BMS's C-, B- which port to connect and why ?

Batteries, Chargers, and Battery Management Systems.
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ichiban   100 W

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BMS's C-, B- which port to connect and why ?

Post by ichiban » Nov 28 2019 3:35am

BMS's C-, B- which port to connect and why ?

We all need BMS on our battery packs. A lot of us use those ready made BMSs from various sources. For example :

14S Smart Li-ion Battery PCB board Bluetooth Mobile BMS for 48V 58.8VLi-Ion E-bike Battery system with 20A to 60A Current
https://www.aliexpress.com/item/3279418 ... b201603_55



Image



Most of them have C- / B- as connecting ports and we connect them as typically recommended by the sellers without knowing the reason. I've seen some of the gurus connect them differently in which I also do not quite understand. Like this thread, I cannot tell which post(s) exactly on that thread since it is so lengthy (but very useful) :


bluetooth BMS?
http://www.endless-sphere.com/forums/vi ... 93af0ef403


Which connection is best and for what purposes / applications ?

Would the experts please help answer this and the reasons behind them for the better understanding of the community. Or any comments from anyone would be appreciated.
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amberwolf   100 GW

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Re: BMS's C-, B- which port to connect and why ?

Post by amberwolf » Nov 28 2019 2:54pm

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. ;)

john61ct   1.21 GW

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Re: BMS's C-, B- which port to connect and why ?

Post by john61ct » Nov 28 2019 4:31pm

^^^^ THIS ^^^^

999zip999   100 GW

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Re: BMS's C-, B- which port to connect and why ?

Post by 999zip999 » Nov 29 2019 12:49pm

The higher quality cells and use them under rated specs lower your huc and lvc cutoff going up ah and putting on extra weight and size for longevity of self monitor always. Or no bms and your the man. Not a loner bike.

ichiban   100 W

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Re: BMS's C-, B- which port to connect and why ?

Post by ichiban » Dec 09 2019 4:17am

My BMS is from JBD 14S 60A just like that picture in the 1st post above. There is only B- and C-, so I just use it as is. Recall that someone (electricgod ?) mentioned in that thread somewhere :

bluetooth BMS?
http://www.endless-sphere.com/forums/vi ... 0f0034b907

as he connected P- from some pad on the pcb. Wonder where that pad might be ? And may be I can do that very same thing.

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