bms is designed for 50A, but when the current draw increase above 5A, temperature starts to rise. Actual resistance of the pack is 63 mΩ but bms resistance is 59mΩ. Why bms resistance so high?
Could also be a defective FET.
The high ON-resistance of 59mΩ points to the FETs getting only a 2~4V On-signal ("Gate voltage" or "driving voltage"), when it probably requires 5V~15V to fully turn on. Would need to look up the datasheet for the part to confirm.
The "left" leg of the FET that's soldered to the smaller PCB pad should be the gate terminal, the right leg with the bulkier connection should be the "source" terminal.
Measure the voltage between source<->gate on each FET. If one (or more) gate has near 0V, it's probably shorted and causing the low gate voltage for everyone else.
If you should find the damaged FET(s), you could just lift up both legs (left and right) to disable the FET(s) and use the BMS, albeit at a slightly lower max current. Replacing with a working FET would of course be better.
Another (or additional) possibility is that the "FET driver circuit" that supplies said 5V-15V voltage is damaged. Fixing that will require a lot more work.
Thank you ajw22. I have found the culprit thanks to you, i lifted the gate leg of bad FET and i measured the resistance to the the source leg. it was showing some resistance. After that bms resistance dropped to normal. it was difficult to de-solder, so i left it like that. now its working properly. Once again thank you ajw22, you saved lots of time for me. I didn't expect that i will find solution for my problem when i posted this thread, thanks everyone who have commented.FETs can only stop electricity flow in one direction (eg. discharge), and cannot stop when flowing the other way (eg. charge). So in a BMS, a pair or FETs arranged head-to-head is used to stop current flow in both directions.
The FETs on the right column are responsible for stopping the charging current, but always lets through discharging. Gate 0V means the BMS is preventing charging... should it be?
The FETs on the left column are responsible for stopping the discharging current, but always lets through charging. Gate voltage of 4.6V for the crss052n08n is kinda-ON, but a bit short of the ~6V it needs to be ON properly.
One (or more) of the FETs on the left might have an internal fault and partly-shorting the gate voltage down to 4.6V. For each FET, try desoldering the gate leg and measure the resistance to the source leg. It should be infinite - if not, you've found the culprit.