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redpoint5 09-20-2020 01:32 PM

Tesla Battery Day Thread
Link to Tesla Battery Day Livestream. It follows the investor meeting which begins at 4:30pm EST, 1:30pm PST.

Tesla battery day is Sept, 22. Figured we could have a thread to speculate on what will be revealed.

Some speculate an announcement to supply batteries to other manufacturers, some speculate a $100 per kWh pack price will be announced, or a million mile battery.

What do you expect?

RedDevil 09-20-2020 02:22 PM

There are a couple of things that are almost certain, because of the patents that Tesla filed for in the last couple of years; tabless cells, simplified pack construction with cells immersed in coolant (rather than having coolant channels weave betwee the cell rows like now), new electrolyte additives that vastly increase the number of cycles, etc.

There are photo's of cells presumably made by Tesla themselves at the Kato Road facility in Fremont. And they are huge; over 7 times the capacity of Model 3 cells, over 10 times the Model S cells.

All of that is impressive and none of it will blow anyone's mind - and that's the very thing Musk promised Battery day will do.
So I don't really know what to expect and am just patiently waiting to have my mind blown. We'll see.

Meanwhile I have been investing in TSLA. On a small scale; just 5 shares I bought at the slump last year. Those raised like a Falcon 9 and split in 5.
I sold a few to have my original investment back so what happens next is all bonus.

I also noticed the stock is quite volatile. It can easily jump or dive 10% or more in a single day of trading.
I decided to make use of that volatility by adopting a strategy where my shares are to represent a certain amount of money; say $8000. If it rises and I can sell a share while the remainder is still above $8000 I will do so. If it drops and I can buy and still be below $8000 again I'll do so.

Now every time I sell a share it is the very one I bought cheaper earlier on, and vice versa. With every round trip I make about 5% of that share's value, and I have about 10 transactions per week so go figure; I should be able to add one share every month.

My mechanism brings extra yields when the stock jumps or dives hard. Then suddenly it trades way beyond what my buy or sell trigger would be and I can trade a couple at way bigger margins than usual.

Which brings me back to Battery Day. I will stretch the buy/sell limits a bit because I expect fluctuations will be wild. Time to take profit!

oil pan 4 09-20-2020 07:36 PM

It would make more sense to use toilet paper roll sized cells.

RedDevil 09-21-2020 04:43 AM

Actually, the idea behind using many small cells instead of a few big ones stems from the unreliability of lithium-ion cells.

Over time and use dendrites form between the cathode and anode and when they meet the cell shorts and dies. If you have a battery with big cells in series that will reduce the voltage of that pack if it is able to bridge that cell, or kill it entirely if it isn't.

Whereas the Tesla approach has 40+ small cells in parallel with a thin lead to each cell which acts as a fuse. If a cell fails it will get out of line with the other cells in its tier, draw more current and blow its fuse. It is then isolated and the tier remains at 98% of its original capacity. Even if dozens of cells fail distributed over the pack the total capacity only drops significantly if many of those happen to be in the same tier; usually the failures will be randomly spread over the pack and no tiers will have more than a pair or so. The pack is much more robust.

Advances in production technique have made lithium cells more reliable over time, so now it is no longer essential to split the pack into small cells. The Model 3 and Y already use bigger cells than the S and X and their packs seem much more robust nonetheless.

redpoint5 09-21-2020 11:37 AM

That, and larger cells have less surface area per volume, meaning it's more difficult to regulate their internal temperature.

I always wondered the same thing in the silicon wafer industry. We made 6", 8" and 12" wafers with larger ones in the works. My question always was why they didn't just determine the optimal diameter from the outset and start with that. It's not that easy.

RedDevil 09-21-2020 05:56 PM

The larger cells are supposed to have a lower internal resistance, which reduces their dependency on coolant - annihilating the negative effect their size would have.

freebeard 09-21-2020 07:52 PM


Meanwhile I have been investing in TSLA.
How do you do that? I've told Arcimoto if I could walk into their office and trade cash for shares I'd do it. Do you use a broker, or is it all in the cloud?


What do you expect?
The speculation I saw [citation needed] has the foil layers rolled up and stuffed in a can. [The whole can is electrode?] That's the tabless part. The ganged cans are clamped to a top plate with the wiring. It's flooded with coolant.*

The advantage with the bigger cells includes 1/10th the parts that need assembly.

There may be additional financial or chemistry announcements. One step closer to Mars.

*What would be really cool is if the can, the coolant, and their container all constitute a supercapacitor. :thumbup:

Hersbird 09-21-2020 10:11 PM

All I know is I have to reserve a new Xbox tomorrow. Batteries not included... Actually I bet it has two crappy AA's for the controller.

redpoint5 09-22-2020 12:21 AM

I'd be inclined toward PlayStation 5 primarily because of Gran Turismo 7. The new controller sounds neat too. Close call though because I enjoy Halo.

I may never own another console again. No time to game, and when I finally do get time in the future, everything will be cloud hosted.

RedDevil 09-22-2020 05:08 AM


Originally Posted by freebeard (Post 631559)

Originally Posted by RedDevil (Post 631498)
Meanwhile I have been investing in TSLA.

How do you do that? I've told Arcimoto if I could walk into their office and trade cash for shares I'd do it. Do you use a broker, or is it all in the cloud?

I first used the trade options in the online portal of my bank (ING). But after the stock split and I expected many transactions per week the cost there ($4 per trade + 0.25% of the share price) became prohibitive.
So I found an online broker (Degiro, aimed at the Dutch market) which only asks about $0.50 per trade.

I still hold the remainder of my stock at ING - the sleeping part that I will not likely touch. Degiro has the shares I am willing to trade with. If that broker was to fail I might lose that (even though there are warranties to protect the clients, but you never know); the ING-held shares are as safe as the bank - or safer still.

Of course if you want to invest you have to find a broker that suits your own needs. Here is a starting point and here's Arcimoto's stock (FUV).
I don't know whether investing in TSLA is wise right now. A year ago it definitely was since it went up 10 times in a year. But it is almost guaranteed to be quite active with lots of swings so you might plan to generate money from that tidal motion, like I do.
Likewise Arcimoto shot up 5 times since March.

Yesterday TSLA opened around $445, then spiked down to $408 and went up again to $449. I automatically bought one share at $416 and sold it again at $436, a $19 profit after transaction costs.
All the time my stock remains worth just above $8,000.

The stock movement in the coming few days will be interesting.

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