#### Mr_funnypuns

##### Active Member

- First Name
- Timothy

- Joined
- Nov 1, 2019

- Messages
- 44

- Reaction score
- 24

- Location
- Chicago Suburbs

- First Name
- Timothy

- Vehicles
- 2006 Toyota Prius, 2009 Hybrid Sierra, 1985 Fiero

- Occupation
- Electrical Engineer and Six Sigma “Black Belt”

- Thread starter
- #1

Rivian has annonounced that their battery modules will contain 864 2170 cells and deliver 15 kWh. According to published data, the LG 21700 can deliver about 18 WH, so the math matches, at a module capacity of 15.6 kWH.

Factoring the 864 batteries it seems to me that the configuration could be 8 x 108 - eight strings of 108 2170 cells. This means each string would have a peak voltage of 108 * 3.6V = 388V and have an internal resistance of 108*0.025 ohms = 2.7 ohms, 8 modules has a resistance of 2.7 ohms / 8 = 337 milliohms. Rivian has published a 0-96 kPH time of 3s. This means 26.7 m/2 * 26.7 m/s * 1/2 * 2670 kg = 951.7 kJ over 3s, or an average power output of 317 kW from 12 modules, with each module delivering 26 kw. Applying a little algebra, this works out to about 71 amps per module, or 8.8 amps per string and cell, making the dissipation for each cell right about 1.9W.

1.9W per cell means each module is dissipating 1.7 kW while delivering 26 kW, and operates at an electrical efficiency of about 93%. The entire pack is generating about 20 kW of heat, which means the thermal conductivity of the cooling system needs to be around 667 Watts per degree C if the pack is kept to 30C, or 400 watts per degree C at 50C.

The point of all this math? It’s fun!!! Well that, and, by known the configuration and some of the implications of that configuration allow us to make other estimations about the Rivian. One of the more interesting things is that the pack seems to be be designed in such a way that when the truck is used around town at much modest loads, say 0-60 in 15 seconds, the pack might last a very long time indeed.

Working out the math for that next.

Factoring the 864 batteries it seems to me that the configuration could be 8 x 108 - eight strings of 108 2170 cells. This means each string would have a peak voltage of 108 * 3.6V = 388V and have an internal resistance of 108*0.025 ohms = 2.7 ohms, 8 modules has a resistance of 2.7 ohms / 8 = 337 milliohms. Rivian has published a 0-96 kPH time of 3s. This means 26.7 m/2 * 26.7 m/s * 1/2 * 2670 kg = 951.7 kJ over 3s, or an average power output of 317 kW from 12 modules, with each module delivering 26 kw. Applying a little algebra, this works out to about 71 amps per module, or 8.8 amps per string and cell, making the dissipation for each cell right about 1.9W.

1.9W per cell means each module is dissipating 1.7 kW while delivering 26 kW, and operates at an electrical efficiency of about 93%. The entire pack is generating about 20 kW of heat, which means the thermal conductivity of the cooling system needs to be around 667 Watts per degree C if the pack is kept to 30C, or 400 watts per degree C at 50C.

The point of all this math? It’s fun!!! Well that, and, by known the configuration and some of the implications of that configuration allow us to make other estimations about the Rivian. One of the more interesting things is that the pack seems to be be designed in such a way that when the truck is used around town at much modest loads, say 0-60 in 15 seconds, the pack might last a very long time indeed.

Working out the math for that next.

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