1. Attachments are working again! Check out this thread for more details and to report any other bugs.

Auxilary battery voltage? Does the Prius do 2 stage charging?

Discussion in 'Gen 3 Prius Technical Discussion' started by Jerry Liebler, Feb 18, 2017.

  1. Jerry Liebler

    Jerry Liebler Member

    Joined:
    Jan 12, 2014
    177
    85
    0
    Location:
    Science Hill Kentucky
    Vehicle:
    2013 Prius Plug-in
    Model:
    Plug-in Base
    This is a long story but I'll try to shorten it. My 100 % recycled 2012 PIP was totaled by being "T Boned" by an inattentive driver. The other driver's insurance paid for my replacement, a 2013 PIP with a few less miles and no damage history. On the drive home in the replacement I used way more gas than I was used to, about 100 less miles per tank. I started searching for the cause. First I Installed the lower grill block next I changed the oil and air filter then I replaced the snow tires with Bridgestone EP422+ inflated to sidewall limit of 51PSI, then I found dragging, badly worn brakes and replaced them these changes helped a little but something was still very wrong. I replaced the dying but not dead 12 volt battery with 40 AH of LIFEPO4 and continued my search for a possible cause. I'm very sure that I finally found the culprit based on trip odometer data over several short trips after I cleaned the mass air flow sensor. I run the Android application "TORQUE" through an OBD -Bluetooth adapter and look at several interesting things, among them the 12 volt system voltage which I kind of assumed was always 14.4 volts whenever the car is "running". But with the new 12 volt battery I'm seeing something I've never seen before, When I first turn on the car the voltage will be 14.4 but after some running, in the daytime, it will drop to 13.3 but turning on the headlights will move it back to 14.4. My interpretation of this observation is, Toyota has implemented a form of 2 stage charging for the auxiliary battery. The 2 stage charging algorithm is something like, hold 14.4 volts until the charging current falls below set-point 1, then drop the voltage to 13.3 (float) until the charging current exceeds set-point 2 which resets the 14.4 volt system voltage. Has anyone else observed this? Can anyone verify the 2 stage charging?
     
    Simtronic likes this.
  2. bisco

    bisco cookie crumbler

    Joined:
    May 11, 2005
    107,571
    48,862
    0
    Location:
    boston
    Vehicle:
    2012 Prius Plug-in
    Model:
    Plug-in Base
    no idea, but it makes sense i guess. i would think amperage would be more important though?
     
  3. StarCaller

    StarCaller Senior Member

    Joined:
    Feb 15, 2014
    1,240
    692
    0
    Location:
    Cedar Crest, NM, USA
    Vehicle:
    2014 Prius
    Model:
    Two
    I don't know about the 2-stage charging, but my aux. battery in a non-pip does the same: 14.4 in the beginning (if it's really cold even higher), 13.5 after a while of driving (if the outside temperature is not too low) /
     
  4. kc410

    kc410 Active Member

    Joined:
    Nov 26, 2013
    261
    250
    0
    Location:
    2010 Prius IV
    Vehicle:
    2015 Prius
    Model:
    Four
    My non-PiP does drop the 12V batt float voltage to ~13.4V, but only if certain conditions are met:
    1) the engine must be warmed up enough to shut off when stopped.
    2) the transmission must be in Drive.
    3) the AC must be off.
    4) the lights must be off.
    When (& only when) these 4 things are satisfied, will the float voltage drop to ~13.4V.
    Otherwise the battery floats at ~14.4V.

    Watching Torque I knew that the voltage would often drop to 13.4V, but had never tried to document under what conditions it would happen. This morning I watched it closely & came up with the above results.
     
    #4 kc410, Feb 20, 2017
    Last edited: Feb 20, 2017
    Simtronic likes this.
  5. mrbigh

    mrbigh Prius Absolutum Dominium

    Joined:
    Sep 6, 2005
    3,686
    699
    2
    Location:
    Long Island, NY
    Vehicle:
    Other Electric Vehicle
    Upon my experience and observations.........
    I think that the 14.4 VDC argument is when the Hybrid System "Inverter" is in operation.
    If not, the 13.8/13.4 VDC would be the AUX battery float voltage with no accessories sucking any juice.