ESS software questions …

[hcsharp]

You are asking the 64 dollar questions that many of us have wondered for some time. I've tried to answer below based on my own speculation.

So :-

(1) Does anyone know if the existing Roadster software has the hidden-facility to initialize and balance an entire ESS fitted-out with a set of new higher capacity 18650's ?

It's likely that it does. But it depends on what software you are talking about. There are circuit boards mounted within the ESS itself with firmware in them. I don't think all of these get updated when you get a so-called software upgrade. I don't think all of them are even connected to the bus. That is based on what I was told by a Tesla tech who said he had disassembled the ESS. I think they could easily update this firmware when rebuilding the ESS with new cells. I suspect they will offer an upgrade to the $12k owners to get more than 53 kWh.

I have also heard of Roadsters with particularly good batteries that after being cycled a few times show more than 245 ideal miles remaining on the vds. That would indicate that there is at least some capacity in the hardware/firmware for bigger cells already. Just how much is anybody's guess.

(2) Do you think that the existing software (or via an upgrade) allows for altering the charge profile for slightly different cells?

Yes. They added the ability to balance the cells when doing a standard mode charge in a recent software update. They tweaked the charging profile quite a bit on the original prototypes so it's reasonable to assume they have the capacity to do this without too much trouble.

(3) Do you think that as Roadsters fall out of warranty in the years ahead, that a 3rd party support network will form offering a reverse engineered ESS cell upgrade ?! (and hopefully not as a result of Tesla going belly up - I've just bought shares too!)

Not sure about this but I doubt it. Tesla has automated equipment to solder and glue the cells that might be too costly to setup for such a limited market. In addition, Tesla is building recycling facilities to re-use most of the material in the cells. They claim to recoup some of the cost that way. It also really depends on whats in there! Some of it might be impossible to reverse engineer (electronics, firmware), or too expensive given the small market.

A service tech told me it takes about a whole day (8 hrs) to swap a ESS out of a Roadster if he periodically gets help from another mechanic. That's a lot of shop time! When I heard that I decided $12k was a good deal for the battery replacement program.

I also think Tesla will offer better cells for an upgrade price to those of us who bought the program.

 

[richkae]

150 in Range mode, or standard mode?

Its hard to predict how I will feel about it in the future, especially when I have the Model S because it will do any of my long distance driving.
If right now magically today my Roadster battery only had 150 mile range - in range mode ( so about 115-120 standard ), I would be pestering Tesla and asking them for a new battery made out of the same cells in the top of the line Model S.
I would wait for that battery to be available and would not buy a replacement battery made of the old cells. If they told me I had to wait until next year, I would wait.

Its purely an academic exercise. I have 99.9999% confidence that they will offer an upgraded battery before my capacity drops below 200 miles.

 

[PV4EV]

Nothing new, but there are some drawings here: Roadster battery (ESS)

Thanks for the link to the images !!

I know there's supposed to be 9 bricks x 69 cells = 621 per sheet, 6831 total.

However, its hard to know how precise the drawings were supposed to be, or if the artist couldn’t count … because influenced by a bit to much wine and 10 minutes to spare, I counted 627 cells in each sheet, giving 6 more than stated, and 6,897 total !

Maybe I should sober up and count again ...


What the illustrations show nicely is how densely the cells are packed and how the cooling system is plumbed in - details I've not seen before.

 

[hcsharp]

It looks like whats going to cause your ESS to lose capacity is when you burn out a few cells here and there. If there are currently 69 cells in parallel in each brick, the current is divided between them. But if 6 burn out in one brick, the other 63 have to carry the load which means they will burn out faster. At some point it will reach a tipping point where the cells in that brick will start going dead faster and faster until the entire brick dies. I don't know if the ESS is useless at that point or the hardware has the capacity to bypass it. In the mean time, your total capacity is limited by that one brick or the sheet it's in. You can't ever discharge it below 3v while the rest of the bricks will still be at, say 3.4v.

You are more likely to "kill" cells when they are low. The car passes more current through them to get the same power so you are more likely to heat them up. This theory would support keeping the car charged in std mode every day as opposed to keeping it closer to 50% SOC with the idea that a little lower SOC is better for the hours you're not driving it.