Near annual replacement of 12V battery is typical according to Tesla Service Tech

[ArtInCT]

This is a very interesting thread. Kudos to all who are participating.

Just a thought... why does Tesla not add an electrical rectifier to the shore AC power circut? The rectifier would convert shore power AC to DC (when attached) and power all of the DC components with DC power, thus bypassing the DC battery as the power source. This method could reduce the discharge / recharge cycles on the DC battery and thus extend its life. This is in keeping with TM's advice, which is to keep the Tesla S connected to AC when not in use at home.

Also, not much has been mentioned regarding the ambient temperature that many subject their model S to when at home. I would suspect that very cold and very hot soaking of the 12 volt DC battery may have some bearing on the battery's life and its effiency. Living in a cold climate winter and hot climate summer environment has a longevity effect on the 12 volt battery, especially in an unheated garage. In the 50 years I have owned cars, most 12 volt battery failures I have encountered were often during very cold spells which tended to exacerbate the weakened state of my battery.

 

[SteveS0353]

It wouldn't make any sense to keep opening and closing the high voltage contactors every time the DC/DC kicks on and off. The DC/DC is low current and could easily have it's own smaller contactor or relay. More likely the DC/DC is always connected to the pack unless there is an accident and an inertial switch opens its contactor or relay. It needs to stay powered up so it can sense the 12V battery voltage and kick on when needed. Obviously I don't know how Tesla does it but I can say I don't know anyone in the DIY world that uses the high voltage pack contactors to turn the DC/DC on and off.

I've been thinking about this a bit more, weaving a theory from the various bits of evidence. I don't think there are separate low-current contacts for the DC-DC converter, I think all of the current, in both directions, flows through the one set of HV contacts. There is evidence for this in wk057's thread documenting the disassembly of the Model S HV drive battery.

We know that when the 12V goes away, the HV contacts inside the HV drive pack open. The directions Tesla provides to first responders is to sever the 12V loop to isolate the 12V battery, which isolates all of the high voltage inside the sealed drive pack and is thus safer for them without having to worry about high voltages everywhere. The HV contacts inside the drive pack are in fact normally always closed, held in that state by the 12V. If that nugget is true, the DC-DC converter is simply monitoring the 12V battery and charging from the HV when the 12V battery reaches a predetermined point on its discharge curve, but still sufficient to keep the HV contacts closed. Keeping the contacts closed, by 12V power, minimizes the number of times the contacts open and close (good for contact reliability). That would also be consistent with the known model that shore power does not charge the 12V battery directly, ensuring that isolating the 12V battery is the safe thing to do in every situation, with or without shore power. It's therefore likely, if this wild-ass guess is accurate, that a chunk of the vampire drain is to keep the HV contacts closed, perhaps a significant chunk.

 

[CarlK]

Not sure where you live, but an oil and filter change for my BMW (at an independent shop) was never less than $150, if not more. For my old 190D, I do one oil and filter change a year (I only put on 2500 miles a year on that car on WVO) and that is now well more than $150. A MBZ dealer in my area would probably charge me more than $200. I also had to change out the battery twice on my BMW in 5 years and twice in 3 years on my 190D. I was surprised the battery life was so short and was told by my tech that he sees a wide range of battery life with no rhyme or reason as to why. He said it is very hit or miss, almost random, how long a normal car battery will last. Could be many, many years, or in my case it wasn't nuts that it lasted less than two years. So anyone assuming that their battery will last for many years based on past experience has probably been very lucky.

I just spent $950 at the Porsche dealer because the check engine light turned on. I needed to get that fixed even though I don't drive it much anymore because the smog check is coming up. That is something that will never happen to an EV.

 

[JRP3]

It's therefore likely, if this wild-ass guess is accurate, that a chunk of the vampire drain is to keep the HV contacts closed, perhaps a significant chunk.

You may be correct, and that makes more sense than constantly cycling the HV contacts for the DC/DC, but to me it makes less sense than running the DC/DC through it's own smaller relay, which could also be disabled by cutting the 12V feed. That way the main HV pack contactors could remain open when parked.

 

[SteveS0353]

You may be correct, and that makes more sense than constantly cycling the HV contacts for the DC/DC, but to me it makes less sense than running the DC/DC through it's own smaller relay, which could also be disabled by cutting the 12V feed. That way the main HV pack contactors could remain open when parked.

I've been wading through wk057's brilliant thread documenting the pack disassembly (Pics/Info: Inside the battery pack, lots of extremely useful pictures and commentary), and it seems that there is only one pair of contacts for the HV, one for the positive terminal and one for the negative terminal. These are normally open HV relays with contacts capable of handling high currents, with a coil which is energized to close the contacts. I don't see any other relay for getting power into or out of the pack. I can't locate any technical information on the specific part numbers (Tyco components), as they seem to be proprietary.

 

[kennybobby]

The HV contactors in the pack are restricted parts from Tyco, see the discussion here Battery Power-Up After an Accident

Here is the datasheet for an available similar contactor, i think the Tesla has lower contact resistance specs than the commercial units.

Has anyone seen pictures of the inside of the DC-DC--that seems to be one box that nobody has opened up yet.

 

[SteveS0353]

The HV contactors in the pack are restricted parts from Tyco, see the discussion here Battery Power-Up After an Accident

Here is the datasheet for an available similar contactor, i think the Tesla has lower contact resistance specs than the commercial units.

Has anyone seen pictures of the inside of the DC-DC--that seems to be one box that nobody has opened up yet.

Thanks kennybobby! My math says that the peak current through each Model S contactor is 350kW / 350V = 1,000A. That's double the max current carrying rating of the contactor you linked, but the data sheet does provide some information on coil resistance, with which we can speculate about the current to hold the contacts closed. At 12V, the coil resistance is 11Ω, meaning 1.1A. That's 13.1W to keep it closed. With two relays in the Model S pack, one + and one -, that's 26W, or half of the roughly 50W average vampire drain! That's such a large number, it makes me question my contractors held closed theory, but it would explain a significant chuck of the vampire drain which is otherwise unexplained.

 

[Moonwick]

With two relays in the Model S pack, one + and one -, that's 26W, or half of the roughly 50W average vampire drain!

Even better, it's probably ~10% more than that when you consider that this power comes from the 12v battery, so you also have to add in inefficiency at the DC converter and charging the secondary battery.

 

[kennybobby]

The + contactor is in the LEV500 family with higher current rating than the 200, i just didn't have a datasheet for that model handy.

It's not clear to me whether the Front Junction Box routes the power to the DC-DC converter or it's a direct feed from the HVJB under the rear seat. It would make sense to feed the FJB from the rear and then parse out the lines to the AC compressor, DC converter, etc. The design and hardware seem to be revised frequently and quickly...

 

[santana338]

Good idea. I'll make note of that when I do the test.

So the first attempt at logging was a bust. I thought I would be able to monitor the 12V from the cigarette lighter, but I don't get any voltage there, not even when I am in the car and driving. Has anyone used their cigarette lighter? I'm wondering if my lighter outlet is bad.

I guess I should have searched before trying the 12V adapter. I would have found out there is not a direct connection to the battery. Anyone know a good place to get direct access to the 12V supply? The battery itself is on the passenger side of the frunk, but how do you get to it? The other option is behind the nosecone, but I don't really want to do that. Any other options?

 

[jerry33]

So the first attempt at logging was a bust. I thought I would be able to monitor the 12V from the cigarette lighter, but I don't get any voltage there, not even when I am in the car and driving. Has anyone used their cigarette lighter? I'm wondering if my lighter outlet is bad.

That's odd because I have a voltage metre that plugs into the power port and it reads just fine. (I use the one by the USB ports--haven't tried the other one).

 

[JRP3]

Blown fuse?

 

[aaronw]

I am now on my 3rd battery (replaced a few weeks ago) and was told that Tesla is working on a permanent solution to the problem. Hopefully they solve this before people start having out of warranty issues.

 

[JPP]

Another data point. My original 12v was replaced 10 months ago at my 12k service. Was in last week for my 24k service. 12v battery tested OK and was not replaced.

 

[AoneOne]

I suspect that's why the car was revised with a small set of vent holes to draw air across the sensor located in the lower arm rest...

I put a thermometer in the cup holders and parked my car outside for the duration of my workday. Eight hours later, when I came to the car, it showed an outside temperature of 24F, inside of 35F, which matched my thermometer. So, the difference is real: the Model S interior is substantially warmer than ambient, even after 8 hours under overcast, snowy skies, with a half-inch or more of snow and ice covering the car.

Next, I need to check the battery energy loss during the workday: keeping the battery happy may be warming the car.

 

[mknox]

I put a thermometer in the cup holders and parked my car outside for the duration of my workday. Eight hours later, when I came to the car, it showed an outside temperature of 24F, inside of 35F, which matched my thermometer.

Mine is an early model without the HVAC aspirator. I have found with similar tests that keeping the settings at 67 F actually yields 72 F in the cabin. Now that I know that, I just leave it at 67 F and don't stress over it.

 

[scaesare]

Mine is an early model without the HVAC aspirator. I have found with similar tests that keeping the settings at 67 F actually yields 72 F in the cabin. Now that I know that, I just leave it at 67 F and don't stress over it.

Like you, I don't have the air aspirator. My car also feels warmer than the thermostat would have one believe... I typically have it set 2-3 degrees below where I typically have my home thermostat set.

 

[NOLA_Mike]

When did they add an aspirator? I keep my brand new P85D set on 67 degrees to be comfortable; I kept my mid 2013 P85+ on 67 degrees to be comfortable; whereas every other iteration of Automatic Climate Control in every other vehicle I've owned I'm comfortable at 70 - 72 degrees.

Makes little difference to me - I'm comfortable at 67 set point and I rarely have to change it.

 

[Gizmotoy]

Add mine to the list. It was in for its annual service last month and they didn't change the 12V, today I got the notice on the dash. Worse, there's apparently a 12V parts shortage and they can't get me one until Saturday. The car's still drivable, for now. I hope I make it until then. 10.5k miles on it as of today.

Edit: Both my home and workplace have underground garages that likely wouldn't be large enough for a tow truck. Can they jump the battery temporarily, or am I in big trouble if this thing dies?

 

[scaesare]

When did they add an aspirator? I keep my brand new P85D set on 67 degrees to be comfortable; I kept my mid 2013 P85+ on 67 degrees to be comfortable; whereas every other iteration of Automatic Climate Control in every other vehicle I've owned I'm comfortable at 70 - 72 degrees.

Makes little difference to me - I'm comfortable at 67 set point and I rarely have to change it.

Sometime mid/late 2013 I believe... I got my car in May and that was one of the first visible running changes that came out not too long after I got mine...