Traction Battery - Volts, Amps & SOC%, kWh, Rated Range

[TonyWilliams]

Great info Tony... But then one would think a 35 kwh normal charge should be about 79% of the battery, or range from 3% SOC to ~82% SOC. The 89% SOC figure for a full normal charge seems really high, or am I missing something?

How perceptive. Here's the background; this data was derived from my serial #1134, with about 12% battery degradation. I also own #2496 and #3021.

It appears that Toyota has found a simple way to hide degradation for a "normal" charge. Even 1134 can get 35kWh on a normal charge at about 89% SOC. But, 2496 only charges to 83.8%.

• 
  Rav4 #-- 1134 --- 2496 ----
  
  Extended - 96.5% to 98% (variable, average 97.3% for both cars)
  Normal ----88.9% -- 83.8%
  
  FUEL BAR SEGMENTS:
  16 gone - 83.4% -- 78.7%
  15 gone - 78.0% -- 73.6%

See a trend here? It appears that they split the difference of the actual degradation and how much they compensate on the fuel gauge.

Of course, this means that an extended charge takes a disproportionate amount of range loss,

97.2 - 88.9 = 8.3% difference for 12% degraded battery
97.2 - 83.8 = 13.4% difference for new car

With my 12% degraded battery on 1134, there is a 61% reduction in SOC for the extended portion of the charge, and a 6% increase in the normal portion.

 

[fooljoe]

Here's the background; this data was derived from 1134, with about 12% battery degradation.

It appears that Toyota has found a simple way to hide degradation for a "normal" charge. Even 1134 can get 35kWh on a normal charge at about 89% SOC. But, 2496 only charges to 83.8%.

Ahh that explains a lot. I had assumed you were doing this testing on your newer Rav... No wonder Toyota never called the normal charge an "80% charge" like the terminology that many of us ex-Leafers were used to. I've often wondered if the Volt uses a similar strategy, since it only uses ~65% of its nominal capacity (when new.) Since most reports I've heard from Volt owners indicate zero apparent degradation, I'm guessing this is the case.

So I guess this also means that the fuel bars represent a more or less fixed amount of energy rather than a fixed SOC%. It'll be very interesting to see what your fuel bars do once your battery degrades to the point where a normal charge is less than 35 kwh (ergo normal and extended would be the same.) I wonder if at some point you might not get all 16 fuel bars to illuminate after a full charge.

Honestly, I think I prefer this approach over Nissan's style of instrumentation (separate SOC and capacity bars), except of course for the glaring omission of any bars for charge over the normal charge limit. But now it becomes clear that the reason for omitting those "extra bars" is to hide early degradation.

Great stuff Tony. Interesting how Toyota (or is it Tesla?) can figure out the software to pull off this trickery, but can't do something simple like accurately figuring out how long the car will take to charge...

 

[TonyWilliams]

 

[TonyWilliams]

Doing some basic math, the Panasonic 2900ma cells weigh 44.5grams each.

With 7104 cells known to be in the 85kWh Model S with 3100-3400ma cells, that leaves us with about 4000 cells.

So, 44.5 * 4000 = 178,000 grams

178,000 / 453.592 grams per pound = 392 pounds in battery cells alone

That means that the advertised 800 pounds of the battery pack is only half the cell weight.

 

[Kohler Controller]

Tony, I think it has been stated that our cars use ~5000 cells (92S54P or 4968), not 4000.
Also the math works out better (3.6V x 2.9Ah = 10.44wh x 4968 = 51.8kWh).
At 46 g / cell (from NCR18650PD data sheet), that's 228kg/502lbs of cells alone or 62% of the 800lb battery system weight.

 

[TonyWilliams]

So, our estimates are 110 pounds apart.

I'm starting to believe that the battery is closer to 44-45kWh, based on how we know the 85kWh is built and used.

 

[Dsinned]

Here's the link to an early thread related to this subject which started back in November 2012 with some interesting perspectives.

http://www.myrav4ev.com/forum/viewtopic.php?f=2&t=72&start=0

 

[kiwiguy]

I have a question, if the RAV4 EV has a 50kWh battery pack, does that mean the Tesla 85kWh Model S actually has a 99kWh pack?

I'm assuming they all operate on the same principals, and if you do 7104 cells * 3.4Ah * 4.1V, you get 99kWh.

With a 17% overhead (99/85), that would make a Tesla 60kW model have a 70 kWh pack.

And the RAV4 EV therefore has a 49 kWh pack.

Does that logic make sense? I'm assuming 3400mAh batteries at 4.1V for the 85 kWh model.

 

[miimura]

I'm assuming 3400mAh batteries at 4.1V for the 85 kWh model.

Based on some people who sound like they know what they're talking about at Tesla Motors Club, you don't use 4.1V for the nominal capacity. I think they were using 3.7V for the nominal capacity. That gives about 89.3kWh for the 85kWh model just based on the 3.7/4.1 ratio. That would put it using 95.2% of the nominal capacity. However, most people find that the dashboard on the Model S never shows 85kWh used even when driving from max range charge to 0 rated miles remaining. I don't recall what the max energy used has been.

 

[TonyWilliams]

Yes, we have to use the nominal voltage, since the cells obviously don't stay at 4.1 to 4.2 volts very long. Panasonic publishes data from 4.2 to 2.5 volt cut-off, but you can't just pick an average, since the voltage drop isn't linear.

I'm sure there's a way that it can be calculated, but I don't know what that is. So, using 3.65 volts nominal * 2.9 amp-hours (2.75 is the published minimum) is:

3.65 * 2.9 = 0.010585 kWh per cell

If we use the same 92% that a Tesla Model S uses, then 1 / 0.92 = 1.087 * 41.8kWh usable = 45.3kWh battery

45.3kWh battery / 0.010585 kWh cells = 4279 cells

 

[TonyWilliams]

Tony, I think it has been stated that our cars use ~5000 cells (92S54P or 4968), not 4000.
Also the math works out better (3.6V x 2.9Ah = 10.44wh x 4968 = 51.8kWh).
At 46 g / cell (from NCR18650PD data sheet), that's 228kg/502lbs of cells alone or 62% of the 800lb battery system weight.

Toyota says 386 volts, but we have no idea what that's is supposed to mean.

92 * 4.13v (the highest that I've observed) = 380 volts

 

[Kohler Controller]

According to Valerun, he observed a top Extended Charge CV at 381.5V.

http://www.myrav4ev.com/forum/viewtopic.php?f=9&t=527&start=70

Assuming 92 cells in series at 3.6V/cell (rated from the datasheet), that's 331V nominal and 381 if Extended Charge is 4.13V/cell.

From my cell testing of the NCR18650PD cell, discharging at C/2 rate showed an average voltage of 3.6V between 4.2V-3V.

Toyota Documentation says 386V because 92S x 4.2V (maximum voltage a cell is allowed to be charged to from the manufacturer) is 386V.

So I'm pretty sure it is 92S. As for the number of cell in parallel, my money is on 53P which puts it about 49kWh, with 41.8kWh usable.

I'm pretty sure Tesla products are the same way, which is a 100kWh pack for the Model S85.

 

[miimura]

This is the graphic from TeslaMotorsClub that describes the Model S 85kWh battery capacity points.

I suppose we would have the following levels in the RAV4 EV:
Extended Full
Standard Full
Low Battery Warning
Very Low Battery Warning
Climate Control Limited
Turtle
Shutdown

 

[Kohler Controller]

Mimmura, have you or anyone else been able to put more than 83kWh back in a Model S85? (75.9 kwh /0.85 efficiency)

 

[miimura]

Mimmura, have you or anyone else been able to put more than 83kWh back in a Model S85? (75.9 kwh /0.85 efficiency)

I don't have a Model S and most people don't have energy monitors or dedicated meters on their EVSE to know for sure. Most of the time, people on TMC are going by the data shown by the car, not an external measurement.

 

[Kohler Controller]

I thought the SuperChargers showed energy returned in the Model S. With all the power installed in your garage, I thought perhaps you had one. Thanks for the info.

 

[smkettner]

Tony, Any chance you have calculated and compared your vehicle battery degradation and compared to this chart?

 

[TonyWilliams]

Tony, Any chance you have calculated and compared your vehicle battery degradation and compared to this chart?

I wouldn't know how the cycles would be counted for 41,000 miles. Few people (maybe nobody) cycles their battery from full to empty every time, and neither do I.

 

[smkettner]

Maybe count 41,000 at 120 miles per cycle would be 341 cycles would have you at ~87% capacity?

Trying to use the graph to extrapolate miles to 70% capacity. Looks like at least 150,000 miles.

 

[TonyWilliams]

... So I'm pretty sure it is 92S. As for the number of cell in parallel, my money is on 53P which puts it about 49kWh, with 41.8kWh usable.

I'm pretty sure Tesla products are the same way, which is a 100kWh pack for the Model S85.

I think you're probably right about 92S for the Rav4 EV, however we already know that the Tesla 85kWh pack is 96S, with 16 modules each of which have 6 "bricks" of 74 parallel cells.

7104 total cells = (6 * 16) * 74

4.15 volts per cell * 96 = 398.4 pack voltage (Tesla Model S-85)

4.15 volts per cell * 92 = 381.8 pack voltage (Rav4 EV)