Aug 27, 2014
ch_model_s
The NCR1850B can deliver 2C. I found not mutch for the NCR18650BE but it looks like its also rated for 2C or less. The 18650PD can deliver 10A which is more then 3C. And the 18650G is not yet on the market maybe for OEMs. http://www.dampfakkus.de/akku_liste-nach-marke.php?marke=Panasonic�
Aug 27, 2014
magnet Hopefully wk057 can get to the bottom of this. I'm working on a quick conversation. I dont know the inner working but what I've been told is it is not a tradition bmsbms means battery mangagement system which also does the balancingor bms means battery monitoring system with no balancing at allas I understand it what Telsa has done in separate the two functionsso there is a Global BMonitorS and a distributed BManageS. How they do the balancing is a trade secret wk057 can reveal�
Aug 27, 2014
magnet You need to hack the service port. This may help:
Some of the disclosed embodiments define and include a dedicated service port that allows for an electrical connection to the battery pack that is independent of CAN communication, separate from the electrical connection to the operating environment, and not required to simulate the some aspect of that environment (e.g., drivetrain electrical signature). A dedicated service port with direct access to a cell side of battery contactors of the battery pack would also simplify the complexity of an external discharge tool to allow it to more easily work across multiple vehicle designs.
Patent US20130307478 - Secondary service port for high voltage battery packs - Google Patents
Who ever figures out a way to use this packs as-is for off-grid energy storage is going to make a lot of money and respect
I agree 48V is the most practical voltage to work with. You don't need conduit for many 48V systems so you don't need an electrician in some instances, but a plug and play 400V wall mount energy storage pack would be awesome for advanced users
�
Aug 27, 2014
magnet The present invention includes two contemplated mechanisms for adjusting a brick 20 voltage. One is to decrease the brick 20 voltage by discharging the brick 20 by connecting a small load to the brick 20 (discharge mechanism). The other is to increase the brick 20 voltage and charge the brick 20 by connecting a source of power to the brick 20 (charge mechanism). Either mechanism may be used with the described methodology.
[036] It should be noted that the mechanism that raises the voltage of the lowest brick up to the level of the highest brick is contemplated to be implemented by only using energy from other bricks in the sheet 12 or battery pack 10 and/or may be from other residual energy collected during operation of the vehicle. It should be noted that the mechanism of raising the voltage of the lowest brick up to the level of the highest brick may lead to a more efficient methodology and ESS 10. This efficiency will be achieved through the use of energy being shifted and moved between bricks 20 and not bled as in the discharge mechanism. Therefore, the redistribution of the energy among the bricks 20 will lead to a more efficient system and increased range of the vehicle. It should be noted that the sampling of voltages occur at intervals that will allow for a constant movement of the target balance voltage for the highest brick voltage of the battery pack 10 and/or sheet 12 to be constantly adjusted in either an upward or downward direction depending on the energy shift between battery bricks 20 during operation of the alternate methodology.�
Aug 27, 2014
scaesare OK, thanks for the clarification.�
Aug 27, 2014
wk057 Well, I've been hesitant to post any pictures of the BMS components. The pack is one thing, the BMS is something that I don't believe anyone else has posted. Still arguing with myself about it.
I removed some parts, temporarily, from around the oddball module (the high one in the front) so that I could see more of the BMS.
There are six sets of four 158 ohm chip resistors in parallel (so about 40 ohms) on the individual BMS boards on the modules. This comes out to nearly exactly 100mA of current at 4.2V, about 0.42W of power dissipated. Should be fine for the four resistors. These are almost certainly used for balancing, since this is pretty much what I calculated out as would be needed to correct a 1% imbalance in < 24 hours.
The chip that appears to be the main chip on this board seems to have no part number or anything on it.
There is one LED on the board (not illuminated in my case). I wonder if it illuminates at all inside the closed pack?
All connections to the battery sub-modules are fused on the PCB.
The back of the PCB appears to only contain connectors for connecting to each sub-module, as well as the daisy chain connector for connecting each board together to the master.
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One interesting thing is that the main fuse seems to be rated for 630A and are "fast acting". Fully charged at ~400V that's about 252kW. My P85 will do 320kW for short periods which would be ~800A... so I wonder if they upgrade the pack fuse for a P85, or if this fuse can handle that for short periods.
�
Aug 27, 2014
apacheguy S85's seem to max out at 320 kW. P85's can go as high as 370 kW.�
Aug 27, 2014
Matias Tesla's competitors have dissected packs long ago, so posting will do no harm to Tesla.�
Aug 27, 2014
spaceballs Roadster ESS sheet fuse is this http://www.discountfuse.com/v/vspfiles/downloadables/Ferraz/PDF/a50qs.pdf it�s slow blow type, i.e. takes ~1,800amps to blow this 400amp rated fuse in 1 second.
�
Aug 28, 2014
magnet Tesla has to walk the walk now that they are giving away all their patent to help speed the transition to electric drive
What better way to do it than do show us how to make safe battery packs. A truely failsafe BMS/BMB is the holy grail and something desperatley needed at all levels of the ev movement including flight, boats, ebikes, emotorcycles, and my solar powered aboomybox
As far as I am concerned Tesla has done really nothing innovative. Nothing radical just plain old fashion damn good engineering. I dont care anout falcons doors. If they start sharing their BMS and BMB tech that will be a good first step. What is stopping the EV revolution is battery life concerns and fire concerns. This all goes back to how you manage the batt not only balancing but charging and safety interlocks and robust EMI proof communications. I can already charge hobby grade lipo at 6C. We all know the 12C five minute charge is coming. TESLA: We only need your help on safety right now as a first step!
Tesla still the best car company and energy storage company in the world bar none. Don't get me wrong. They have brought aerospace level quality engineering and mfg to the car market. Their AC motor control is also pretty impressive efficiency wise but not the most advanced. I hope the next gen inverter for AWD torque vectoring will utilize Direct Torque Control. Motor control algorithms and torque vectoring algorithms they need to open source if they are sincere. They dont need to open source the central control system or anything too extreme, it is just thst faster we perfect AWD torque vectoring the faster we transition. Once you have experience true torque vectoring there is no going back, especially off road or on slippery tracks.�
Aug 28, 2014
tom66 They have the same battery part # so it seems unlikely. I wonder if this fuse popping is the cause of the dying batteries? It could explain why people experience a "pull over safely" event under high acceleration, freeway exit etc. Could just be the pack fuse popping.
You can be sure that almost every big competitor has taken a Tesla pack to pieces... we know Audi was testing the superchargers, and BMW too... you won't be revealing any unknown trade secrets/designs with pictures of the boards. Plus Tesla have gone open on their patents, so in the spirit of openness...�
Aug 28, 2014
scaesare I agree that any secret sauce has already been discovered by the competition.
Of course please don't do anything you feel uncomfortable about, but I personally wouldn't expect this to be an issue. And again, thank you for sharing what you've found thus far.. I find it very interesting...�
Aug 28, 2014
wk057 My concern with the photos of the BMS is that maybe someone notices something about them (or thinks they do) that could be blown out of proportion negatively. I wouldn't really want to be the source of that kind of drama, not that I've found anything about the pack disturbing or anything.
Anyway, I will probably be posting some pics after I study yhe boards a bit more myself.
I've tried contacting Tesla about perhaps getting a bit of insight into potentially utilizing the BMS... and so far I've been rejected.
Not a threat or ultimatum, so I hope no one takes this the wrong way, but if they (Tesla) aren't able or willing to help me interface with them then I'll probably post as much info as possible on the setup so that perhaps someone else could get some insight on how I could utilize it. Nothing personal, I like Tesla and all, but I am invested in my own project and would like it to succeed one way or another.�
Aug 28, 2014
wk057 Tesla suggested that I instead look into Solar City's battery pack instead of working on my own with the Model S pack.
I'm not 100% if I'm just hitting a slightly modified canned responses or not, so, I'm going to physically mail a couple of letters the old fashion way.�
Aug 28, 2014
lolachampcar I looked at SC and they are only doing pilot work in CA...... Nothing to buy here friend; move along.�
Aug 28, 2014
tom66 As a last resort, you could also try emailing key people in Tesla, for example Kurt Kelty, who is the battery systems manager at Tesla. They probably have more leverage than the people opening the letters.�
Aug 28, 2014
NigelM Mod Note: whole bunch of posts went here - Tesla patent move - Real world obligations? And please let's not descend into snippiness.�
Aug 28, 2014
wk057 Not sure. The sound people describe when this happens seems more like the contactor opening under high load. The fuse popping would be much less dramatic I think.
Although the fuse popping may cause the contactors to open also... no idea.
However, if it were simply the fuse, the fuse is easily accessed after disconnecting the pack from the vehicle. It has its own cover on the top (see my pics in the first post). So I would figure they would replace the fuse and not the whole pack since replacing the fuse would be simple.
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Sorry for sparking that discussion.
I think it is worth noting that I personally do not expect any help from Tesla regarding my particular project. While something simple like a pinout description for the low voltage connector on the pack would be nice, I'm not holding my breath, nor do I hold such a decision to withhold this info against them.�
Aug 28, 2014
magnet Note the fuse is rated at 690v but used at a little over 400V. I think this means the heat developed is less and the fuse is slower to pop. Clearing factor (amps squared seconds) would be ~.6 running these fuse on 400V. The fuse has to clear the voltage across it, it is not simply Amps squared times resitance heating. You would think the trip curve would be independent of voltage but it is more complicated than that�
Aug 29, 2014
tom66 Replacing the fuse would require high voltage training, arc flash gear, and additional paperwork. Maybe it's cheaper to only have the factory do refurbishments?�
Aug 30, 2014
wk057
I'm not sure where the voltage measurement on the dash comes from while supercharging. I has assumed it was measured by the car.
I was actually just now trying to find islandbayy's pics from his discharge adventure, but wasn't having any luck.�
Aug 30, 2014
wk057 So, back to charging. I decided to up the input power to 30A. My input voltage is about 232V right now at that load which comes out to about 6.5kW out on the DC side from 6.9kW input, or about 93.3% efficient (PF 99.5%).
The pack voltage hadn't changed at all since I left it last night, so that's positive. Will check back soon.�
Aug 30, 2014
scaesare Any real word experience of how often this happens, and what the observable impact is?
And if it's bleed-only during charging then not even possible at all during use it would seem.�
Aug 30, 2014
JRP3 Kevin Sharpe has experienced a low brick with range loss, there's a thread around here somewhere. Doesn't seem to happen very often.�
Aug 30, 2014
wk057 Yeah, you're right. For some reason I was thinking something along the lines of using the BMS to hold the under-powered module's voltage during top off of the remaining good modules, but that's probably not practical regardless.�
Aug 30, 2014
wk057 Alright, so, I stopped charging with a final resting voltage of 370.1V. (3.855V per cell) The modules are actually all within about 10mV of each other now, interestingly enough. (I physically disconnected the main BMS board before I started.)
I'm comfortable storing it like this for now until I can get some more components for my project.�
Aug 30, 2014
JRP3 I would expect modules to remain close with no active management for quite some time. One of the advantages of using so many smaller cells is that individual differences are averaged out when paralleled, so you effectively have large single "cells" that are closely matched in capacity and charge/discharge diffusion rates. I use no active balancing in my car using 100 ah prismatic cells, which are essentially just smaller layers paralleled together. The cells in series after 4 years of use don't differ enough over time to worry about it.�
Aug 30, 2014
wk057 So I figured out what the sharpie lines near some cells are. Looks like the cell level fuse was misplaced or something and manually repaired. Red for when the messed up fuse is found, blue for when it is repaired.
The pack I have only has 3 such occurences visible.�
Aug 30, 2014
qwk Going by the supercharger display on the dash causes confusion. At 3.8V the pack is at 50%. 3.0V is Tesla's minimum voltage, 4.15V is the maximum. Those are individual cell resting voltages.�
Aug 30, 2014
wk057 Source?
3.0V is very low IMO. 4.15V sounds reasonable for a max though.�
Aug 30, 2014
tom66 3V to me sounds like "oh s*** throw the contactor" voltage, probably the point at which HVAC, DC-DC lose power. The motor won't run much below 3.2~3.3V. It's limited to 40kW, or less.�
Aug 30, 2014
scaesare So in thinking about this... this voltage "baseline" is what seems to make the other numbers you are seeing "off" in terms of voltage vs. overall SoC/range.
Is it possible that when the charging rates are so high (1.0 - 1.6C) that the voltage potential of the supercharger is some degree greater than what the cell would be at rest?
IOW: at the low rates we use at home (fractions of a C), cell V roughly equals charger output V... but at 120+ kW there's a larger disparity?�
Aug 30, 2014
islandbayy If you are reading the voltage while the current is being applied, then yes. However, their is a point at start of the charge on a SC where no current is flowing yet, and voltage is displayed, as well as when the pack is finishing charge when the current is practically nil, only time it would be off to any noticeable extent would be during the actual charging.�
Aug 30, 2014
wk057 If I understand correctly, if you simply apply a greater voltage it doesn't necessarily allow faster charging and would just create more losses due to the voltage drop. I could be wrong, as I've never attempted this.
Continuing with more stuff about the pack...
The microcontroller that accompanies the CPLD ont he main BMS is a TMS which is probably an ARM processor by Texas Instruments, but I can't discern the rest of the writing to get a model number.
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It shouldn't be off by much at all, really. Most off-the-shelf single cell LiOn chargers apply the full charged voltage (4.2V) to the battery constantly, but if read while charging the voltage is within 100mV of the cell voltage, from experience. I've also seen this with 3-cells-in-series setups (11.1V batteries) with nearly the same result. So, extrapolating that out to 96 cells in series would be a difference of up to 9.6V. Probably incorrect thinking, but, I doubt there is a huge disparity in voltage readings during charging.
I'd have to say the supercharger pushing 404V (4.2083V per cell) makes some sense, since if the actual target voltage is 4.15V per cell (398.4V) then that's only 6V difference. I'd love to get some readings from an actual normally fully charged pack at rest though.�
Aug 30, 2014
stopcrazypp The NHTSA crash test of the 60kWh Model S (14 modules) lists a minimum operating voltage of 210V (2.5V*14 modules*6 series group per module) and max operating voltage of 350V (4.167V*14 modules*6 series group per module).
http://www.teslamotorsclub.com/showthread.php/21850-NHTSA-Opened-Up-the-Model-S-Battery-Pack-Pics/page2?p=449465&viewfull=1#post449465
Another point is that Tesla says the voltage window for the Roadster was 3.0V to 4.15V:
http://www.teslamotors.com/blog/bit-about-batteries
Not a whole lot of reason to change from this.�
Aug 30, 2014
islandbayy I agree
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When my car shut itself down due to low charge, i do believe my 60kWh pack was at 262v. Visual tesla showed 2% remaining at shutdown (older firmware though). fully charged is 353.�
Aug 30, 2014
wk057 OK, so, fully charged, assuming 4.2V per cell readout like I get when reading my Model S at the SC would lead to about 84 cells in series, or 14 modules. This fits with the images from the NHTSA I think, showing some modules with missing cells in the parallel portions presumably to make them 60kWh.
Applying this to the shutdown voltage of 262V puts the cells at 3.12V... much lower than what I saw at 12 rated miles which showed 352V, or 3.67V per cell. I'd be very surprised if there were a 0.55V per cell difference between 12 rated miles (3.6kWh) and "empty."
Whats the lowest seen for an 85kWh pack at a supercharger? 353V for me, 12 rated miles. (I've been down as low as 4 rated miles, but not at a supercharger.)
For perspective, the pack I have for my project was at ~313V / 3.26V per cell when I got it.
From the Tesla blog post about the Roadster battery... I'm not 100% sure the same applies to the Model S.
If they were the same batteries, I would go by this... but I think it's been determined they are not the same cells? (citation needed... forget source)
I'm skeptical about the 3.0V on the Model S, since I can not find a single source showing this level of discharge.�
Aug 31, 2014
JRP3 Roadster cells are LiCo, S cells are NCA, (LiNiCoAlO2). I'm not sure the operating voltages are significantly different.
To be clear, when you saw the voltage at 12 miles was current flowing into the pack? Because as soon as current flows the voltage is driven much higher, especially at a supercharger.�
Aug 31, 2014
qwk The way rated miles are calculated have changed in almost every major firmware revision. 12 rated miles could have been as high as 35 rated miles until the BMS shut the car off.�
Aug 31, 2014
islandbayy forgot about these,
both the 60 and 85
Hope they canhelp somewhat, though a number of firmware revisions ago.�
Aug 31, 2014
wk057 Interesting. So it seems I have no idea where the voltage is measured during supercharging.
In your video on the 85kWh charge from dead you look away from the screen at the moment it would have had 0A flowing but a voltage reading. But, by the time you go back its only about 20A or something and is reading ~320V.
In the 60kWh video I see 273V as a low, so, 3.25V per cell... which is reasonable. Extrapolating to the 85, that would be 312V per cell.
Seems if I stick with say 3.3V to 4.1V for my SoC range I'll probably be fine.�
Aug 31, 2014
stopcrazypp That's an important point, as during that point, it'll be the charging voltage, not the actual battery voltage. Things will also be different when measuring an open circuit voltage (OCV) as in the salvage battery versus a battery that is still connected (and running accessories and/or vampire drain).
I should add though that having a narrower range is always safer, although you get less capacity out of the pack.�
Aug 31, 2014
wk057 Added a few pics to the first post of this thread.�
Aug 31, 2014
FredTMC very interesting!�
Aug 31, 2014
JRP3 Worth noting that during cycle life testing Panasonic takes the cell to 2.5V under load, for 2000 cycles, so anything above 3V should be fine. They also only charge to 4.1V in that test. Page 34 http://www.embedded-world.eu/fileadmin/user_upload/pdf/batterie2011/Sonnemann_Panasonic.pdf�
Aug 31, 2014
tom66 The contactors are probably different parts because one will have to interrupt full rated current, whereas the other will never have to, if they design the software right to disconnect them in order.
I wonder if/where the inrush limiting is. Maybe in the inverter, but space is very cramped, for another contactor. Any sign of a pre-charge resistor in the pack?�
Aug 31, 2014
FredTMC Thanks for posting this! Model S has 3.1AH cells. Based on this published graph, the cells have amazing life even after 2500 cycles (> 70% capacity remaining).
I currently have 36k mi on my 60 kWh battery. That's ~200 cycles. I get 198 on a range charge. It was 208 mi when brand new. So, I've experienced ~5% degradation. I'm doing better than the graph. I'm sure that's because I don't do deep discharges and don't do many range charges.
This graph implies my battery will still have over 70% capacity after 300k miles. That's insane.
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Panasonic graph
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Graph.�
Aug 31, 2014
JRP3 In fact your range "loss" may be just a balance or software calculating issue, since some people have "recovered" range by doing extended full charge/discharge cycles and leaving the car sitting plugged in for a while. Not that I'd want to do it with the minimal changes you've had.�
Aug 31, 2014
drees Just keep in mind that accelerated cycle life tests may have very little to do with actual battery life over 300k miles unless the conditions of your battery match those of the cycle test (which is highly unlikely). Capacity loss over time plays a large role in how much capacity one will lose over the life of the battery pack.�
Aug 31, 2014
scaesare Are you surmising this, or have some authoritative source?
I ask because it's widely held that Tesla's cell chemistry (which is not disclosed) differs from that of the standard Panasonic parts.
Earlier in this thread it was suggested that they are 3.3Ah cells, which, along with the observed voltages of the packs, makes the overall pack capacity numbers match more closely.�
Aug 31, 2014
FredTMC Assumption due to discussions on TMC. It's at least 3.1. Yes, chemistry TM uses is tweaked from stock Panasonic. Since stock graph from Panasonic shows out to 2600 cycles, I believe TM tweaked batteries are at least as good as graph from Panasonic.�
Aug 31, 2014
TonyWilliams So, Tesla quotes two different minimum cell voltages. Since I have physically ran down to 2.6v sag (2.8v OCV) per cell in the Rav4 EV, I'm going to suggest that the 3v threshold from the Roadster no longer applies. The prototype Rav4 EV used Roadster 2200ma cells, but the production Rav4 EV version did not.
Again, 2.5v minimum per cell appears to be the current threshold. Yes, that is well past the voltage knee, and the voltage drops fast past about 3.1v. I'm also not suggesting that's a good idea, or not. I'm merely following the data.
As was properly pointed out earlier, there is a big difference between OCV versus under charge / regen and / or discharge.�
Aug 31, 2014
yobigd20 FWIW I am at 54k miles now. outside of my first 4 or 5 months where range charge went from 265 to 259 over around -14k miles, the last 13 months doing another 40k miles I have seen exactly 0% degradation and my range charge is still 259.
Given this rate, at 300k miles I fully expect to have way more than 70% capacity.�
Aug 31, 2014
NigelM Although there's been a few tweaks of the SW calculations in that time.�
Aug 31, 2014
scaesare I'm trying to see if we have consensus on thinks like voltages within the pack for various states, cell capacity, balancing schemes, etc... However, there's a number of variables and assumptions thus far in the thread:
- Observed pack Vmax ~404V (= Cell vMax 4.21), however that was while supercharging
- Suggested cell Vmax of either 4.1, 4.15, or 4.2V
- Suggestion the Vmax value of 4.15 is at only 90% charge, whereas others have suggested that's at 100%
- Suggested nominal cell voltages of either 3.6 or 3.7 volts
- Suggested Vmin of 3.6, 3.2, 3.0, or 2.5 volts
- Suggested cell capacity of either 3.1, 3.3, or 3.4Ah
- Pack has active balancing via variable impedance vs. bleed-off resistors for charge-only balancing
- Some odd observations with the pack at 352V and trying reconcile rated miles reported vs. energy consumed during a charge
Most of the observations wk057 have posted are direct measurements and documented, however they are OUTSIDE of the car, so we aren't sure what the normal voltage extents would be.
Several observations folks have made are from the console when supercharging, so those were NOT at rest voltages.
A number of voltages tossed around are from the Roadster, which is understood to have different cell chemistry.
A number of capacity, voltage, and chemistry claims are made with no substantiation or source cited.
So I'm hoping to determine what we actually KNOW about the pack as it operates WITHIN the Model S. It seems like that really is only rated pack capacity (~85kWh), logical pack layout (74P/962), and max supercharging voltage (~404). There's some good evidence for bleed resistors, but that doesn't preclude some other balancing capability as well.
The rest appears to be conjecture.
It would be nice to know at some point what the reported SoC-to-voltage correlation is (altho firmware revision dependent it seems), and if it's linear.
For example: It's been suggested that 90%=4.15V and 100%=4.20V... if that's true, there's either some significant non-linearity or the V Vmin is something like only 3.7V (which doesn't seem likely).
Unfortunately, it seems like the answer to most of these questions will require either making pack measurements while connected to the car somehow, or access to some other authoritative data (or something like the BMS service screens).
How did the roadster guys get some of this data?�
Aug 31, 2014
tom66 Just a note: There won't be a direct SOC-to-voltage translation. SOC will be calculated from an energy balance equation, measuring total pack energy output, and decreasing a counter as the pack energy is decreased. Possibly the below zero mile shut down will occur at a specific cell voltage, but this will not be used to determine capacity.�
Aug 31, 2014
djp Good summary.
Back in the Roadster days, Tesla wrote a technical blog that covered behind-the-scenes details on the car's design and operation (I miss those!). The Roadster also dumps a set of log files every time a properly formatted USB stick is inserted in the port, which members on this forum have reverse engineered. Parsers and graphing tools are available on several threads. A few members also have access to the service screens, which have real-time brick voltages and SOCs.
Model S is a lot more locked down by comparison, but it's just a matter of time before the collective intelligence of this forum figures it out.�
Aug 31, 2014
scaesare Ah, good points. I'd also assume that local variables such as temperature might be included.
Nonetheless, I'd expect that some things, such as a full 10% difference in reported charge from 90 to 100% correlating to only a 50mV voltage differential might set off some alarms as being unlikely.
Nonetheless, it would be interesting to see if we can at least document the extents as within the car's normal operational envelope.
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I should have said: "How did YOU Roadster guys get this data!"
Seriously, a lot of trailblazing was done there, and even if not all the specs area directly transferable, a number of the principles and methods no doubt are.
I agree that it's threads like this one that will help document what the S and it's pack does. My post was not intended to throw any cold water on this effort, quite the contrary: I applaud this thread and the work wk057 is doing.
What I'm really hoping for is clarification from folks so we can determine what is known as fact, either via direct observation/measurement, or from some authoritative source (manual, part # spec, etc..). For the rest of the input, I think it would be helpful to qualify it as a informed speculation (and upon which basis), and/or extrapolation from elsewhere (Roadster data, similar cell specs, etc...)
Cool stuff...�
Aug 31, 2014
Banahogg For AC charging, the REST API reports the battery current as well as the charger power. If we assume the battery current is measured rather than computed internally and ignoring losses (a less reasonable assumption), then we can get the pack voltage as (charger_voltage * charger_actual_current) / battery_current. Running that through my database and throwing out derived voltages outside [300V,400V], I get what looks like a wide straight line on the graph. The spreadsheet puts the fit line at about 313.6V + 0.685*battery_level (SOC percent from REST) and from eyeballing it, the band looks to be a pretty constant 30V wide at a given SOC.
Pretty indirect, but seems to give plausible values and is easy for anyone logging the REST values from their cars to replicate.�
Aug 31, 2014
scaesare Tony, this is the best evidence yet I've see of ~4.15 being Vmax for 100%. What's that a screenshot of?�
Aug 31, 2014
TonyWilliams It's from the Tesla powered Toyota Rav4 EV's BMS via CAN bus. We just decode it and put it in a display (again, it's all part of our "JdeMO" project to put CHAdeMO outlets directly on Tesla powered cars).
Like stated above (somewhere), 4.15v OCV is likely the cell voltage max, but SOC% is certainly variable with a "full" charge; about 96.X% to the highest observed of 99% in that photo.
All the other data I've posted (and which seems to be mostly discounted outright here as "doesn't apply") is from the Tesla BMS. It is live 24/7, whether the car is on or off.
4.202v for one update, then 4.200v continuously, is the absolute highest cell group voltage observed, during regen going down a big hill after a "full" charge (what Toyota calls "extended", like a Roadster "range" charge).
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Yes, maybe somebody will in fact post that stuff...�
Aug 31, 2014
islandbayy I would agree that the voltage will not go past 4.200 (With margin for error of a slight amount). This is why the regen power is reduced when close to a full pack. Ive even seen my car limit regen to a much lower level then the dotted line.
Now going higher then 4.2v speeds up degradation exponentially.
I'm sorry if I'm going off topic here, but thought this information would be helpful to some not as familiar with Lithium cells and longevity. I posted this link, How to Prolong Lithium-based Batteries - Battery University
about a year ago, and thought this will be a good place to show it again. Specifically would like to point out the voltage graph & Capacity VS Degradation chart. I've attached the picture below, but please visit the site (Dont want to plagiarize or break copyrights and want to give credit where it is due)
Please note the increased degradation. at 4.3v, the cell will hold about 10% more power (10% higher capacity) however, service life is reduced by half compared to 4.2v, likewise 4.1v doubles the life of the cell. Good quote "Every 0.10V drop below 4.20V/cell doubles the cycle; the retained capacity drops accordingly. Raising the voltage above 4.20V/cell stresses the battery and compromises safety."
Forgive me my rambles, I'm on the Ny-Quil.�
Aug 31, 2014
scaesare Ah, ok thanks.
Well if you are referring to my earlier post, my intent is not to necessarily discount anything, but simply to identify what's directly measured/observed behavior on the S, versus what's being extrapolated from other sources (or outright simply guessed at).
In this case, I'd suggest that a Rav4 of similar vintage to the S (as opposed to the older Roadster), is a pretty likely case for having similar behavior... so thanks for posting your data. Your experiences with seeing cells down in the 2.8V range is interesting as well.
Am I understanding correctly that Vmax varied upt to 4.2V for one firmware update? Are your other pics demonstrating a Vmax of only 4.15V indicative of being a different firmware revision?�
Aug 31, 2014
TonyWilliams Yes, the Tesla part of the Toyota Rav4 EV project ended in about May 2012, with the Tesla Model S coming out the very next month. My original motor (replaced like on so many Model S cars, particularly those early ones) was Tesla serial #331. No, Tesla didn't reinvent the wheel for the Rav4 EV. It shares as many parts as humanly possible with Model S.
But, we do know the cells are the lower 2900ma cells, vice 3100-3400ma on Model S.
The cell voltages are the difference between fully charge OCV of 4.14v and maximum regen with a fully charged battery of 4.2v see the difference?
It's much like the data about charging. Sure, it likely charges at the equivalent of 4.2v (96 * 4.2v = 402v pack voltage), but the cells are more likely at 4.15v OCV, just like the Rav4 EV.�
Aug 31, 2014
magnet That is true but also consider the case of a short circuit, the fuse will blow faster on 690v than 400v as the current will be higher. For an equal overload current the voltage drop across the fuse is independent on system voltage, but in the case of a short circuit higher voltage means higher current. What you are saying is true because we on the same time vs current curve in either case. It is just in the case of a short circuit we are at different points on that curve. So is the blow time truly voltage independent in all cases? Yes and no.�
Sep 1, 2014
scaesare Ok, so we know the cells at least are different. So your voltage measurements in a Rav4 setup are likely a good starting point for assumptions, but not direct observations of what the Model S BMS does with it's cells.
Ah ok, I wasn't sure what was meant by "update". Interesting that some regen is enabled even when the cells are at 100%.
Thanks.
It will be interesting to see how the overall system (pack + BMS) behaves when somebody is able to take the guts from a wrecked Tesla and charge a pack with it in some fashion where internal measurements are possible. Or makes a set of "extensions" for the HVDC and BMS connectors as well as coolant loops...�
Sep 1, 2014
lolachampcar I've got a BMS from my Zero (logic buck switcher failure I suspect) where the part numbers are "readable". Let me know if you want to embark on a stand alone BMS solution to use the 85KW pack as is. If you do, I may be interested in pitching in with PCB layout and micro-controller development as I have all the tools (and a little free time).
I'd also be interested in working with the group to solve the problems associated with using the pack in parallel with PV serial arrays of similar voltage. Specifically, how the MPPT stuff works when running off a low impedance source like the battery. It would also be nice to find alternatives that allow for using the MS pack as wired. I suspect this would also require an MPPT function when using PV to charge the battery directly.�
Sep 1, 2014
islandbayy I have experience with running a Grid Tie directly from a lead acid battery pack. The MPPT function had no difference in performance with the battery pack. While it does make a difference with Solar, as the voltages and output fluctuate much more, with the steady current from a battery, no difference with the function on or off.
The problem I had was the cheap inverter I have to play with, didn't limit current. So while it was rated for 500 Watts, it would start low and ramp up, and keep going. I pulled the plug at 600 watts as I didn't want to fry the inverter. I need a way (resistors worked, but wasted WAYYY too much power as heat) to limit the current to keep it below 500 watts without such great loss, I know how to do this with AC, but not experienced in DC.
That may be a issue that one runs into with these setups.�
Sep 1, 2014
lolachampcar My assumption is that you would be using battery for off grid operation. In this instance, you would have something like an 8 KW AC rated inverter supplying your house whose consumption would, presumably, stay below the constant and peak capabilities of the inverter. The inverter would also have to be of the type that does not require the presence of voltage to sync to (ala grid tie inverter) which means it would likely be more flexible on input type (in anticipation of this type of question).
All guessing and speculation on my part. Once I found that FPL's net metering was a no transaction fee or free "battery storage" solution I lost interest in the battery option.�
Sep 1, 2014
wk057 This was my thinking as well, until I really thought about it and realized nothing prevented this from changing soon after I made the investment.�
Sep 1, 2014
magnet There are two new global power standards emerging, 48v dc and 380v dc. Maybe look into data center equipment that supports this standard:
http://www.etsi.org/deliver/etsi_en/300100_300199/3001320301/02.01.01_40/en_3001320301v020101o.pdf
Some of the gear that supports this standard is already designed for 400v backup packs and solar; and stepdown to 48v where you can safely distribute (or convert to ac if you must)�
Sep 1, 2014
SeminoleFSU Really hope you guys get this going... Watching this thread closely because it is such a cool idea and would love to see it work in reality. Good luck! And very cool thread so far!�
Sep 1, 2014
Nickjhowe Service centers are being set up with battery refurb equipment as we speak. My local SC was getting set up a couple of months ago.�
Sep 1, 2014
ACDriveMotor This seems inevitable as the volume of vehicles in service grows.�
Sep 2, 2014
tom66 It will be especially important for European service centers as shipping batteries back to Fremont will be very expensive. I don't think Tilburg has any powertrain manufacturing, so they probably won't refurb packs.�
Sep 3, 2014
wk057 So, haven't had a chance to do much with this project the past few days.
I checked the pack voltage earlier and it has self-discharged only 0.3V since I charged it 5 days ago. Can't complain too much there.
(The main BMS board is still disconnected)�
Sep 9, 2014
lolachampcar so I'm firing up my new PV array and some inverters are not cooperating.....
A quick internet search and I find some neat stuff to play with-
http://www.ti.com/lit/ml/sprt615c/sprt615c.pdf A full point/string inverter development kit from TI. This is where answers can be generated when it comes to seamlessly integrating a HV battery like the MS with a PV system.
http://www.ti.com/lit/an/snosb76c/snosb76c.pdf PV based battery charging development board with MPPT. This might be scalable to work with much higher voltages???�
Sep 9, 2014
wk057 Well, finally gave up on keeping the pack in tact. One reason being I want the garage space back... hehe. But mainly because nothing off-the-shelf and even remotely reasonably priced (I found a solution that would work for roughly $150k...) works with this high voltage DC in a useful fashion. So, breaking it down into modules is the only plan that makes sense since it will essentially allow me to configure the pack for whatever voltage I need.
Anyway, started the full tear down tonight. Just going to reiterate: This thing is super heavy duty. Dismantling it is not simple.
I had to first drain the coolant loop. I couldn't find anything that would mate with the quick disconnect easily, so, I rigged up some PC liquid cooling tubing to each outlet, which fit somewhat snug inside them. I then fed air into one side and drained from the other until I didn't get any more coolant. About a gallon of coolant was liberated.
In order to remove the modules I had to first remove the entire spine where everything ties together... which consisted of a heavy gauge HV cable, dozens of bus bars, the BMS cabling, and all of it inside injected rubber insulation...
The modules would not lift out with the bus connections in place because you have to lift that side out first, slide it up and over, then disconnect the coolant loop connections, then lift the module out. It appears the modules sit on rails and are elevated about 1/4" above the the pack's inside floor... I have no way to easily do this outside of the pack, currently, so, I'm just carefully setting them down and out of the way sitting on their thin plastic covers. The plastic covers have ridged sections over top of the rows of cell fuses, so, they're reasonably well protected from damage even sitting like this. I plan to build a frame for them later, though, or at least some legs to keep them off the ground.
I stopped after removing all of the spine connections and six modules. Ten to go... another day.
I did learn that all of the modules are in fact identical. The driver and passenger side modules are just rotated 180 degrees. The top module in the front (the oddball) is just upside down. But they are in fact all the same, just their orientation is changed to suite its position.
I was kind of surprised to find a heavy gauge wire inside the rubber in the middle spine. The only things visible prior were heavy bus bars. So, I had assumed there was one which ran the entire length of the pack returning to the main contactors, but I was fooled! The exposed bus bar portion is welded to the heavy copper wire (2/0 gauge I believe) at both sides inside the rubber of the spine. The wire is 150 degree rated (C) and is *also* sheathed in a thick fire resistance material (the same material used all over the inside of this pack).
I'll sort through some pictures and post some later on.�
Sep 10, 2014
lolachampcar Bummer. I was hoping against hope that this would progress as a HV integration into a full PV system. That would have been a lot of work and I do not blame you for a second making the decision to deal with bite sized chunks at reasonable voltages. My only fear for that path was the lack of cell level safety making having the modules exposed a serious hazard.
Anybody in the S. Florida (WPB) area interested in doing some experimentation/development of a high voltage MS pack integration into PV? My curiosity is killing me here.�
Sep 10, 2014
rabar10 One thing I didn't see in any of the pics -- where are the coolant loop connections made between pack and car? You showed the two electrical connectors (HV and LV) on the back edge of the pack (w.r.t how it is mounted under the car). Are the press-fit coolant connections on the front part/edge?
Th coolant loop is interesting to me b/c to support quick battery changes, there is no air-purge step between disconnecting battery #1 and reconnecting battery #2. Loop has to be designed to capture and deal with what little air is introduced during the swap...�
Sep 10, 2014
wk057 The coolant loop quick disconnect is in the front. It has spring loaded caps that close when disconnected so I doubt that much air, if any, would make it in.
Pretty sure its visible in one of my earlier pics. If not I'll post one.
- - - Updated - - -
Yeah there is one. It's captioned "Another shot of the coolant loop connections and front modules."�
Sep 10, 2014
rabar10 Yep, I missed them.
Next question -- did you note the series-connection order of all of the modules? i.e. tracing the series connection path from low-side contactor through the modules/fuse and to the high-side contactor?
My initial guess would have been from the connector/contactor, then up one side, through the stacked modules and fuse, and back down the other side to the other contactor and connector. But your description of the 2/0 cable running the length of the pack mid-line wouldn't make sense in that arrangement...�
Sep 10, 2014
magnet That sucks you had to break it down. It doesn't sound like the pack will be able to be rebuilt by robots easily...
I'm still trying to figure out what is going on with the negative terminal on each 18650. It looks like there is some kind of end cap on each cell. There is also a central oval shape piece on the terminal itself that connects the bond wire. They appear to be made from the same metal by looking at the texture, and appear to be attached to the cell, not part of the cell. It looks like both the endcap and oval are connected to the negative busbar.
On the postive terminal it looks like there is also "two connections" with a bond wire to the main triangle on the the cell and then a U-shaped ring contact. Can you clarify what is connected to what. Thanks
�
Sep 10, 2014
wk057 The series connection started at one of the rear modules, then snaked back and forth (side, up, side, up) to the front of the car to the oddball modules, then out of the last one, into the fuse, then back to the contactor in the rear through the 2/0 cable.
- - - Updated - - -
So, Tesla seems to have gone silent on my requests for data on the BMS interface... maybe someone can make use of these high resolution scans of one of the boards from a module and gain some insight. (Click for full res version, ~12MB).
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.
Front of BMS Module board (one of these on each of the 16 modules)
Back of the BMS Module board.
You can clearly see the bleed resistor setup for balancing now with the board removed (it is hard to see the whole board when installed).
The little halos around some of the components are artifacts of the flatbed scanner passing over the coating that is on the board.
More pics later when I organize them and finish dismantling the pack tonight.�
Sep 10, 2014
Cottonwood Great pictures!
Below are some enlargements of one of the repeating pattern of 6 bleed circuits, one for each group of paralleled cells; one enlargement for each side of the board. Don't get fooled by the bottom set; all the components are there, just rearranged a little for board layout.
This is a serious multi-layer board; it will be a nice task to recreate the circuit diagram from it, but it is clear that the board contains bleed circuits for balancing. In particular, notice how the four, surface-mount, power resistors with the "1580" label, one of which is labeled "R11", are in parallel for extra power dissipation. My guess is that these resistors are 15.8 Ohms each, and 4 in parallel would be a resistance of 3.95 Ohms. If the full cell voltage is a little over 4 Volts this would mean a power per resistor in parallel of a little over a Watt. With some PWM techniques, this could easily be modulated down to lower power levels.
�
Sep 10, 2014
magnet Interesting....they are using a off the shelf TI chip to do monitoring and bleed balancing. What does the host controller board look like?
They are using RF-coupler instead of an opto-coupler for isolation
Are they any other BMS or BMB boards? The more pics the better. Thanks�
Sep 10, 2014
rlang59 Looks to me like it is only a 4 layer board.�
Sep 10, 2014
wk057 "1580" would be 158 ohms, 1% tolerance. So 39.5 ohms for the parallel set. That'd be 0.44W for the the set (0.11W per resistor) at 4.15V. Each set of 74 cells contains about 885 Wh of energy, so, to drop it 1% would mean about 21 hours of bleeding.�
Sep 10, 2014
Cottonwood Probably correct, but still multilayer, and a pain to trace out the connections...�
Sep 10, 2014
wk057 Expanding on that, the BMS could at most draw about 42W from the pack if all 96 bleeders were active at once... which would take 84 days to bring the pack (85kWh) from 100% to 0%, lol.
I think most imbalances would be a few 10s of mV, which should be only a couple hours of bleeding probably.�
Sep 10, 2014
apacheguy Ok, well that's all well and good, but can you explain this in terms understandable to someone who doesn't hold a degree in electrical engineering? Particularly the bolded phrase. What is the take away that tells us something meaningful about how the pack balances itself?�
Sep 10, 2014
rlang59 The big surface mount resistors are used to bleed down the voltage on cells that measure higher than the others by sinking current though them.
- - - Updated - - -
Maybe but since they are using this chip http://www.ti.com/product/bq76pl536A I'd bet looking at the reference design or datasheet would tell you exactly what they are doing.
Here is a link to an app note: http://www.ti.com/lit/an/slaa478/slaa478.pdf�
Sep 10, 2014
Cottonwood Thanks for the correction!
Hmmm.... They seem like big resistors for a 1/10th of a Watt. OTOH, maybe all they need is 0.1% corrections, from time to time.�
Sep 10, 2014
rlang59 They look like 1206 resistors which are typically rated at 1/8 of a Watt and it's not unusual to de-rate by 20% though for a constant load.�
Sep 10, 2014
apacheguy Ok, so the excess electricity is wasted as heat, right? Sounds to me that balancing can occur at any SOC regardless of whether or not the car is charging. So does this bust the long standing TMC theory that pack balancing only occurs on a max range charge?�
Sep 10, 2014
ACDriveMotor It does seem to suggest that it could happen at lower SOC. Is there a reason not to balance at, say, a 70% SOC?�
Sep 10, 2014
wk057 Missed this almost...
The 18650 cells are bare, no label or anything. So the entire casing, including the negative end, is negative. So you're looking at the negative end of the cell. The bus plate sits on top of a piece of plastic with cut outs for each individual cell. The cutout in the plastic with it's raised walls around the hole (to protect the small fuse) are what you're seeing on top of the negative end of the cell. The cell level fuse then connects from the bus plate to the cell itself through this opening in the plastic.
The same for the positive side, except the positive end of the cell has a triangle-like positive terminal that is insulated from the negative casing.
Note that the plastic protective cover is in place on the modules in most of my pictures, also.�
Sep 11, 2014
arg You certainly can perform the balancing at any SoC, but the problem is to be sure of knowing exactly how much balancing is required. All cells equal voltage at 100% SoC is the target, since that's an absolute limit - can't take any cell above the max voltage. Since the voltage/discharge curves might not be identical for all the cells, balancing at 70% might not leave you perfectly balanced when you then charge to 100%.
Of course you could do things like correcting gross imbalance when a 70% charge is requested, and only fine-tuning when doing a 100% charge.�
Sep 11, 2014
vielster
Great shot of the balancing circuit. You can even see the FET (Q3) which is shunting the current through the resistor bank.
P=V^2/R BTW, so you're talking 4W if those are 15.8ohm in parallel. Not only are the resistors incapable of handling that current, the circuit board doesn't appear to have much in the way of copper pours to dissipate heat in this area so that would suggest the circuit would not be capable of dissipating 4W (or even 1W) continuously without possible damage. For safety you should assume that the balance circuit may get stuck on (say FET fails closed), and this condition should not endanger the battery. I read those as 158x10^0 (so 158ohm resistors), which would be under a half watt.
This passive balancing scheme is fairly common, and it is pretty slow. When batteries are severely out of balance, the charger must be set to a very low charging current towards the end of the charge (once the highest charged cells approach their max voltage). Essentially, the charging current will then max out at the balancing current (in this case about 100mA) until the remaining cells complete their charge. The first charge cycle this trickle charge may take a long time 10s of hours) but once the cells are balanced, they only drift apart slowly over time as they age differently. Balancing these disparities each charge cycle is negligible. Additionally if their BMS does a reasonable job at modeling the cells, they can actually predict the aging and do balancing throughout the entire charge rather than waiting towards the end of the cycle....another reason the firs cycle(s) would be slower since the BMS doesn't have enough data to model the cells in that battery.
My guess is that by the time it enters a car it has already gone through several cycles, thus is balanced and has appropriate info to model the cells to maintain short balancing operations.�
Sep 11, 2014
scaesare More cool info.
This sounds like it was a gallon or so per module, not the whole pack, right?�
Sep 11, 2014
eepic Possibly a dumb question but what happened to the intumescent goo? Was it never in production packs or only in earlier/later versions?�
Sep 11, 2014
scaesare Although I heard it discussed in some threads... and have heard of references to it in early pre-production packs and/or patent apps, I don't believe I've sever seen evidence of it making it in to a production pack...�
Sep 11, 2014
magnet --------------
I know I'm seeing the top of the negative end of the cell but what I'm not certain about is if that end is an added endcap on the "raw" cell or has been added on over a "standard" panasonic cell. In the Tesla patent where they describe adding a the C-shaped or O-shaped vent. When I say raw cell vent I mean: "The venting region, defined by scoring on the battery terminal, ruptures when the internal battery pressure exceeds the predefined battery operating range"
This scoring is done is a C-shaped manner as seen on the 18650PD:
View attachment 58839
Or in an O-shaped manner such as the 18650BE
View attachment 58838
(note both these cells are the only on the market with the triangle shaped postive terminal as we see in the Model S and RavEV)
View attachment 58842 View attachment 58843
Note in the Tesla patent they describe in Figure 19 adding an endcap that COVERS the O-shaped vent on the raw cell end such that when the raw cell vent breaks it blows off the end cap and break the wire bond/fuse.
View attachment 58840
"In an alternate embodiment, illustrated in FIGS. 18 and 19, the inner edge of mounting support substrate 1801 extends beyond, i.e., overlaps, scoring 1803. Note that scoring 1803 is shown in phantom in FIG. 19."
As I read it adding an endcap supposedly reduces the chances of a re-connect after the vent breaks the wire bond.
Can you get a closeup of this area...this picture shows maybe an endcap, not sure, also it appears to show something like black plastic sandwiched in between than maybe holds the cells spaced apart, or I could be seeing thing haha thanks:
View attachment 58844�
Sep 11, 2014
wk057 Oh no, it was about a gallon for the whole pack. Maybe closer to 1.5 gallons. It's just what was inside the tubing inside the pack and modules... didn't expect much more than this.�
Sep 11, 2014
tom66 On that board
U4 - Silabs isolator (http://uk.mouser.com/ProductDetail/Silicon-Labs/Si8642ED-B-IS/?qs=NVLsoTRMv1oBDPBFWNUX/g==) for the interface back to the BMS board
U100 - Silabs MCU (http://www.ko4bb.com/Manuals/12)_Components_Specs&Datasheets/Silabs/C8051F520A-F530A.pdf) very basic - probably only interfaces with TI chip
U1 - TI battery management IC, part number seems custom or possibly re-marked (it seems unlikely Tesla would be worth spinning an IC for - but maybe since this is a later revision it is?)
Interesting that they have a huge isolation barrier for the pack board. I wonder if the main BMS board is completely isolated from the pack, as I wouldn't have thought something like 8mm isolation would otherwise be necessary.
edit: nvm - the TI IC is definitely not custom or re-marked, it's this:
http://www.ti.com/product/bq76pl536a
designed specifically for EV/Hybrid, $8.00 a pop so Tesla must think it's simpler than a lot of diff-amps and a faster MCU with multiple channels. (it probably is in the end.)
Tesla use -Q1 variant "zero defect".�
Sep 11, 2014
wk057 Hmm... did not realize this earlier. This chip requires a power supply on both sides of the isolation, so, I wonder where the board is powered on the battery side... from one or more of the cell sets? That's interesting...�
Sep 11, 2014
lolachampcar Dang!
I hate SiLabs parts. Tesla used them in the fob as well.
No rear surprise on the degree of isolation as the modules are at vastly different potentials.�
Sep 11, 2014
tom66 There is a fuse on its own and the TI chip has a built in 5V LDO, so I suspect it's powered from that. There's also a device "U2" which might be a voltage regulator, but I can't read the part #.
I'm surprised they use an LDO for 25V -> 5V drop but I guess the quiescent current must be pretty low.
- - - Updated - - -
Looks like Silabs got a big design win on the Model S then. 32 chips per car, plus fob, plus who knows what elsewhere. (Although TI get $128 per battery, not bad either.)
The modules are only about 25V apart from their neighbours but I guess that the BMS board doesn't chain them together, so the isolation makes some more sense, though it's still wider than I expect, they don't spend any more or less money on making it wider.�
Sep 11, 2014
wk057 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.
OK! So, bunch of pics from my tear down phase...
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Some tubing from a past PC water cooling project. I put some holes in the tube near the end so that when I put it into the quick disconnect there is a path for the fluid to flow...
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Yup. Shoved the tubes in and taped it up...
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Pumped air into the one tube and pushed the coolant out.
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One final check of the full pack voltage before I start electrical tear down. 368.2V (3.835V per cell after topping off with HV charger).
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Removal of the pack main fuse and plastic housing.
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Removal of the first bus bar!
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Side view of the BMS boards on the front oddball modules. Clearly shows the top module is upside down.
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Small bus bar connecting the two oddball modules. It is layers of copper pressed together and tin coated.
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Starting to remove the next bus bar.
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Disconnecting the coolant loop from the top oddball module. Turns out I drained 99% of the coolant out.
Does anyone know what the heck kind of fitting this is?
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Top module removed!
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Oddball module is now loose! First one! (Bottom view)
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Side view of the module... and my shoe.
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"Front" of module, still has small extensions connected to the terminals for the odd placement.
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Oddball module top view with extension pieces still in place...
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Removal of small extension pieces, revealing that the oddball module isn't actually all that odd...
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Tesla part label for the module. 1009312-00-E.
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Bottom front module removed.
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Removal of remainder of bolts for electrical connections to the modules.
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Removal of the first bus bar which is revealed to be inside some kind of injection filled solid rubber inside the spine of the pack... the inner modules can't be removed easily without removing the bus bars first because there is not enough room to disconnect the coolant loop without first lifting the module up and out a bit...
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Surprise! Not a bus bar afterall... ~2/0 gauge wire runs the length of the spine, surrounded in thick fireproofing material. This image is really showing the shunt and its PCB.
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Close up of the weld on the 2/0 wire.
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Ripping more of the spine out. Yep... spineless pack soon.
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Close up of one of the small bus bars from the side.
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Attacking from the other end.
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Man that stuff is really in there...
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First module from the rear of the pack.
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And its former home.
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Close up of some kind of safety relief vales on the outside edge of the pack where the module used to be and the coolant loop connectors.
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Label on the cable removed from the spine.
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Spine removed, More modules liberated!
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Modules off to the side. (sticker is from me not Tesla)
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More modules, shot of the empty spine.
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The bus bar collection that was removed.
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Pack casing ready to be scrapped, coolant loop removed, main BMS board removed...
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Stacked the modules out of the way with their original covers in place for weight distribution.
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Whats left of the coolant loop, main BMS board, some bus bars in a bin.
[URL="http://files.wizkid057.com/teslapack/update3/2014-09-11 20.58.43.jpg"][ATTACH=full]142566[/ATTACH]URL]
Shot of the bare cells from the side. This one has a barcode printed on it...
[I][B]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.[/B][/I][/URL][/URL][/URL][/URL][/URL][/URL][/URL][/URL][/URL][/URL][/URL][/URL][/URL][/URL][/URL][/URL][/URL][/URL]�
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URL]Sep 11, 2014
scaesare Spectacular pics... thanks!
So, any thoughts about what that small shunt board attached to the bus bars is?�
Sep 11, 2014
pgiralt Awesome pics! The one thing I haven't been able to figure out is how the coolant actually flows through the modules to cool the individual cells. Is that grey rubber-like material shown on the last picture related to the cooling?�
Sep 11, 2014
teslaspotter WOW! As I install LiFe in my little car I am in awe of the beauty of this pack!! I love the international nature of all the components.. hopefully this means more ships than one are rising on this tide!
teslaspotter
I figured someone would find these pics and comments interesting and/or informative. I will try to take some more as I get to actually doing something with the pack.
-wk
Update 2014-09-10 --- Added scans of BMS board from a module.
Update 2014-09-11 --- Added link to new post with more pics (so not to make this page impossible to load...)[/QUOTE]�
Sep 11, 2014
stopcrazypp You can balance at any SOC, but if you want the absolute max capacity out of your pack, balancing at 100% SOC (or close) is going to give you the highest number.
This link kinds of explains how top balancing stores more energy (vs bottom balance).
http://books.google.com/books?id=o-QpFOR0PTcC&printsec=frontcover#v=onepage&q=top%20balancing%20allows%20batteries%20to%20store%20more%20energy&f=false
Also, because of how the voltage curve is shaped vs. SOC, balancing at 100% is a lot more accurate than anywhere near the middle (because the slope of the curve is much higher). It's also possible the software is set so it doesn't balance unless it is near 100% SOC.�
Sep 11, 2014
wk057 It is a current monitoring board for the BMS to know how much energy is flowing in or out of the pack as a whole. The shunt is a piece of metal with an accurate and known resistance, and the voltage drop across it at various current draws is directly proportional to the amount of current flowing through it. The small board reads this and calculates the power flow and reports it to the main BMS board.
The grey rubber like material is actually thermally conductive material (like thermal pad material), and it presses against the coolant loop and every cell. The coolant loop goes into the module, flattens out, then weaves around all of the cells conducting heat through the thermal material.
- - - Updated - - -
I'll also note for completeness that the presence of the isolation IC on the BMS module board rules out any inter-module active balancing.�
Sep 11, 2014
scaesare Ah OK.... It's a standard current shunt, not anything to do with shunting charge between modules to balance. Thanks.�
Sep 11, 2014
magnet That sounds about right. When the pack is not connected to the vehicle the max intentional self discharge rate is 50w (10W preferred) using the bleed resistors
When connected to the vehicle it can use the load from the heater and fans and what not to intentional self discharge up to 20kw (10kw preferred)
This feature is so you dont have to have an external load to dischrage the pack down to a safer voltage for shipping or after an accident or for service�
Sep 11, 2014
magnet Inter-module active balancing is done by shuttling during charging but this shuttling is not done in the traditional dangerous way. Balancing is done by increasing the voltage not only bleeding. Bleeding is not an efficient way of balancing as it just creates heat. Virtual shuttling is done by continuously changing the target balance voltage which will in effect shift charge through the whole pack�
Sep 12, 2014
Matias Those safety relief valves are for venting exhaust fumes of fire to safety vents of car chassis. Somewhere in TMC is link to Tesla�s patent regarding this. Anyone remembers where that link is?
edit here it is
http://www.google.com.bz/patents/US8361642
http://www.google.com.bz/patents/US8367233�
Sep 12, 2014
lolachampcar So how is voltage to each module varied while charging to balance the modules (WRT each other) when the modules are in series? Is there a some sort of series variable resistance that changes the voltage each series module sees?�
Sep 12, 2014
rabar10 Changing the target balance voltage for one module to be different than others (based on small V/Ah differences between modules) would still result in passive balancing -- as the pack charges, some modules' bleed resistors would be used before others. As others have posted, I don't see any way to do inter-module active balancing with the circuitry shown.�
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