TMC is an independent, primarily volunteer organization that relies on ad revenue to cover its operating costs. Please consider whitelisting TMC on your ad blocker or making a Paypal contribution here: paypal.me/SupportTMC

A 12v battery solution?

Discussion in 'Model S: Battery & Charging' started by rtz, Jan 25, 2015.

  1. rtz

    rtz Member

    Joined:
    Nov 26, 2013
    Messages:
    142
    Location:
    United States
  2. Majerus

    Majerus Member

    Joined:
    Jan 21, 2010
    Messages:
    689
    Location:
    Illinois
  3. islandbayy

    islandbayy Active Member

    Joined:
    Feb 25, 2013
    Messages:
    2,016
    Location:
    Greendale, Wisconsin
    No. While it might work in the south, it would not work in colder climates.

    Problem being Lithium needs to be at or above 33*F (1*C) or higher to charge. At or below freezing, the internals of the cells will Electroplate, causing permenent capacity loss. This would then require a 12v battery heater, and also a chiller. It can, believe it or not, get rather hot in there, especially when supercharging, and Lithium also likes 113*f or lower.

    It can be done, but question is should it. Lead acid is actually fairly robust. As long as you get a DECENT quality battery to begin with. That, and follow proper charging and maintaining of the batteries.

    And I have lots of experience with the Shorai's, and... my experience shows... very low quality product.... They were so bad, Batteries Plus pulled them from EVERY store. My local rep said they were coming in with a 95% failure rate within 30 days of purchase.
     
  4. apacheguy

    apacheguy Sig 255, VIN 320

    Joined:
    Oct 21, 2012
    Messages:
    3,715
    Location:
    So Cal
    Ok. Dumb question. Why not just get rid of the 12 V completely and supply all electronics with the main pack and just have a transformer in the middle? Would also solve the contactor issues - no need for them. Is it safety related?
     
  5. rtz

    rtz Member

    Joined:
    Nov 26, 2013
    Messages:
    142
    Location:
    United States
    Well if Tesla insists on staying with lead for the 12v; this may be the best battery made? Rolls Battery - Home

    This may be second? Concorde Battery - Aircraft Batteries

    It would be interesting to know the reasons Tesla has for using the battery they do use: C&D Deep Cycle Battery


    I was just thinking maybe for the cars that get the cold weather package; they could use whatever battery; and the rest of the cars could use something that lasts longer/more reliable.

    - - - Updated - - -

    What if someone took out their 12v battery and wired one of these DC/DC converters in it's place? http://store.evtv.me/products.php?cat=19
     
  6. islandbayy

    islandbayy Active Member

    Joined:
    Feb 25, 2013
    Messages:
    2,016
    Location:
    Greendale, Wisconsin
    Wont work. The power from the 12v battery initiates the contactor to enable the High Voltage pack. No 12v power, no contactor, meaning no power flow from the High Volt pack to the car. Or in other words, no DC to DC converter (thats already installed in the car).

    When the 12v requires a top off while parked, the contactor, powered by the 12v battery, closes, allowing the 12v battery to charge. It is a safety feature.
     
  7. apacheguy

    apacheguy Sig 255, VIN 320

    Joined:
    Oct 21, 2012
    Messages:
    3,715
    Location:
    So Cal
    Yep. Exactly what I was alluding to in the post above yours. So the only reason for the 12 V is safety? Just because there has to be some way to isolate a HV pack? Seems like there could be better solutions.
     
  8. jerry33

    jerry33 S85 - VIN:P05130 - 3/2/13

    Joined:
    Mar 8, 2012
    Messages:
    12,756
    Location:
    Texas
    Besides isolating the traction battery there needs to be a way to power the power brakes and steering if the traction battery fails for some reason. Kind of hard to do if you don't use a battery.
     
  9. apacheguy

    apacheguy Sig 255, VIN 320

    Joined:
    Oct 21, 2012
    Messages:
    3,715
    Location:
    So Cal
    Fair point. Although most failures have resulting from the contactors failing, which you wouldn't have if you could bypass the 12 V system. For the rare instance where a module failed and caused catastrophic loss of power then I can absolutely see that as being a valid reason.
     
  10. David99

    David99 Active Member

    Joined:
    Jan 31, 2014
    Messages:
    2,054
    Location:
    Brea, Orange County
    It would be very dangerous and very expensive to get rid of the 12 Volt system and wire and power everything with 400 Volt DC from the main pack. Direct Current at 400 Volt is extremely dangerous and it would be all over the car. It would also require that everything in the car needs to be special made for 400 Volt. Every light bulb, switch, wipers, fan, audio system, windows, seats, ABS, steering, every electrical component would have to be special design instead of standard 12 Volt parts. It would be impractical.

    The problem isn't that a 12 Volt system is bad. It works just fine for every car, thus the solution isn't to eliminate the 12 Volt system. The root of the problem is that Tesla isn't 'taking care' of the 12 Volt battery well. We don't know why so many of these batteries fail. It could be that they are not charged properly, it could be that they are too small for the load, it could be that they got bad units, it could be just an oversensitive monitoring system that shuts reports the 12 Volt battery going bad when it isn't. It could be a combination of several things. We don't know. Speculating and concluding solutions doesn't help. Tesla needs to find the source of the problem and fix it. Everything else is just digging in the dark and hoping something will stick.
     
  11. santana338

    santana338 Member

    Joined:
    Apr 11, 2012
    Messages:
    333
    Location:
    Manchester, NH
    The topic of vampire drain and its effect on the 12V battery is discussed in this thread in great detail. The root of the problem is the vampire drain. Fix that and the 12V problem could likely go away.

    Near annual replacement of 12V battery is typical according to Tesla Service Tech - Page 10
     
  12. apacheguy

    apacheguy Sig 255, VIN 320

    Joined:
    Oct 21, 2012
    Messages:
    3,715
    Location:
    So Cal
    Well, no. You could easily have a DC DC converter in the middle to step down the voltage. Not so dangerous then until a module fails and brings down the whole pack and you're left without power steering on the freeway. That's where the safety implications come into play.
     
  13. jerry33

    jerry33 S85 - VIN:P05130 - 3/2/13

    Joined:
    Mar 8, 2012
    Messages:
    12,756
    Location:
    Texas
    Every car that has a "big battery" has a small 12V battery, and for the cars I'm familiar with all the owners complain about it failing. The problem is that you don't get a warning when it's about to fail. With an ICE car, you can hear the starter motor cranking more slowly so you know you had better do something soon. An EV or hybrid just needs to power some electronics and throw a couple of relays, so it can be very weak and still get the job done. I was able to start the Prius with two dead cells.

    The only explanation I have for the Model S' short 12V life is that the battery gets cooked. AGM batteries don't like to be overcharged. The back of the napkin solution is two 12V batteries used on an alternating daily schedule. That would keep them from being cooked and still have the right amount of power available.
     
  14. islandbayy

    islandbayy Active Member

    Joined:
    Feb 25, 2013
    Messages:
    2,016
    Location:
    Greendale, Wisconsin
    I agree with the Cooking/Overcharging of the batteries. While Monitoring the 12v batteries voltage, While the car was "off" I always saw 13.2-13.5v (SLIGHTLY high side, especially for a aged battery), and while car was in operation, saw 14+ volts. This is high for a AGM.
     
  15. FlasherZ

    FlasherZ Sig Model S + Sig Model X + Model 3 Resv

    Joined:
    Jun 21, 2012
    Messages:
    7,019
    First responders / extraction equipment operators really appreciate the HV being isolated to the battery pack when it comes time to cut the car open with hydraulic extraction equipment. You don't want those big orange cables alive after an accident when we need to roll the dash off someone.

    That's the primary reason that contactors exist in the battery pack - for safety.
     
  16. David99

    David99 Active Member

    Joined:
    Jan 31, 2014
    Messages:
    2,054
    Location:
    Brea, Orange County
    The Model S does have a DC to DC converter to charge and power the 12 Volt system/battery. There is a good reason you need a 12 Volt battery and not rely on the DC-DC converter alone. Every production EV has a 12 Volt battery.
     
  17. rtz

    rtz Member

    Joined:
    Nov 26, 2013
    Messages:
    142
    Location:
    United States
    If the 12 volt battery is being overcharged(on purpose); then maybe Tesla would rather work with a 16 volt battery instead?

    TurboStart a division of Axion Power


    Is there anything in the car that couldn't handle the slightly higher voltage?
     
  18. apacheguy

    apacheguy Sig 255, VIN 320

    Joined:
    Oct 21, 2012
    Messages:
    3,715
    Location:
    So Cal


    Yep, I'm aware of all that. Just think there could be more elegant solutions down the line that achieve the same purpose and degree of safety.
     
  19. tga

    tga Active Member

    Joined:
    Apr 8, 2014
    Messages:
    2,214
    Location:
    New Hampshire
    It looks to me like the issue is constant moderate cycling from vampire load. If we're proposing hardware changes to fix the problem, a float charger powered from the J1772 inlet (a la "Battery Tender") would prevent cycling while the car is plugged in.
     
  20. AmpedRealtor

    AmpedRealtor Active Member

    Joined:
    Jun 30, 2013
    Messages:
    4,704
    Location:
    Buckeye, AZ
    This would imply that those who don't use power saving mode are probably going to go through more 12v batteries than those that do.
     

Share This Page