Help understanding BMS - Page 1
Forum section: electronics / beginners

author: Epovo
author_rank: Contributor
timestamp: April 01, 2024, 09:18:22 pm
content: I am using a BMS to manage 4 Li ion batteries in series. The batteries are to power an amplifier.I don't understand how BMS can possibly protect the batteries from overdischarging when the charger is not connected to the power supply. I plan to connect the amplifier to B+ and B-. If the amplifier is drawing current from the batteries, there is nothing the BMS can do about it, right? I am confusedI attach a photo of my BMS in case it helps.

author: Bud
author_rank: Super Contributor
timestamp: April 01, 2024, 11:30:28 pm
content: Perhaps you should connect your amplifier to P+ and P-.

author: Siwastaja
author_rank: Super Contributor
timestamp: April 02, 2024, 06:55:11 pm
content: Read the instructions / manual / datasheet of the BMS. It should explain how to connect the battery, charger, and load. Myguessis that battery should be connected to B+ / B-

author: kjr18
author_rank: Regular Contributor
timestamp: April 03, 2024, 06:55:49 am
content: This BMS has no manual, or anything like that probably. Looks more like ebay/aliexpress cheap bms.As for connecting it:P+ positive output terminalP- negative output terminalB- negative of first cellB1 connection between first cell positive terminal and second cell negative terminalB2 connection between second cell positive terminal and third cell negative terminalB3 connection between third cell positive terminal and fourth cell negative terminalB+ connection to fourth cell positive terminalAs for charging you could use P+ and P-. That 5 pin cable is for connecting it to balancing charger, probably they should work with only those, or use that and P+ and P-. I don't know if this type of BMS can keep cells balanced.

author: p.larner
author_rank: Frequent Contributor
timestamp: April 03, 2024, 08:12:46 am
content: just a word of warning,i have had a few ebay bms boards where the low volt cutoff did not work therefore killing a few packs!.

author: aliarifat794
author_rank: Regular Contributor
timestamp: April 03, 2024, 02:42:13 pm
content: Isn't there any manual available? is there any model number or something which can give a lead?

author: Bud
author_rank: Super Contributor
timestamp: April 03, 2024, 09:17:39 pm
content: You do not get user manuals with stuff you buy on Ali.

author: shapirus
author_rank: Super Contributor
timestamp: April 03, 2024, 10:43:06 pm
content: Quote from: Bud on April 03, 2024, 09:17:39 pmIn most (or many) cases you do. Every BMS I ordered on Ali had a connection diagram provided on the product description page.

author: Bud
author_rank: Super Contributor
timestamp: April 03, 2024, 11:28:44 pm
content: Then help the guy with how it should be connected.

author: shapirus
author_rank: Super Contributor
timestamp: April 04, 2024, 09:57:06 am
content: Quote from: Bud on April 03, 2024, 11:28:44 pmHow would I do that without knowing the URL of the BMS product description page?

author: Bud
author_rank: Super Contributor
timestamp: April 04, 2024, 04:27:07 pm
content: They are all same on Ali, differing only in number of cells.

author: Vovk_Z
author_rank: Super Contributor
timestamp: April 04, 2024, 04:47:25 pm
content: Quote from: Epovo on April 01, 2024, 09:18:22 pmThat's why you always connect any load and chargers to a battery only after a BMS, using P+ and P-. Sometimes BMS have only one output (P+) so other is a common ground.

author: Vovk_Z
author_rank: Super Contributor
timestamp: April 04, 2024, 04:51:19 pm
content: Quote from: Bud on April 03, 2024, 09:17:39 pmBut some sellers provide circuit diagrams and some description. It's better to buy from them (from those who show you need info). I'm sure you may find this exact BMS at other sellers who show a connection diagram for it. (But it's quite typical. B+ and B- goes to battery only, P+/P- goes to output and charger).

author: shapirus
author_rank: Super Contributor
timestamp: April 04, 2024, 06:13:45 pm
content: Quote from: Bud on April 04, 2024, 04:27:07 pmNo. There are several types: load and charger on same terminals or separate, varying schematics, not to mention power rating.