Size Nickel Strip for "Continuous Discharge" or "Peak Discharge" of BMS?

[YoshiMoshi]

BMS ratings have a "Maximum Continuous Dishcarge" rating and a "Maximum Peak Dishcarge" ratings.

Do I need to size my nickel strips for the continuous or peak ratins? It's my understanding that the continuous rating, is the maximum current allowed by the BMS. The BMS allows for current over the continuous ratings, called "peak" in short bursts and small time intervals. I've seen testing on YouTube where as much as 9 seconds is allowed at the peak rating before the BMS cuts off the battery. Not sure if there's a standard time interval allowed by BMSs at the peak current?

Anyways the peak ratings are sometimes double the continuous rating. Should I size my nickel strip for my battery at the continuosu rating or the peak rating and why? so say for example 30 A continuous and 60 A peak from the BMS. Am I able to use cope wire rated for 36 A in this battery pack, or nickel strip rated at 32 A from Matador's table? This is greater than 30 A continuous rating, but significantly less than the 60 A peak allowed by the BMS. Is this OK?

Thanks for any help in understanding this concept!

 

[amberwolf]

What is your system actually going to draw from the pack, worst case, and typically? These are what you'll have to size things for.

Peaks are typically supposed to be very short usages, of a few seconds, so as long as the system as a whole is not used at peak often or long then sizing things for non-peak use should be ok.

However, if it is well-insulated thermally, the heat generated by peak use may not dissipate very quickly, and will heat up the cells, etc. If you don't want that, size things for well-above peak use, so that the resistance is low enough to not generate heat.

You can calculate the overall resistance of various pack elements, and then use that to determine how many watts of heat would be made, and then use pages like this one

Watts to Heat Calculator

Use the watts to heat calculator to know the power you need to heat a particular substance.

www.omnicalculator.com

to guesstimate the heat generated within a part or system, if you want to go that deeply in.


The safest way to design a system is to use parts with higher ratings than they will ever be used at, but this costs more and can be physically larger, and might not be possible in various use cases.

So you have to balance budget, size/weight limitations, actual usage, required safety levels, to decide what level of "overspec" (if any) to use.