40v at busbar, self built battery, daly 250 bms

[T1nTodd]

"Bms is shutting down every once in a while. Mostly at night." - seemed to be pretty context specific.

In any case, the possible ways for 40V to be at the bus bars at night is pretty much zero. Instrument error or user error are the overwhelming likelihood. She measuring AC voltage instead of DC?

So far the only certainty is the battery is out of balance. 0.111V is way too high unless all cells are over 3.45V.

That's a good point. Does it matter that under load the cell voltages are almost identical? Difference in voltage is only while charging. Cell #4 only that far off when charging and is where the positive wire is connected to the battery bank.

 

[time2roll]

40v? Replace the meter internal battery. Test the meter on the 12v car battery. Get a new meter.

 

[sunshine_eggo]

That's a good point. Does it matter that under load the cell voltages are almost identical?

Not one bit. Even substantially imbalanced batteries have near identical cell voltages in the operating range from about 3.1 to about 3.4V.

Difference in voltage is only while charging. Cell #4 only that far off when charging and is where the positive wire is connected to the battery bank.

Charging is almost always where balance issues manifest themselves. It's either a significant connection issue, balance issue or failing cell.

 

[T1nTodd]

Not one bit. Even substantially imbalanced batteries have near identical cell voltages in the operating range from about 3.1 to about 3.4V.



Charging is almost always where balance issues manifest themselves. It's either a significant connection issue, balance issue or failing cell.

Any sure fire way to know if she has a failing cell? Just visual inspection for damage/swelling? If i top balance and voltage difference comes back means bad cell is probable?

Only 36 cycles

 

[T1nTodd]

Not one bit. Even substantially imbalanced batteries have near identical cell voltages in the operating range from about 3.1 to about 3.4V.



Charging is almost always where balance issues manifest themselves. It's either a significant connection issue, balance issue or failing cell.

Thanks

 

[Rednecktek]

40v? Replace the meter internal battery. Test the meter on the 12v car battery. Get a new meter.

How does a 4s battery made of 3.5ish volt cells hit 40v??!!

 

[T1nTodd]

How does a 4s battery made of 3.5ish volt cells hit 40v??!!

Yeah, that's why I'm stumped. Even if you were to add in the 13-14v from charge controller it doesn't add up to 40v. Gotta be a lose connection or short somewhere but can't find anything with multimeter. Doesn't happen with the battle born battery. So weird. Only things connected to that busbar is the battery, charge controller, inverter, fuse box (red positive side). And only difference on the black bus bar (negitive side) is the wire to body of her bus. No fuses blown. No issues with starter battery (also grounded to metal body of her bus). That's why I reached out here.

 

[sunshine_eggo]

Any sure fire way to know if she has a failing cell? Just visual inspection for damage/swelling? If i top balance and voltage difference comes back means bad cell is probable?

Only 36 cycles

Those conditions would suggest a bad cell.

36 cycles in 1.5 years doesn't sound right unless the DoD is 5%, and it's not every day. BMS cycle counts are pretty inconsistent.

What are the MPPT parameters?

More importantly. What is showing 40V? So far it's been implied that it's the meter. What other device is reporting 40V?

 

[T1nTodd]

Those conditions would suggest a bad cell.

36 cycles in 1.5 years doesn't sound right unless the DoD is 5%, and it's not every day. BMS cycle counts are pretty inconsistent.

What are the MPPT parameters?

More importantly. What is showing 40V? So far it's been implied that it's the meter. What other device is reporting 40V?

I am relying on the bms cycle count. She's not using a lot of power. 310ah is 6x the useable power of the 100ah lead acid she had previous. And she doesn't live in bus every day, takes a week or two off frequently. Only a few led lights, water pump, radio, and charging a cell phone thru a 12v USB. Fridge is only thing on inverter and is not used (inverter off) 80% of the time.

I assume Mppt is set to preset "smart lithium lifepo4" setting as she told me she set to lifepo4. But I will get a screenshot to verify.

No other device is showing 40v. Other than a cheap multimeter set to DCv (see pic). Waiting until she returns to her bus and issue happens again to troubleshoot further. Will advise her to open victron connect and leave running to verify any voltage spikes from there as well.

 

[sunshine_eggo]

As of this moment, I am discounting the possibility that there is actually 40V at the bus bar. It would be an absolute shit show if true. The inverter should scream and shutdown. The MPPT would also likely error out as I don't believe that model is 48V capable.

I have a couple of those meters. The leads are not in the correct terminals. The black should be in the center position. She should NEVER have anything in the DC 10A position unless she knows EXACTLY what she's doing.

Have her correct the leads and re-measure.

For comparison sake, have her set it to ACV and re-measure.

 

[Rednecktek]

Wrong ports for the leads, that's not gonna work.

 

[T1nTodd]

Good catch! I don't know how I didn't notice that. I was just looking at the settings switch...

Will have her fix and measure again... lol.