I am working off of a schematic where I was given a battery pack with the following specifications. The battery being used is a panasonic NCR18650 lithium ion cell. https://engineering.tamu.edu/media/4247819/ds-battery-panasonic-18650ncr.pdf

The battery pack is stated to have 84 cells in each series string and 79 strings in parallel.

The total amount of cells is 6,636 cells (84 * 79).

The pack voltage rating is given as 302V and the total pack current is given as 236 Amps.

The nominal voltage for this battery is 3.6V so 3.6 x 84 = 302.4 which indicates the pack voltage.

Where I am confused is how the total pack current of 236 Amps is being obtained. 79 strings of cell in parallel would add the total capacity of the batteries.

The capacity of one cell is 2,900 mAh. I would think that the total pack current should be 2,900 x 72 = 208,800mAh or 208.8 Amps.

I am not seeing where the value of 236 Amps is being obtained.

What is also confusing to me is the battery pack has a life estimation of 2,800 seconds at a rating of 300V @ 3 Amps.

The equation for battery life is the battery capacity divided by the load current. I have not found a way to make these numbers make sense.

Is there anything that I am overlooking in this calculation, that would cause me to obtain the specified values? Any insight is appreciated.

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    \$\begingroup\$ You question reads like a high school math test. Could you clear up the wall of text? \$\endgroup\$ – Jeroen3 Jun 5 '18 at 18:05
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    \$\begingroup\$ If you don't know the difference between amps and amp-hours, you certainly shouldn't be working on a 350kg battery. \$\endgroup\$ – Brian Drummond Jun 6 '18 at 8:49
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    \$\begingroup\$ @BrianDrummond, correction, "on a 350kg Li-Ion battery" -:( \$\endgroup\$ – Ale..chenski Jun 6 '18 at 13:59

Capacity of a battery ("C", in mA-hours) has nothing to do with the amperage rating of the cell. There are low-dicharge batteries (at 0.2 0.5C rate), and there are high discharge cells (at 15C-50C), which can give a lot of current but over a short time. So if a cell is rated as 2900 mAh, this doesn't mean much about its discharge rating. This is first.

Second, 79 cells in parallel will have 2900x79= 229 A*h capacity. Times 302 V it means that this battery is a "70kWh" battery. If the battery specs say "236 A max current", it means that the cells can be safely discharged at just about 1.05C, which sounds like an ordinary home-made battery and well within the NCR18650 cell specifications. At this load (at 236 A) the battery will last ("pack life"?) about 50-55 minutes. I don't know what the "total pack current" is, but it sounds like the max peak current for the entire battery.

However, the "pack life" at 3 A discharge doesn't make sense. At 3 A discharge this battery pack should last about 76 hours, or 273,000 seconds. So there is a clear issue with specifications given to you.

  • \$\begingroup\$ Unless "3A discharge" meant 3A per cell, which would mean 237A (oddly, not 236) for the whole pack. Factor in the DOD and the specs pretty much make sense. \$\endgroup\$ – Brian Drummond Jun 6 '18 at 14:04

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