faulty bms?

m3vuv

100 W
Joined
Nov 16, 2017
Messages
222
Location
horncastle lincs uk
Hi all,im not sure if this is the right forum but here goes,i have just built a 13s 9p 17ah 48volt triangle battery using samsung cells,i brought an mgod 20 amp smart bms from aliexpress,the charger is outputting 54.6v,firstly the bms keeps dropping connection over bt and the same over uart with jbd tools,the charger light is always green!,i removed the bms and fitted a dumb one,same issue,green charge led always on and wont turn red!,lowest cell group is at 3.04v highest 4.03v,currently i bypassed the bms,-ve charger wire strait to b-,now the charger has gone red ,the bms has a string of leds,most are lit up,i assume they light when a cell group has hit cuttoff volts?,,all leds are lit except 3
the pack is sitting at 54v and charger turned to green from red,the question is,is it safe charging it this way and should i leave it untill all leds are lit?,all cells are samsung 15q and test ok ,most over 1.5ah,is it just a case of bad balance stopping the smart bms allowing the battery to charge?,the cell hvc was set to 4.2v,the bms seems shit and the pc and android app terrible and buggy!,tia.
 
guess what i need to know is will the bms still balance cells like this?is that the purpose of the leds to bleed off excess volts from groups of cells that are charged,i dont want it going up in flames due to a cell group going over volts.
 
Few BMS are bleeding cells. They usually stop charging those that are full, and continue charging the lower ones until they reach the others. Also, a led is not bleeding enough. There would need to be some cooled down resistance on the bleeding circuit.
 
i fully understand what you say but it doesent answer my question,:ie is it safe to continue charging it this way?,i plan to leave it on the charger until all leds are lit then reconect the smart bms and see what happens,if it dont burst into flames first.
 
It is safe if you had tested them cell blocks to make sure the BMS stops charging them after they are full. :D

To trust a BMS, you first need to test by yourself, or take the risk...
 
I think you are missing the point here,the charger is connected strait from b+ to b- so the bms cant shut off the charger!!!,read my post and try and understand what i am saying.
 
If you bypass the BMS, then you are the BMS. So you need to monitor them yourself and stop charging those that are full. This means you can’t charge using the battery + and - leads after one group of cells had reached full charge. You need to address each cell group separately, if you want to end up with a fully charged and balanced battery.
 
Do not let a badly designed balancing circuit dictate your charge profile.

For longevity you should not be using 4.2V.

4.05Vpc is much better, 4.10V the highest I would go.

No CV, just "charge to xV and stop" using a simple HVC circuit.

Use a decent dedicated balancer or a hobby charger to do balancing only when needed

with a decent pack might only be quarterly, or even annually.
 
You said JBD. I think JBD is crap. Bought two of their units. Neither worked. No refund. No nothing,

Also, always check your wiring on the balance connector, Make sure the voltage walks up incrementally, Make sure the balance connector wasn't wired backwards. I admit to doing both of that, but I always caught it before I plugged in my balance connector. Very rare to have two BMS in a row not work, unless it's those cursed JBD's. .

Your question about charging with the BMS bypassed? It's too risky. You can overcharge the cells that are full and damage them. Might make for a fire later. I would get a variable DC-DC converter, they're about 5 bucks, and set it to output 4.0V. Than balance any low groups. Run the cells down a little bit, and see if the BMS will now take a charge, You have to run the DC-DC unit off a separate battery, not the 13S you are building.
 
this is all i get with the mgod smart bms hooked up,its with jbdt tools,this is the chinglish msg i get when trying to read the bms with the uart port,its got the drivers etc installed,set as com 3 in device manager and set as that in the sw,anyone point me to a better program than this chinky shit?.
 

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Very few people want to reco specific BMS because then they get blamed.

Cheap ones are all Chinese, JBD = LLT and are well respected

https://www.aliexpress.com/item/32794186005.html

but yes you need to know what you are doing, learn by googling and experimentation

get support from members of forums

by knowing enough to ask smart questions

and show a reasonable attitude not acting as if you are entitled to an easy path.

There are better quality BMS but most are bulky and cost more than what people want to spend on their whole battery pack.

...
Here are some notes and links I've collected on the LLT/JBS ones:

LLT / JBD BMS, Smart Battery PCB board Bluetooth BMS, also Ant

reco supplier - diysolar forum
https://store.currentconnected.com/product/jbd
I've spoken to the owner Dexter a few times now, actually just got off the phone with him about some BMS settings questions.
CurrentConnected BMS looks to be the same as the Overkill Solar BMS, which is actually made by LLT Power (and available for less from them):

I have been using the 120A LLT Power BMS for several years and it has worked beautifully. The bluetooth means you don't need battery monitor as it provides a direct readout of SOC/Voltage/Current/Temp etc

_______
open source firmware
https://endless-sphere.com/forums/viewtopic.php?p=1605787#p1605787

Xenodius Ampy project
ASI controller, BMS & display integrated!
10-21S onlt
https://github.com/Xenodius/ASI_AmpyDisplay/tree/master
https://endless-sphere.com/forums/viewtopic.php?t=108580

different from this?
https://www.cloudsto.com/ebikes/bms-1/smart-bms-8-24s-for-vbms-detail.html
Vortecks BMS app. https://play.google.com/store/apps/details?id=com.vortecks.vbms

https://expeditionportal.com/forum/index.php?posts/2922005

JBD Ali store
https://www.aliexpress.com/item/32794186005.html

very highly reco on ES but not the LCD, ElectricGod
https://endless-sphere.com/forums/viewtopic.php?p=1524151#p1524151

site:endless-sphere.com/forums/ bms bluetooth

aka JBD BMS https://endless-sphere.com/forums/viewtopic.php?t=101837

https://endless-sphere.com/forums/viewtopic.php?t=100981

https://endless-sphere.com/forums/viewtopic.php?p=1470433#p1470433

JBD style of BMS you have recommends not using the P- port, and just use C- for both charging and discharging. I've wired three of them that way, and they all work fine.
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://s.click.aliexpress.com/e/qUAMAkA8

Xiao Xiang or BDS smart BMS. There's a few others I've considered trying, but the BDS BMS's do most of what I think I need in a smart BMS

Xiaoxiang type reco
Jiabaida Technology
Dongguan Jiabaida Electronic Technology Co., Ltd.
SZLLT

Overkillsolar.com and batteryhookup.com sell them
I have three of them in parallel

software
https://endless-sphere.com/forums/viewtopic.php?p=1515412#p1515412


Ali seller JBD Battery PCB Board Store
https://s.click.aliexpress.com/e/OstYsoYY
https://s.click.aliexpress.com/e/qUAMAkA8

_____
JBD subsidiary
LLT Power, SHEN ZHEN LI LU TONG ELECTONIC TECHNOLOGY

LLT Power https://www.lithiumbatterypcb.com/product-instructionev-battery-pcb-boardev-battery-pcb-board/ev-battery-pcb-board/smart-bms-of-power-battery

Similar to what EM3EV uses in their batteries

Smart BMS with bluetooth, Protection Circuit Board
intelligent lithium battery bluetooth bms

well recommended, by engineers, many well-experienced users

better than Ant?
here Ant reco
https://endless-sphere.com/forums/viewtopic.php?t=104997
https://endless-sphere.com/forums/viewtopic.php?p=1538162#p1538162
tried a few ANT BMS's, but the android app for them is not as usable as the BDS app. As far as I know, BDS does not make more than a 31S BMS and ANT does.


XiaoXiang (yellow elephant) android App
basically any BMS that uses the "xiaoxiang" app is almost the same HW
https://endless-sphere.com/forums/viewtopic.php?p=1477735#p1477735

https://www.expeditionportal.com/forum/index.php?posts/2687443

are they all Xiaoxiang?
https://github.com/smagicld/xiaoxiangBMS

ones that use the cute elephant app have an LCD, not reco

JBD-SP15S001 (LiIon)
RJXZS
JBD-SP05S002 (LiFePo4)

So are there lots of "other bluetooth" BMS that don't use the "xiaoxiang" app?
There are, I think Em3v uses a different one in their battery packs.

RJXZS Ali shop https://m.aliexpress.com/item/32669831187.html


--------
BotoXbz LLT "smart BMS" BQ76940 based
https://github.com/BotoX/xiaomi-m365-compatible-bms
https://endless-sphere.com/forums/viewtopic.php?p=1477671#p1477671

keywords: RJXZS same?
https://a.aliexpress.com/n9xwVd1m

active-bms Li-ion smart pcm android Bluetooth UART

_______

hardware very simple, repair or mod/hack, OpenSource firmware

Atmel ATmega Mega328P

BQ76940, 9S-15S version

Arduino + BQ76940 (including sources for a board) here: https://github.com/nseidle/BMS 

Bluetooth serial module that is external and is connected using the available header on the board, with pins VCC, GN, TX and RX

available in 3.2V vs 3.7V, LTO?

485 UART?

------
also UART, CAN, SMBus, RS485 or RS232

use the Texas Instruments bq769x0

analog front-end IC for undervoltage, overvoltage and overcurrent.
The TI IC also drives the MOSFETs directly.
The software that is running on the ATMega328P communicates to the AFE via I2C and does many additional things like:
charge overcurrent, overtemp, undertemp, balancing settings.
Almost all settings are user programmable and very flexible.

I used that hardware and made an open source firmware for the SP15SV0001-LLT
https://www.lithiumbatterypcb.com/product/13s-48v-li-ion-battery-pcb-board-54-6v-lithium-bms-with-60a-discharge-current-for-electric-motorcycle-and-e-scooter-protection-2-2-3-2-2-2-2-2
Ali: https://www.aliexpress.com/item/12S-44-4V-smart-Lithium-li-ion-battery-protection-board-BMS-system-60A-20A-Bluetooth-phone/32976215661.html

used on a Xiaomi M365 scooter, 30A version is recommended, >30A versions have both sides of the BMS PCB populated with MOSFETs and will not fit in the limited space of the M365.
https://github.com/BotoX/xiaomi-m365-compatible-bms
I recommend the 30A and 60A version of this BMS which use KNB3308A MOSFETs, been using it on a few e-scooters and e-bikes myself with my own firmware and also the original firmware.


 
well i took the dumb bms off,think there were 6 leds on,but most of the coresponding cell groups were down to just over 3.5v,the dumb bms was one i brought s/h ages ago,i now recall this fault with it,sure would be a good way too kill cells,it sits on the bench at the moment while i wait for a new smart bms from china,hope the new one works,as so far its cost me £100 and i dont have a working bms,will keep you posted,cheers all.
 
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