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

[T1nTodd]

I'm trying to troubleshoot a battery that I built for a friend. I used four CATL 310ah cells and a daly 250 bms. She is getting 40v at her busbar intermittently. Battery has been working fine for 1.5 years. She is in Cali and I'm in Denver at the moment, so doing this via FaceTime and phone calls. She is using a cheap multimeter. Had her test individual cells via live video and all 4 cells are showing 3.35-3.40. Bms is shutting down every once in a while. Mostly at night. Her Aims 3000w inverter will beep with high voltage alarm. Bms gives high voltage alarm on daly bms app. Had her test the victron charge controller in and outgoing (batt and solar) with multimeter. 20v in and 13.6 out going. Over the past few weeks she has been getting 40v at busbar intermittently. I had her unplug inverter, bluesea fusebox, and victron 100-50 charge controller. Busbar then reads 13.6v. Plug everything back into busbar and magically busbar reads 13.6 and everything works for a day or two. Then high voltage alarms and bms shutoff come back. She borrowed a battleborn 100ah battery for a couple weeks. No issues for 4 days with battleborn. Plugged my battery back in and 2 days later she's getting high voltage alarm again and system shuts down. During 40v condition I had her measure voltage at busbar while she unplugged fuses and one of the fuses dropped the voltage at busbar to 3v. Plugging it back in and still at 3v till bms comes back on, then at 13.6v again. I'm stumped as the 40v condition is not permanent and I can't narrow it down. Thoughts on what to do next? Could it be an issue with my battery?

 

[T1nTodd]

Oh, the Aims 3000w inverter has been sporadically beeping high voltage since she installed (upgraded) her inverter a year ago. She bought it used.

 

[sunshine_eggo]

Shutdowns + BMS over-voltage protection.

Sounds like cell imbalance or BMS failure. Based on my perception on this website, DALY failures are frequent.

BMS over-voltage protection can cause sources to spike; however 40V sounds too high; 17-18V more typical and only for a moment, but definitely long enough for something to squawk a high voltage warning.

Assuming smartsolar MPPT, open the victron connect app, trends tab and show battery voltage and PV voltage. You'll need to leave the app open for it to log. There is also a setting to keep the screen on when the app is open. I would look to validate the readings in the log.

 

[T1nTodd]

Also, I top balanced the batteries before installing them but now the 4th battery is about 0.7 higher than other 3 cells according to daly bms app.

 

[sunshine_eggo]

Also, I top balanced the batteries before installing them but now the 4th battery is about 0.7 higher than other 3 cells according to daly bms app.

Clearly you found your issue.

Bad connections, failing cell or gross imbalance.

 

[BentleyJ]

Also, I top balanced the batteries before installing them but now the 4th battery is about 0.7 higher than other 3 cells according to daly bms app.

As in 0.7 volts (700mV)!! Yikes. Sounds like sunshine_eggo is right on target. If the BMS disconnects abruptly during charge the voltage will spike. Although it seems strange that the voltage spike would last long enough to be measured on the bus bar. Is the AIMS an Inverter/Charger?

 

[T1nTodd]

Shutdowns + BMS over-voltage protection.

Sounds like cell imbalance or BMS failure. Based on my perception on this website, DALY failures are frequent.

BMS over-voltage protection can cause sources to spike; however 40V sounds too high; 17-18V more typical and only for a moment, but definitely long enough for something to squawk a high voltage warning.

Assuming smartsolar MPPT, open the victron connect app, trends tab and show battery voltage and PV voltage. You'll need to leave the app open for it to log. There is also a setting to keep the screen on when the app is open. I would look to validate the readings in the log.

I'll have her try to log the voltage on the victron app. It is the mppt smartsolar with bluetooth.

 

[T1nTodd]

As in 0.7 volts (700mV)!! Yikes. Sounds like sunshine_eggo is right on target. If the BMS disconnects abruptly during charge the voltage will spike. Although it seems strange that the voltage spike would last long enough to be measured on the bus bar. Is the AIMS an Inverter/Charger?

Sorry 0.07v is max deviation. Currently 3.31v on 3rd cell and 3.371 on 4th cell

 

[T1nTodd]

Sorry 0.07v is max deviation. Currently 3.31v on 3rd cell and 3.371 on 4th cell

 

[T1nTodd]

This is a pic of her inverter.

 

[T1nTodd]

Here is a screenshot of daly app right before shutdown, have it set to 3.465v cell limit.

 

[BentleyJ]

So it looks like the Charge MOSFETS are Off. Is that because the Cell OVP is set to 3.465V? Over voltage protection should be set at 3.65V or higher to prevent nusiance trips. LFP can tolerate short excursions up to 4V. At least that's my experience.

 

[sunshine_eggo]

Here is a screenshot of daly app right before shutdown, have it set to 3.465v cell limit.

This is almost certainly the source of your problem. This is absurdly low. You may have effectively disabled the BMS's ability to meaningfully balance.

This also implies you might have been using the BMS to cut off the charge on a routine basis. Another recipe for disaster.

BMS should be set to cell limits and only used when things go wrong.
Hardware should be set to work INSIDE those limits.
BMS should be set to balance at and above 3.40V.

Set MPPT to
13.8V absorption with a fixed 8 hour absorption charge and no tail current (in expert settings).
13.5V float

 

[T1nTodd]

Yeah I had her set it down from 3.65 to 3.465 to see if that would eliminate the inverter beep. Not sure if inverter is set up for lifepo4 or if older and only knows v from lead acid or agm batteries.

 

[T1nTodd]

This is almost certainly the source of your problem. This is absurdly low. You may have effectively disabled the BMS's ability to meaningfully balance.

This also implies you might have been using the BMS to cut off the charge on a routine basis. Another recipe for disaster.

BMS should be set to cell limits and only used when things go wrong.
Hardware should be set to work INSIDE those limits.
BMS should be set to balance at and above 3.40V.

Set MPPT to
13.8V absorption with a fixed 8 hour absorption charge and no tail current (in expert settings).
13.5V float

It's been my experience that with 310ah cells the puny small wires on the bms do a crap job of balancing. I have similar battery in my setup and 3.65v shutoff on my overkill bms. But same 4th cell slightly higher voltage.

 

[sunshine_eggo]

It's been my experience that with 310ah cells the puny small wires on the bms do a crap job of balancing. I have similar battery in my setup and 3.65v shutoff on my overkill bms. But same 4th cell slightly higher voltage.

Has nothing to do with the wires. Has everything to do with the pathetic balance current of almost all popular BMS with passive balancing. 30-70mA is typically the most you see. At that rate, it's 1 full day of continuous balancing to burn off 1Ah.

 

[T1nTodd]

Okay. I can send her my "top balancing setup" and have her put the ovp back to 3.65. But I'm still stumped at why this is happening after dark and getting 40v at busbar. If this was happening while cc is working and hitting ovp that would be one thing but after sun goes down is still confusing me.

 

[sunshine_eggo]

Okay. I can send her my "top balancing setup" and have her put the ovp back to 3.65. But I'm still stumped at why this is happening after dark and getting 40v at busbar. If this was happening while cc is working and hitting ovp that would be one thing but after sun goes down is still confusing me.

Pretty sure this is the first time you mentioned 40V after dark.

How are the batteries in her voltmeter?

 

[T1nTodd]

The multimeter is new from Walmart or something and I'm assuming she didn't replace the battery it came with. I mentioned in my original post that this is happening mostly at night, but that was not sufficient info. She gets off at 9pm and that when I've been doing the troubleshooting with her. Inverter beeping has been happening at all hours of the day.

 

[sunshine_eggo]

"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.