Inside a Tesla Model S Battery Pack
teslamotorsclub.com
teslamotorsclub.com
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 )
(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...
Original asking price was $29K.
Also, if you don't mind me asking, how much did your battery bank cost?
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:
Let me give a couple of reasons why AC just as dangerous as DC.
1) Your body shares some of the same characteristics a capacitor, a capacitor with small capacitance, but one none the less. This means that an AC current can shock you without forming a classical circuit that would be needed for a shock from DC.
2) You mention RMS as a reason why AC is safer? The root mean squared voltage of AC is going to be less then the peak voltage induced by the name plate voltage. Wall socket voltage may by 120V RMS but will peak around 170V.
3) With a peak voltage of 170V the current through a resistor (like a human body) is going to be ~40% greater than that of an average 120V for DC. Stating that current kills but voltage doesn't is also ridiculous (unless you are talking about static charges). It would be like saying that the flow rate of water down a stream is dependent on the amount of water in the stream and not the speed of the flowing water. The fallacy is also point out in the link your provided.
4) Hearts are much more likely to suffer from complication due alternating current than from direct current
Again, I stand by my initial assertion, both AC and DC are just as dangerous. Anecdotal stories, while entertaining, don't mean much considering that you may have been hydrated while dealing with DC, which can increase the bodies internal resistance greatly. You may have been more grounded, you may have been touching a piece of metal that was grounded, the circuit may have been created across the chest which gives a nasty shock. There are many external variables which can alter your perception of what it feeling like while being electrocuted.
Here is a good video about that: https://www.youtube.com/watch?v=8xONZcBJh5A
never went near dc hv stuff with isolation so never got a chock from that yet. i intend to keep it that way
The house sold a few years ago.
Apparently the DC current required is 10 times higher to do comparable damage than the AC current. This is totally at odds with both my first-hand experience and a ton of interaction with professionals. So I'm a bit confused now, there is a whole pile of literature out there that says one thing and then the wikipedia page claims the factor of 10 going the other way, citing a book that I don't have access to.
The fact that the electrical chair is AC was possibly a hint, but the electrical chair was developed during the 'current wars' by the AC proponents. (I'm not sure if they tried to convey the idea that AC was more dangerous that way, it seemed to have been an ill thought out decision from a marketing point of view.)
I'll keep looking and reading to see if I can find an authority that decisively claims either the one or the other.
The factor of 10 seems hard to believe, to generate a 30 mA current through a human body at 230VAC would become 2300V DC for a 300 mA current through that same body (per Ohms law), that's ~800 Watts delivered versus ~80.
2300V 300mA sources are hard to come by but a 600V DC source that can do only a few mA will blow you clear across the room, which makes me wonder what would happen if you happened to interact with a source that is capable of substantially more than that. This would also mean that a 300V DC source such as that battery pack should be perfectly safe to work with but I don't believe that's true for even a moment.
So, my apologies for the unsourced rejection of your claim, to be continued.
By the DC proponents. Or AC opponents. Definitely part of a long campaign to try to make AC appear dangerous.
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.
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.
thanks again archive.org
I know it's kind of a losing battle, but "publicly available" does not mean "in public domain".
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.
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).
"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...)
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.
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).
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
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.
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.
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.
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.
Love that warning.
"Do not look at it funny or it will explode and you will die."
http://www.flightglobal.com/news/articles/elon-musk-boeing-7...
"Large cells without enough space between them to isolate against the cell-to-cell thermal domino effect means it is simply a matter of time before there are more incidents of this nature," he adds.
"Moreover, when thermal runaway occurs with a big cell, a proportionately larger amount of energy is released and it is very difficult to prevent that energy from then heating up the neighboring cells and causing a domino effect that results in the entire pack catching fire," says Musk.
"They [Boeing] believe they have this under control, although I think there is aUnfortunately, the pack architecture supplied to Boeing is inherently unsafe," writes Musk in an email to Flightglobal.
"The fundamental safety issue with the architecture of a pack with large cells," writes Musk in an email. "It is much harder to maintain an even temperature in a large cell, as the distance from the center of the cell to the edge is much greater, which increases the risk of thermal runaway."
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.
I wonder as well if the honeycomb type structure formed is inherently less prone to structural deformation.
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.
Do you know if Tesla has any way of improving or making this faster?
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.
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.
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.
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.
I would be terrified to drive a car with this technology.
From what I understand these are stock Panasonic NCR-18650 3100 mAH batteries though.
Any ideas on what "special chemistry" they are using?
It's a fairly common 18650 battery, lots of laptops use this specific model.
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...
I'm sure given the 'right' conditions you could get a catastrophic release of energy out of a pack this size but I'm fairly certain that the occupants of the car would not be in a state where they would realize that the battery had also exploded since they'd be too distracted by evaporating themselves.
I think what needs to be done is to build a car around many gallons of highly flammable liquid.
I am not terrified to drive a car with that technology.