LiFePO4 Battery isn't working properly

[xsasj]

Hii!

I really hope someone here can help me out. I have some problems with my lifepo4 280ah EVE battery and/or BMS

Sometimes, the power cut off for like a second. 12 lights will turn off for a second and restart again.
Unfortunately, the Inverter does not restart automatically and I have to do it manually like all the time. My fridge runs on 230 volt so this is really annoying

I added some screenpicture of the battery during charging and discharge and in rest. In rest they seem to be balanced fine, but during charging or discharging, the app tells me that the cells are heavily discharged/charged and very unbalanced. As soon as I turn the load off, they seem balanced.

Anyone out here who knows what could be the problem?

 

[Vigo]

Is it a sealed battery? Unless the BMS's readings are incorrect (which they might be), that would have to be an issue of either serious cell issues, or issues with the connections between each cells terminals.

If it is a sealed battery you might be screwed on diagnosing it any further yourself without 'invasive' procedures.. Is it a newer battery that might be under warranty?

 

[FilterGuy]

The most logical explanation is that the BMS is deciding one of the discharge limits has been hit....shuts off discharge for a bit and then resets.
Here is a list of most of the things that could cause this:

1) Too Cold - Very unlikely unless it is a bad sensor
2) Too Hot - Very unlikely unless it is a bad sensor
3) Too much current - Possible, but not likely. (This would not explain the problems during charging)
4) Short Circuit level current. - not likely
4) Too Low of battery voltage. It- Possible.... but my expectation is the Inverter would shut down first. (It depends on all the different settings)
5) Too high of a cell voltage. - Based on the little info you have provided, this seems most likely.
- Need to check all cell connections
- Need to make sure cells are balanced.

What Causes Runaway Cell Voltage?

Quite often, a cell will hit a High (or low) voltage unexpectedly and/or faster than the other cells. (On the DIY Solar Forum, this is usually called a ‘Runaway Cell’. ) The runaway cell can eventually cause the BMS to unexpectedly shut down...

diysolarforum.com

 

[Vigo]

Does the 'ah remaining' field move unexpectedly? As in, more rapidly than it should given the current flow, or seems to change without actually touching the battery?

Assuming all 3 pics were taken on the same day, those pics are only about 30 minutes apart from each other and yet the ah range is from 0-251, which is impossible other than that it's not calculating that number properly at all.

If this symptom started suddenly I would suspect it is some kind of BMS failure. I don't think it's remotely likely for the cells themselves to have such horrendous IR that they show that much voltage difference between cells with a whopping 10-30a of current flow.

 

[Steve_S]

IF this is a Battery you built yourself and not a Pre-Built like an SOK or Amperetime then initial diagnostics woudl say that connections are not tight or correct. As it does take charge & discharged it's correct BUT unless the busbars, screws etc are tight (4-6 Newton Metres) you can run into issues such as this. Ensure that ALL Contact points between busbars & terminal faces are Clean, that everything is Tight, that Voltage Sense leads from BMS are on the (+) post of the cells.

Also, IF these cells were not Top-Balanced prior to the assembly they may have varying voltages which will draw down the pack AND possibly contribute to "Runner Cells" which can either drop voltage really fast triggering a Low Volt Disconnect OR go High voltage triggering a High Volt Disconnect.

LFP Working Voltage is 3.000-3.400 Volts per cell.
Solar Controller:
Change the Charge profile to Bulk/Absorb Charge at 13.7V (3.425 Volts per cell) and float at 13.6V (3.400 volts per cell)
BMS:
- Overvoltage to 3.510
- Overvoltage Release to 3.475
- Undervoltage 2.8 OK
- Undervoltage release 2.9V
- Pack overvoltage 14.4 (3.51Vpc)
- Pack overvoltage Release 13.9V (3.475Vpc)
- Pack Undervoltage 11.0V (2.750Vpc)

During a deep discharge (surge pull) the Voltage Sag could cause a cutoff and that needs to be accounted for.
Also if you have a heavy load going AND have charge input from SCC and the Heavy Load stops, there can be a momentary Spike tripping a Hi Volt disconnect. This is why there are delays.

BTW EndAmps/Tailcurrent for the 230AH Battery: 280 x 0.05 =14.0A. Once the battery is taking only 14.0A or lower, it has reached full Absorbtion (CC/Constant Current) and can change to Float (Constant Voltage/Variable Current). CC will only charge LFP to 95% then CV takes care of the rest as the amps taken decrease while the cells are saturating to the set voltage.

 

[Ampster]

Cells 3 and 4 appear to have less capacity than the others and will limit the voltage range of your pack. They are out of balance at the top and bottom and there is not much you can do about those cells because they are the first to hit high voltage limit and first to hit low voltage cutoff. As suggested above lower charge settings and careful discharge to 12.5 volts may enable you to limp along. Also check for loose connections.

 

[xsasj]

Does the 'ah remaining' field move unexpectedly? As in, more rapidly than it should given the current flow, or seems to change without actually touching the battery?

Assuming all 3 pics were taken on the same day, those pics are only about 30 minutes apart from each other and yet the ah range is from 0-251, which is impossible other than that it's not calculating that number properly at all.

If this symptom started suddenly I would suspect it is some kind of BMS failure. I don't think it's remotely likely for the cells themselves to have such horrendous IR that they show that much voltage difference between cells with a whopping 10-30a of current flow.

Yess it is mostly like the battery is 100% full, I on the fridge and in 3 seconds, it is 200 AH emptier ant 0%.

 

[xsasj]

If I read the comments, I think the best thing to do is remove the bolts and busbars, make sure it is clean and put the bolts and busbars back.

The cells are top balanced before I added it to the electric system of my van.

 

[Vigo]

Oh good! Since it is home-built and not sealed up with glue there is both a much higher likelihood of connection problems between the cells, AND an easy path to correcting them. I think if you inspect those carefully you will find your issue.

 

[xsasj]

I by the way see that I did not pic the best screen pictures of the battery in rest.
Often they seem pretty equally balanced.

 

[Vigo]

This just corroborates that the voltage readings are due to a large voltage drop because of poor connections. Voltage drop only occurs when current flows, so at rest it will appear normal.

 

[hankcurt]

If I read the comments, I think the best thing to do is remove the bolts and busbars, make sure it is clean and put the bolts and busbars back.

I agree this is the best thing to check first.

Pictures of your battery might help people make other suggestions. I thought of a couple of things based on mistakes I've seen other people make.

First, make sure your batteries sit level with the top of the battery cells even, so that the bus bar makes contact with the entire surface of the battery post. If they are uneven, the bus bar might only contact on one edge and the resistance will be high.

Second, the bus bar should sit directly on the post first. There should be no washers or anything else under the bus bar. The voltage sensing leads for the BMS should be on top of the bus bars.

 

[robby]

Agree with @Vigo. Either you have a bad connection or the BMS is reading wrong or Cells 3 and 4 are dying.
Is this a DIY Battery?

 

[Steve_S]

Ironically, with DIY Battery Packs 90% of the issues start with the user.... Much like the "Keyboard to Chair" issue in the Computer world. The simplest of things can toss a Monkey Wrench in the works and cause all sorts of havoc. Many of us have been around a Looonnnnggggg Time and seen a myriad of "Ohhh Damn's" go past.

BTW: The aluminium on the cells typically has a light coating of wax from the factory to prevent corrosion, this can be wiped off with Rubbing Alcohol. Bus Bars used for cells can have oils / waxes as well... most often oils... Again all of this needs to be wiped clean. Also check for any Burrs or Ridges on the busbars, even the slightest Ridge from the drilling or stamping out of the holes CAN cause issues with them properly Seating against the terminal face. even 0.5mm is enough to cause major brain pain. I've seen busbars with very sloppy edges around the holes.

 

[Zwy]

This just corroborates that the voltage readings are due to a large voltage drop because of poor connections. Voltage drop only occurs when current flows, so at rest it will appear normal.

Correct, open circuit or unloaded circuit voltage doesn't mean much.

When performing a voltage drop test, the circuit has to be loaded.

 

[Berseker]

Likely culprit is loose connections. Buy a digital torque wrench and ensure all cells are torqued down to 4 to 7nM,
You should eliminate this variable first ..