ID:259

[djp]

In simpler terms, will rebalancing ever produce a value lower than Tesla reports to a prospective buyer.

The CAC gets recalibrated after a long drive on a single key turn, so yes it's possible that Tesla might report a stale CAC which quickly drops after a long drive, even with no change in balancing.

My point on the CAC is that it isn't a magic number that gives you the "true" capacity of the pack. The ideal miles are equivalent to the CAC, both will vary based on calibration and balancing.

 

[wiztecy]

The CAC gets recalibrated after a long drive on a single key turn, so yes it's possible that Tesla might report a stale CAC which quickly drops after a long drive, even with no change in balancing.

My point on the CAC is that it isn't a magic number that gives you the "true" capacity of the pack. The ideal miles are equivalent to the CAC, both will vary based on calibration and balancing.

CAC is a better mechanism that ideal miles is derived from. As for the single key turn, I think there's many ways CAC gets recalibrated... the one I heard was drive the pack down from 80+% soc down to at least 30% SOC on one key cycle. I haven't driven my pack down that far and it recalculated... it also is recalculating each day and I'm just driving it down from 84% to 60%. I see it gets recalibrated after each standard charge I'm doing... also when its sitting below 80% I see the CAC increasing.... where it doesn't increase is after I let it sit at 60% SOC over the weekend without driving... meaning it went through a recalculation already and can't do one after that. What I do see is my CAC is increasing, but my ideal miles are staying the same.... actually I'm seeing this, after the Roadster sits after work I gain 2 miles after my drive.... so its doing some rethinking with the ideal miles from the newly adjusted CAC. I'm thinking that if I do drive the pack down far enough that it'll sync up the CAC and ideal miles even more, my hunch is when driving on one key turn above is performed may give quicken things...



>"It clears up what you're saying but you've gone way away from my example.
>I'll try again:
>Shopper (no "original pack" involved) of a used Roadster has a minimum CAC (D) value in mind.

I think buying a brand new pack without having 1st an original pack is a unique case and I don't know if Tesla would even sell a refurbished pack... As with this thread, the original pack had a known CAC and that was what I'm pointing out and that's what Tesla would try to target/match within reason. I don't think Tesla would give any guarantees as to what a refurbished pack's CAC is without having any pack to start with and most certain they'd push you to buy a brand new one.

 

[brianman]

I think buying a brand new pack without having 1st an original pack is a unique case and I don't know if Tesla would even sell a refurbished pack... As with this thread, the original pack had a known CAC and that was what I'm pointing out and that's what Tesla would try to target/match within reason. I don't think Tesla would give any guarantees as to what a refurbished pack without having any pack to start with and most certain they'd push you to buy a brand new one.

Sorry, all, if I'm detouring the thread which the confusion suggests I might be.

My scenario is the shopper considering buying a CPO Roadster from Tesla (with no other Tesla Roadster in his/her personal history) and wanting a "minimum CAC value" for this used vehicle. While I (mostly) trust Tesla to not sell a CPO Roadster with barely any battery capacity left, I'm curious how the Tesla-reported CAC should be read/evaluated and what expectations the buyer should have when measuring the CAC days/weeks after purchase.

 

[wiztecy]

Sorry, all, if I'm detouring the thread which the confusion suggests I might be.

My scenario is the shopper considering buying a CPO Roadster from Tesla (with no other Tesla Roadster in his/her personal history) and wanting a "minimum CAC value" for this used vehicle. While I (mostly) trust Tesla to not sell a CPO Roadster with barely any battery capacity left, I'm curious how the Tesla-reported CAC should be read/evaluated and what expectations the buyer should have when measuring the CAC days/weeks after purchase.

I see, that makes sense now I don't know for sure, but I would ask for the CAC from Tesla. And with the CAC inquire how long has the Roadster been sitting without a charge, when was the last full "std mode" charge performed, how long has it been since the Roadster has been driven on a long trip / when was it traded in. The ideal miles (after sitting for a full day from a std mode chg) would be the best way to feel out how healthy a CPO Roadster is if no other information is given.

 

[brianman]

Thanks. Stashing this in my long term memory (or trying to) for when Roadster prices break thru my resistance level.

 

[Mitrovic]

The CAC of my car is 152,43.

Whar are the CAC readings of your cars?

 

[djp]

The CAC of my car is 152,43.

Whar are the CAC readings of your cars?

Tom Saxton's battery survey has the CAC's from over 100 cars, here is the link:

http://www.pluginamerica.org/surveys/batteries/tesla-roadster/PIA-Roadster-Battery-Study.pdf

The range is about 132 to 160, and is tightly correlated to Ideal miles after a Standard and Range charge. The highest mileage Roadsters have the lowest CACs, with a loss of about 0.24 CAC per 1,000 miles driven.

 

[ChadS]

I just found these same two errors in my car this morning. Tesla tried to do some remote diagnostics but couldn't; they need me to get the car to them.

Tesla does not sell extended warranties in my state (they started to once -they even gave me paperwork to look at- but then they said it "needed more work" and they would get back to me when the warranty was available. That was a year and a half ago), so this will not be covered under warranty. Sigh.

The car is in my garage. It won't move out of Park, so I've going to have a tow truck operator drag it out of my garage. Assuming, of course, that a tow truck can get up my driveway (most cars barely can due to clearance at the end) and get behind my car on the angled driveway. Sigh again.

 

[Mitrovic]

Chad, so sorry to hear you have this same problem!
Did Tesla say you need a new battery pack?
You can not put it in the tow mode?
How many miles and how many years for your car?

 

[ChadS]

I knew the Model S had a tow mode, but forgot the Roadster did. The service center reminded me, and I used that to back the car on to the straight part of the driveway. The tow truck driver (Crossroads Towing) was able to get up my driveway and loaded it on his flatbed; he was familiar with the cars (in fact it sounds like he towed Vger once), careful and friendly, and the tow only cost me $100. So far, not so bad.

It is probably just arriving at the service center now. They will diagnose and let me know what I need. I hope I can escape with a smaller fix than a full pack replacement...

The car is 4.5 years old, and has 42k miles on it. It's been a peach until this morning.

EDIT: I am told it needs "an internal battery rework". They are still figuring out exactly how much they'll have to do. I presume in the past for warranty repairs they typically just swapped in a new pack for this and sent the old one to headquarters for work, but now they hopefully are trying to keep costs down and get this one fixed locally. I hope this works well and they can keep the cost WAY down...

 

[Mitrovic]

Chad, keep us informed!

 

[ChadS]

I got a call from the service center to give me a detailed explanation today; unfortunately the call came just as somebody was coming up my driveway for a meeting so I had to cut it off. So I may not have this completely straight, but I think what is going to happen is that they are going to put in a new pack, and send my old pack back to headquarters to be revamped.

It looks to them like the problem is entirely in one sheet, so although they are giving me a new pack for expediency's sake, they are going to basically charge me the cost of pulling a sheet, fixing it, and putting it back in (and doing the other stuff you have to do when you replace the pack, like adjust the suspension, do an alignment...and the firmware?!?). It's a little more than I expected for a sheet at $4200 all-in (including tax, shipping, etc) but it's a heck of a lot cheaper than a full battery, and I will get a one-year warranty with it. The majority of the cost is labor, so I hope that means this sort of issue would be cheaper on a Model S. (I also hope it is less likely on the Model S due to more automation putting the packs together in the first place).

They are now trying to figure out how long it will take to get parts. I am trying to be patient but I had to drive a friend's gas car today, and it was painful.

 

[Tacket]

Oh no! I saw you car come in on the truck when I was at work. Wondered if it was yours!

 

[wiztecy]

...(and doing the other stuff you have to do when you replace the pack, like adjust the suspension, do an alignment...and the firmware?!?). It's a little more than I expected for a sheet at $4200 all-in (including tax, shipping, etc) but it's a heck of a lot cheaper than a full battery, and I will get a one-year warranty with it.

The suspensions doesn't get touched nor is there any need any alignment/readjustment after a pack drop. The control arm bolts are removed to allow them to swing out and away and the pack is lowered down from the chasis. As for the firmware, you're firmware in your Roadster will stay the same but they have to flash/encode the new pack with your VIN. The $4200 doesn't sound bad, just think if you bought the battery warranty. And since your pack is refurbished they're going to warranty the whole pack. So I'd say that's pretty good customer service. Going your route sounds cost effective, also know that your new pack has undergone refurbishment meaning they ran a bunch of health tests when rebuilding it. Just keep an eye on the CAC of the new pack and be patient when balancing it / allowing the CAC to climb.

Chad do you have OVMS? If not I'd dump the logs every once and a while to track it. Any idea what your CAC was of the pack they're swapping? The CAC can show some sort of indication of what type of failure was occuring, but also you need to view the low, min, and adv. voltages of bricks in the pack to understand the full picture of whats going on for us since we don't have that handy CAC graphing tool Tesla has.

 

[ChadS]

It sounds like the new battery is in my car; they just need to do a little more testing and I should get it back tomorrow. Good thing I have a friend out of town and I've been able to use his car.

My repair estimate says Tesla will adjust the suspension and do an alignment as part of the pack replacement. I will ask if that was really necessary. I'm not happy about having a bad sheet or about paying that much money to fix it, but given that I am paying the money, yeah I'm glad to get a reconditioned pack and a warranty.

I do have OVMS, though just with a texting plan because I mainly used it to learn if charging stopped while on a trip - and I haven't even been using that since we got the Model S. I can get at the CAC on the diagnostics screen. It was a little low on my old pack, though I forgot exactly what it was. Not sure why, my pack was always at the low end (for its miles) in tomsax's Roadster battery survey (it wasn't getting worse faster; just seemed to start life a little below the others). Here's hoping for a better number on the new pack...although it gets adjusted over time, so it should be close to the old CAC at first, right?

Last time I looked at my old pack, min and max brick voltages were pretty darn close together. That was probably a year ago, though.

 

[ChadS]

It took them a little longer than expected (largely because of the alignment); I just got my car back this morning.

The bad news about this experience:

1. my car suddenly failed (at least it was in my garage, and not when I was trying to drive anywhere)
2. it was gone for a week and a half
3. it cost me $4,000 (no tax, since WA waives sales tax on EV battery-related stuff; that saved me $400)

No doubt, that's a bummer. But there is good news:

1. This is the first time a Tesla has ever failed me; not too bad for a total of 6 years and 65k miles of driving our two cars
2. Tesla communicated extremely well during the process
3. A week and a half is not so bad for a major operation on a car of this class; and I had a friend's car to drive so really no big deal. And they delivered it to my house this morning.
4. It sounds like all I needed was a new sheet - heck, maybe even just a sensor inside a sheet (I asked for more info, but they didn't seem to have much) - but I ended up with a new (well, refurbished) pack
5. The old pack's CAC was 136 (partly so low because I hadn't been charging it all the way for a few months, I suspect). The new one is 151, so that's a significant boost
6. I get a year's warranty on the whole pack, despite not paying for a whole pack
7. I was overdue for annual maintenance; but they did most of the stuff (cleaning PEM, checking coolant, road test) so I essentially got a free maintenance
8. It turns out the car did need significant alignment work - I am not sure if it was a problem before (though I didn't notice anything) or due to the pack swap, but glad it got done. They say it's required every time they swap packs

It's hard to be happy about a car failing and needing major repair...but Tesla's great service sure does make up for a lot.

 

[ChadS]

I had asked for more info on my failure, as well as tips on keeping the CAC up. I heard back last week. Regarding my failure, they said:

Basically the battery module has collector plates on each side of the cells. On each collector plate there is a sense lead, a wire with a ring terminal on the end and it is riveted to the collector plate. The function of the sense lead is to monitor brick voltage and feed that info back to the BMBs and BSM. The battery then uses this info to make decisions on charging and available battery power to drive the car.

In the case of your car, one of the sense lead rivets developed some impedance at its connection to the collector plate. This then causes a voltage drop and the BMB and BSM get incorrect data from the sense lead. The impendence of the connection had grown to the point that the BSM basically thought the pack was overcharged and would not allow the car to start or charge.

So that doesn't sound (?) like anything I could have avoided. As far as looking forward and keeping the CAC up, they said to avoid the following:

· Harsh storage temperatures (too hot or too cold) The closer you can stay to the 50F to 80F degree window the better.
· High storage SOC.
· Super low storage SOC
· Charging solely with a 110V charge cable. There is a certain level of error in the measurement when you use this cable that can cause the CAC calculation to decrease (actual pack capacity does not decrease, only the calculated capacity, it will recover with HV charging over time)

Which mostly sounds very familiar; the only news to me is the bit about 120V charging causing CAC (though not pack capacity) to drop. As it happens, I have been using 120V charging for about a year so that may explain the low CAC on my old pack. But I'm moving to a new place with a convenient 240V outlet in a couple of weeks.

 

[hcsharp]

I had asked for more info on my failure, as well as tips on keeping the CAC up. I heard back last week. Regarding my failure, they said:

That's interesting! Thanks for sharing that info with us. I have occasionally let my pack sit for a few days at extreme cold temps when I wasn't driving it. I only thought it was bad to charge it at cold temps, which of course it won't let you do.

 

[Jackyche]

Please correct me if I'm wrong.

On a standard charge, the SOC is 90% (ideal range displays 80%, 10% uncharged and 10% hidden) right?

Now, I don't drive the car very much, weekends only really.

Is sitting there @ 90% for a week or two at once considered high storage SOC?

I used to do storage mode and drive around "in storage mode" as well. But the ideal range went from 191 to 183 during that span (half a year). So I got scared and thought it was a bad idea so I stopped doing that.

I guess I should go check the CAC to be sure.

 

[wiztecy]

I had asked for more info on my failure, as well as tips on keeping the CAC up. I heard back last week. Regarding my failure, they said:

· Harsh storage temperatures (too hot or too cold) The closer you can stay to the 50F to 80F degree window the better.

So that's pack temp, not ambient temp I take it which would be 10C - 26.6C.

On a standard charge, the SOC is 90% (ideal range displays 80%, 10% uncharged and 10% hidden) right?

Now, I don't drive the car very much, weekends only really.

Is sitting there @ 90% for a week or two at once considered high storage SOC?

Standard Mode SOC (where 100% is a fully charged pack in Range Mode) is around 84% I believe, possibly as high as 87. I have to check to be exact. No higher or lower. No its not bad to let the Roadster sit charged full in Std. Mode, sometimes it needs it to balance the pack. Just keep the Roadster out of direct sunlight / heat when you do and initiate a cool down of the pack to chill the pack before it sits.