Pics/Info: Inside the battery pack

[ch_model_s]

Can you get a picture of the negative terminal of an individual cell?

The Rav4EV uses the 2900 mAh NCR18650PD with a C shaped vent designed to break the bond wire on the terminal when it opens. The C shaped vent is pictured in the Tesla patent but more recent patents also describe a circle shaped vent.

Pansonic recently released the NCR18650BE cell which is also an NCA cell rated at 2C max just like the PD cell, but rated at 3300 mAh! This cell has the same triangular postive terminal as the PD cell but has a circular vent. No other Panasonic cells besides the PD and BE have negative terminal vents! The nominal voltage of a NCA cell is 3.65V so a 3.3 Ah cell would result in a 85.5 kWh pack

The 3400 mAh NCR18650B is a high energy cell not suitable for EV use. The latest high energy cell is the NCR18650G rated at 3600 mAh. Neither of these cells has the Tesla vent on the neg terminal.

Tesla does not use the BMS to balance the pack. They use active impedance control to shuttle charge between bricks. It is always working and it much safer than a typical BMS (battery murder system)

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

 

[magnet]

wk057 is the OP and he certainly does... but I did not know that about magnet as well?Is this documented anywhere we can see? I ask because magnet is suggesting active impedance and/or a capacitor to shuttle charges between bricks, yet wk057 is reporting resistors on the BMC PCB's that imply a charge-bleed system.I'm trying to reconcile the differences, but don't have any background context that magnet is supplying, whereas we have pics of what wk057 is doing...(don't get me wrong, I'm not imputing bad motive to magnet... I just want to understand how accurate this info might be)

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

 

[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

 

[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.

 

[scaesare]

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

OK, thanks for the clarification.

 

[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.

- - - Updated - - -

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.

 

[apacheguy]

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.

S85's seem to max out at 320 kW. P85's can go as high as 370 kW.

 

[Matias]

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.

Tesla's competitors have dissected packs long ago, so posting will do no harm to Tesla.

 

[spaceballs]

...
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. ... so I wonder if they upgrade the pack fuse for a P85, or if this fuse can handle that for short periods.

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.

 

[magnet]

Tesla's competitors have dissected packs long ago, so posting will do no harm to Tesla.

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.

 

[tom66]

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.

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...

 

[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...

 

[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.

 

[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.

 

[lolachampcar]

I looked at SC and they are only doing pilot work in CA...... Nothing to buy here friend; move along.

 

[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.

 

[NigelM]

Mod Note: whole bunch of posts went here - Tesla patent move - Real world obligations? And please let's not descend into snippiness.

 

[wk057]

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.

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.

- - - Updated - - -

Mod Note: whole bunch of posts went here - Tesla patent move - Real world obligations? And please let's not descend into snippiness.

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.

 

[magnet]

S85's seem to max out at 320 kW. P85's can go as high as 370 kW.

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

 

[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?