Pulling my hair out how many cells do I use

[professorkaos]

I have two bms's there are 72 volts 20s 120 amps and I need to build a battery for my 3,000 watt hub motor that is on my juiced cargo bike but I can't figure out for the love of me how many cells to put in to each and blah blah blah so if anyone can help me that be great can't even put any pictures to show me how to do it but it be possible for me to do 20 sets of 12 in each set or is that too much battery or I don't know

 

[lnanek]

You have to pick the cell first, then check the data sheet, then divide 120A by the max continuous discharge of the cell. If the cell data sheet says it can handle 20A continuous, you need 6 in parallel to handle 120A. So 20 groups of 6 connected in series.

You can add more in parallel to each group to increase pack capacity and decrease voltage sag under load. 20s6p pack will only last half as long as a 20s12p pack.

Note that 120A is 8,640 watts at 72V, though. So make sure your 3,000 watt motor has a temperature sensor and your controller handles thermal rollback if your controller can actually drive the motor at 120A. My Baserunner can only do ~50A, so not an issue.

 

[E-HP]

I have two bms's there are 72 volts 20s 120 amps and I need to build a battery for my 3,000 watt hub motor that is on my juiced cargo bike but I can't figure out for the love of me how many cells to put in to each and blah blah blah so if anyone can help me that be great can't even put any pictures to show me how to do it but it be possible for me to do 20 sets of 12 in each set or is that too much battery or I don't know

It looks like your translator removed some of the details from your post and substituted gibberish, so not enough details to help. However, once you find someone in your area to build the pack, you can provide him with all of that, including your system, space and budget requirements, and he should be able to provide a few options.