Killed a cell Docan lifepo4 48v home bank

[LukeL]

Hey all! I’m 15 days into running my home off my new lifeo4 banks I purchased from Docan. We’ve lived Offgrid for 7 years. New batteries.

Using the JK B5A25S60P BMS (in case anyone else has) 1 requires 3 separate contactors TE 500 A.

Batteries are CATL 3.2v 280 ah. 16 per bank.

1. Background. When I paralleled the two 48v banks I ended up bulging 1 cell on bank A (cell 16 - positive terminal contact point for charging/inverting) and killing same cell on bank B (16b I call it - again positive side contact point). These cells both holding a charge now but I’m not using and scared of the bulges one.

My bad, I didn’t parallel at proper point. Docan great sending two replacements (I pay one, they pay other and freight covered). Impressed.

2. Currently running on 1 bank only until replacements arrive. Just the other day I killed cell 16 again (positive terminal that connects bank to inverter/charging system). Had no charge at all and will not take a charge at all. Totally dead. So I suspect I have a wiring problem that I’m not seeing. OR these cells just aren’t made to have that much current going through?! Which I doubt. They are far less robust than my monster lead acid batteries. Here is a picture of the 16th cell placement and that it keeps getting fried. Please excuse the rats nest. Need to iron the wrinkles before I tidy it up.

Here’s a picture of the BMS screen on 1 bank and it all appears to be working:



3. Specific to how I wired this BMS and the contacts - is it possible this my issue? Specifically where I connected all the contactors on their negative terminals. Will also show diagram:





4. These seplos battery box kits. Would that ensure not one cell is getting so much current through it?

Anyway just hoping a fresh set of experienced eyes might see why I keep having issues on that last cell on the bank. Or have insights.

Thank you kindly in advance.

Luke

 

[MisterSandals]

Anyway just hoping a fresh set of experienced eyes might see why I keep having issues

Those battery pics are pretty darn small!

Can you post a link to that BMS? Its design is new to me.

 

[JeepHammer]

By any chance did you check bottom and top on the cells before you built the battery?

When a supplier pawns off used cells on customers, I've heard of this happening but I've never actually seen it myself.

I can't tell if #16 is your positive or negative in the picture.

This is sounding like #16 has become a 'Fuse' for some reason... Cell balance, BMS, whatever...

I'd ask around about Seplos BMS, some people like them, some hate them, they do have 'Quirks' and there are entire forum sections devoted to finding the issues... I'm not an expert on them and won't pretend to be one on the internet.

 

[LukeL]

By any chance did you check bottom and top on the cells before you built the battery?

When a supplier pawns off used cells on customers, I've heard of this happening but I've never actually seen it myself.

I can't tell if #16 is your positive or negative in the picture.

This is sounding like #16 has become a 'Fuse' for some reason... Cell balance, BMS, whatever...

I'd ask around about Seplos BMS, some people like them, some hate them, they do have 'Quirks' and there are entire forum sections devoted to finding the issues... I'm not an expert on them and won't pretend to be one on the internet.

Thanks for the response. I looked over the batteries before setting them up and they had no indication of being used or damaged or refurbed. So far seller is super good.

Same time I think I wired it all correctly. Appreciate your input thank you again!

 

[LukeL]

Those battery pics are pretty darn small!

Can you post a link to that BMS? Its design is new to me.

Yes they all seem to be that size. 10 lbs vs 110 lbs for my lead acid cells.

This is link to BMS.

https://a.aliexpress.com/_mtZRGTI

 

[LukeL]

Those battery pics are pretty darn small!

Can you post a link to that BMS? Its design is new to me.

Yes they all seem to be that size. 10 lbs vs 110 lbs for my lead acid cells.

This is link to BMS.

https://a.aliexpress.com/_mtZRGTI

I see you meant pics lol. I’ll try and repost better pic

 

[LukeL]

Not sure if this pic any better. Original is 9 mb so I assume it got thumbnailed down.

 

[JeepHammer]

When batteries switched to aluminum skin instead of rigid housing, I had some swelling.

Limit expansion, slight compression.

I still can't answer why the same battery in your strings failed, but a little compression helps a bunch.

 

[Techie007]

Batteries are CATL 3.2v 280 ah. 16 per bank.

1. Background. When I paralleled the two 48v banks I ended up bulging 1 cell on bank A (cell 16 - positive terminal contact point for charging/inverting) and killing same cell on bank B (16b I call it - again positive side contact point). These cells both holding a charge now but I’m not using and scared of the bulges one.

Anyway just hoping a fresh set of experienced eyes might see why I keep having issues on that last cell on the bank. Or have insights.

It's really hard to tell what's going on from the supplied pictures. However, I do have a few thoughts. You indicated that the problem occurred when connecting the two banks in parallel. If one bank is fuller than the other, and cell 16 is full (on the lower bank) or empty (on the higher bank), this connection could force that cell above (or below) its maximum voltage ratings while the two banks equalize out. Going over/near a cell's rated maximum voltage can cause it to bulge. But you should see this on your BMS. Did you balance these cells before putting them into use? Also, I would parallel the cells first, and then series them, resulting in one large bank, rather than having multiple banks of series cells. This helps the cells balance against each other, averaging their differences out instead of making the BMS do all the work.

 

[JeepHammer]

It's really hard to tell what's going on from the supplied pictures. However, I do have a few thoughts. You indicated that the problem occurred when connecting the two banks in parallel. If one bank is fuller than the other, and cell 16 is full (on the lower bank) or empty (on the higher bank), this connection could force that cell above (or below) its maximum voltage ratings while the two banks equalize out. Going over/near a cell's rated maximum voltage can cause it to bulge. But you should see this on your BMS. Did you balance these cells before putting them into use? Also, I would parallel the cells first, and then series them, resulting in one large bank, rather than having multiple banks of series cells. This helps the cells balance against each other, averaging their differences out instead of making the BMS do all the work.

mW BMS internal balancing is worthless.
This is WAY too much power for mW capacity balancers.
I figured the balance time once, it was like 3 months if the battery WASN'T used...

Add a balancer that has some capacity, they aren't expensive and not difficult to install if you can install a BMS.

 

[Techie007]

mW BMS internal balancing is worthless.
This is WAY too much power for mW capacity balancers.
I figured the balance time once, it was like 3 months if the battery WASN'T used...

Add a balancer that has some capacity, they aren't expensive and not difficult to install if you can install a BMS.

The particular BMS pictured appears to have a 5A (approximately 17W) balancing capacity. As far as balancers are concerned, that's pretty good and more than enough to keep a large battery pack like this in line once they are balanced; but the batteries need to be pre-balanced prior to being put into a pack with normal charging currents (or high currents seen when connecting two banks at different voltages). Also keep in mind that as good as it is, this 5A is only half a cell at a time, not all cells at once.

 

[LukeL]

It's really hard to tell what's going on from the supplied pictures. However, I do have a few thoughts. You indicated that the problem occurred when connecting the two banks in parallel. If one bank is fuller than the other, and cell 16 is full (on the lower bank) or empty (on the higher bank), this connection could force that cell above (or below) its maximum voltage ratings while the two banks equalize out. Going over/near a cell's rated maximum voltage can cause it to bulge. But you should see this on your BMS. Did you balance these cells before putting them into use? Also, I would parallel the cells first, and then series them, resulting in one large bank, rather than having multiple banks of series cells. This helps the cells balance against each other, averaging their differences out instead of making the BMS do all the work.

Thanks for the response!! I apologize these pictures are hard to decipher lol. I did balance all the cells manually with a bench power supply before connecting. Problem 1. was on the paralleling but I believe I solved that issue/found my mistake. Presently I’m more concerned with why this 16th cell in the solo bank is not working.

As for having one large bank with 32 cells vs two of 16 each. I would have to see it on paper to see how I would make all the connections. It just seemed natural to me to double everything I’ve done - 2 BMS, 6 contactors etc. This is definitely something I’m open to doing especially if it puts less pressure on the respective BMS’. I suppose I’ll still use two BMS regardless of the configuration. Still, as one large bank the connecting - terminal on the one end and the + terminal on the other end would see a pile of current through those cells. Positive especially. This seems to be my issue, or perhaps it is a faulty cell and bad luck. Anyway I’ll explore this. Thank you!

 

[LukeL]

mW BMS internal balancing is worthless.
This is WAY too much power for mW capacity balancers.
I figured the balance time once, it was like 3 months if the battery WASN'T used...

Add a balancer that has some capacity, they aren't expensive and not difficult to install if you can install a BMS.

My BMS is a 5a balancer and I would’ve bought bigger but this is all they had. I do agree though - those leads are 20 gauge wire I think and I’ve got 4/0 coming in from my inverter/charger

 

[LukeL]

The particular BMS pictured appears to have a 5A (approximately 17W) balancing capacity. As far as balancers are concerned, that's pretty good and more than enough to keep a large battery pack like this in line once they are balanced; but the batteries need to be pre-balanced prior to being put into a pack with normal charging currents (or high currents seen when connecting two banks at different voltages). Also keep in mind that as good as it is, this 5A is only half a cell at a time, not all cells at once.

Yes this was the biggest they had. Before connecting each cell they were all top balanced with a bench power supply. Good to know. Maybe my BMS failed in low power protection in that cell. Doesn’t make sense to me why it was allowed to be totally drained when all the other cells were totally fine. I assumed it was its place in the string (16th, with positive terminal connecting to inverter). Thanks for the insights!!

 

[LukeL]

When batteries switched to aluminum skin instead of rigid housing, I had some swelling.

Limit expansion, slight compression.

I still can't answer why the same battery in your strings failed, but a little compression helps a bunch.

Thank you

 

[Skypower]

View attachment 150788
Not sure if this pic any better. Original is 9 mb so I assume it got thumbnailed down.

Maybe I’m missing something, but it looks like the relays are not doing anything and it’s passing straight through from bottom to top. Something I can’t see? I’m confused.

 

[100FUEGOS]

You are destroying your top balance by balancing at 3.2 volts and under. Some of your cells, not only 16th, appear bulged, too bulged for 15 days old cells. No idea why you have killed two cells, or three I cannot remember now, and always the most positive.

 

[Skypower]

You are destroying your top balance by balancing at 3.2 volts and under. Some of your cells, not only 16th, appear bulged, too bulged for 15 days old cells. No idea why you have killed two cells, or three I cannot remember now, and always the most positive.

Good catch, I didn’t notice the balance was active that low.

 

[Nobodybusiness]

Hey all! I’m 15 days into running my home off my new lifeo4 banks I purchased from Docan. We’ve lived Offgrid for 7 years. New batteries.

Using the JK B5A25S60P BMS (in case anyone else has) 1 requires 3 separate contactors TE 500 A.

Batteries are CATL 3.2v 280 ah. 16 per bank.

1. Background. When I paralleled the two 48v banks I ended up bulging 1 cell on bank A (cell 16 - positive terminal contact point for charging/inverting) and killing same cell on bank B (16b I call it - again positive side contact point). These cells both holding a charge now but I’m not using and scared of the bulges one.

My bad, I didn’t parallel at proper point. Docan great sending two replacements (I pay one, they pay other and freight covered). Impressed.

2. Currently running on 1 bank only until replacements arrive. Just the other day I killed cell 16 again (positive terminal that connects bank to inverter/charging system). Had no charge at all and will not take a charge at all. Totally dead. So I suspect I have a wiring problem that I’m not seeing. OR these cells just aren’t made to have that much current going through?! Which I doubt. They are far less robust than my monster lead acid batteries. Here is a picture of the 16th cell placement and that it keeps getting fried. Please excuse the rats nest. Need to iron the wrinkles before I tidy it up. View attachment 150768

Here’s a picture of the BMS screen on 1 bank and it all appears to be working:

View attachment 150764

3. Specific to how I wired this BMS and the contacts - is it possible this my issue? Specifically where I connected all the contactors on their negative terminals. Will also show diagram:

View attachment 150767
View attachment 150769


4. These seplos battery box kits. Would that ensure not one cell is getting so much current through it?

Anyway just hoping a fresh set of experienced eyes might see why I keep having issues on that last cell on the bank. Or have insights.

Thank you kindly in advance.

Luke

Kind of weird it balancing at 3.1/ 3.2 vdc but shouldn’t be the problem.

Not familiar with this BMS that uses contactors.

Can’t get a feel for how it works or how they are connected.

If you had a OVP then the BMS should have stopped charging unless something isn’t connected correctly or settings are wrong.

Hard to troubleshoot without laying eyes on it.

 

[Skypower]

Kind of weird it balancing at 3.1/ 3.2 vdc but shouldn’t be the problem.

Not familiar with this BMS that uses contactors.

Can’t get a feel for how it works or how they are connected.

If you had a OVP then the BMS should have stopped charging unless something isn’t connected correctly or settings are wrong.

Hard to troubleshoot without laying eyes on it.

Continuous balancing balancing doesn’t work for everyone. A lot of has to do with use patterns of the battery. That’s why some say it’s okay and others say it isn’t. I’ve seen that bms before. It’s theoretically only limited by the capacity of the relays and shunt. The coils do have the power drain associated with this type. It looks to me like he’s not using the precharge function (can’t see the resistor and continuous buss across all three relays). You right, OVP should have saved it OR how many times did it actually protect it? It’s hard to diagnose it remotely and not seeing the event.