Daly 12v 100a BMS with bluetooth connection issue

[zonnebloem]

Hello
I recently setup 12v LiFePO4 battery(289AH) with Daly BMS and under testing. For Bluetooth connection, I used SMART BMS in my iPhone. During normal operation, no issue but once low voltage cutoff occurred, I can not connect the BMS. However this is not always case. When I set the low voltage cutoff as 11.6 (2.9 per pack), it cut off at 13 volt but I am able to connect BMS. However when I set the cutoff voltage as 10 (2.5 per pack), it cutoff at 11.6 but I can not connect the BMS. In order to be able to connect BMS, I shot B- and P- or something similar action - not consistent way is found yet
All voltage are read from BMS as well as measured with multimeter in order to confirm BMS reading. So voltage looks reliable.
Anyone can help me for reliable connection after cutoff and voltage discrepancy in BMS set and actual voltage.

 

[carlrx7]

sounds like you are hitting a Cell LVD if overall pack voltage is that high. Your cells maybe out of balance or mismatch capacity. If you are always running the pack down low, maybe best to bottom balance and limit max charge voltage. I have a similar Smart BMS that the Bluetooth acts the same way.

 

[zonnebloem]

Thanks Carlrx7. I should mention each cell voltage at the first place. Each cell voltage was very much the same - well balanced. Actually I can NOT set total battery cutoff voltage in my SMART BMS application. It allow only each pack voltage limit and thus total limit is 4 times pack voltage limit.
My primary question is how to connect BMS once low voltage cutoff occurred. Once low voltage cutoff occurred, BMS does NOT use bluetooth? I expect regardless low or high voltage cutoff, BMS should communicate to the SW?

 

[carlrx7]

Mine is the same. Cell LVD x Series = Total LVD. i think i spent 3 hours researching a way to make them different. Think of low voltage condition as the safe mode. even the bms is cutting its extra loads to save the pack. High VDC doesn't disconnect my Bluetooth connection. If you have the battery in a working system, when a charge voltage kicks in the bluetooth will come back on as soon as it sees a higher voltage than pack.

You may be able to edit it more via UART-USB, but i'm not ready to go down that road. another option is to go with an external Low voltage disconnect device and let the BMS be the backup.

Can you post the cell voltage as it dips into the knee and sets the LVV flag?, i bet one of them is dropping more than the other.

 

[zonnebloem]

Thank you very much carlrx7. I will check more carefully next time. Bit of uncertainty here and there. For example, actual cutoff voltage is under load and thus it will be bit lower than what I see on my phone because once I connect BMS via my phone, the load is disconnected and BMS is somehow recovered.
That is why I also looking for UART-USB. One question on Bluetooth dongle. Bluetooth dongle is connected via short cable. Is this UART-USB cable?

 

[Yurtdweller]

First off, lifepo4 newbie. Just got a pre-assembled pack from lynx battery two days ago. Has 100a Daly smart bms. I am finding that I must occasionally physically disconnect the bt dongle from its cable and reconnect it in order to reestablish bt connection. I had to do this once or twice on day one, and had to do it again after a lv disconnect last night.

 

[zonnebloem]

Thank you for sharing your experience Yurtdweller. When you have LV cutoff, are you able to reconnect BMS after simply disconnect/reconnect the dongle? I have tried but it won't connect for me.

 

[Yurtdweller]

This has been the case three times in two days. To be clear, I have only been able to connect my Android phone, so far. Still no luck at all with my iPhone se.

 

[Yurtdweller]

Update: I frequently lose my connection, probably from moving my phone out of range, but sometimes it just disconnects for no apparent reason. 95% of the time the app will reconnect with no issue, but once, repeated attempts to reconnect Bluetooth fails. Short disconnection of the dongle was also ineffective. It seems as if a long disconnect of up to an half hour was required. I will continue to try to find replicatable details.

 

[Yurtdweller]

Thank you for sharing your experience Yurtdweller. When you have LV cutoff, are you able to reconnect BMS after simply disconnect/reconnect the dongle? I have tried but it won't connect for me.

I just re-read this whole thread, and I think I better understand this question. I solved the lvd and had the bms restarted BEFORE I reconnected to the bms, (I think). I did not expect the bms to be active after LVD.

 

[djjazzy28]

Update: I frequently lose my connection, probably from moving my phone out of range, but sometimes it just disconnects for no apparent reason. 95% of the time the app will reconnect with no issue, but once, repeated attempts to reconnect Bluetooth fails. Short disconnection of the dongle was also ineffective. It seems as if a long disconnect of up to an half hour was required. I will continue to try to find replicatable details.

I'm just setting up my 120Ahr Lifepo4 12v 4S battery with Daly BMS and testing it. I'm connected with BT and set the parameter to 15300 secs. Default was 3600 secs. Apparently the 15300 bypases BT sleeping. So far no disconnects, BT connects every time so far the past 24 plus.hours. Have not triggered a LVD yet.

 

[zonnebloem]

Connection behavior seems to be clear now. Once BMS cut off the battery due to LVD, Bluetooth also does not respond anymore which is not what I expect... So far reliable way to wake up the BMS is to short B- and P-
Last night I have LVD again and measure all the pack voltage and they are all above 2.5 even I set low voltage cutoff as 2.5. Here are the values for each pack - 2.92/2.77/2.91/2.96 - total voltage = 11.57. As I mention previously, BMS seem to cut off at 11.6 regardless setting via SMART BMS sw. I get an impression that there is HW setting. I don't have variable voltage power supply. Thus I can not test with easy but can anyone help for this unexpected behavior or share experience