Bloated Cells after failed 300A DCC Contactor.

[sto]

Unfortunately my DCC300a contactor failed and my some of my 280AH EVE cells ( 8s1p 24v bank) were extremely overdischarged.
Just over 1v on each cell.

I brought the cells back up to 3v relatively slowly and have pulled out the few cells that have evidently bloated to some degree (see pictures).
Do I cut my losses on the bloated cells? Or is recovery possible.

I attached some pictures of the bloated cells. Fortunately the other 4 cells seem to have gotten away without much if any expansion. I'm currently top balancing them.

 

[upnorthandpersonal]

Do I cut my losses on the bloated cells? Or is recovery possible.

Doesn't seem too excessive. Charge them up, see if they hold the charge. The swelling should go down over time as well. If they hold the charge, put them to use - just consider them degraded in any case.

 

[HRTKD]

The cells should be in a compression fixture.

Your busbar connections between cells 2 and 3 is completely wrong. Fix that immediately before you do anything else.

 

[Hedges]

Busbar seems to be just sitting there, like a fit-check. Probably was not actually being charged/discharged that way.

8s1p - everything in parallel right now. Just top balancing before use? Or did you operate the 24V battery already, and either disassembled or these pictures are from before?

Welded contactors has happened due to inrush current charging large inverter's capacitor bank. Did yours experience that? Use a precharge resistor.

Contactor is normally BMS, secondary protection. Charge controller should also stop at correct voltage and inverter at correct discharge voltage so not relying on contactor. If inverter doesn't have suitable low-voltage disconnect, does it have external enable pins?

 

[MisterSandals]

Unfortunately my DCC300a contactor failed

What BMS were you using to control this contactor? Chargery?
Is the contractor failed in a closed state? Or what is the failure?

 

[sto]

Doesn't seem too excessive. Charge them up, see if they hold the charge. The swelling should go down over time as well. If they hold the charge, put them to use - just consider them degraded in any case.

Thanks,
I'll give that a try.

The cells should be in a compression fixture.

Your busbar connections between cells 2 and 3 is completely wrong. Fix that immediately before you do anything else.

That was my bad for taking the photo before I actually connected them properly. I had 2 pairs of cells in parallel after pulling apart the 8s1p, then popped the bus bars on there just temporarily for the photo.

Re: Compression fixture, they were in a wooden box tightly fit (not force fit) prior to the over-discharge event. I've read conflicting opinions on compressing swollen cells so I wasn't sure if I should put them back together compressed.

Busbar seems to be just sitting there, like a fit-check. Probably was not actually being charged/discharged that way.

8s1p - everything in parallel right now. Just top balancing before use? Or did you operate the 24V battery already, and either disassembled or these pictures are from before?

Welded contactors has happened due to inrush current charging large inverter's capacitor bank. Did yours experience that? Use a precharge resistor.

Contactor is normally BMS, secondary protection. Charge controller should also stop at correct voltage and inverter at correct discharge voltage so not relying on contactor. If inverter doesn't have suitable low-voltage disconnect, does it have external enable pins?

Re busbars: Correct, not used this way.
Top balancing the 4 non bloated cells and the other remaining 4 cells (in the photos were in 2 parallel cells which I was going to slowly charge up depending on what kind of opinions I saw regarding their state).

I didn't have a pre-charge resistor. I thought the 300a DCC doesn't require one. The failure occrured when the Inverter wasn't turned on (MPP Solar) however I should note the Charge Controller / Inverter [low-high] disconnect's are set appropriately. Unfortunately the 24v fridge continued to draw the batteries down after the DCC remained closed

What BMS were you using to control this contactor? Chargery?
Is the contractor failed in a closed state? Or what is the failure?

Yes Chargery. Failed closed, would not turn on after failure.

 

[Hedges]

I didn't have a pre-charge resistor. I thought the 300a DCC doesn't require one. The failure occrured when the Inverter wasn't turned on (MPP Solar) however I should note the Charge Controller / Inverter [low-high] disconnect's are set appropriately. Unfortunately the 24v fridge continued to draw the batteries down after the DCC remained closed

Yes Chargery. Failed closed, would not turn on after failure.

Inverter may not have a disconnect before its capacitors. I believe my SI has breaker before.
Contactor may have welded when closed, charging capacitors from low-IR lithium battery pack.
Figure that out and probably implement precharge circuit.

There may or may not be a benefit to multiple disconnects. Inverter/charger indicates those functions share one path.

I believe in load control, shedding some loads while keeping charge for other more important ones.

 

[MisterSandals]

Failed closed, would not turn on after failure.

I thought failed closed was always on?

Just out of curiosity, what inverter do you have?
28V battery x 300A contactor = 8400W

That seems like an awful lot of inrush to exceed the 300A, right?

 

[Hedges]

Surge to start a load might be 8400W, but that's with contactor already closed, no damage.

Capacitor precharge inrush the moment contactor closes and bounces is what would weld it.
Possibly up to 20,000A by my math, but maybe reality of short circuit current from LiFePO4 cell is < 3.4V / 0.00017 ohm due to some chemistry or ion transport reasons.

 

[sto]

Inverter may not have a disconnect before its capacitors. I believe my SI has breaker before.
Contactor may have welded when closed, charging capacitors from low-IR lithium battery pack.
Figure that out and probably implement precharge circuit.

There may or may not be a benefit to multiple disconnects. Inverter/charger indicates those functions share one path.

I believe in load control, shedding some loads while keeping charge for other more important ones.

I thought failed closed was always on?

Just out of curiosity, what inverter do you have?
28V battery x 300A contactor = 8400W

That seems like an awful lot of inrush to exceed the 300A, right?

To clarify, the inverter was turned off at the time of the failure.

PIP-2424MSE1 24 VOLT MPPT

The battery system is in an RV and the inverter is only turned on manually when needed. At the time of the failure it was not enabled, effectively only charging (500w solar) was taking place by the PIP2424MSE. I believe the only load that was connected to the battery was the 24v fridge and a RaspberryPi + Wireless AP.

I should note that I am located in Australia, and this failure took place when I was away from the RV and after a recent heat wave that was followed with 5-7 days of torrential downpour overcast weather. However the RV is triple insulated and rarely gets above 30c where the battery is sitauated.

 

[mikefitz]

Victrom Battery Protect for the DC loads, excepting the inverter, would have prevented the issue.
Contactor welding closed could have occurred at any time the inverter was connected/disconnected to the battery

 

[sto]

Victrom Battery Protect for the DC loads, excepting the inverter, would have prevented the issue.
Contactor welding closed could have occurred at any time the inverter was connected/disconnected to the battery

Yes, VBProtect would have prevented this. It was an expensive mis-step for me to not have included it into my build.
Lesson learnt.

 

[Hedges]

Yes, VBProtect would have prevented this. It was an expensive mis-step for me to not have included it into my build.
Lesson learnt.

Unidirectional, limited to loads (or charging), not both.
Available for 65A up to 220A

BatteryProtect - Victron Energy

Disconnect the battery from non essential loads before it is completely discharged with Victron Energy's BatteryProtect. Find a dealer near you.

www.victronenergy.com

I think this is solid state. OK for moderate loads. May or may not be OK in the path charging inverter input capacitors, if precharge resistor not used.

Victrom Battery Protect for the DC loads, excepting the inverter, would have prevented the issue.
Contactor welding closed could have occurred at any time the inverter was connected/disconnected to the battery

Serves to disconnect loads.

But if contactor welded when battery was connected to inverter (likely not disconnect; that draws an arc under load and burns contacts, but doesn't weld them together), precharge resistor should be used regardless of whether battery protect is used.