Does this mean I have a bad cell in my 48V system?

[SeaGal]

I also have the Victron BMS on their so I can do another test tomorrow and compare the two (shunt vs bms). What else should I check with the multimeter?

Using a multimeter to check individual cells and comparing them to what the BMS is telling you, would be a good way to diagnose the issue you're having.

Any progress / updates please?

 

[Nobodybusiness]

Any progress / updates please?

Curious myself..

 

[shvm]

The battery is a 48V using 16x 100AH EVE cells and a JK BMS. I built the batter back in March and it's worked great all year till now. Yesterday I noticied that anytime I put a load of 2,000W or more on the battery cell number 7 goes from the same as the rest to a lot lower and fast. The wire resistance is the same as the rest of the cells and all the terminals are torqued to the same measurement. I checked the wires and nothing is hot or lose. I looked at the cell without taking the entire battery apart and it doesn't look bloated (see pictures). Here's two videos showing when I put just 1,000 W on it and then one showing over 2,000W. The 2,000W+ one you will see the "Protection (Cell Under Voltage)" error at 1:25 seconds into the video.

1000W video1000W video

2000W video2000W video -

Chiming in to show the behaviour in my 100 Ah setup at 3 KW/ ~0.6 C. It is not as extreme as what you are facing.

Cells 8, 11 with Cell 10 right behind have higher resistance than rest of the pack !!

If you too have retightened terminals and verified voltages with a multimeter then the last thing likely remaining is Cell's internal resistances.

The JK doesn't recalculates wire resistances again unless rebooted. Highly probable that your wire resistance measurements are from day 0.

 

[Benjamin Yang]

Voltage Check:

Measure the voltage of each individual cell using a multimeter. If possible, check the voltage both under load and without a load to see if there is a significant drop during load.
Cell Balancing:

Ensure that the cells are balanced. If one cell consistently shows lower voltage under load, it might indicate an imbalance among the cells. Balancing the cells can be done using a balancing charger or a BMS that supports balancing.
Temperature Check:

Monitor the temperature of the #7 cell during load. An unusually high temperature could indicate a problem with that specific cell. Make sure that all cells are within a similar temperature range.
Internal Resistance:

If possible, measure the internal resistance of each cell. An increase in internal resistance could suggest a problem with a cell.
Physical Inspection:

While you mentioned that the battery did not appear to be expanding, a physical inspection of the #7 cell for any abnormalities, such as leaks, bulging, or unusual smells, might provide

 

[Berseker]

When watching the 2000watt video.
It’s blurry but when you hit 32 seconds the battery capacity goes from 94% to 0 and stays there.

Something is definitely not right.

Voltage sag shouldn’t be that big on a .5c pull.

You definitely have a runner with #7 but your other cells are pulled down to 2.8-3.1.
That shouldn’t happen.

Short of putting a shunt or VOM on the negative side to see if you are pulling 50 amps or it’s actually more?

Checking all the connections to make sure tight.

Swap in a new cell for #7.

Swap BMS for spare?

If you can take it offline measure individual cell voltages.

These are the things I would start with.

It’s definitely strange..

likely poor cells, i have a similar experience with about 0.6kw load. Daly report 96% soc...but cells sag to 3.293v

 

[SeaGal]

likely poor cells...

Unlikely, IMHO. All was working fine till last weekend, now 16 cells poor?

 

[SeaGal]

Any progress / updates please?

again... 4 days later - thanks

 

[Berseker]

Unlikely, IMHO. All was working fine till last weekend, now 16 cells poor?

Oh, i missed that part...
Strange issue then....loose connection??

 

[SeaGal]

Oh, i missed that part...
Strange issue then....loose connection??

Sounds likely... as I suggested in post #19. Sadly though, until the OP responds we won't know

 

[jdy2kgt]

Sounds likely... as I suggested in post #19. Sadly though, until the OP responds we won't know

Sorry for the delay but thank you guys for all the advice. It rained Sunday and I've been working all week so haven't been able to get back out there to check for lose connection or measure with the multi-meter. I did run the load again and used my victron shunt to verify what the BMS was showing for load was the same the shunt was showing. I'm heading out in a bit with my tools and will report back if I find a loose connection and what my readings were.

On person posted that the JK wire resistance readings aren't constantly updating and only from when you first power the bms up? That's news to me, and if true how do I reset them to see what the resistance reading is now?

 

[shvm]

On person posted that the JK wire resistance readings aren't constantly updating and only from when you first power the bms up? That's news to me, and if true how do I reset them to see what the resistance reading is now?

Just power cycle your BMS. If it came with a power switch it should be a 20 second step

 

[jdy2kgt]

Just power cycle your BMS. If it came with a power switch it should be a 20 second step

I know it came with the switch and I have the display with a button the side of it too.

 

[jdy2kgt]

Well I figured out the problem. Cells 7 and 11 had loose nuts . Once I tightened those down I was able to put 5K loads on it without problem. However, I saw a new problem. All the nuts on the cells were lose. So I set my torque wrench to 5NM (specs say these cells are rated for 6NM) and I wanted to play it safe. I was able to torque all nuts down except on cells 7 and 11. Those two just kept going until the grub screws came out . It looks like the treads let loose and striped. I'm going to hit up the company I bought them from as they are under a 1yr warranty and see what they say.

 

[Nobodybusiness]

Well I figured out the problem. Cells 7 and 11 had loose nuts . Once I tightened those down I was able to put 5K loads on it without problem. However, I saw a new problem. All the nuts on the cells were lose. So I set my torque wrench to 5NM (specs say these cells are rated for 6NM) and I wanted to play it safe. I was able to torque all nuts down except on cells 7 and 11. Those two just kept going until the grub screws came out . It looks like the treads let loose and striped. I'm going to hit up the company I bought them from as they are under a 1yr warranty and see what they say.

That does happen.

You can try to retap them to a bigger size or helicoil them.

 

[Skypower]

Well I figured out the problem. Cells 7 and 11 had loose nuts . Once I tightened those down I was able to put 5K loads on it without problem. However, I saw a new problem. All the nuts on the cells were lose. So I set my torque wrench to 5NM (specs say these cells are rated for 6NM) and I wanted to play it safe. I was able to torque all nuts down except on cells 7 and 11. Those two just kept going until the grub screws came out . It looks like the treads let loose and striped. I'm going to hit up the company I bought them from as they are under a 1yr warranty and see what they say.

You may want to get another torque wrench as it may be off. I have mine set at 4Nm as this is plenty for most terminals. It’s very common to set a balance issue just like yours from loose terminals.

 

[SeaGal]

You may want to get another torque wrench as it may be off...

Maybe, but also at such low Nm values you have to 'feel' it... see my posting here (and the sad image above it)

custom made battery box for eve LF280K cells

Thank you for all the replies and advices. I torqued the BMS busbars at 7 Nm and the cells busbars at 5 Nm I torqued the compression plate at 9 Nm and the rest manually, like houseofancients said it's less important. I also watched the Andy's video and saw he didn't put the copper washers...

diysolarforum.com

 

[Skypower]

Maybe, but also at such low Nm values you have to 'feel' it... see my posting here (and the sad image above it)

custom made battery box for eve LF280K cells

Thank you for all the replies and advices. I torqued the BMS busbars at 7 Nm and the cells busbars at 5 Nm I torqued the compression plate at 9 Nm and the rest manually, like houseofancients said it's less important. I also watched the Andy's video and saw he didn't put the copper washers...

diysolarforum.com

You got that right! Come up on it slowly wait for it. A nudge passed is a lot more.
My biggest “parrot” here on this forum is to go back and check the torque. Every single type of battery terminal has had some give. Be it lug, flat solid buss or laminated, they all need attention later.

 

[Skypower]

The funny thing is if you find a loose terminal it takes almost nothing to loosen it further(without it being in service of course!!!). I believe it’s far better to use less initial torque , combined with a follow up torque later, perhaps multiple times. I’ve used Bellevue washers and have been very disappointed by their performance. I’ve used several different sources of stainless Bellevues and all have had flattened with little rebound or force over a short time of installation. I’m thinking that real spring steel would work better but have not found any with correct parameters and pricing (minimum order). I’ll probably look again. Loose terminal issues are probably why so many manufacturers have gone to welded busses. I can’t blame them.

 

[42OhmsPA]

@Skypower
They aren't the cheapest but I've used Nord Locks in high heat and vibration (exhaust manifold / turbo) successfully after I tried every other option besides safety wire.
I see no reason they wouldn't work for a battery application.

McMaster-Carr

McMaster-Carr is the complete source for your plant with over 595,000 products. 98% of products ordered ship from stock and deliver same or next day.

www.mcmaster.com

 

[Nobodybusiness]

@Skypower
They aren't the cheapest but I've used Nord Locks in high heat and vibration (exhaust manifold / turbo) successfully after I tried every other option besides safety wire.
I see no reason they wouldn't work for a battery application.

McMaster-Carr

McMaster-Carr is the complete source for your plant with over 595,000 products. 98% of products ordered ship from stock and deliver same or next day.

www.mcmaster.com

Almost anything serrated works better than not.