Can't access Xiaoxiang BMS after LVD

[Mrdanielmh]

Hi all, my lifepo4 self build and BMS has been fine for about a year now. Recently everything shut down due to a low voltage disconnect, however I'm not unable to access the BMS via Bluetooth and make sure everything is ok.

I have unplugged BMS and Bluetooth module, but it still doesn't appear in the application. I've tried multiple phones, same issue.

Any ideas?

 

[John Frum]

What is the voltage between the positive and negative battery terminals?
What is the voltage between the positive terminal and the system side of the bms?

 

[Mrdanielmh]

What is the voltage between the positive and negative battery terminals?
What is the voltage between the positive terminal and the system side of the bms?

Pos to neg battery - 13.98
Pos to BMS neg - 13.45

I think o measured that roghty, I just put the negative probe on one of the 3 BMS negative connections

 

[John Frum]

Pos to neg battery - 13.98
Pos to BMS neg - 13.45

I guess you just got finished charging it until the charge fets disconnected the charge path, confirm?

 

[Mrdanielmh]

 

[Mrdanielmh]

I guess you just got finished charging it until the charge fets disconnected the charge path, confirm?

It's been fully charged for a few days now but I've only just tried to connect to the BMS, the reason I'm worried is because there is a massive cell voltage difference

 

[John Frum]

When you say unplugged bms, do you mean you unplugged the balance leads?

It's been fully charged for a few days now but I've only just tried to connect to the BMS, the reason I'm worried is because there is a massive cell voltage difference

13.98 volts is very full.
13.45 volts on the system side of the bms hints that the charge path opened.

Please list the individual cell voltages.

 

[Mrdanielmh]

When you say unplugged bms, do you mean you unplugged the balance leads?

13.98 volts is very full.
13.45 volts on the system side of the bms hints that the charge path opened.

Please list the individual cell voltages.

Unplugged balance leads - confirmed, hoping this would reset the BMS and bring it back online
I've disabled charging now
Cell voltages:

A 3.38
B 3.4
C 3.57
D 3.56

^ This difference worries me

PS. I have an ISDT BatteryGo connected trying to balance them

 

[John Frum]

Yep 190mv is a pretty big delta.
Do you have the usb dongle?
If you do and it works then it suggests the problem is with the bluetooth module.
Does the blue light come on?

 

[John Frum]

Are you using the bms to terminate charge on a regular basis?

 

[Mrdanielmh]

Yeah that is what worries me, without the BMS 2 of those cells could hit 3.65 easily. I don't have a USB dongle.

No blue lights appear on the bluetooth module. I'm still getting power to lights etc so power it still going through the BMS I just can't validate if the features are going to apply.

Not using the BMS to terminate charge at all.

 

[Mrdanielmh]

Unless the BMS has been shutting down charge because one of the cells has been overcharging, possible but I can't prove.

 

[John Frum]

Unless the BMS has been shutting down charge because one of the cells has been overcharging, possible but I can't prove.

530mv difference between the bms and battery negative suggests that the charge fets are open.

 

[Mrdanielmh]

I've disabled charging post first message! So, sounds like it could be Bluetooth. Nightmare.

 

[John Frum]

Just to be clear the bms is powered via the balance leads.

 

[John Frum]

I've disabled charging post first message! So, sounds like it could be Bluetooth. Nightmare.

How did you disable charging?

 

[Mrdanielmh]

Oh, I just turned off the solar input

 

[mikefitz]

have unplugged BMS and Bluetooth module, but it still doesn't appear in the application.

as suggested both the balance leads and the UART feed to the Bluetooth need to be connctd to the BMS.

Mike

 

[Mrdanielmh]

as suggested both the balance leads and the UART feed to the Bluetooth need to be connctd to the BMS.

Mike

Thanks Mike, yup both cables are connected. Still can't access it via BT

 

[John Frum]

@Mrdanielmh did you get to the bottom of this?