Issue with 4S BMS, ABLIC S-8254AA and AOD403 Mosfet - Page 1
Forum section: electronics / projects

author: Ratti3
author_rank: Newbie
timestamp: October 27, 2020, 08:02:00 pm
content: Hi All,Hopefully someone can help with this issue, any help would be appreciated, this has been driving me nuts, something so simple should work, I've made more complicated things.I decided to make my own 4S BMS circuit based on the ABLIC S-8254AA BMS chip. I pulled the schematic from the ABLIC datasheet, I also noted that the same schematic was used by the common 4S red board you see on Ebay.The only diference is that the Ebay board has a 510k resistor between the output and battery (P+ and B+).The issue I have is that the BMS power out works for about 5 mins before shutting off, I can reset this by shorting B+ and P+ (as per the datasheet). I can't figure out why.I've tried the following:Made 4 PCBs so far, I tried grounding myself and lowering the temp to 310 deg and the MOSFET pins temporarily wire wrapped whilst handling and soldering.Tried 2 different versions of the ABLIC chip.Tried 2 different MOSFET types.I've tried the 510K resistor across P+ and P+.I took apart the Ebay circuit (which works fine) and verified the component values are same or close enough.The first PCB I made worked for 6 hours first time before the low voltage shut off, it did not work at all after that.The 2nd 3rd and 4th PCB only work with the 510k resistor, I've tried different values, each PCB reacts differently to the resistor value, e.g 510k = 10 secs on time, 360k 8 mins on time etc.All components are genuine.Datasheets:BMS:https://www.ablic.com/en/doc/datasheet/battery_protection/S8254A_E.pdfPMOSFET 1st choice:http://www.aosmd.com/pdfs/datasheet/AOI403.pdfPMOSFET 2nd choice:http://www.vbsemi.cn/data/upload/file/VBZE50P03.PDFEasyEDA project:https://easyeda.com/Ratti3/4s-18650-li-ion-s-8254-battery-management-systemThe attached images are as follows:Red PCB working Ebay PCB, same as mine but with a 510k resistor (something I added to mine later).Black PCBs, my circuit.Schematic from EasyEDA.Thanks

author: Ratti3
author_rank: Newbie
timestamp: October 28, 2020, 11:24:47 pm
content: Well I'm an idiot, the batteries were slightly out of balance when I connected them, they were out by 0.8v, this caused the ABLIC chip to shutdown.I tried some new LG 18650s and the PCB work fine.

author: aiq25
author_rank: Regular Contributor
timestamp: October 29, 2020, 01:44:48 pm
content: I work for a Li-Ion battery supplier and we use this IC as secondary protection.Just wanted to note, this IC is not a proper BMS. It is used for protection purposes only. For example, it can't do cell balancing, state of charge, etc...Not sure if you are looking for a BMS or just protection but if you want an independent BMS, not requiring an MCU, you can look at something like this: ISL94202.

author: Ratti3
author_rank: Newbie
timestamp: October 29, 2020, 04:36:20 pm
content: Hi,Yes I called it a BMS incorrectly, I use another circuit for charging, the issue was caused by me mixing batteries.I did look for a balance schematic, they seem too complicated or the IC is not nice to work with. ISL94202 does not look hobbyist friendly.If anyone has any suggestions for simple protection\balance ICs that would be greate. I'm ok with hand soldering TSSOP16.There are so many mislabled BMS boards on Ebay.Thanks

author: aiq25
author_rank: Regular Contributor
timestamp: October 29, 2020, 06:08:03 pm
content: Is this for a hobby project? I assume so but just wanted to check.We use a QFP BMS IC. I can recommend others but a proper BMS IC will not be cheap for hobbyist quantities.

author: Ratti3
author_rank: Newbie
timestamp: October 29, 2020, 06:39:22 pm
content: Yes purely for hobby, it's part of a tube amplifier circuit that is battery operated (I use a DC booster to get the 100vdc plate voltage). The batteries are charged using using TP4056X.It would be nice if there was a simple all in one IC.The company name you see on the PCB is not real, it's just something I've been using for years.Thanks

author: Vacainer
author_rank: Newbie
timestamp: March 05, 2023, 09:59:34 am
content: Dear Ratan, can you explain how you do the reset?I had a kind of similar problem here:https://www.eevblog.com/forum/projects/issue-with-a-reapaired-xiaomi-s50-vacuum-robot-accu-with-an-ablic-s-8254aa/msg4735502/

author: Ratti3
author_rank: Newbie
timestamp: March 05, 2023, 10:07:55 am
content: Check bottom of page 20:https://www.ablic.com/en/doc/datasheet/battery_protection/S8254A_E.pdf

author: Vacainer
author_rank: Newbie
timestamp: March 05, 2023, 01:36:41 pm
content: So it seems like I need to short the VMP pin and the VDD? These pins are covered with some glue on my chip but I think I can remove the glue carefully.Do I have to do this in the state when my battery pack is connected to my vacuum robot? Probably not, right?However, the instructions also say: "or connect thebattery charger to return to the normal status."The charger of my robot tries to charge the battery with 16.42V (measurable at P+ & P-). However, the voltage of my batteries always remains at 14.64V (measurable at B+ & B-). If I leave the battery pack connected in my robot so that it tries to charge it, I only measure approx. 1.2V at P+ & P- after some time.When my battery is not connected, the values at B+ & B- are always at 14.65V and at P+ & P- at approx. 12.8V.EDIT:I did the reset with shorting the VMP pin and the VDD. Unfortunately, the same behaviour as before. I do not understand this. I have previously balanced all batteries to 3.65V. That is above the cut-voltage. When I put the battery pack into my robot hoover, it shows me that the battery is 100% full. However, 14.65V battery voltage should be interpreted as 50% battery level.