ichiban wrote: ↑Nov 28 2019 3:35am
We all need BMS on our battery packs.
No, we don't.
Some do.
Some don't.
Some should and don't.
Most of them have C- / B- as connecting ports and we connect them as typically recommended by the sellers without knowing the reason.
Depends on the design of the BMS.
B- is where you connect the main
Battery negative of the pack of cells, so you have to use that for that purpose, and only that purpose, if you want the BMS to be able to protect your cells.
C- is where you connect the charger to
Charge the battery.
P- is where you connect the controller to
Power it from the battery.
If the BMS has a common charge/discharge (charger/controller) port, then you only need to use whichever single wire / pad goes to that port for the Charge input and Power output connections. This may be either C- or P- or it may have a completely different designation and not even have a C- / P-; the manufacturer instructions for that specific BMS must be followed. You still have to use the B- for the Battery negative of the pack of cells.
If the charge and discharge ports are separate, then you must use the correct port for the correct input or output connection.
If you do not do it this way, then your cells are not protected against overcharge and/or overdischarge, depending on how you miswire it.
Also:
If the manufacturer (or seller) does not have a completely matching diagram for the BMS they are selling you, don't buy from them, and go get one somewhere else, because it probably means they don't know what they are selling and won't be able to help you with it because they don't even have the right directions for the stuff they're selling. They are likely just getting whatever is available to them cheapest at the time, from wherever they can get it, and that means you have no idea if it's any good or not until something goes wrong. Testing a BMS before using it is possible, but time consuming. A poorly made one could also fail in various ways at any time without warning.
If you don't get a good reliable BMS, you don't have a good reliable battery. The BMS can destroy the battery pack if it fails, and/or it can leave you stranded with no power, and/or it can cause a fire that could destroy the battery, bike, building it is in, and lives.
I'd venture that the most common cause of the pack failures we see here on ES (other than old worn out cells or batteries abused beyond their capabilities) is defective BMSs.
So don't get a BMS (or cells) from a place you don't trust, and don't put your trust in places you don't know.
