Prius 12V battery charging at 14.9V/10A???

Discussion in 'Prius v Main Forum' started by TWrecks99, Dec 8, 2020.

  1. cnc97

    cnc97 Senior Member

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    Car scanner pro for iPhone.
     
  2. TWrecks99

    TWrecks99 New Member

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    Sam, yes I get that 14.9V is charge voltage, and I agree its too high for continuous charging. I have checked the battery with a DVM countless times, and your right it is always about 0.1V higher than the MFD diagnostics. But I can see the diagnostic reading from the drivers seat:)

    My point was that at 4hrs at 14.9V with the charge current dropping from ~8A down to under 1A, then the battery is certainly fully charged... so 18 hrs later it should not be 12.2V (at the MDF) or 12.3 (at the battery). So either an unexpected drain happened, or the new battery is intermittently dying. Overnight last night it dropped from 12.52V to 12.5V (just dome lights on), which sounds like a good battery...

    Last night with the MFD diagnostics on in standby, when I started the car I can see the charge voltage start at around 14V and quickly step up to 14.9V or a second or two.

    I keep thinking sticking relay or something is killing the charge. Attached is the battery test report from the dealer last week after I brought it back in. State of charge was ~80%.

    Tim
     

    Attached Files:

  3. sam spade 2

    sam spade 2 Senior Member

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    That is the charging system voltage.
    You can NOT deduce much about the state of charge from that.
     
  4. sam spade 2

    sam spade 2 Senior Member

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    I agree that is a reasonable assumption.

    If it is indeed true, then there is a fault in your charging system that REALLY needs to be fixed.
    OR there is an unusually high continuous load somewhere other than the battery that makes it charge at a higher voltage.

    While it is possible for a battery to fail in a manner so that it will continue to accept a high charging current without actually charging much, it doesn't look like this is the case here.

    To review, the symptoms were basically the same before and after putting in a new battery, right ?
     
  5. TWrecks99

    TWrecks99 New Member

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    I didn't really check much on the old battery - it was ~4 years old, and after needing a jump start after not being run for a couple days on several occasions this fall, and finally dying after a just a day or two I just had it replaced as I needed the car. Maybe I should have been more curious.

    Forecast calls for a blizzard coming in tonight, so probably not much work on the car outdoors for bit. Hopefully it starts when the plow comes to clear the parking.

    Tim
     
  6. Stevevee

    Stevevee Active Member

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    Must be a thing. After three cold days, single digits, and a snowstorm, I just went out and it gave me that tired, I'm Really Old and Cold sound. I suspect that after 7 and a half years, it's just too old to put up with this crap. Wish I started it yesterday, now it's Friday, as usual.
     
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  7. TWrecks99

    TWrecks99 New Member

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    Wrenched my knee good pushing a stuck car when my foot slipped out, surprisingly it was not my Prius. I know the old and cold sound, I made it. Now I have 2 weeks off and can't do anything. My Prius used to get stuck in an inch of snow, then I realized the stock tires were abysmal in snow. I found the best rated in snow all-seasons and put them on and it's been a different car in winter since. I suspect snow traction is not one of the criteria they use to choose OEM tires.
     
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  8. Air_Boss

    Air_Boss Senior Member

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    The OEM Toyo A20s were horrible in rain and snow. Continental ecoPlus PureContacts year round, and Dunlop M3 Wintersports for the heavy stuff.
     
  9. Air_Boss

    Air_Boss Senior Member

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    Classic case of battery comorbidity - age and cold.
     
  10. Stevevee

    Stevevee Active Member

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    Covid-related, hadn't started it since Monday.


    Santa got me a new 1200 portable battery thingie. How handy.
     
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  11. Stevevee

    Stevevee Active Member

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    I had such good luck with Generals, I have a new set of the AltiMax Artic snows on this year, and studded too. Interesting the the Generals are amongst the cheapest, perform excellently, and have lasted me longer than any other tire.
     
  12. Stevevee

    Stevevee Active Member

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    Well Santa's Schumacker batter worked, Prius all started and happy. wished the cables were longer. It really needed about 5-10 minutes just hooked up before it would charge. Since it's an easy fix, I might just want to go to the dealer and have them put another one in. This is not the kind of thing I want to do often.
     
  13. Air_Boss

    Air_Boss Senior Member

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    Every seven years, whether you need it or not...
     
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  14. sam spade 2

    sam spade 2 Senior Member

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    I don't understand.
    I don't think that there are Schumacker brand batteries.
    So..... what exactly did you replace ?
    And how are you gauging "charging" ??
     
  15. rjparker

    rjparker Senior Member

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    It is a jump starter for his 7.5 year old battery. He is getting a new battery because "its an easy fix". "Charging" as related to a dead battery and a jump start module means leaving the jump on long enough to pull the car battery up some to allow the Prius to initialize.
     
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  16. Gokhan

    Gokhan Senior Member

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    For conventional cars the typical alternator IC regulator voltage is 14.3 V, with 13.5–15.1 V being considered a normal rage.

    Looking at the Prius Prime OEM repair manual, the specified range is 13–15 V.

    If you are using an external charger, the OEM repair manual is recommending 5 A for normal charge and 15 A for quick charge.

    So, everything is fine.

    [​IMG]
     
    #56 Gokhan, Dec 20, 2020
    Last edited: Dec 20, 2020
  17. Stevevee

    Stevevee Active Member

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    Yes, that's what I meant. I saw that online in a couple of places, so I didn't worry when the first try failed. After probably 15-20 minutes hooked up, it finally started.
     
  18. TWrecks99

    TWrecks99 New Member

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    So my battery seems to hold a charge well for a few days at least, it's ~12.5V with the car off and dome lights on (~1.5A). But when I put the car in Standby (~10A) it drops to ~12 instantly. After shutting the car all the way off, it rebounds up to 12.4V or in a minute or so. Does this sound like a healthy battery? The voltage at the jump point vs across the battery terminals themselves is about 0.1V difference so not a bad connection in the wiring.

    Q: Is 10A normal for standby? (no stereo, no exterior lights, no fan, no seat heater).
    Q: Is it normal for the battery to drop 0.5V under 10A load?

    Thanks

    Tim
     
  19. Gokhan

    Gokhan Senior Member

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    Yes, batteries have an internal resistance, that's why you see a voltage drop when a current passes:

    V = ( V open circuit ) − ( I × R internal )

    If the voltage drop is 0.4 V @ 10 A, it means R internal = 0.04 Ω. This corresponds to an SOC of roughly 35% according to the plot below; so, you still need to charge your battery.

    [​IMG]

    Likewise, you can use the open-circuit voltage per cell to estimate the SOC. Yours is 12.4 / 6 = 2.07 V. This corresponds to an SOC of roughly 50%. 11.8 V is almost fully discharged and 13.1 V is fully charged (SOC at 100%).

    [​IMG]
     
  20. sam spade 2

    sam spade 2 Senior Member

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    Not exactly sure what you mean by "standby" but in "accessory only" mode, I'm pretty sure that it should not draw anywhere near 10 amps with all of the obvious things that you mentioned switched OFF.

    If it starts at 12.6 or above, a .5 V drop when a 10 amp load is applied wouldn't be particularly noteworthy. It IS a fairly small battery.
     
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