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Model 3 12V system

Discussion in 'Tech Talk' started by arnis, Aug 27, 2017.

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  1. arnis

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    So we know about big battery. What about small battery.
    As soon as I saw new placement of HV electronics, I'm
    thinking about change in 12V system design.
    It is possible, now, to tap into HV with disconnected contactor.
    That means that it is possible to not have 12V battery at all.

    I don't know what Tesla did, but if I had DC-DC converter inside the HV pack,
    I would definitely skip 12V battery and rather have two DC-DC converter circuits.
    One being online forever (down to 250V) capable no more than an amp or two
    just for telematics (GPS, LTE, BT, NFC) and alarm.
    Main DC-DC circuit (not enabled if vehicle is asleep)
    There is no reason to charge/discharge/monitor 12V battery. It is constant inefficiency.
    Plus, as we all know, lots of problems with 12V batteries going bad or empty.

    This new solution would have many weird advantages. For example:

    It would be possible to complicate theft: imagine GPS+telematics that can not be unplugged easily.

    It would be possible to leave the vehicle in the parking lot unplugged for a year.
    Small DC-DC converter can be way more efficient than solution Model S/X has.
    Imagine 30mA load, with high efficiency (40mA draw from HV pack as the worst scenario)
    That is 12,5Wh per day. Up to 0,4kWh per month. Piece of cake for 50kWh pack.
    My BMW with massive 12V battery has theoretical 1.0-1.2kWh of energy.

    It would be possible to add a solar panel that actually makes sense (not going crazy with area).
    Though it would not add any considerable range daily, it would be able to run vital functions
    indefinitely if parked outdoors: this includes telematics, alarm. Even ventilation. All it needs is
    always on, high efficiency, low power (remember that 1-2A DC-DC thingy) converter.

    It would be considerably cheaper. In addition to removal of 12V battery, there would
    be considerably less copper on 12V system. Less maintenance.

    This would simplify switching to switch to 48V system in the future (promised on Model Y?).
    Power steering pump, rear window heater, coolant pump, cabin air fan, outside radiator fan,
    wiper motor - they are all in desperate need to switch to 48V as soon as possible.
    With this design, it would be possible to just add those components one by one. Just
    add 48V output circuit under the rear seat and slight change in wiring harness.

    Ran out of time. There is a lot more to tell.
    Can anybody name few disadvantages.
     
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    • Gizmo

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      What about all the lighting system which will be 12V?
       
    • garsh

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      Most current automotive electronics are designed to run on 12v. But there's nothing magical about that level. Most solid state parts (including LEDs) operate on 5v or less.

      Many high-power parts (HVAC, fans) would be less expensive & more efficient at higher voltage. They would require less current for the same power draw, so wiring could be thinner (insulation would need to be thicker/stronger, but that's easy/cheap).
       
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      • Guy Weathersby

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        Mr Musk has said that they would eliminate the 12 volt battery in the Model Y. Since the Model Y, or whatever, is now based on the Model 3, I am not sure that that is still the plan, at least in the short run.

        They definitely want to get rid of the 12 volt,but I have no idea of a time frame.
         
      • MelindaV

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        he actually revoked that statement in the last earnings call - saying this senior staff talked him down from the crazy that that plan was, but plans to do this on a future model for sure.
         
      • arnis

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        At these voltages, not noticeable. Thin 12V wires have much thicker insulation than minimum set by voltage. Reason is it can't be too thin as it can be damaged easily, mechanically. Going up to 48V system (actually 60V expected) is still safe to use pretty much same insulation thickness. (I'm comparing with German vehicles. I've never dissected Asian vehicles, not sure about wire parameters on those).

        Though there will be some weird things going on. For example, rear defroster relay would be 12V on command pins and 48V on power side. It's doable. For example, BMW offers front radiator fan with power level between 300W and 600W (similar is power steering motor).
        That is 20-45A. Fan power cables can easily be 48V. Control wire is anyway usually 5V PWM. With 48V system, amps will fall 4x. Therefore 10-15A fuse. Wires would be as small as majority of the whole harness. With no "orange cable" hassle.
        Actually, it is not Tesla that started the 48V race.

        "What about all the lighting system which will be 12V?"
        This is low priority for 48V system. Consumption (especially with LED's) is low. Though no problem to do the swap anyway .
        LED's anyway do not run on voltage but rather current. Most have their own driver. They run at voltages between 3.6V and 40V, depending on LED model. No LED runs on 12V directly.

        Can anybody share a reason why Model 3 must have 12V battery IF 12V DC-DC converter(s) is inside the HV pack?
         
      • John

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        Could be wrong, but this black box with a red and black bumps on top looks like a 12V battery.

        [​IMG]
         
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        • AEDennis

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          Guys... Tesla actually did not have a 12V battery on Roadster 1.5...

          So, it's in their DNA to skip it... 2.X added the 12V...

          There are positives and negatives to either strategy...
           
        • John

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          "The 12V battery maintains power for critical systems when the main battery pack is damaged or disabled. It powers the hazard lights, airbags, door locking and unlocking operations, as well as other critical components of the Model S. The 12V battery also ensures that electronics are “awake” and listening to the key FOB in order to automatically lock and unlock the vehicle based on proximity. It also allows the car to maintain its 3G connection for remote access when the rest of the vehicle is powered off. If the 12V battery happens to fail, it will isolate the main battery pack from the car and prevent charging. This is a safety feature of the Model S designed to help protect first reponders in the event of an accident."
           
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          • Sandy

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            #10 Sandy, Aug 27, 2017
            Last edited: Aug 27, 2017
            OK, So here is the cool thing about this. The 12 volt battery is right back against the firewall and more importantly behind the front axle line line. When I had my track Cobra we corner weighted it. Meaning putting it on a scale that weighed the weight on each tire. Ideally you want them all equal. When I moved the battery from the heaviest wheel (front left in front of the axle) to the to the lightest wheel (right rear in FRONT of the axle) in the trunk the 50lb battery took 80 lbs off the left front wheel. This is due to leaverage. You want as much weight to be between the axles as you can. The suspension and tires work better and the car is easier to rotate (turn). Weight in front of the front axle and behind the rear axle act as a pendulum.
            This is the reason the Model 3 front engine is behind the front axle and the rear engine is in front of the rear axle. Unlike the S and X it keeps the weight between the axles. It does limit battery size but does amazing things for handling and looks (minimizes front and rear overhang).
             
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            • garsh

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              That sounds familiar. :)
               
            • Sandy

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              Ha! When ur on 3 M3 forums it's hard to remember what u have posted before!!!! Unless Musk said that? Weight distribution and unsprung weight are what I guess are engineers nightmares. I was a pilot professionally so my nightmares are completely different!
               
            • JWardell

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              I agree there are a lot of advantages to replacing a heavy 12v battery with an always-powered converter, but the redundancy pointed it is also very important.
              I do hope they at least use a smaller than normal 12v battery. No reason to use lead acid either.
              Of course moving to 48v presents a ton of advantages, including reduction of copper weight and cost. Since Tesla has no problem custom making most of its parts it is better positioned to do this than any other manufacture.
              There was a time when 24v automotive electronics were not uncommon.
               
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              • Guy Weathersby

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                When I was young, and Dinosaurs roamed earth some cars were still 6 volt.
                 
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                • garsh

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                  If you click the link I provided, you'll see that I made a post very similar to the one you made.
                  That's all. Just pointing out that great minds think alike. :)
                   
                • Gabzqc

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                  Jump starting the car?

                  I guess we will never have problems with the "12v battery" if its coming from the main pack. Unless however we "pull a Bjorn" and run ours down to 0km range.... then what happens? and where does Tesla service "Jump" the big battery from?
                   
                • Badback

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                  You cannot charge the big battery from the 12V battery.
                   
                • arnis

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                  AFAIK he revoked "new platform" to Y. This only means same body production line and major parts. I still think Model Y will have considerably less wiring. It is possible, it just needs brainpower and lots of integrated microcontrollers, communicating on power lines (which is extremely easy, especially on DC).

                  Yes. This applies only in case DC-DC converter is disabled by contactor (model S/X). Also we know that time Tesla's small 12V AGM battery can do those tasks is not adequate.

                  The smaller the 12V battery, the more probability of it being incapable of engaging contactor. Lights on while vehicle off, for example. Also it must be Lead-Acid family. NiMH and Li-ion is not suitable.
                  Well, semi-truck are 24V. Use 24V halogen bulbs etc. Though 12V is still there. Semis have multiple 12V batteries in series.
                  Well, it is easy to limit contactor to 250V and DC-DC converter(s) to 245V. 0.5kWh is all we need (small 12V battery actually has less). And 0,5kWh is actually available, though not for drivetrain (too heavy load). Also it is possible to disable a lot of stuff (HVAC, wipers, headlights, radio etc) and keep hazards, screen, charge port control, parking brake actuator and contactor management module live with those 245+V. But only if DC-DC converter is inside the pack and bypassing contactor. With thin, fused wires. To be absolutely safe.

                  Not necessary as, theoretically, it is possible to make running out nearly impossible (integrated DC-DC converter can reduce load until nothing works, except contactor control) . Though it is possible to just connect 12V source in case main pack went below whatever lowest limit and it did disable even the low-power DC-DC module/circuit (let's call it auxiliary DC). Diodes will block reversed current and nothing interesting happens. Charging controller will be live and allow contactor to engage.
                  PS: It would be possible to charge HV pack through 12V line (on vehicle with no 12V battery). Same way like solar panel (read above) could trickle charge through small DC-DC converter (contactor bypassed). Though it is exotic feature.

                  PS2: BMW has integrated consumer cutoff algorithm. If left parked for months, it will kill different stand-by lines. Starting with radio/clock memory, navigation memory. And ending with remote control antenna. One must wake up vehicle manually (I think it was manual unlocking that resurrected key sensing for keyless ignition). There should be enough bang left for one successful crank, though most RAM-held settings will be lost for that time (4-7 months, depending on lead acid battery health). One module that never dies is 12V BMS, directly bolted to battery terminal. It will not be able to log anything if voltage below 5V, which is lethal for lead acid anyway. BMS is also always active on electric vehicles as well (even without 12V battery connected, Leaf will heat main pack if it drops below -17C until certain SOC reached). It is not complicated to extend that to telematics etc.
                   
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                  • John

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                    Also, there were still Truffula trees, amiright?
                    [​IMG]
                     
                  • arnis

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                    I have verified that Model 3 has normal 12V battery and all the clunkiness. Like Model S/X.
                    Located under the hood.
                    [​IMG]
                     
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