Short in wiring or a bad cell?

[T1nTodd]

Lifepo4 4s 310ah cells with a Daly 200a BMS I built for a friend. She has it installed in her bus she lives in. She has had it installed for 1.5 years now. She is in Cali and I am in colorado, so I am trying to troubleshoot remotely by phone.
Issue is as follows. Sometimes (not all the time) when she turns on her water pump and her string lights, the lights flicker, then everything shuts down. They are both on different fuses of her bluesea fusebox. She borrowed a battleborn battery from a friend and did not have the issue with the battleborn battery swapped in for a month. As soon as she hooks my battery back up, the problem comes back. It happens about 40% of the time. Can there be a problem with one of the cells in the pack without the bms throwing a fault? Would a bad cell cause this type of issue? BMS app shows no drop in voltage on individual cells when issue presents itself. I think it's a short somewhere in pump or her wiring, she thinks it's an issue with my battery. My plan is to have her check voltage at fuse box with a multimeter when the issue comes back to confirm a short somewhere. Any ideas? Should I have her check anything else?
Thanks.

 

[sunshine_eggo]

If the BB lasted for 1 month, it does sound like the problem is between the battery connections.

Short list:

1. Battery not being sufficiently charged.
2. #1 + imbalance causing LVD protection.
3. Poor connection at main terminals.
4. BMS cell connection issue.
5. Failing BMS (DALY's track record seems very poor as of late).

Is the battery getting fully charged on a regular basis?

Is the 40% at random, or does it happen when the battery is likely at a lower state of charge?

Have the BMS cell connections been checked? They can degrade over time.

Probably not a short. A short is a short, and shorts usually drain a source, so it doesn't sound like a short as there would likely be some fireworks involved with little to no regular operation.

If a 12V RV water pump, the load is probably pretty small, but if it's an AC powered jet pump, those can have some respectable surge which might make the DALY unhappy.

 

[T1nTodd]

1. Battery is getting charged. Cells at 3.35v now and just happened again.

2. Not getting a low voltage disconnect alarm

3. Connections confirmed tight, no corrosion present

4. Nothing loose, bolts tight, no corrosion, maybe the ring terminals connection to the wire?

5. No alarms on bms, anything to check to further confirm possible bms failures?

Battery is getting charged via solar and victron 100/50 cc. Maybe not fully charged often. But gets charged daily, not being fully discharged.

Issue happens at all stages of charge, currently 70% and issue is present

Bms cell connections show no signs of degradation. Where balance wires connect to bms, white plug is a little loose.

 

[sunshine_eggo]

Sounds like #5 moves to #1.

Is it possible for her to temporarily bypass the BMS for testing?

 

[T1nTodd]

Sounds like #5 moves to #1.

Is it possible for her to temporarily bypass the BMS for testing?

Is that dangerous? I've never charged/discharged lifepo4 without a bms. What precautions should she take? Disconnect the charge controller?

 

[sunshine_eggo]

Is that dangerous?

Yes.

I've never charged/discharged lifepo4 without a bms.

Good. Would only consider it for diagnostic/emergency purposes. You're confident the cells are operating within specifications at all times, so the risk seems manageable.

I am not indicating that the BMS be disconnected but bypassed, i.e., the (-) lead attaches directly to the battery while the BMS remains connected to allow cell monitoring.

What precautions should she take?

Conduct all testing with continuous monitoring of cell voltages.

Disconnect the charge controller?

Yes.

Test A: In normal config, cycle the pump 10 times. Count the number of faults while noting cell voltages.
Test B: In BMS bypass, cycle the pump 10 times. Count the number of faults while noting cell voltages.

Compare A to B. If same # of faults, unknown failure mode #6 is in play. If A = 1 or more and B = 0 while cell voltages are always in spec, failing BMS.

 

[Berseker]

If the BB lasted for 1 month, it does sound like the problem is between the battery connections.

Short list:

1. Battery not being sufficiently charged.
2. #1 + imbalance causing LVD protection.
3. Poor connection at main terminals.
4. BMS cell connection issue.
5. Failing BMS (DALY's track record seems very poor as of late).

Is the battery getting fully charged on a regular basis?

Is the 40% at random, or does it happen when the battery is likely at a lower state of charge?

Have the BMS cell connections been checked? They can degrade over time.

Probably not a short. A short is a short, and shorts usually drain a source, so it doesn't sound like a short as there would likely be some fireworks involved with little to no regular operation.

If a 12V RV water pump, the load is probably pretty small, but if it's an AC powered jet pump, those can have some respectable surge which might make the DALY unhappy.

loose connected masked by cross threaded nut was the culprit, when i experienced this issue. only a torque meter was able to pinpoint the issue.

replacing the bad nut resolved the issue

 

[mikefitz]

If the BMS is not reporting shutdown , and complete power is lost, this suggests a break in the supply after the BMS. Without suggesting your battery was poorly constructed, it may be, after a year of RV use, a failing connection is causing issues. I suggest investigating everything in the path between BMS load output , if accessible, and the Blue Sea fuse box, especially fuse holders or breakers.

Comments,
How does the issue correct itself, does it self rectify or is some action taken?
Do other or large loads have the same effect or is it just the pump?
Victron 100/50 should still supply some power to 12v system in daytime even with battery disconnected?
Picture or video may help

 

[T1nTodd]

Sent her a new overkill bms. Seems to have fixed the issue. Thanks sunshine_eggo for helping me narrow it down and isolate the issue.

 

[sunshine_eggo]

Sent her a new overkill bms. Seems to have fixed the issue. Thanks sunshine_eggo for helping me narrow it down and isolate the issue.

Appreciate the follow-up.