# Model 3 12V system



## Guest

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

arnis said:


> Can anybody name few disadvantages.


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


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## garsh

Gizmo said:


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


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

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.


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## MelindaV

Guy Weathersby said:


> Mr Musk has said that they would eliminate the 12 volt battery in the Model Y.



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.


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## Guest

garsh said:


> insulation would need to be thicker/stronger


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?


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## John

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


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## AEDennis

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...


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## John

"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

John said:


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


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

Sandy said:


> 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).


That sounds familiar.


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## Sandy

garsh said:


> That sounds familiar.


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!


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## JWardell

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

JWardell said:


> There was a time when 24v automotive electronics were not uncommon.


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


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## garsh

Sandy said:


> Ha! When ur on 3 M3 forums it's hard to remember what u have posted before!!!! Unless Musk said that?


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.


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## Gabzqc

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?


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## Badback

Gabzqc said:


> 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?


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


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## Guest

MelindaV said:


> he actually revoked that statement in the last earnings call - saying this senior staff talked him down from the crazy


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).



John said:


> The 12V battery maintains power for critical systems when the main battery pack is damaged or disabled.


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.



JWardell said:


> use a smaller than normal 12v battery. No reason to use lead acid either.


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.


JWardell said:


> There was a time when 24v automotive electronics were not uncommon.


Well, semi-truck are 24V. Use 24V halogen bulbs etc. Though 12V is still there. Semis have multiple 12V batteries in series.


Gabzqc said:


> run down to 0km range.... then what happens?


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.



Gabzqc said:


> Jump starting the car?


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

Guy Weathersby said:


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


Also, there were still Truffula trees, amiright?


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## Guest

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


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## JWardell

We've heard first person that the 12v battery is easily accessed. The remaining question is what continuous 12v current the DC-DC converter will support so I know how large of an AC inverter I can add for tailgating, power outage, camping etc.


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## Guest

Step one is to measure the big + wire. Which looks like is not very thick. 
Though 100A is a safe bet. And that should be enough for pretty much everything that doesn't heat water/air.
Why at least 100A? Well, outer fan is 35-50A. HVAC fan is 20A. Coolant pump 5A, cigarette lighter 15A,
Seat heaters 10A each. EAP computer 10-15A. Wiper motor 10A. Rear+mirror defrost 30A.
And some random loads can add 100A more for a moment, power steering, window&seat motors, audio amp, lights etc.
Though it doesn't mean Tesla isn't using smart load limitations (like BMW does), but likely not necessary.
That should be around 3/4 of the whole thing.

I would die to see wiring diagram


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## KarenRei

arnis said:


> 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).


He nonetheless added that they still plan to remove the 12V in the subsequent conference call to the one where it was announced that the Model Y would be built on the Model 3 architecture.


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## PaulK

Has anyone seen a photo of the actual M3 12v battery? Make & model. 

Mostly, I just want to know if it comes with an AGM battery (which is lightweight and leakproof). 

Paul


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## Sandy

pkarmouche said:


> Has anyone seen a photo of the actual M3 12v battery? Make & model.
> 
> Mostly, I just want to know if it comes with an AGM battery (which is lightweight and leakproof).
> 
> Paul


Guessing here but as it's not lithium I can't imagine today it being anything else but an AGM battery.


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## Vladimír Michálek

JWardell said:


> ...The remaining question is what continuous 12v current the DC-DC converter will support so I know how large of an AC inverter I can add for tailgating, power outage, camping etc.


BTW, in the Model 3 Release Event Elon mentioned the big projector was running off a Model S(or X?) battery. It would be a crazy feature to have a 1-3 phase 120/230/240V AC line output directly from the motor invertor. You could run whatever electrical appliance you wish anywhere you can drive. Huge selling point for future utility car. And the added cost is just few cables, connector and some software, since you already have the invertor.


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## Frank99

The inverter likely isn't capable of generating 120/230/240V. It's output voltage is likely the battery voltage, with lower power levels created by changing the on/off duty cycle.


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## Vladimír Michálek

Frank99 said:


> It's output voltage is likely the battery voltage


Right, and the main battery voltage is around 350-400V


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## Model34mePlease

It would be good if there was some standard way, beyond the 12v power outlet, to convert battery DC to, at-least 120V AC. It could be just a standardized power outlet standard, with inverters sold in the after-market.


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## Badback

The inverter is capable of generating any voltage up to where the peak is equal to the battery voltage. The main issues are that the inverter is designed to operate into the impedance of the motor and the control algorithms expect to see a speed feed back from the motor.

There is much more, but I won't bore you with the details.

A completely separate, purpose designed, inverter operating off of the battery would be a more likely approach but would be quite expensive.


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## Frank99

Actually, I'd love it if you bored us with the details.

What you're proposing " capable of generating any voltage" is, to the best of my knowledge, a much more complex inverter design than one with a fixed peak voltage (400V) and variable duty cycle/PWM. Unless, of course, we're describing the same thing, with you speaking in terms of "average voltage" and me in terms of "instantaneous voltage". A 500 hp motor won't care about the difference, but a 120V electronic device would.


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## Badback

Frank99 said:


> Actually, I'd love it if you bored us with the details.
> 
> What you're proposing " capable of generating any voltage" is, to the best of my knowledge, a much more complex inverter design than one with a fixed peak voltage (400V) and variable duty cycle/PWM. Unless, of course, we're describing the same thing, with you speaking in terms of "average voltage" and me in terms of "instantaneous voltage". A 500 hp motor won't care about the difference, but a 120V electronic device would.


OK. The switching devices in the inverter have a peak current rating that should not be exceeded. The rate of current rise during each inverter pulse (di/dt) is a function of the motor impedance and any other impedance the inverter may have internally. If you tried to operate the inverter into something with significantly less impedance, you risk damaging the inverter. This is besides the instantaneous current limit circuit in the inverter which may or may not be fast enough to shut down the inverter depending on the load.

There are many more reasons, but my fingers are tired.


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## JWardell

Vladimír Michálek said:


> BTW, in the Model 3 Release Event Elon mentioned the big projector was running off a Model S(or X?) battery. It would be a crazy feature to have a 1-3 phase 120/230/240V AC line output directly from the motor invertor. You could run whatever electrical appliance you wish anywhere you can drive. Huge selling point for future utility car. And the added cost is just few cables, connector and some software, since you already have the invertor.


Tesla can do what they want. They have any access they need and full design details. For all we know the projector was running off the 12v system anyway. If we were given direct access to the battery then we could design a powerful inverter fro 120v AC. This is, afterall, exactly what is in the powerwall systems. 
But it is very dangerous to allow access to the 400v and near infinite current of the battery. Several levels of safety are there to prevent it. Any connection becomes a huge issue in a device that has a decent chance of being crushed in an accident.
Of course Tesla can hack their car in any way. The same can not be said for us electrical hackers that like to do creative things with our most expensive gadget.


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## Frank99

Thanks, Badback, what you've described is what I expected.


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## Timotion

Interesting posts!....It seems that Tesla Model 3 has the main dc-dc converter inside the main battery behind the contactors which was not the case for Model S/X and the vampire load (load when the vehicle is on off-state) is supplied by the main battery..Can someone someone confirm that?


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## PaulK

Sandy said:


> Guessing here but as it's not lithium I can't imagine today it being anything else but an AGM battery.


Unfortunately it seems confirmed that the 12V battery is a lead acid battery with a vent. Manufactured in Korea. See the images of it in this video:



garsh said:


> This video shows how the frunk area is separate from the front motor area.


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## Sandy

pkarmouche said:


> Unfortunately it seems confirmed that the 12V battery is a lead acid battery with a vent. Manufactured in Korea. See the images of it in this video:


What else would be other than lead acid?


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## Frank99

Lithium ion, specifically lithium iron phosphate, would seem to be a good alternative. Obviously Tesla has good battery engineers, so i assume that lead acid still has better characteristics.


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## PaulK

Sandy said:


> What else would be other than lead acid?


Sorry, I meant it seems to be a wet cell vs. lithium battery or at least AGM (which is lighter, has a longer service life and tolerates discharge cycling much better).

EDIT: I've been trying to research what this battery model actually is, and I can't determine for sure that it's not an AGM battery. It looks large for an AGM and has a vent/breather tube. But I've just read elsewhere that some AGM batteries do have breathers. Can anyone determine the chemistry of this battery?

Paul


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## Guest

pkarmouche said:


> Sorry, I meant it seems to be a wet cell vs. lithium battery or at least AGM


It does appear to be regular wet cell. Don't know why. Seems weird. Though Model S/X AGM's have a high failure rate anyway.
Maybe they try regular wet cell. At least it appears they have a serviceable version.
Though it's weird they use random battery maker.

LiFePo needs more research. I bet Tesla doesn't want to try new stuff with mass market vehicle.
Whatever they choose, 12V battery should last a decade if used correctly (like with solar installations).
It's all about 12V DC-DC inverter software.


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## Sandy

pkarmouche said:


> Sorry, I meant it seems to be a wet cell vs. lithium battery or at least AGM (which is lighter, has a longer service life and tolerates discharge cycling much better).
> 
> EDIT: I've been trying to research what this battery model actually is, and I can't determine for sure that it's not an AGM battery. It looks large for an AGM and has a vent/breather tube. But I've just read elsewhere that some AGM batteries do have breathers. Can anyone determine the chemistry of this battery?
> 
> Paul





arnis said:


> It does appear to be regular wet cell. Don't know why. Seems weird. Though Model S/X AGM's have a high failure rate anyway.
> Maybe they try regular wet cell. At least it appears they have a serviceable version.
> Though it's weird they use random battery maker.
> 
> LiFePo needs more research. I bet Tesla doesn't want to try new stuff with mass market vehicle.
> Whatever they choose, 12V battery should last a decade if used correctly (like with solar installations).
> It's all about 12V DC-DC inverter software.


I did some research into AtlasBX as well:

http://www.atlasbx.com/

I'm guessing this battery is not 'off the shelf' and was manufactured for the 3. The 3 version doesn't seem to line up with any of their existing lines. It's marked as a 85B24LS 45ah. Seems to be JIS spec. The yellow tops appear to be their UHPB (ultra high performance) and the black tops are SMF (sealed maintenance free) and the Tesla is a black top with a yellow handle and a VENT TUBE? I haven't seen a vent tube on a battery for years. No idea what the construction is.


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## Guest

Sandy said:


> I haven't seen a vent tube on a battery for years. No idea what the construction is.


Liquid, possibly with valve (VRLA). BMW had vent tube as standard on all vehicles until AGM came... 2004-2006. Firstly, battery is in the trunk and gassing inside the trunk is not the best idea. Secondly, acid can and will ruin the paintjob (every 3rd 4th vehicle have acid damage, I've seen at least a hundred of those). Thirdly, maximum safety in case of shorted battery and jump starting/charging sparks (hydrogen gas is vented far away from terminals).



Sandy said:


> the black tops are SMF (sealed maintenance free) and the Tesla is a black top


That's good. EV's definitely need to have batteries with thicker plates, NOT high performance plates. Lead acid battery can be either deep cycle or high current- not possible to have both of them. EV's should *not *use high current batteries!

Here's an idea. Can anybody check the end of the tube. Hope there is no hydrogen sensor


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## JWardell

Agreed, My recent BMW had battery vent tube as well, as it was in the trunk, and I've seen them included with replacement batteries in the store. They can generate gasses when charging. I used to charge up big electric machines in the basement at work with dozens of lead acid batteries overnight. It definitely did not smell right in there the next day. Though I would think not such a big deal in a car with a ventilated cabin and slow battery charge rate.


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## SalisburySam

From those who have seen the 12v battery, has Tesla added anything to make it easier to connect/disconnect a battery tender? Or is that even necessary (it is definitely needed on my Nissan LEAF!)?


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## Guest

SalisburySam said:


> From those who have seen the 12v battery, has Tesla added anything to make it easier to connect/disconnect a battery tender? Or is that even necessary (it is definitely needed on my Nissan LEAF!)?


No. Customers should never do that.


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## CoastalCruiser

My brain can think of nothing to add to the existing speculation regarding this interesting question. My sense is that it has something to do with a need to activate the contactors from a source independent of the traction battery (and thus the DC-DC converter). Safety? More fault tolerant? Must be a damn good reason or it would NOT be there now. ;>


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## garsh

I've never had to put a battery tender on my 6yo Leaf.


SalisburySam said:


> From those who have seen the 12v battery, has Tesla added anything to make it easier to connect/disconnect a battery tender? Or is that even necessary (it is definitely needed on my Nissan LEAF!)?


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## Vladimír Michálek

It's a shame, small flexible PV sheet connected to the 12V system could solve the problem of (vampire/phanom/self drain/discharge) during longer parking.


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## Guest

How long is long


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## Vladimír Michálek

week? Long enough to bother with deploying the solar sheet


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## Guest

If vehicle is not able to withstand 1 months of no user it has a defect. And yes, Tesla cars are notoriously known to have absolutely excessive sleep drain. At least they keep 12V battery alive with HV battery juice. 
Old Leaf's had software problem with 12V trickle charge algorithm. 

In case of Tesla, just keep it plugged in, vehicle will suck power from the grid.

Most advanced vehicles in the world (S-class, 7-series etc) can do 3-5 months on regular 12V battery, though a big one, 90-110Ah.


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## JWardell

arnis said:


> If vehicle is not able to withstand 1 months of no user it has a defect. And yes, Tesla cars are notoriously known to have absolutely excessive sleep drain. At least they keep 12V battery alive with HV battery juice.
> Old Leaf's had software problem with 12V trickle charge algorithm.
> 
> In case of Tesla, just keep it plugged in, vehicle will suck power from the grid.
> 
> Most advanced vehicles in the world (S-class, 7-series etc) can do 3-5 months on regular 12V battery, though a big one, 90-110Ah.


Only when new. After a few years ICEs will die if not driven around once every week or so as well. Really nothing new here.


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## Vladimír Michálek

Yes, but normal ICE cars can easily accept small PV panel with Pb charger connected to the 12V socket to keep the battery alive. I believe Teslas just have so much drain in the 12V system (computers running, etc) that it needs to recharge it from the main battery too often.
Of course they'd first need to fix the huge drainages like 3kWh per day some ppl see, but then a small PV panel would take care of the "always connected, always consuming" issue. Even when you can't plug it in.


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## Guest

JWardell said:


> Only when new. After a few years ICEs will die if not driven around once every week or so as well. Really nothing new here.


Myth. My bimmer is 17 years old. And after getting EV, sometimes, it feel lonely for weeks and weeks. Until I need it to haul construction material or smth. My friend had 2010 BMW and he left it for 3 weeks every months (work abroad). Absolutely fine.
Also there is nothing to "die" actually. Oil life is max 2 years. Driving for short routes is worse than driving once per month for an hour.



Vladimír Michálek said:


> Of course they'd first need to fix the huge drainages like 3kWh per day some ppl see, but then a small PV panel would take care of the "always connected, always consuming" issue. Even when you can't plug it in.


True. Tesla should consume same amount as Leaf or BMW/Volvo/Merc etc with telematics (always connected). ICEvehicles do not have HV battery to recharge 12V battery. BMW's can handle 3 months easily on a big 12V battery (40% larger than Leaf 12V battery). And it is unreasonable to leave 12V battery connected if vehicle is abandoned for like half a year.


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## JWardell

arnis said:


> Myth. My bimmer is 17 years old. And after getting EV, sometimes, it feel lonely for weeks and weeks. Until I need it to haul construction material or smth. My friend had 2010 BMW and he left it for 3 weeks every months (work abroad). Absolutely fine.
> Also there is nothing to "die" actually. Oil life is max 2 years. Driving for short routes is worse than driving once per month for an hour.
> 
> True. Tesla should consume same amount as Leaf or BMW/Volvo/Merc etc with telematics (always connected). ICEvehicles do not have HV battery to recharge 12V battery. BMW's can handle 3 months easily on a big 12V battery (40% larger than Leaf 12V battery). And it is unreasonable to leave 12V battery connected if vehicle is abandoned for like half a year.


Not a Myth. They have lead batteries with low internal resistance that discharge themselves as well. I thought you were an EE?
I had to replace the battery in my last car twice in a year, because I barely drove it.
Your single experience does not make a fact or a myth.
This is why we have science.


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## Guest

Pb batteries should be charged every 6 months if not connected to anything (on the store shelf) to keep them healthy. AGM type is even more capable. 
Whatever car you had, had a defect (excessive 12V battery drain). Using the vehicle daily just hides that problem.


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## JWardell

Even the deep cycle battery in my basement needs to be charged much more often than 6 months or else it will seriously degrade. Frankly lithium ion cells have a better shelf charge life


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## Guest

Time is not what degrades. It's the SOC and time at that state. Lead Acid batteries start to sulfate below 60% SOC. 
That is around 12.2-12.3V open circuit voltage per 6 cans (depends on specific type of battery).
Lead acid battery self discharge depends on temperature. Anything colder than 25-30*C is fine in terms of 6 months
if we start above 80% SOC.


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## MelindaV

having just sold a second car that had sat in the garage only very rarely driven over the last 6+ years, I can tell you AFTER needing to be plugged into the battery charger (if the battery was left connected or disconnected), the car would run much rougher than prior to it being parked. seals, gaskets, lines, belts, etc do not hold up well to sitting idle. My 1967 car that sits for even longer stretches often ends up needing mechanical parts replaced (starter, alternator, PS pump, etc) that end up seized up from sitting unused.


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## Guest

MelindaV said:


> My 1967 car that


These should seize up no matter what you do with it. 
It is extremely old and back then, materials were not really high quality. In terms of corrosion...clearances...

My friend has Toyota Celica, I believe 1997. He is a truck driver. His Celica was outside for 3-8 months, all winter or all summer.
For 4-5 years as far as I remember. Annual mileage less than few thousand.
And then he arrived home and used that vehicle for 2-3 weeks. Even battery was fine (replaced for gel type).
Absolutely no maintenance. Tires were slightly underinflated. Rust here and there (he almost never washed it).


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