIII so can't comment on whether there is any control.
     
  5. tumbleweed

    tumbleweed Senior Member

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    As mentioned above both the Gen2 and Gen3 supply the 12V system from an inverter off the HV system and it makes no difference if the ICE is running or not.

    But the Gen3 uses a larger step change, it charges at about 14.6V until the 12V battery voltage comes up then it switches to about 13.8V. I have noticed that if it is operating at 13.8 and I turn something on, heater fan, headlights, etc. it will switch back to 14.6 for a while.
     
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  6. Jon Hagen

    Jon Hagen Active Member

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    Thanks for the info guys. It sounds like the gen 3 has a very smart continous charging system for the 12V battery which should allow it to "float" in the system with little change in state of charge and no overcharge.

    That being the case, I am a bit puzzled as to why the 12V battery seems to have a fairly short life of 3-5 years ?
     
  7. spiderman

    spiderman wretched

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    ^ because it is so darn small.
     
  8. jdenenberg

    jdenenberg EE Professor

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    And most of the complaints come from Gen2 owners.

    JeffD
     
  9. qbee42

    qbee42 My other car is a boat

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    And the Prius puts a pretty good drain on it when sitting in the garage.

    Tom
     
  10. David Beale

    David Beale Senior Member

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    Well, five years is not "short life" for a car battery. That's pretty much normal for most cars here.
    Now, if you were willing to pay about $100 more for the car Toyota could have put in a much better quality float battery which might last 10 years. But they didn't so it doesn't. ;)
     
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  11. Jon Hagen

    Jon Hagen Active Member

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    I guess your right. It's just that I have most machines on my farm fitted with Optima and Exide Orbital spiral AGM batteries. Their a little more expensive,($150) but I normally get 12-15 years out of them in cars ,trucks and farm machinery. Pretty much an install it and forget it battery.
     
  12. David Beale

    David Beale Senior Member

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    Well you're in luck! Optima has one for the Prius now! Or you can get the D51 from eLearnaid with the adapter kit for standard size posts (standard for us).
     
  13. Britprius

    Britprius Senior Member

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    I have a gen2 (2008) in the UK with the MFD display when first made ready it shoes 14.4v after some time this drops to 13.8 that suggest the gen2 has a 2 stage charging system, bulk then float.
     
  14. David Beale

    David Beale Senior Member

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    Well, I see Pearl start out at 13.9 or even 14.1 if I've left something on for a while, eventually dropping to 13.8, but I don't think it's a "two stage" system. I think it just senses the battery is low and charges accordingly.
    BTW, I think this is an indication the battery is getting old and is about to die. When younger, Pearl's system stayed at 13.8 no matter what.

    Pearl no longer goes up to 14+V since I added water to the battery. But I suspect that battery will die this year.

    I've started asking around looking for a 50 A-Hr NiMH set of cells (10 are required for a 12V battery). Even if it cost as much as $300 it might be worth it. Just think, full discharge might not damage it! What a concept! ;)

    My experience with NiMH and NiCd batteries tells me they should work in the GII Prius. At 13.8V float they won't fully charge but they also won't overcharge.
     
  15. Jon Hagen

    Jon Hagen Active Member

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    Green Car Congress: Porsche Offers Li-ion Starter Battery Option
     
  16. Rybold

    Rybold globally warmed member

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    Searching through threads, this appears to be the best thread to post my question on.

    Question about 12V battery and starter in Prius.

    I recently experienced a dead battery in my non-hybrid car and had to call AAA to come jump start it. While I was sitting there, waiting for AAA to come, I thought to myself: if I had a Prius, I would not have a 12V battery and this would never happen. When I got home, I jumped on Google and started looking into this. I discovered that the Prius does have a 12V battery! (to my complete surprise). I started thinking about when I go on road trips and out into the desert, I leave my engine running when I pull to the side of the road to take a picture or "water the plants." Police officers normally never turn their engines off either. The reason is that it might not start back up and you don't want that when you're out in the middle of nowhere.

    From this thread, I have learned that the hybrid battery DOES charge the 12V battery. Great, so does that mean I will never have to worry about the engine not starting as a result of a weak battery? From this thread, it seems that is not the case.

    Hmmm. But then this post confused me:
    http://priuschat.com/forums/gen-iii...03036-should-13-7-14-7-volts.html#post1463944

    So here are my two questions:

    1) Does the Prius have a starter motor, like a normal car, or does MG 1/2 start the engine? (both cold start and once the car is moving)

    2) If I'm out in the desert, do I have to worry about the car not starting, or will the car always be able to start in electric mode, and then MG 1/2 start the engine? Do I have to worry about getting stranded as a result of a starter motor and 12V battery not starting my car?

    THANKS!!!!!!!!!! :)
     
  17. JimboPalmer

    JimboPalmer Tsar of all the Rushers

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    The 12 Volt battery gets you to READY, it powers up the computers and pulls the relays to energize the HV cables. If it is dead, it can't do that, and the computers will set 'odd' codes.

    Once we are READY, the HV Battery powers MG1 to start the ICE. (Never MG2, it is locked to tire RPMs) On rare occasion you can run down the HV Battery to where MG1 has no power to start the car, mostly trying to get to a gas station without any gas.
     
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  18. tumbleweed

    tumbleweed Senior Member

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    MG1 is used to start the ICE. The 12V battery is needed to boot the computers and close the relay that supplies power from the HV battery.

    If you shut the car off completely and make sure all the interior lights are off you should be able to leave it indefinitely. Assuming your 12V battery is good. Just as with any other car.

    If you leave it in Ready (not recommended procedure) it will run until it is out of gas, it will sit there until the HV battery gets low then run the engine to recharge over and over. A tank of gas would last for days.

    If the car is off and you leave an interior light on and/or you leave it in Accessory or On you may be at risk, depending on how long you are gone.

    I usually shut mine off, unless I'm stopping to take a few pictures and won't be away from the car then I may leave it in Ready. If you leave it in ready anyone can get in and drive off, even without the key fob. It will keep running until they turn it off, then they would not be able to restart it.
     
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  19. qbee42

    qbee42 My other car is a boat

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    Once in Ready, you can remove the 12V battery from the Prius and it will still run, starting and stopping the engine as needed. The 12V battery is there to run accessories when powered off, to maintain persistent settings, and to boot the computers. Once booted, its job is done.

    Tom
     
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