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Current in battery packs
#1
Why doesn't the current in a battery pack destroy the cells. Let's say you're building a 5s20p pack of 18650 cells, and each cell provides 1A of current. To my knowledge that is 20A 18V. Does the high current of 20A not destroy the cells?
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#2
Not IF the cells can handle that current.
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#3
(07-04-2019, 12:17 PM)daromer Wrote: Not IF the cells can handle that current.

Okay I get it, but what if the current of the pack is higher than what the cells can handle. What do you do then? And how do you know what the maximum current through a battery is?
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#4
In short it'll shorten the life of the cell. They won't blow up (normally) or fail catastrophically. Most laptop or similar cells can handle up to 5C for short bursts without much effect. But continued use at this rating will destroy them.
Powertool type cells on the other hand, can handle far more current flow. They are normally rated at around 5C continuous, with bursts around 20C or such. Just depends on the chemistry used a particular cell.

It doesn't matter if a single cell delivered 1A, or 20 cells in parallel deliver 20A, the effect is more or less identical to the cells. We could get into differences in internal resistance (IR) and other factors, but we'll leave that for another day Wink
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#5
(07-04-2019, 12:51 PM)Korishan Wrote: In short it'll shorten the life of the cell. They won't blow up (normally) or fail catastrophically. Most laptop or similar cells can handle up to 5C for short bursts without much effect. But continued use at this rating will destroy them.
Powertool type cells on the other hand, can handle far more current flow. They are normally rated at around 5C continuous, with bursts around 20C or such. Just depends on the chemistry used a particular cell.

It doesn't matter if a single cell delivered 1A, or 20 cells in parallel deliver 20A, the effect is more or less identical to the cells. We could get into differences in internal resistance (IR) and other factors, but we'll leave that for another day Wink

Thanks for your reply, I understand it now.
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#6
You add a fuse to protect the battery from overcurrent. A battery should never have to see to much current.

On powertools the limit is either the motor itself or its calculated by the resistance in the cells
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