10 ms·

Inside a Tesla Model S Battery Pack

264 points by cyanoacry 12y ago

deleted 12y ago
[deleted]
agumonkey 12y ago
Pictures wouldn't load so I used https://web.archive.org/web/20140910232549/http://www.teslamotorsclub.com/showthread.php/34934-Pics-Info-Inside-the-battery-pack https://web.archive.org/web/20140910232549/http://www.teslam... thanks again archive.org
- toomuchtodo 12y ago
  Glad the archive I did yesterday was useful! :)
- jonah 12y ago
  It appears he was serving them off his personal NAS. Whoops.
  - bigiain 12y ago
    His copyright notice and explanatory paragraphs make it clear he's trying to keep some level of control over those photographs, while still sharing them with "his community" - which means I feel a little uneasy about having archive.org unilaterally slurp the images up like that... I know it's kind of a losing battle, but "publicly available" does not mean "in public domain".
    - jacquesm 12y ago
      How do you feel about google images?
      - bigiain 12y ago
        Pretty much the same - "uneasy". I'm enormously grateful it exists when I want to use it, but still have a distinct feeling it's "not OK" to do that with other people's images (and especially not just relying on the "but you didn't put anything in robots.txt to say we couldn't do whatever the hell we wanted with your pictures! And we _credited_ you!!!" excuse).
    - greglindahl 12y ago
      Archive.org respects robots.txt. Nothing unilateral about it.
      - bigiain 12y ago
        How many of the webforums you post on give you access to update the robots.txt file to inform Internet Archive about your copyright desires? Like I said - I'm conflicted about this, I _want_ these images to be available, and whatever the guy wrote in his forum post we know Google (and Blekko!) will index and download them and will pretty soon be causing them to be "otherwise distributed outside of this forum" - but the guy's wishes are clear, even if not explicitly machine-readable.
        greglindahl 12y ago
        The photos aren't on the forum, they are on an image hosting website. Other images on the forum are hosted on the forum. If the guy knows how to host his images elsewhere, he should be able to figure out how to host the images someplace with a robots.txt that he likes.
        deleted 12y ago
        [deleted]
    - dublinben 12y ago
      I've never seen such an aggressive and hostile copyright notice in a forum signature before. It's not entirely clear that you can even claim copyright over trivial online comments.
      - tokenadult 12y ago
        It's not entirely clear that you can even claim copyright over trivial online comments. Trivial or not, you have copyright in your own writings, online or off-line. Each participant on HN owns the copyright in the written expression of his or her comments. Similarly, a photographer has copyright in photographs taken by that photographer. See a user profile of a high-karma HN participant https://news.ycombinator.com/user?id=tptacek https://news.ycombinator.com/user?id=tptacek for an example of asserting copyright in HN comments, something that any of us could do, because the copyright is already there under modern copyright law, and asserting the copyright openly and publicly helps battle infringement.
        nitrogen 12y ago
        There is the complication that photographs of 2D works of art intended to represent the original are not subject to copyright, so some of those photos might not be either if someone with enough money wanted to press the issue. (Not a lawyer)
        dublinben 12y ago
        A work must be creative enough to earn copyright. Most tweets would not qualify, for example. You can assert anything you want without it being legally enforceable.
        jacquesm 12y ago
        Good luck enforcing such a claim. The damages part will be especially interesting.
      - secabeen 12y ago
        There's a history of buzzfeed and other link-farm sites writing inflammatory posts based on TMC forum posts. Many posters don't want their content stolen that way, so they put on those notices.
    - jonah 12y ago
      Being possibly the first photos of the inside of a Model S battery sled, I understand his desire to protect them from getting spread around and used by others. Seems sensible to me.
      - jonknee 12y ago
        So people don't accidentally learn something? If you take the time to post the photos I don't know why you would not want people to see them. I could see his point if he was running a Tesla related business or that was his website, but he just seems like an enthusiast.
    - toomuchtodo 12y ago
      Hey bigiain! I'm the one who initiated the archive against the page(s) in question. While I understand copyright is important, I also believe in the preservation of digital history on the internet. The page in question isn't password protected, nor were the images prevented by the Internet Archiver's archive process from committing the page to their archive. The author still receives their attribution, and The Archive is fairly solid in the non-profit category (which I believe respects the copyright owner's wishes).
      - bigiain 12y ago
        The copyright owners wishes are very well explained: "Images I post in this thread and my related commentary are posted and published by me, the original photographer. All copyrights and all other rights reserved. These images may not be copied or otherwise distributed outside of this forum without my express permission." To me, it pretty clear that initiating an archive against that page was explicitly ignoring the copyright owners wishes, not respecting them, and placing your belief in "preservation of digital history" above the rights of the person who took the photos. I'm conflicted, because like you I'd hate to see those images vanish - but I now strongly suspect _next_ time this guy takes some pictures of something I'm fascinated by, he won't be posting them publicly any more. (And you do know "but we gave you _attribution!_" is about the lamest and most infuriating thing you can say to a rightsholder who's copyright you're violating, right? And probably one of the favourite things their lawyers can possibly have in writing...)
        jacquesm 12y ago
        You're absolutely right but this is a strange situation. It would take a pretty good NLP to figure out that this is the case and all things otherwise being equal I don't know how the archive would be told not to archive certain data if not through robots.txt, which is the non-human readable form. Otherwise you could always use the absence of either to do an end-run around the other. So for practical reasons it is probably best to claim both copyright on the page and to set up robots.txt to specifically forbid those pieces that you don't want spread around from being indexed/archived. In the eyes of the law probably only the copyright bit matters.
phkahler 12y ago
I think he's wrong about one thing. A good BMS not only monitors cell voltages, it has the ability to bypass some charging current around individual cells. Not a lot, but enough to balance the charge of all cells over a cycle. That capability can do wonders for the reliability and life of a pack. While I worked in EVs for 6 years, I have no knowledge of the Tesla BMS - they were not our customer and I worked mostly in motor control anyway.
- probablyrobots 12y ago
  Here is the spec sheet for the main square chip on that board. http://www.ti.com/lit/ds/symlink/bq76pl536a-q1.pdf http://www.ti.com/lit/ds/symlink/bq76pl536a-q1.pdf You're right. It does have a cell balancing feature.
  - jacquesm 12y ago
    Where is the actuation mechanism for that that though? There does not appear to be any circuitry for that here. At a minimum you'd need something that would engage/disengage the cells, either a FET or a IGBT. (the voltage drop on other devices would be too large).
    - SpacemanSpiff 12y ago
      Take a look at http://files.wizkid057.com/teslapack/update2/Tesla%20BMS%20Module%20-%20Front.jpg http://files.wizkid057.com/teslapack/update2/Tesla%20BMS%20M... For cell #1, my guess is that the 4 parallel resistors (R3) are the balancing resistors and that Q1 is a small logic level MOSFET which enables cell balancing. On a BMS project I'm working on balancing current is only 250mA, so a small SOT-23 MOSFET is all you would need.
      - jacquesm 12y ago
        Good eye. There are exactly 6 of those so yes, you are very likely right!
aresant 12y ago
I had a similar appreciation reading this that I felt for the original iPhone tear-aparts by ifixit and their brethren. EG - looking at a truly innovative use of existing technologies pushed to their limit and engineered to a sum greater than their individual parts. Makes me want a Tesla even more.
Gracana 12y ago
Interesting to compare this to the ford fusion battery[1], which uses clever construction to prevent a technician from being exposed to high voltages during construction and teardown. [1] http://www.etotheipiplusone.net/?p=3109 http://www.etotheipiplusone.net/?p=3109
- v13inc 12y ago
  That almost looks like it was built by a mechanical engineer, not an electrical engineer. All the effort seems to be focused on building a sturdy case for the batteries, and the actual electrical connections are all steel screw terminals and crimping, without any spot welding anywhere. I'd be worried about the electrical resistance of all those contacts, and the heat it produces. Tesla's battery pack seems like a more intelligent electrical design, with a barebones mechanical design to back it up.
  - jacquesm 12y ago
    At these elevated voltages the currents are manageable. If this were a 24V pack then your concerns would carry far more weight. The biggest issue is vibration loosening a connection in the longer term but there are plenty of time-tested ways to avoid that from happening. Even fork lift battery packs (which can carry immense currents) are still built using the crimp terminal/bolt through method.
  - cc439 12y ago
    Having a mechanical engineer drive the design of a battery pack isn't necessarily a bad thing, IMO it's the sensible route for a mass-market car made by a mass-market company. Modern high volume, quality focused manufacturing will often prioritize ease of assembly over elegance in design. Fewer, simpler steps make for fewer defects and greater product consistency. It's the whole "lean manufacturing" ideal at play, done right it will lower costs and improve quality to a point that you can splurge on a little engineering elegance such as a small-volume hybrid model capable of being assembled on the same line as your high-volume offerings. Tesla doesn't have to worry about this for now as they compete in a high-margin segment of the industry and they are trying to set a benchmark of excellence that will create demand for their products. A real world example I've seen in person is the Nissan Leaf. The battery is designed to be as safe as possible for handling by a line worker and that allows Nissan to produce the Leaf at the exact same time as plain vanilla Altimas are rolling down the line. If you ever take a tour of their Smyrna, TN plant you'll see 1 line with a 9 or 10 Altimas interspersed with a Leaf every once in a while. It's smart engineering at a production-level viewpoint as a "worse" battery allows an entirely different product to be produced with minimal production overhead.
clumsysmurf 12y ago
From what I've read these packs have around 7000 3100mAH NCR-18650s. Over the years I've used these NCRs (or lower mAH versions) individually in special flashlights - and while they seem to have good reliability overall, one did fail on me while charging. Thats why often hobbyists charge these outside in fireproof bags. I would be terrified to drive a car with this technology.
- greglindahl 12y ago
  18650 is the form factor. These cells don't use the usual chemistry. Do you really think that the form factor is dangerous?
  - clumsysmurf 12y ago
    Yes, of course 18650 is the form factor. From what I understand these are stock Panasonic NCR-18650 3100 mAH batteries though. Any ideas on what "special chemistry" they are using?
    - greglindahl 12y ago
      Every article I've seen about the battery says that it doesn't use the usual chemistry, and that only the form factor is standard. I figured you would have something factual to say, given that you're saying you know it's dangerous.
      - makomk 12y ago
        All the information I've seen says they use stock Panasonic NCR-18650A lithium ion batteries just like clumsysmurf said. (The "A" just means that it's the 3100mAH nominal capacity version - there are several NCR-18650 batteries with different capacities.) It's a fairly common 18650 battery, lots of laptops use this specific model.
      - clumsysmurf 12y ago
        I'm not sure what you are trying to do - but I almost fell for it. First, I specifically stated "3100mAH NCR-18650s" which is a specific part, not a form factor which anyone who handles these batteries would know - which was your first (confused) reply. Second, from everywhere I have read, like (1) these are just standard cells. Lastly, I was originally stating that I would feel unsafe being around this technology. I did not say "the technology is unsafe." If it makes you feel better, Tesla as a company gives me great hope and I am rooting for them. I do not have ties to anyone at all. It would have been nice if you could have simply pointed to some factual reason (like breser did above) why I shouldn't be worried. (1) http://www.greencarreports.com/news/1084682_what-goes-into-a-tesla-model-s-battery--and-what-it-may-cost http://www.greencarreports.com/news/1084682_what-goes-into-a...
awonga 12y ago
One problem I've had before was if one cell in a pack is damaged and replaced, the BMS balance current would take forever to flatten the pack. Do you know if Tesla has any way of improving or making this faster?
ck2 12y ago
Seems like there is a lot of room for improvement? Reducing the sheer number of casings on individual cells would radically reduce weight/volume. Then with less groups of cells you could actually have the BMS monitor them like my lifepo lithium battery for bicycle.
- aberkowitz 12y ago
  I'm pretty sure the casings are there for fire isolation
  - ck2 12y ago
    Yes but couldn't you have a casing that holds a dozen cells instead of a casing on each individual cell? If a cell burns it is going to take out its neighbors anyway. Or they could start to do something similar to LiFePo4 which will not burn.
- retroencabulato 12y ago
  Fuck safety, they should just stuff the door panels with cells!
- Gravityloss 12y ago
  There are reports that the casing is a significant portion of the pack price. It might not be that the number of layers makes it fundamentally expensive.But instead the design and manufacturing might not be yet very optimized.
jacquesm 12y ago
That was one very quick trip to the recycler, pack dates from August 2013. Crashed car? Totally nuts to work with DC voltages this high without taking safety precautions. Anything over 50V DC is to be treated with very serious respect. AC is different, you get a good number of opportunities to dis-engage, but with DC your muscles contract and that's that. I'd rather mess with 2 KV AC than with 200 V DC. Lovely engineering on that pack by the way, the number of safety features is very impressive. Sure looks a lot better on the inside than mine ever did! ( http://pics.camarades.com/d/90045-1/IM000398.JPG http://pics.camarades.com/d/90045-1/IM000398.JPG ) (That's only 48KWh but at 48V so much higher current) I think I've found the source of the pack: http://www.teslamotorsclub.com/showthread.php/32687-For-sale-Tesla-Model-S-85-kWh-main-lithium-battery-pack-with-less-then-500-miles-SOLD http://www.teslamotorsclub.com/showthread.php/32687-For-sale... Original asking price was $29K.
- hellgas00 12y ago
  Not sure where this myth started, the idea that somehow AC is less dangerous to handle at high voltages over DC. Wall socket AC alternates at ~50Hz, that's an oscillation every 0.02sec, for perspective, the average human reaction time is in the range of 0.15 to 0.3sec [Wikipedia]. There almost no chance that you willingly disengage a circuit once it's made for both high voltage AC or DC. Be careful whenever handling high voltage sources of electricity IN ALL CASES. Also, if you don't mind me asking, how much did your battery bank cost?
  - jacquesm 12y ago
    That's not a myth, it's a fact and reaction time has nothing to do with it. You're not consciously pulling back, your muscles will simply stop contracting for a short bit after which you (hopefully) disconnect. The DC damage is a condition called 'muscular tetanus'. The main risk with AC at medium voltages (say 40 to 250 V) is that your heart goes haywire. Though those voltages could easily kill you too. Yes, you should always be careful. But DC is most definitely more dangerous at the same voltage once you get over 48 V DC (the so called 'safe voltage', but that's a misnomer because under the wrong conditions voltages lower than that can still be fatal). The critical component by the way is current not voltage. Voltage really doesn't kill but current will. AC voltages are typically reported RMS, whereas with DC the 'peak' is also the average. Assuming the DC supply can produce as much current as the AC supply. Being shocked by neither is good. But the choice between 200V DC and 200V AC is a fairly easy one for me and I've been shocked multiple times by both during my very long time of taking stuff apart and fixing things (yes, I try very hard to avoid that). The AC ones were mostly non-events, the DC ones were (even at lower currents) things to remember years later. Quite possibly that's not correlated with safety but it is definitely a data point (or rather several of them). Avoiding being shocked is a very good way of never having to find out how accurate this all is. One particularly memorable incident was hooking myself accidentally to the HV supply of an old tube radio. Don't do that. And be extremely careful with capacitors and DC batteries, they can supply a ton of current long enough to kill you. HV transformers much less so. (At least, the ones that you would normally encounter outside of industrial gear). And I suspect that the internal resistance of those supplies has a lot to do with whether you're going to be dead or writing about your experiences because it has a very direct impact you the current resulting. HV AC supplies that will supply very high current are hard to find, usually are transformers with relatively thin secondary windings. A battery pack like this is made to supply 100's of Amps at 100's of volts. That's lethal, make no mistake about that. That battery bank cost $7200, 2005 or so prices. More than you ever wanted to know: http://www.allaboutcircuits.com/vol_1/chpt_3/4.html http://www.allaboutcircuits.com/vol_1/chpt_3/4.html
DanBlake 12y ago
Asides from price, why not engineer a battery that did not rely on 18650 cylindrical cells? Seems like a bit of extra weight and lost capacity/space by using tons of 18650 batteries which each have their own casing instead of just making a 'brick' style battery, similar to those found in mobile phones (but obviously much larger).
- jacquesm 12y ago
  The ability to fuse the cells individually is a huge benefit. That means that if a cell shorts out internally only that little bit of capacity will disappear.
- bjackman 12y ago
  Hopefully someone knowledgeable can elucidate properly but I believe cylinders are an inherently good shape for certain types of battery. The internal chemical process relies on two surfaces being in contact. You can roll up two surfaces and put them inside a cylinder which gives you lots of contact surface area in a small volume.
  - jacquesm 12y ago
    And a space in between to cool them. Charging and discharging a battery goes through Ri (the internal resistance of the battery) and as a result they get warm or even hot if not adequately cooled.
- hellgas00 12y ago
  In a video Musk addressed this. The 18650 batteries are produced on such a large scale that they provide the cheapest source of prefabricated batteries on the market. I would guess that this would change once the Tesla battery production facility opens, and they can tool for a battery that better fits their needs. I wonder as well if the honeycomb type structure formed is inherently less prone to structural deformation.
- marvin 12y ago
  I'm pretty sure that the cell form factor was a very deliberate cost/benefit decision. The 18650 cell is the most-produced Li-Ion battery cell in the world, and Tesla has been enjoying the benefits of low prices on these cells as Roadster/Model S/Model X battery pack development has coincided with the switch to laptop form factors where this battery cell doesn't fit. In fact, Panasonic has re-opened production lines for these cells that were shuttered due to falling demand, due to purchase agreements with Tesla. Tesla's incredible demand for batteries means that cell choice is a very important decision. It's worth noting that Tesla's engineering leadership has indicated they are both form-factor and chemistry agnostic, and will always go with the option that makes most economic sense.
allegory 12y ago
That's pretty interesting and is testament to the versatility of the 18650 cell package! I'm rebuilding ThinkPad X200 9-cell this weekend that is filled with 18650s and repaired a PBX about 15 years ago that had them in it so they appear literally everywhere.
zizzer 12y ago
Anyone else notice that in the Tyco contactor picture it's labelled "Coil 3.14 Ohms"? It makes me think they only needed it to be 3 Ohms, but an engineer somewhere couldn't resist making it πΩ
- lotsofmangos 12y ago
  It might be to normalise other components to nice units, given that pi turns up when calculating the inductance of a coil.
beagle90 12y ago
Can we hurry with the electric buses already...
mercnet 12y ago
Are the QR codes only used for manufacturing lines or tech support? It would be awesome if there was an open database where I could find replacement parts for particular devices.

264 points by cyanoacry 12y ago

deleted 12y ago

[deleted]

Pictures wouldn't load so I used https://web.archive.org/web/20140910232549/http://www.teslamotorsclub.com/showthread.php/34934-Pics-Info-Inside-the-battery-pack https://web.archive.org/web/20140910232549/http://www.teslam... thanks again archive.org

toomuchtodo 12y ago
Glad the archive I did yesterday was useful! :)
jonah 12y ago
It appears he was serving them off his personal NAS. Whoops.
- bigiain 12y ago
  His copyright notice and explanatory paragraphs make it clear he's trying to keep some level of control over those photographs, while still sharing them with "his community" - which means I feel a little uneasy about having archive.org unilaterally slurp the images up like that... I know it's kind of a losing battle, but "publicly available" does not mean "in public domain".
  - jacquesm 12y ago
    How do you feel about google images?
    - bigiain 12y ago
      Pretty much the same - "uneasy". I'm enormously grateful it exists when I want to use it, but still have a distinct feeling it's "not OK" to do that with other people's images (and especially not just relying on the "but you didn't put anything in robots.txt to say we couldn't do whatever the hell we wanted with your pictures! And we _credited_ you!!!" excuse).
  - greglindahl 12y ago
    Archive.org respects robots.txt. Nothing unilateral about it.
    - bigiain 12y ago
      How many of the webforums you post on give you access to update the robots.txt file to inform Internet Archive about your copyright desires? Like I said - I'm conflicted about this, I _want_ these images to be available, and whatever the guy wrote in his forum post we know Google (and Blekko!) will index and download them and will pretty soon be causing them to be "otherwise distributed outside of this forum" - but the guy's wishes are clear, even if not explicitly machine-readable.
      - greglindahl 12y ago
        The photos aren't on the forum, they are on an image hosting website. Other images on the forum are hosted on the forum. If the guy knows how to host his images elsewhere, he should be able to figure out how to host the images someplace with a robots.txt that he likes.
      - deleted 12y ago
        [deleted]
  - dublinben 12y ago
    I've never seen such an aggressive and hostile copyright notice in a forum signature before. It's not entirely clear that you can even claim copyright over trivial online comments.
    - tokenadult 12y ago
      It's not entirely clear that you can even claim copyright over trivial online comments. Trivial or not, you have copyright in your own writings, online or off-line. Each participant on HN owns the copyright in the written expression of his or her comments. Similarly, a photographer has copyright in photographs taken by that photographer. See a user profile of a high-karma HN participant https://news.ycombinator.com/user?id=tptacek https://news.ycombinator.com/user?id=tptacek for an example of asserting copyright in HN comments, something that any of us could do, because the copyright is already there under modern copyright law, and asserting the copyright openly and publicly helps battle infringement.
      - nitrogen 12y ago
        There is the complication that photographs of 2D works of art intended to represent the original are not subject to copyright, so some of those photos might not be either if someone with enough money wanted to press the issue. (Not a lawyer)
      - dublinben 12y ago
        A work must be creative enough to earn copyright. Most tweets would not qualify, for example. You can assert anything you want without it being legally enforceable.
      - jacquesm 12y ago
        Good luck enforcing such a claim. The damages part will be especially interesting.
    - secabeen 12y ago
      There's a history of buzzfeed and other link-farm sites writing inflammatory posts based on TMC forum posts. Many posters don't want their content stolen that way, so they put on those notices.
  - jonah 12y ago
    Being possibly the first photos of the inside of a Model S battery sled, I understand his desire to protect them from getting spread around and used by others. Seems sensible to me.
    - jonknee 12y ago
      So people don't accidentally learn something? If you take the time to post the photos I don't know why you would not want people to see them. I could see his point if he was running a Tesla related business or that was his website, but he just seems like an enthusiast.
  - toomuchtodo 12y ago
    Hey bigiain! I'm the one who initiated the archive against the page(s) in question. While I understand copyright is important, I also believe in the preservation of digital history on the internet. The page in question isn't password protected, nor were the images prevented by the Internet Archiver's archive process from committing the page to their archive. The author still receives their attribution, and The Archive is fairly solid in the non-profit category (which I believe respects the copyright owner's wishes).
    - bigiain 12y ago
      The copyright owners wishes are very well explained: "Images I post in this thread and my related commentary are posted and published by me, the original photographer. All copyrights and all other rights reserved. These images may not be copied or otherwise distributed outside of this forum without my express permission." To me, it pretty clear that initiating an archive against that page was explicitly ignoring the copyright owners wishes, not respecting them, and placing your belief in "preservation of digital history" above the rights of the person who took the photos. I'm conflicted, because like you I'd hate to see those images vanish - but I now strongly suspect _next_ time this guy takes some pictures of something I'm fascinated by, he won't be posting them publicly any more. (And you do know "but we gave you _attribution!_" is about the lamest and most infuriating thing you can say to a rightsholder who's copyright you're violating, right? And probably one of the favourite things their lawyers can possibly have in writing...)
      - jacquesm 12y ago
        You're absolutely right but this is a strange situation. It would take a pretty good NLP to figure out that this is the case and all things otherwise being equal I don't know how the archive would be told not to archive certain data if not through robots.txt, which is the non-human readable form. Otherwise you could always use the absence of either to do an end-run around the other. So for practical reasons it is probably best to claim both copyright on the page and to set up robots.txt to specifically forbid those pieces that you don't want spread around from being indexed/archived. In the eyes of the law probably only the copyright bit matters.

phkahler 12y ago

I think he's wrong about one thing. A good BMS not only monitors cell voltages, it has the ability to bypass some charging current around individual cells. Not a lot, but enough to balance the charge of all cells over a cycle. That capability can do wonders for the reliability and life of a pack. While I worked in EVs for 6 years, I have no knowledge of the Tesla BMS - they were not our customer and I worked mostly in motor control anyway.

probablyrobots 12y ago
Here is the spec sheet for the main square chip on that board. http://www.ti.com/lit/ds/symlink/bq76pl536a-q1.pdf http://www.ti.com/lit/ds/symlink/bq76pl536a-q1.pdf You're right. It does have a cell balancing feature.
- jacquesm 12y ago
  Where is the actuation mechanism for that that though? There does not appear to be any circuitry for that here. At a minimum you'd need something that would engage/disengage the cells, either a FET or a IGBT. (the voltage drop on other devices would be too large).
  - SpacemanSpiff 12y ago
    Take a look at http://files.wizkid057.com/teslapack/update2/Tesla%20BMS%20Module%20-%20Front.jpg http://files.wizkid057.com/teslapack/update2/Tesla%20BMS%20M... For cell #1, my guess is that the 4 parallel resistors (R3) are the balancing resistors and that Q1 is a small logic level MOSFET which enables cell balancing. On a BMS project I'm working on balancing current is only 250mA, so a small SOT-23 MOSFET is all you would need.
    - jacquesm 12y ago
      Good eye. There are exactly 6 of those so yes, you are very likely right!

aresant 12y ago

I had a similar appreciation reading this that I felt for the original iPhone tear-aparts by ifixit and their brethren. EG - looking at a truly innovative use of existing technologies pushed to their limit and engineered to a sum greater than their individual parts. Makes me want a Tesla even more.

Gracana 12y ago

Interesting to compare this to the ford fusion battery[1], which uses clever construction to prevent a technician from being exposed to high voltages during construction and teardown. [1] http://www.etotheipiplusone.net/?p=3109 http://www.etotheipiplusone.net/?p=3109

v13inc 12y ago
That almost looks like it was built by a mechanical engineer, not an electrical engineer. All the effort seems to be focused on building a sturdy case for the batteries, and the actual electrical connections are all steel screw terminals and crimping, without any spot welding anywhere. I'd be worried about the electrical resistance of all those contacts, and the heat it produces. Tesla's battery pack seems like a more intelligent electrical design, with a barebones mechanical design to back it up.
- jacquesm 12y ago
  At these elevated voltages the currents are manageable. If this were a 24V pack then your concerns would carry far more weight. The biggest issue is vibration loosening a connection in the longer term but there are plenty of time-tested ways to avoid that from happening. Even fork lift battery packs (which can carry immense currents) are still built using the crimp terminal/bolt through method.
- cc439 12y ago
  Having a mechanical engineer drive the design of a battery pack isn't necessarily a bad thing, IMO it's the sensible route for a mass-market car made by a mass-market company. Modern high volume, quality focused manufacturing will often prioritize ease of assembly over elegance in design. Fewer, simpler steps make for fewer defects and greater product consistency. It's the whole "lean manufacturing" ideal at play, done right it will lower costs and improve quality to a point that you can splurge on a little engineering elegance such as a small-volume hybrid model capable of being assembled on the same line as your high-volume offerings. Tesla doesn't have to worry about this for now as they compete in a high-margin segment of the industry and they are trying to set a benchmark of excellence that will create demand for their products. A real world example I've seen in person is the Nissan Leaf. The battery is designed to be as safe as possible for handling by a line worker and that allows Nissan to produce the Leaf at the exact same time as plain vanilla Altimas are rolling down the line. If you ever take a tour of their Smyrna, TN plant you'll see 1 line with a 9 or 10 Altimas interspersed with a Leaf every once in a while. It's smart engineering at a production-level viewpoint as a "worse" battery allows an entirely different product to be produced with minimal production overhead.

clumsysmurf 12y ago

From what I've read these packs have around 7000 3100mAH NCR-18650s. Over the years I've used these NCRs (or lower mAH versions) individually in special flashlights - and while they seem to have good reliability overall, one did fail on me while charging. Thats why often hobbyists charge these outside in fireproof bags. I would be terrified to drive a car with this technology.

greglindahl 12y ago
18650 is the form factor. These cells don't use the usual chemistry. Do you really think that the form factor is dangerous?
- clumsysmurf 12y ago
  Yes, of course 18650 is the form factor. From what I understand these are stock Panasonic NCR-18650 3100 mAH batteries though. Any ideas on what "special chemistry" they are using?
  - greglindahl 12y ago
    Every article I've seen about the battery says that it doesn't use the usual chemistry, and that only the form factor is standard. I figured you would have something factual to say, given that you're saying you know it's dangerous.
    - makomk 12y ago
      All the information I've seen says they use stock Panasonic NCR-18650A lithium ion batteries just like clumsysmurf said. (The "A" just means that it's the 3100mAH nominal capacity version - there are several NCR-18650 batteries with different capacities.) It's a fairly common 18650 battery, lots of laptops use this specific model.
    - clumsysmurf 12y ago
      I'm not sure what you are trying to do - but I almost fell for it. First, I specifically stated "3100mAH NCR-18650s" which is a specific part, not a form factor which anyone who handles these batteries would know - which was your first (confused) reply. Second, from everywhere I have read, like (1) these are just standard cells. Lastly, I was originally stating that I would feel unsafe being around this technology. I did not say "the technology is unsafe." If it makes you feel better, Tesla as a company gives me great hope and I am rooting for them. I do not have ties to anyone at all. It would have been nice if you could have simply pointed to some factual reason (like breser did above) why I shouldn't be worried. (1) http://www.greencarreports.com/news/1084682_what-goes-into-a-tesla-model-s-battery--and-what-it-may-cost http://www.greencarreports.com/news/1084682_what-goes-into-a...

awonga 12y ago

One problem I've had before was if one cell in a pack is damaged and replaced, the BMS balance current would take forever to flatten the pack. Do you know if Tesla has any way of improving or making this faster?

ck2 12y ago

Seems like there is a lot of room for improvement? Reducing the sheer number of casings on individual cells would radically reduce weight/volume. Then with less groups of cells you could actually have the BMS monitor them like my lifepo lithium battery for bicycle.

aberkowitz 12y ago
I'm pretty sure the casings are there for fire isolation
- ck2 12y ago
  Yes but couldn't you have a casing that holds a dozen cells instead of a casing on each individual cell? If a cell burns it is going to take out its neighbors anyway. Or they could start to do something similar to LiFePo4 which will not burn.
retroencabulato 12y ago
Fuck safety, they should just stuff the door panels with cells!
Gravityloss 12y ago
There are reports that the casing is a significant portion of the pack price. It might not be that the number of layers makes it fundamentally expensive.But instead the design and manufacturing might not be yet very optimized.

jacquesm 12y ago

That was one very quick trip to the recycler, pack dates from August 2013. Crashed car? Totally nuts to work with DC voltages this high without taking safety precautions. Anything over 50V DC is to be treated with very serious respect. AC is different, you get a good number of opportunities to dis-engage, but with DC your muscles contract and that's that. I'd rather mess with 2 KV AC than with 200 V DC. Lovely engineering on that pack by the way, the number of safety features is very impressive. Sure looks a lot better on the inside than mine ever did! ( http://pics.camarades.com/d/90045-1/IM000398.JPG http://pics.camarades.com/d/90045-1/IM000398.JPG ) (That's only 48KWh but at 48V so much higher current) I think I've found the source of the pack: http://www.teslamotorsclub.com/showthread.php/32687-For-sale-Tesla-Model-S-85-kWh-main-lithium-battery-pack-with-less-then-500-miles-SOLD http://www.teslamotorsclub.com/showthread.php/32687-For-sale... Original asking price was $29K.

hellgas00 12y ago
Not sure where this myth started, the idea that somehow AC is less dangerous to handle at high voltages over DC. Wall socket AC alternates at ~50Hz, that's an oscillation every 0.02sec, for perspective, the average human reaction time is in the range of 0.15 to 0.3sec [Wikipedia]. There almost no chance that you willingly disengage a circuit once it's made for both high voltage AC or DC. Be careful whenever handling high voltage sources of electricity IN ALL CASES. Also, if you don't mind me asking, how much did your battery bank cost?
- jacquesm 12y ago
  That's not a myth, it's a fact and reaction time has nothing to do with it. You're not consciously pulling back, your muscles will simply stop contracting for a short bit after which you (hopefully) disconnect. The DC damage is a condition called 'muscular tetanus'. The main risk with AC at medium voltages (say 40 to 250 V) is that your heart goes haywire. Though those voltages could easily kill you too. Yes, you should always be careful. But DC is most definitely more dangerous at the same voltage once you get over 48 V DC (the so called 'safe voltage', but that's a misnomer because under the wrong conditions voltages lower than that can still be fatal). The critical component by the way is current not voltage. Voltage really doesn't kill but current will. AC voltages are typically reported RMS, whereas with DC the 'peak' is also the average. Assuming the DC supply can produce as much current as the AC supply. Being shocked by neither is good. But the choice between 200V DC and 200V AC is a fairly easy one for me and I've been shocked multiple times by both during my very long time of taking stuff apart and fixing things (yes, I try very hard to avoid that). The AC ones were mostly non-events, the DC ones were (even at lower currents) things to remember years later. Quite possibly that's not correlated with safety but it is definitely a data point (or rather several of them). Avoiding being shocked is a very good way of never having to find out how accurate this all is. One particularly memorable incident was hooking myself accidentally to the HV supply of an old tube radio. Don't do that. And be extremely careful with capacitors and DC batteries, they can supply a ton of current long enough to kill you. HV transformers much less so. (At least, the ones that you would normally encounter outside of industrial gear). And I suspect that the internal resistance of those supplies has a lot to do with whether you're going to be dead or writing about your experiences because it has a very direct impact you the current resulting. HV AC supplies that will supply very high current are hard to find, usually are transformers with relatively thin secondary windings. A battery pack like this is made to supply 100's of Amps at 100's of volts. That's lethal, make no mistake about that. That battery bank cost $7200, 2005 or so prices. More than you ever wanted to know: http://www.allaboutcircuits.com/vol_1/chpt_3/4.html http://www.allaboutcircuits.com/vol_1/chpt_3/4.html

DanBlake 12y ago

Asides from price, why not engineer a battery that did not rely on 18650 cylindrical cells? Seems like a bit of extra weight and lost capacity/space by using tons of 18650 batteries which each have their own casing instead of just making a 'brick' style battery, similar to those found in mobile phones (but obviously much larger).

jacquesm 12y ago
The ability to fuse the cells individually is a huge benefit. That means that if a cell shorts out internally only that little bit of capacity will disappear.
bjackman 12y ago
Hopefully someone knowledgeable can elucidate properly but I believe cylinders are an inherently good shape for certain types of battery. The internal chemical process relies on two surfaces being in contact. You can roll up two surfaces and put them inside a cylinder which gives you lots of contact surface area in a small volume.
- jacquesm 12y ago
  And a space in between to cool them. Charging and discharging a battery goes through Ri (the internal resistance of the battery) and as a result they get warm or even hot if not adequately cooled.
hellgas00 12y ago
In a video Musk addressed this. The 18650 batteries are produced on such a large scale that they provide the cheapest source of prefabricated batteries on the market. I would guess that this would change once the Tesla battery production facility opens, and they can tool for a battery that better fits their needs. I wonder as well if the honeycomb type structure formed is inherently less prone to structural deformation.
marvin 12y ago
I'm pretty sure that the cell form factor was a very deliberate cost/benefit decision. The 18650 cell is the most-produced Li-Ion battery cell in the world, and Tesla has been enjoying the benefits of low prices on these cells as Roadster/Model S/Model X battery pack development has coincided with the switch to laptop form factors where this battery cell doesn't fit. In fact, Panasonic has re-opened production lines for these cells that were shuttered due to falling demand, due to purchase agreements with Tesla. Tesla's incredible demand for batteries means that cell choice is a very important decision. It's worth noting that Tesla's engineering leadership has indicated they are both form-factor and chemistry agnostic, and will always go with the option that makes most economic sense.

allegory 12y ago

That's pretty interesting and is testament to the versatility of the 18650 cell package! I'm rebuilding ThinkPad X200 9-cell this weekend that is filled with 18650s and repaired a PBX about 15 years ago that had them in it so they appear literally everywhere.

zizzer 12y ago

Anyone else notice that in the Tyco contactor picture it's labelled "Coil 3.14 Ohms"? It makes me think they only needed it to be 3 Ohms, but an engineer somewhere couldn't resist making it πΩ

lotsofmangos 12y ago
It might be to normalise other components to nice units, given that pi turns up when calculating the inductance of a coil.

beagle90 12y ago

Can we hurry with the electric buses already...

mercnet 12y ago

Are the QR codes only used for manufacturing lines or tech support? It would be awesome if there was an open database where I could find replacement parts for particular devices.