Bms for 5s2p pack using 10 3Ah 30A VTC6

[groinedvault]

I am rebuilding a 5S2P pack using 10 3Ah 30A VTC6 Murata cells. The original cells had only 1.3Ah capacity.

I connected the original bms, charged the pack, but the grinder won't run although I read 20.44V across the terminals. I think the original bms is no longer suitable as the new 6Ah capacity and the new continuous current rating of the cells are much higher.

But my knowledge is limited and would appreciate any help to get the pack working. Do i need a new bms? Am i right to think that bms should be rated 60A because of the 2P connection. There are lots of 30A boards on AliExpress but not 60A. Or am I wrong with the 60A rating that I am proposing. The size of the board should be 85mm x 63mm.....standard i guess for the 5S2P configuration. Can someone point me to a suitable bms. Any comment is appreciated. This is my first time on this forum, so apologies if this is not the right way or place to do this.

 

[amberwolf]

I am rebuilding a 5S2P pack using 10 3Ah 30A VTC6 Murata cells. The original cells had only 1.3Ah capacity.

I connected the original bms, charged the pack, but the grinder won't run although I read 20.44V across the terminals.

What are each of the cell voltages? If they're far enough imbalanced, it might keep the BMS from allowing output (and sometimes even charge).

I think the original bms is no longer suitable as the new 6Ah capacity and the new continuous current rating of the cells are much higher.

The capacity / current rating wouldn't change whether it would run or not, it would just change how long it can run and how hot the cells would run (or rather, how little heat would be generated).

However, it's possible your toolpack BMS is one of those that detects whether it's cells have failed (dropped below safe LVC) it bricks the pack by permanently disabling its' input/output, to protect the user from a fire from charging/discharging damaged cells. It doesn't know that cells were replaced, only that they failed. The factory might have a way to reset that for some of these, but they dont' really have a reason to do that--they just sell you new packs.

What happened to the original cells that required replacing them? Depending on what it was, it might be related to the present issue.

But my knowledge is limited and would appreciate any help to get the pack working. Do i need a new bms? Am i right to think that bms should be rated 60A because of the 2P connection. There are lots of 30A boards on AliExpress but not 60A. Or am I wrong with the 60A rating that I am proposing. The size of the board should be 85mm x 63mm.....standard i guess for the 5S2P configuration. Can someone point me to a suitable bms.

You need a BMS that is suited to the tool(s). Do the tools take 60A? If not, you don't need a 60A BMS. If they only take 5A, you only need a 5A BMS, for instance.

How many cells in parallel doesnt' make any difference for the BMS; they're all just one big cell to it, for all parallel cells. You could have 100 cells in parallel, and all it sees is one cell that's 100x bigger than the cells you used 100 of.

You do want to use a BMS that prevents anything that can damage the cells (taht's what it's there for), so it shouldn't allow current output higher than the cells can handle, or voltages higher or lower, etc.


You also need a BMS that's compatible with the tool. Does the tool communicate with the battery in any way to check to see if it's ok to operate? Some tools do the actual controlling, and the BMS just checks things and says yes or no.