
Inside a Tesla Model S Battery Pack - cyanoacry
http://www.teslamotorsclub.com/showthread.php/34934-Pics-Info-Inside-the-battery-pack
======
jacquesm
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...](http://www.teslamotorsclub.com/showthread.php/32687-For-sale-Tesla-
Model-S-85-kWh-main-lithium-battery-pack-with-less-then-500-miles-SOLD)

Original asking price was $29K.

~~~
hellgas00
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
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)

~~~
hellgas00
You kind of jump around from point to point. If your hand is wrapped around a
a source of electricity (Assuming that it's not static charge and can provide
a current equal to the source voltage over your bodies resistance) I'm sorry
but you are not going to let go, even if you are hanging from the wire. Until
a formation of soot has formed and the oils in your hands have burned off to
increase the resistance, there is no letting go.

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.

~~~
jacquesm
See other comment lower in the thread.

------
phkahler
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
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
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
Take a look at
[http://files.wizkid057.com/teslapack/update2/Tesla%20BMS%20M...](http://files.wizkid057.com/teslapack/update2/Tesla%20BMS%20Module%20-%20Front.jpg)

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
Good eye. There are exactly 6 of those so yes, you are very likely right!

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

thanks again archive.org

~~~
jonah
It appears he was serving them off his personal NAS. Whoops.

~~~
bigiain
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".

~~~
dublinben
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
_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.

~~~
dublinben
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.

------
Gracana
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
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.

~~~
cc439
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.

------
DanBlake
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).

~~~
hemancuso
Isn't that the type of cell the 777 use(s/d)? I think Elon Musk very addressed
the issue pretty well.

[http://www.flightglobal.com/news/articles/elon-musk-
boeing-7...](http://www.flightglobal.com/news/articles/elon-musk-
boeing-787-battery-fundamentally-unsafe-381627/)

"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."

~~~
idlewords
787

~~~
hemancuso
Indeed, oops

------
aresant
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.

------
zizzer
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
It might be to normalise other components to nice units, given that pi turns
up when calculating the inductance of a coil.

------
awonga
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
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
I'm pretty sure the casings are there for fire isolation

~~~
ck2
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.

------
allegory
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.

------
mercnet
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.

------
beagle90
Can we hurry with the electric buses already...

------
clumsysmurf
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
18650 is the form factor. These cells don't use the usual chemistry. Do you
really think that the form factor is dangerous?

~~~
clumsysmurf
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
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.

~~~
clumsysmurf
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...](http://www.greencarreports.com/news/1084682_what-goes-into-a-tesla-
model-s-battery--and-what-it-may-cost)

~~~
deeviant
Yeah, I would be terrified of driving around in a car that's basically a metal
box around a bomb ready to go, those batteries are deadly.

I think what needs to be done is to build a car around many gallons of highly
flammable liquid.

~~~
clumsysmurf
I'm waiting for Mr Fusion.

