SOLVED: Is it Normal For BMS Voltage Reads Less Than Battery Pack Voltage?

st4rgut
st4rgut Registered Users Posts: 36 ✭✭
edited April 2021 in Off Grid Solar & Battery Systems #1
I tried installing a 16S 48V Lifepo4 Daly BMS today that I bought off Ebay I have a lot of 16 100 Ah 3.2V Lifepo4 Cells that I connected in series and top balanced until the cell voltages were equal. After connecting in series, the batteries had a voltage ranging from 3.631 to 3.637 V, which I find odd. I confirmed the wire order of the balancing wires to the BMS by measuring the voltages before connecting to the BMS. I then connected B- lede of the BMS to the negative terminal of the battery pack and then plugged in the balancing wires to the BMS. However, when I measure the voltage across the BMS P- cable and the Battery Pack's positive terminal, I am only getting 47V even though the pack measures 58V. I read that the BMS output is supposed to match the pack output, but can't think of anything I did wrong. Do you think I received a defective BMS? There was no smoke or anything when I plugged everything in, but the output voltage doesnt seem right. 

The top picture shows the output voltage of BMS, and the bottom shows the voltage of the battery pack. 

SOLVED: 
The B- lead should go on TOP of the negative balancing lead. I guess having it the other way causes power to bypass the negative balancing lead, which screws up everything. 


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  • jtdiesel65
    jtdiesel65 Solar Expert Posts: 242 ✭✭✭
    #2
    I think the manual says there should be 0 ohms from p- to b-. Do you have 0 ohms?



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  • demille
    demille Registered Users Posts: 4 ✭
    #3
    I do have the same problem. Batt voltage 54.32V, BMS output only 45V.   Connecting the B- lead on top op the black balancing lead or not I do have the same result. it did not solve a thing. all wires have been tested and the sampling wires measure 54.3V between black and 16 and each contact has the same voltage as does the batt cell. With sampling wires connected to BMS but BMS  B- not connected to the batteries I  measure 45V between P- and P+. I am afraid to start up the BMS and connect it to the inverter as long this is not solved.
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  • demille
    demille Registered Users Posts: 4 ✭
    #4
    In my case the resistence is not OK . I do NOT have conductivity.
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  • demille
    demille Registered Users Posts: 4 ✭
    #5
    Apparently the  BMS may go into the sleep mode. ( no conductivity between B- and P-) By default sleepmode is set to 3600s in some DALY BMS. Also BT will not work. Most chargers will not function because they do not see a batt is connected. One will not solve this by rearanching the B0 connection. One may wait until time is up or jump the B- to P- with the batt connected.  For me the problem has been solved bij jumping the BMS. one then can use the BT and app to change the sleep modus time.



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  • demille
    demille Registered Users Posts: 4 ✭
    #6
    Solved:
    If the BMS discharging MOS is off for some reason, the BMS will sleep within 1mins. Most chargers will not see there is a battery present. To restart one can jump  B- and P-


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