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Unread 02-17-2019, 09:00 AM   #31
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Default Re: Nothing to see here. Team Tesla

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Originally Posted by BobBoyce View Post
Cell chemistry, not cell configuration. Since my prior reference to aerospace engineering was shot down, I'll not bother referring to extensive NTSB aircraft accident investigations and the subsequent testing that eventually led to the redesign of lithium pack countainments to prevent further loss of airliners and passengers due to fires caused by the introduction of lithium packs to commercial airliners by the manufacturers, to replace the former industry standard of NiCd. They still suffer from passenger carried devices that contain cobalt containing lithium cells that catch fire in luggage and carry-on bags that slip through the passenger screening process. There is a reason that we must pay for HazMat shipping fees when shipping lithium cells. There have been so many incidents that it has created a fear of anything lithium in certain circles. This is unfair to those that buy and use safer alternative chemistries that do not exhibit the same reaction to failure.

Please don't take my feedback wrong... The pack he built is really done well for his application, and I enjoyed reading about it here. My criticism is reserved for the way Elon chooses power density over safer chemistry.

Now that I’m through licking this window..
Is basically what you are saying is that the different chemical formulas used in the cathode are what gives these different 18650 cells their “characteristics”?
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Unread 02-17-2019, 02:10 PM   #32
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Default Re: Nothing to see here. Team Tesla

I was under the premise that Tesla batteries required a liquid cooling system. But maybe that isn't necessary in a cart situation?
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Unread 02-17-2019, 03:48 PM   #33
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Default Re: Nothing to see here. Team Tesla

Tesla batteries are being drawn off of at a higher rate, and are in a much tighter enclosed area. I've specifically spaced mine and not enclosed it completely to assist with this. I will also monitor their temp and adjust accordingly.

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Unread 02-17-2019, 05:58 PM   #34
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Default Re: Nothing to see here. Team Tesla

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Originally Posted by BBBHC View Post
Saw a recent video of Elon discussing adding a second level of batteries to the existing battery packs in the cars... That seems a bit scary

I was under the impression that one of the reasons Elon decided to go with 18650 cells, was to reduce cost. As opposed to the cells that Nissan, Chevy, etc., use. Their "specialized" housings require more design and manufacturing of parts to fit them. Is this the case Bob?
The reason that Elon chose to use the 18650 cells mostly had to do with the existing chinese manufacturing base making these cells for laptop battery packs. The economy of scale dictated that the price per kW/Hr of these cells to be lower and more available. Elon soon overwhelmed the availability of the cells from existing manufacturers, resulting in rising prices. Chinese manufacturers began cutting tolerances (thickess) of the seperators between anode and cathode, resulting in higher incidence of age/cycle related penetrations and catastrophic cell failure. Elon built his own 18650 cell manufacturing plant in more recent years.

So cost was one factor, as well as available supply, initially. Supply to meet his huge demand, then QC, became driving factors in his decision to manufacture cells himself. Due to his control over QC, his newer packs should have lower failure rates unrelated to physical damage to those packs.

Yes, due to the higher packing density, the Tesla packs are liquid cooled. The 18650 cells packed in a lower density fashion can be passively air-cooled. Unfortunately, the chinese manufacturers are still making cells (all cells, not just 18650) that are at risk of failure due to thinner seperators. Crystal growth in Li-ion cells is directly related to peak charge voltage and cell chemistry. It is these crystals that penetrate the seperators, resulting in cell failure.

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Unread 02-17-2019, 06:56 PM   #35
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Default Re: Nothing to see here. Team Tesla

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Originally Posted by izzybird View Post
Now that I’m through licking this window..
Is basically what you are saying is that the different chemical formulas used in the cathode are what gives these different 18650 cells their “characteristics”?
It can be differences in chemistry of the anode, cathode, or both. And yes, chemistry denotes characteristics, which typically affects cell voltage and current. Anode, cathode, and seperator configuration typically affects the efficiency of chemistry interaction. How well this is packaged greatly affects power density. Prismatic cell configurations have led to higher power densities than cylindrical cell designs such as the 18650, but also leads to more difficulty in cell mounting. Prismatic cells must be held under pressure, while cylindrical cells are each a pressure vessel. You just have to connect so many of them in parallel to equal the current of much larger prismatic cells.

Bob
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Unread 02-18-2019, 08:34 AM   #36
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Default Re: Nothing to see here. Team Tesla

Most EV batteries are liquid cooled (and heated in cold weather). Leaf was the exception and they had big problems with battery life in hot climates like where I am in the Phoenix area. A Tesla can pull very high power from the battery - for short periods of time. My golf cart application would not require cooling in a pack rated over 100 AH. I use 18650 batteries in my Electric Bike and they don't get hot. The other thing with Tesla is that they try to make it possible to fast charge the battery on their "SuperChargers". That is hard on those batteries that are normally charged at less than 1C. My charger only puts out 17 amps which usually takes about 5 hours to charge my cart battery. Superchargers do around an 80% charge in something like 30 minutes.
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Unread 02-18-2019, 02:42 PM   #37
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Default Re: Nothing to see here. Team Tesla

Volt, so your pack is around 100ah? How long is your runtime? How are your cells configured?

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Unread 02-18-2019, 03:30 PM   #38
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Default Re: Nothing to see here. Team Tesla

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Originally Posted by Joelwdryden View Post
Volt, so your pack is around 100ah? How long is your runtime? How are your cells configured?

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I have a 14 Leaf module pack - about 120AH. I get about 4 rounds of golf on a charge but I usually recharge after 3 rounds.
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Unread 02-18-2019, 06:35 PM   #39
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Default Re: Nothing to see here. Team Tesla

That's awesome! I'm so excited. 5 inches snow tomorrow so that will have to wait. Got my balance leads all installed. Only thing not working is my golf swing.

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Unread 03-05-2019, 01:05 PM   #40
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Default Re: Nothing to see here. Team Tesla

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Originally Posted by izzybird View Post
So are these a mix of different chemistries since you sourced them from various places? Are the pink ones Li-cobalt? I was under the impression those were the most “dangerous” of the different chemistries. Not attacking your build in any way, honestly just trying to learn more.
For those interested, here is a link you can use to get more information on specific 18650 cells. https://secondlifestorage.com/celldatabase.php

You can use Brand, model, wrap color and ring color; to cross reference them. That will get you access to data sheet, cell data, photos, specifications and discussions.
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