Pics/Info: Inside the battery pack

[thegruf]

..just trying to get additional information to rip off the Tesla battery .. dont feed them.

 

[Bazinha]

Question: What are the dimensions for one of the Tesla Model S battery modules? See picture below. I would like to know the module Wh/L and pack Wh/L?

 

[tbader2]

Also what is the max current and max voltage of each module?

 

[Johan]

Bahzina and tbader: both your questions have been thoroughly answered in this thread and in wk057's battery disassembly thread.

 

[Bazinha]

What is the module Wh/L and pack Wh/L?

 

[Bazinha]

I did a quick 3d modeling of the tesla pack based on the wheel base dimensions and patent drawings....and measured the pack volume to be ~ 365L which gives the pack --> 85 kWh/365L = 234 Wh/L ... Also if you assume a module to be 300x680x80 mm --> 16.32L --> 5.31 kWh/16.32 --> ~ 325 Wh/L. Can anyone confirm? Thanks!

 

[Rory]

The BMS really doesn't seem involved in the actual charging in the Model S and battery. The Model S charger itself, as visible in some photos others have posted, just feeds the battery high voltage to the main connector. The same with supercharging. So, sanely applying a charge voltage to the pack should charge it fine.

The BMS has limited capability to balance the pack using the bleed resistors of which there are 4 in parallel per cell block. On the picture R20,R21 & R22 are examples. They cannot dissipate much power say 2W total at a guess so may need to operate for longish periods.

 

[CHL]

My discharge test was at 500mA, which would be closer to a 12.7kW average draw for a full pack, much lighter load I'd guess.

The fact that both my test and the car's dash yield a number around 75kWh is definitely interesting, though.

If I get the time I can try to do a more car-like test, but probably won't be soon.

Suffice it to say, I'm very curious where the 85kWh number actually comes from now.

Don't forget that part of energy pushed in the pack during charge is lost in heat (internal resistance) during discharge.

 

[Pajda]

The BMS has limited capability to balance the pack using the bleed resistors of which there are 4 in parallel per cell block. On the picture R20,R21 & R22 are examples. They cannot dissipate much power say 2W total at a guess so may need to operate for longish periods.

Exactly, Tesla uses passive cell balancing method based on dissipating balancing current via shunt resistors. In this particular case, we can see four 158 Ohm SMD resistors connected in paralel which gives us 39,5 Ohm total value.

We know that Cell chemistry used by Tesla has maximum charging voltage of 4,200V. So we can calculate, that maximum possible balancing current is Id = 4,200/39,5 = 106mA. Then we can calculate, that maximum dissipated power is Pd = 446mW and this power is divided between four small 0805? size SMD resistors, so there is no need for special cooling of these resistors.

So the point is, that Panasonic cells must have super tight production tolerance, so there is no need for high balancing currents (especially when compared to crappy LFP Winston cells). You should remember that there are always 74p 3400mAh cells which acts as one big ~251Ah cell and Tesla can balance them with only ~100mA current.

- - - Updated - - -

I did a quick 3d modeling of the tesla pack based on the wheel base dimensions and patent drawings....and measured the pack volume to be ~ 365L which gives the pack --> 85 kWh/365L = 234 Wh/L ... Also if you assume a module to be 300x680x80 mm --> 16.32L --> 5.31 kWh/16.32 --> ~ 325 Wh/L. Can anyone confirm? Thanks!

Thanks Bazinha, I think that your battery pack model is accurate enough. I was calculating this with dimensions wxhxl found in Tesla patents and my result was ~220Wh/l. If you appreciate, the battery pack info for other EVs batteries are:

VW e-UP!: 211 l / 230 kg / 18,7 kWh = 89 Wh/l and 81 Wh/kg
Kia Soul EV: 241 l / 275 kg / 27 kWh = 112 Wh/l and 98 Wh/kg
Chevy Spark EV(wit A123 cells): 139 l / 254 kg / 21,4 kWh = 154 Wh/l and 84 Wh/kg

 

[Pajda]

So, finished my first 500mA discharge curve for a single cell from a Model S module. Charged to 4.2V @ 1A constant-current, then constant-voltage until current dropped to 120mA, 5 minute delay, then discharge at 500mA until voltage read 2.85V. Test was done using FMA Powerlab 8 and the custom settings above. After charging the cell settled to a resting voltage of about 4.16V.

Was able to draw 2,963mAh. Using 10 second voltage averages this came out to 10.605 Wh. That'd be about 4.7kWh for a module, or about 75kWh for a full 85kWh pack using this method. I think there is room for improvement on the extreme ends, however.

My 120mA charge current during CV stage could probably be dropped to squeeze some more juice into the cell, and I could probably discharge it lower than 2.85V. There was ~100mV voltage sag at the begining of the discharge, also, and this seemed to increase quite a bit during the cycle as evident by a resting voltage of ~3.1V after removal of the 500mA load. I may try soldering heavier gauge wire to my 18650 cell holder later and retesting to see if that improves the voltage sag.

Thanks wk057 for your cell measurement. I assume that this discharge curve is quite OK. :smile: But I have a few hints or comments (sorry if they are well known for you )

Methodology: Did you use 4-wire (Kelvin) measuring method with your PL8 station? I mean bananas together with balancing connector?

For Coulomb counting (Ahr counter) it doesn't matter on the wire gauge which you use. You can use "nail" and still you got the same mAh capacity results with your PL8. (Because you make a series circuit and the discharge current is then the same in the whole circuit - so it doesn't matter where you dissipate the energy - inside the PL8, in the wires or in the Internal resistance of cell). The only thing which matters is how precise is your amperemeter in PL8 (it uses 16.bit ADCs so yes, we can consider the measurement as quite precise)

But the problem is with cell voltage measurement, which affected the measurement of total dissipated energy. There in 2-wire method the heavier wire gauge can help, but still there will be some influence (In fact you don't have problem with wire resistance, but with the contact resistance which is much harder problem to solve). So for precise cell voltage measurement is in Kelvin method used idependent voltmeter with high internal resistance and two independent wires (this method completely eliminates the influence of resistance of wiring).

Cell parameters:
Tesla uses NCA cells with 12Wh / 3350mAh nominal (11,7Wh / 3250mAh minimum for new cell), This minimum energy/capacity can be discharged below this test cycle:

Charge: 0,5C (1,625A) to 4,2V with cut off current C/50 (65mA)
Discharge: 0,2C (625mA) to cut off voltage 2,5V.

But we already know that Tesla doesn't allow you to brick the battery and also for initial production cell capacity variation so:

maximum pack usable energy is about ~81kWh (discharge to ~2,7V).
For "range driving" it is about ~75kWh (discharge to ~2,9V)
For "normal driving" it is about ~68kWh (discharge to ~3.1V).
For both driving modes you can discharge aditional ~5kWh as a zero mile protection.
______

Can you please measure a cell Internal Resistance with your PL8? (for this you definitely need the 4-wire method)

 

[Pajda]

I found in the shelf never used Panasonic NCR18650B (industrial grade equivalent to Tesla 12Wh cells). Cell was made in Q3/2013 and I do measurement under the upper mentioned test cycle: (charge: 1,65A to 4,2V with 65mA cut off, 15min rest time, then discharge: 620mA to 2,5V cut off) with these results:

Cell IR: 31,4 mOhms (this is DC resistance measured by PL8 algorithm which is not so precise, anyway manufacturer specs say that it should be less than 45mOhms)

cell cut off voltage - cell measured capacity - cell measured energy - pack energy (x7104 cells for 85kWh pack) - pack cut off voltage (x96 for 85kWh pack)

2,5V - 3268mAh - 11,75Wh - 83,49 kWh - 240 V
2,7V - 3244mAh - 11,69Wh - 83,05 kWh - 259 V
2,9V - 3209mAh - 11,58Wh - 82,25 kWh - 278 V
3,0V - 3172mAh - 11,49Wh - 81,61 kWh - 288 V
3,1V - 3120mAh - 11,33Wh - 80,49 kWh - 297 V
3,2V - 3036mAh - 11,07Wh - 78,63 kWh - 307 V
3,3V - 2883mAh - 10,58Wh - 75,13 kWh - 317 V
3,4V - 2664mAh - 9,85Wh - 69,97 kWh - 326 V
3,5V - 2308mAh - 8,64Wh - 61,35 kWh - 336 V

You can see that there is no magic in Tesla pack in the term of 85 kWh energy rating.

By the way this sample losses minimum energy due to almost 2 year of storage and still it is above minimum capacity (3250mAh). This cell is an older version "B" with graphite only anode, cells made in 2014 are marked as "BF" and it uses SiO aditive to graphite Anode. Here you can see the datasheet https://www.akkuteile.de/tpl/download/NCR-18650BF.pdf which shows the main differences. The SiO aditive improve almost all parametrs of NCA cells, but the most important improvement is in the power and cycle life region, not the energy density. I think, that Tesla already uses this SiO cells equvalent for the whole 2014.

The new 90kWh pack cells are for sure with SiO additive, but i think that the increase of capacity is not caused by SiO itself. This cells are most probably rated as 12,6Wh/3500mAh nominal and 12,2Wh/3400mAh minimum for new cell. We can see their industrial equivalents from LG, Samsung and Sanyo.

 

[apacheguy]

@wk057 - Any idea how well these modules buffer temperature changes with coolant present in the lines? I'm curious how well a standing module does while it's sitting out in my driveway. Could be a neat experiment to try to model the environment of the cell resting in the main pack and have two temp sensors - one on an individual cell and another ambient and make a plot of the two.

 

[Ingineer]

I think wk057 is off the forum until further notice.

 

[apacheguy]

Yeah. Thought he said he was still maintaining this thread tho.

I think wk057 is off the forum until further notice.

Oh, but wait. Since you somehow have access to the cars logs you can answer this question without us have to go to the trouble of doing an experiment. Can you make a plot of module temp v ambient on one of these hot days? That'd be really great.

 

[wk057]

I think wk057 is off the forum until further notice.

Actually, I'm keeping an eye on my project threads and technical threads like this one. Just staying out of the nonsense.

@wk057 - Any idea how well these modules buffer temperature changes with coolant present in the lines? I'm curious how well a standing module does while it's sitting out in my driveway. Could be a neat experiment to try to model the environment of the cell resting in the main pack and have two temp sensors - one on an individual cell and another ambient and make a plot of the two.

I haven't messed around much with the coolant loop just yet. The cells I have installed in my rack are in a room that is temperature controlled to 64F, and even under maximum load or charge for my system the ambient air is enough to keep them under 70F.

The modules DO have two temperature sensors each. One is on a cell close to the inlet of the cooling loop, and the other is on a cell close to the outlet of the cooling loop. So, the temperature data is available to the car at least, and I'm going to use these sensors in my custom BMS (they're just 10k thermistors).

 

[JST]

Actually, I'm keeping an eye on my project threads and technical threads like this one. Just staying out of the nonsense.

I know this is OT for the thread, but as someone who's dug perhaps more than anyone else into the nuts and bolts of the Tesla pack, any thoughts on Porsche's proposal to use an 800V pack? Does this say anything particularly interesting about the technology they're planning to use?

Porsche annnounces BEV version of 911 -

 

[Scotty]

Although I have no experience with the Tesla pack, I do with EV's. I've done an EV upgrade from VRLA gel batteries ti LiFePO4 battery packs, and there are advantages and disadvantages to higher voltage battery packs. My upgrade is from a 72 Volt Nominal system to an 80 Volt nominal system, and even that small increase is noticeable.

Here's some info.

At a certain load, the motor and motor controller use a set amount of power. Assuming the system can handle higher voltage (which could be simple or compex), the following applies

Increasing the voltage will decrease the current drawn, when delivering the same amount of power
Current through a resistance generates heat, which is fine for a toaster, but not so fine for motors and lighting
Since increasing voltage decreases current, at higher voltages. less heating at the same power point will occurr
Since current through the resistance decreases, smaller diameter conductors can be used, decreasing weight and cost of the cables
Charging a higher voltage pack may be more complicated and/or expensive I.E. charging an 800 Volt pack will requires much higher rated components/assembles than 400V.
-- However, dividing the pack into modules will allow for optimized and independent module charging, which is dependent on individual module monitoring and control
Higher voltages can be more efficient.
Other assemblies in the vehicle can be more costly i.e higher voltage DC/DC Converters to switch 800 VDC to 13 Volt DC for ancillary equipment... lights, displays, etc
Current chargers already incorporates more efficient design, but higher voltages bring more expense in design, fabrication and component / assembly specifications

DC Battery pack feeds DC high voltage, high current to Motor controller, which then converts and controls it's output, which is 3 phase power to the AC Motor.
The design and integration of the AC Motor Controller to the 3 Phase AC Induction Motor is complex and complicated, in itself (Look at the Tesla MS Motor Controller in the How It's made Youtube Video to see it).

Scotty

 

[wk057]

I know this is OT for the thread, but as someone who's dug perhaps more than anyone else into the nuts and bolts of the Tesla pack, any thoughts on Porsche's proposal to use an 800V pack? Does this say anything particularly interesting about the technology they're planning to use?

Porsche annnounces BEV version of 911 -

800V is a whole different ball game. Different wire insulation requirements, DC arc arresting, etc. Good luck finding a reasonably priced high current 800V DC contactor.

An advantage would be that the higher voltage would allow higher power at lower currents, if the pack could handle it. But voltage alone doesn't really tell us a whole lot.

Plus, I don't believe any existing charging standard supports 800VDC. So, I'm thinking someone typod this, honestly. It's likely be way more trouble than it's worth to go above ~500V.

 

[lolachampcar]

Not to mention IGBTs for 800 Vdc working :0

 

[JRP3]

I thought 800V sounded a bit high, but, at least for industrial motors, up to 13,200 Volts seems to be labeled "medium voltage" http://www.esrmotors.com/Motors-Medium_Voltage.html