jonpad01
10 mW
Hey guys,
A few months ago a I built my first 20s7p battery using molicel p42a cells. I used the copper nickel sandwhich method using a malectrics spot welder and a 12v car battery. After reading about the differences between the two, I now wish I had bought the kweld. I had some trouble getting good welds as the car battery would drain and had to recharge it a few times.
On my BMS I have a cell group that is about 0.02v lower than the rest of the groups at 90% charge. The rest of the groups are all within 0.005v of each other. I noticed when riding hard last night I managed to fully drain the battery to the point where the BMS shut off. I looked at the voltages and that group was at about 2.8v while the rest were at about 3.2v. That group has returned to the usual 0.02v offset after recharging the battery.
Please note that I dont know very much about lithium batteries.
So I have a few questions, do I need to worry about this cell group?
Lets say one of my welds was really bad and broke loose, what would happen? The battery is secure but I have already dropped this bike down a hill.
This last question is about discharge current. On the datasheet it says these batteries are rated for 45 amps, but Ive seen real world testing that puts them closer to 30 amps before overheating. What would happen if I were to draw 50 amps from them for a very short period of time, about 5 seconds, is it just the heat that damages them? Would they even get hot enoguh to worry about? Currently my controller is set to about 300 line amps, which is about 42 amps per cell. Im not even sure I can draw that much because the bike pulls a wheely and I let go of the throttle.
A few months ago a I built my first 20s7p battery using molicel p42a cells. I used the copper nickel sandwhich method using a malectrics spot welder and a 12v car battery. After reading about the differences between the two, I now wish I had bought the kweld. I had some trouble getting good welds as the car battery would drain and had to recharge it a few times.
On my BMS I have a cell group that is about 0.02v lower than the rest of the groups at 90% charge. The rest of the groups are all within 0.005v of each other. I noticed when riding hard last night I managed to fully drain the battery to the point where the BMS shut off. I looked at the voltages and that group was at about 2.8v while the rest were at about 3.2v. That group has returned to the usual 0.02v offset after recharging the battery.
Please note that I dont know very much about lithium batteries.
So I have a few questions, do I need to worry about this cell group?
Lets say one of my welds was really bad and broke loose, what would happen? The battery is secure but I have already dropped this bike down a hill.
This last question is about discharge current. On the datasheet it says these batteries are rated for 45 amps, but Ive seen real world testing that puts them closer to 30 amps before overheating. What would happen if I were to draw 50 amps from them for a very short period of time, about 5 seconds, is it just the heat that damages them? Would they even get hot enoguh to worry about? Currently my controller is set to about 300 line amps, which is about 42 amps per cell. Im not even sure I can draw that much because the bike pulls a wheely and I let go of the throttle.