Auxillary Battery
Grab our Forum Feed

+ Reply to Thread
Page 1 of 8 1 8 LastLast
Results 1 to 10 of 78

Thread: Auxillary Battery

  1. #1
    Join Date
    Sep 2008
    Location
    Sierra Foothills, Northern CA
    Posts
    315

    Default Auxillary Battery

    While I was at the SF Unplugged test drive event I ask one of the GM reps what was under the door in the hatch area that was labeled Battery. He said it was the 12vdc Aux battery but did not know any details on how it was charged. I asked several times for a session with the Engineering Tech but he was never available or within sight. I assume there is a separate inverter that charges it from the Li battery.

    Does anyone know what loads the 12vdc battery supplies and where the charging power comes from?

    Norm
    Last edited by Xzlon; 10-21-2010 at 04:04 PM.

  2. #2
    Join Date
    Sep 2010
    Location
    San Diego, CA. VIN B-95
    Posts
    2,632

    Default

    Quote Originally Posted by Xzlon View Post
    Does anyone know what loads the 12vdc battery supplies and where the charging power comes from?

    Norm
    I've gotten curious about that lately as well. If the aux battery doesn't drain current during CD mode, does that imply aux battery loads don't affect AER? For example, if the radio runs on aux, you can crank the tunes without reducing EV range? Could that explain the difference between eco and comfort mode on the HVAC? Do DRL and indicator LEDs run on aux?

    The "little" battery may be a little sleeper...

  3. #3
    Join Date
    Jul 2010
    Location
    Atlanta GA
    Posts
    1,156

    Default

    Funny, I just wrote up the explanation below in response to a similar question on ChevroletVoltage.com ... (dont' bother going there, there really is FAR more activity here, and anything new posted there first usually shows up here within hours anyway)

    Some of this comes from a WopOnTour post here a while back.

    First, some background. Hybrid vehicles like the Volt and Prius have two separate battery systems: the big, high voltage "traction" battery and the small, low voltage "accessory" battery. The traction battery obviously provides the power to move the car, but it also provides the power to start the gas engine.

    During operation, the 12 Volt battery's voltage is maintained by the "accessory power module" (APM) whenever the Volt is "ON", and maintained by the main battery charger assembly (On-Board Charging Module) when the Volt is plugged in and charging is ACTIVE (steady green LED). The APM is a DC to DC converter that takes high voltage (380V?) from the Volt's traction battery and converts it to ~13.0-15.5 Volts in order to maintain the low voltage accessory loads (including the Volt's computers and modules). It also charges the 12V system's battery, also know as an "absorbant glass mat" (AGM) battery. The 12V battery's voltage is maintained when the car is running or charging (by the APM or charger, respectively), but not when parked and unplugged.

    Both the APM and the 12V auxiliary battery are located in the rear of the vehicle under the removable rear hatch compartment floor.

    Someone had asked a question about jumping the Volt. The scenario that you'd need a jump for is when you've somehow managed to drain the 12V battery (e.g. leaving lights on). In that case, you just need to connect to the 12V battery and give it a little juice, to literally boot up the brains so that the car will start up.

    Even if it wasnt (plugged in), you wouldn't be able to drain the 12V battery by leaving a door open, map/dome light on, or even headlights on as after approximately 10 minutes the Body Control Module (BCM) will shut down the various fused feeds to these devices via the inadvertent power relay (aka battery run-down protection).

    The Volt is also equipped with a "Battery Saver" mode used for periods of storage. The battery saver mode reduces the parasitic load of some of the electronic modules during long shipment or during vehicle storage conditions. This improves the drain time on the battery (up to 70 days without the battery going dead). (more on this here)

    You can't jump the car if it has a dead traction battery (the HV battery), but it's nigh impossible to run that battery dead anyway. The accessories don't drain the traction battery when the car is parked, and the car won't let you drive it until the traction battery is completely dead -- it stops at 25% SOC (we think) and certainly well before 0% SOC.

    The Volt manual has quite a bit of detail on A) jump starting the Volt and B) using the Volt to jump start another car. See pages 10-72 through 10-76. Note that the 12V battery is in the rear of the car, and you can attach the jumper cables there, but for convenience there are also jump connection points in the front of the car, as shown in this post. However you should only use those front points when jumping the Volt; if jumping another car use the rear points. This is probably because of a lighter gauge wire used to feed the front points.
    Last edited by WopOnTour; 04-24-2014 at 02:10 PM. Reason: corrections
    2011 Volt #284, ordered 30-Jul-2010, built 30-Nov-2010, shipped 15-Dec-2010, delivery 22-Dec-2010, lease return 22-Dec-2013, Hidden Content
    - Hidden Content
    - Hidden Content
    - do yourself a favor and register at Hidden Content immediately so you can track your Volt's performance

  4. Remove Advertisements
    GM-Volt.com
    Advertisements

  5. Advertisement

  6. #4
    Join Date
    Sep 2010
    Location
    San Diego, CA. VIN B-95
    Posts
    2,632

    Default

    Quote Originally Posted by ChrisC View Post
    It also charges the 12V system's battery, also know as an "absorbant glass mat" (AGM) battery.
    Reminded by your other post, I looked up this type of battery on Wikipedia. They have a good overview of this class of lead/acid battery on http://en.wikipedia.org/wiki/VRLA_battery

  7. #5
    Join Date
    Sep 2008
    Location
    my little grass shack
    Posts
    4,620

    Default

    Quote Originally Posted by ChrisC View Post
    . I believe it only does this (charges the 12V battery) when the car is running, but I'm not sure.
    Good post.
    FYI The On-Board Charging Module (not the APM) maintains the 12V battery but only during "active" charging. This is because numerous charging electronics that operate off the 12V system, including the HV contactor relays that connect the charger output to the 360V battery during charging sessions. Without OBCM output, the 12V sytem would be drained and like you said results in a "No Go" scenario.
    HTH
    WopOnTour



    EDIT: The above 12V charging behavior is currently correct for 2011 and 2012 models only. For 2013 and newer Volts a new "12V Battery Maintenance Mode" has been added to better deal with keeping the 12V battery SOC up during OFF - NON-CHARGIING periods fro up to 30 days.
    For more information see my post #73 later in this thread- WOT
    http://gm-volt.com/forum/showthread....14#post1292514
    Last edited by WopOnTour; 04-24-2014 at 05:25 PM.

  8. #6
    Join Date
    Jul 2010
    Location
    Atlanta GA
    Posts
    1,156

    Default

    Thanks WOT! I've updated my post above with that info.

  9. #7
    Join Date
    Aug 2010
    Location
    Santa Barbara, California
    Posts
    467

    Default

    This sounds very similar to the Prius. The 12-volt battery is used for the typical vehicle electrical loads such as lights, stereo, etc. as well as the computers. With OnStar there is going to be some continuous low-level drain for the cellular modem to allow remote unlocking, remote start, etc. but this should be quite low drain all things considered.

    The bad news is that this battery is smaller than a conventional car battery in terms of capacity which means that it can be run down by leaving a dome light on much faster. The good news is that without a starter motor to crank, you can jump-start it relatively easily from a lantern battery or the like as you just need enough juice to boot the computers and kick in the contactor to the traction battery. Then the DC/DC converter fires up and supplies the 12-volt loads.

  10. #8
    Join Date
    Sep 2010
    Location
    San Diego, CA. VIN B-95
    Posts
    2,632

    Default

    Quote Originally Posted by Marty View Post
    With OnStar there is going to be some continuous low-level drain for the cellular modem to allow remote unlocking, remote start, etc. but this should be quite low drain all things considered.

    The bad news is that this battery is smaller than a conventional car battery in terms of capacity which means that it can be run down by leaving a dome light on much faster.
    Figuring that a modern cell phone (which is basically what OnStar is) can last a week on a 2.5 Wh battery (and much better, if OnStar has a longer slot cycle - which it should), I don't think the phone drain's a big deal.

    What *is* the capacity of the Volt auxilliary battery? A local (at work) mailing list notes the Prius as having a 36 AH (430wH) battery. The concern there was somebody left their dome light on today, and it was worried that the battery would be dead by the end of the day...

  11. #9
    Join Date
    Sep 2008
    Location
    my little grass shack
    Posts
    4,620

    Default

    I believe it is 70ah but will try to verify. In any case it has a parasitic drain managment system that would prevent someone from killing the battery with the dome light.
    WOT

  12. Advertisement

  13. #10
    Join Date
    Sep 2010
    Location
    San Diego, CA. VIN B-95
    Posts
    2,632

    Default

    Quote Originally Posted by WopOnTour View Post
    I believe it is 70ah but will try to verify
    Hmmm.... If I read it right, wiki says standard lead-acid tolerates an 80% discharge, while AGM prefers 50%. So that would make the Prius aux have ~350 wH capacity and the Volt ~420 wH. So about the same, with the added advantage that the Volt battery is basically in the passenger compartment and not directly exposed to the elements.

+ Reply to Thread
Page 1 of 8 1 8 LastLast

Quick Reply Quick Reply

  • Decrease Size
    Increase Size
  • Remove Text Formatting
  • Insert LinkInsert ImageInsert Video
  • Wrap [QUOTE] tags around selected text

Bookmarks

Posting Permissions

  • You may post new threads
  • You may post replies
  • You may not post attachments
  • You may not edit your posts