Calculating Approximate Max Current in 400V 3Ah Series Example Using 18650 cells.

During the “Battery Module” video of the EV Batteries module there is an example explaining connecting battery 18650 cells in series at timecode 2:25. I understand how we obtain the total voltage of 400V and that since we are only connected in series the 18650’s capacity of 3Ah stays constant in our series “pack”, but I don’t understand how I should calculate the approximate 30Amps of max current that are given in this example. Is this figure coming from the data sheet of one individual 18650 cell and are we assuming it is value that is not improved when connecting in series, or is it calculated using a relationship/equation that I’m missing?

I attached two images showing the Closed Caption message where the 30Amps of max current is being brought up.

I may be mis-understanding your issue, but battery cells in series add the voltages and have the same current, battery cells in parallel add the current but have the same voltage. It may, of course, be a simple typo' on their part, with it supposed to be 3A?

This is why it's normal practice to arrange the battery's cells so they're partly in series, and partly in parallel, so the voltage is higher and so is the current.

For example, using 96 of the 4.2V, 3A cells, some arrangements are

all 96 in series = 4.2V x 96 = 403.2V but only 3A

all 96 in parallel = 288A but at only 4.2V.

However if used in a grid of, say, 12 parallel by 8 in series, we have 12 x 3A = 36A, 8 x 4.2V = 33.6V, which is more usefull. Or the other way round, 8 x 12 respectively, we get 24A at 50.4V.

Etc.

Thanks for the confirmation and examples Gord!

That makes sense to me. I was thinking along the same lines that it was supposed to be 3A.

I didn’t want to assume in case I was misunderstanding something since I’m new.