One cell dropped to 2.92v (!?) after bashing. What should I do?

[Barmaleus]

UPD:
CNHL sent a replacement battery. In my book, that's a proper solution to the problem. Thumbs up to them.


Hi all!

Had a bash with a Kraton 4S v2.5 today. Stock. The only thing I did was set motor timing 1 step lower (from 22.5 to 18.75) and LVC one step lower as well (from 3.5 to 3.4).
- Temperature outside was around +3C/37.4F
- Battery almost new, just a few full charges, 4S, 6600mah. All cells were 4.20v when charged (maybe one was 4.19v or so).
- Nothing crazy. No jumps at all, just surface bashing.

I did hit LVC. The car stopped, ESC LED was flashing red with short single beeps. Checked the battery. It was 3.49 / 2.92 / 3.50 / 3.57. After a few hours got back home. Checked again and it is 3.52 / 3.14 / 3.53 / 3.60.

What should I do? Try to balance? (I use Ovonic X1)
Or this is considered dangerous and I should do the salt water thing?

Any advice appreciated.

I will of course contact the battery seller and ask questions.

Thanks a lot!

 

[dure16]

Yes just storage charge it at this point like you normally would.

There’s a decent chance that cell is ruined though. Keep an eye on it.

And I’d turn your LVC back up.

 

[Hector_Fisher]

If your charger can measure IR, one thing you could do is "start" a regular full charge, wait until you get IR measurements, then stop the full charge and swith back over to storage charge.

That would at least give you some idea about the health of each individual cell. Generally speaking, when one cell is much lower than the others, it likely because has much higher IR than the other and will continue to get worse over time. Getting IR measurements is a good way to confirm that.

 

[Diem Turner]

I've had chargers refuse to balance charge batteries where the cell voltage delta is too great or when it's below 3V on a cell. If you run into that, disconnect the balance lead and set the charger to NiCd mode and trickle charge it at 0.5-1A until the cell is over 3V. Reconnect the balance lead and storage charge the battery as already mentioned above.

 

[Barmaleus]

Thanks for your advice, everyone.

I started a regular charge to measure the IR. Now it's storage charging the battery.

IR numbers. Does it look bad? Clearly cell#2 is not feeling well. I wonder if it can recover.

 

[Diem Turner]

Thanks for your advice, everyone.

I started a regular charge to measure the IR. Now it's storage charging the battery.

IR numbers. Does it look bad? Clearly cell#2 is not feeling well. I wonder if it can recover.

View attachment 352499

Bad is relative. This isn't a pack I would use for any high performance endeavors but, should do just fine for bashing about.

 

[Barmaleus]

Bad is relative. This isn't a pack I would use for any high performance endeavors but, should do just fine for bashing about.

Thanks, understandable. By "bad" I meant more like "is it dangerous" - in terms of potential battery failure that may lead it to catch fire.

 

[Diem Turner]

Thanks, understandable. By "bad" I meant more like "is it dangerous" - in terms of potential battery failure that may lead it to catch fire.

It should be fine (assuming the battery isn't physically damaged or puffed up or something like that). Going under 3V for a little while isn't going to send the battery into thermal meltdown so I wouldn't worry about it more than you should worry about any lipo you have in the house.

 

[Eno]

There’s a decent chance that cell is ruined though.

Yes. Going below 3V under load damages the cell.

A reputable German lipo manufacturer even goes so far as to say everything below 3.3V under load damages the cell. It won't break immediately but the cell is harmed.

 

[Hector_Fisher]

Thanks, understandable. By "bad" I meant more like "is it dangerous" - in terms of potential battery failure that may lead it to catch fire.

"Dangerous" is relative, according to your level of risk tolerance

Would I keep using it? Yes.
How would I mitigate risk for further drops below 3v per cell? By changing to a more conservative LVC setting on the ESC.
How would I check to make sure i don't have problems in the future? By more frequently/closely monitoring the pack with after-use voltage level checks and IR checks every time I charge it.

To put things into perspective, I have some 3s lipos that are at 20-30mOhms per cell. I keep using them, just adjust their purpose (lower power applications like crawlers, powering lipo chargers in the field for volt checks and IR check, etc).

 

[Barmaleus]

It should be fine (assuming the battery isn't physically damaged or puffed up or something like that). Going under 3V for a little while isn't going to send the battery into thermal meltdown so I wouldn't worry about it more than you should worry about any lipo you have in the house.

It's a hard case battery. Looks like exactly as I received it. Not puffed or visually damaged. I'll keep an eye on it.

Yes. Going below 3V under load damages the cell.

Is there an easy way to verify if a cell is damaged "beyond repair"?

 

[Diem Turner]

It's a hard case battery. Looks like exactly as I received it. Not puffed or visually damaged. I'll keep an eye on it.

You should be fine then.

 

[Barmaleus]

"Dangerous" is relative, according to your level of risk tolerance

Would I keep using it? Yes.
How would I mitigate risk for further drops below 3v per cell? By changing to a more conservative LVC setting on the ESC.
How would I check to make sure i don't have problems in the future? By more frequently/closely monitoring the pack with after-use voltage level checks and IR checks every time I charge it.

To put things into perspective, I have some 3s lipos that are at 20-30mOhms per cell. I keep using them, just adjust their purpose (lower power applications like crawlers, powering lipo chargers in the field for volt checks and IR check, etc).

Thanks! Good thoughts. I'll get the LVC to factory settings. Tho it's just 0.1v.

 

[Hector_Fisher]

Thanks! Good thoughts. I'll get the LVC to factory settings. Tho it's just 0.1v.

Also keep in mind that the ESC only sees "total pack voltage", so roughly 13.5v in your case when you first measured. And since lipo cells dump voltage hard at the end of their voltage curve, it means that the 0.1v could make a big difference for than once cell.

For example, if your three good cells were at 3.8v per cell, and the "bad" cell was at 2.5v, your total pack voltage would be 13.9v, and ESC would still think that you have more life left in the pack.

With a big disparity in IR like that, i might be looking to use the highest LVC setting (unless that IS the default).

 

[Neelis]

Please never use the salt water method to drain the battery. You can find enough reasons online to not to it. It's not safe.

This was my result, after having this, I started to read a bit more about and found out it was not ok.

Regarding your battery: I would not be worried about fires, but I think you will notice a power decrease sooner or later.

 

[Garcbomber]

Don't personally like to see average cell count below 3.6V on a basher so mine are all set to 3.7(hobbywing High LVC).

Usually the end of my bashes are big ramp sends, last thing I want is to lose complete air control mid-flight. If it was a crawler or SCT then that's a difference story. You're gaining maybe a minute longer in average run-time at the expense of a ~$100 lipo.

 

[Barmaleus]

@Hector_Fisher I see, thank you. Makes sense. Will put LVC back to default for now (3.5v)
Also, seems like getting lipo alarm is a must.

 

[Barmaleus]

Here's how it looks like now.

 

[cazrack]

Ive noticed some chargers charge very slow to 3,20 if its lower and after 3,20 they go full speed.
Everything higher than 3,40 is safe in my book. Even the charges say there is some % fuel remaining then.

When you buy a new batteries after running them if you have a good charger look at them.
If one cell is bad its good to notify the store earlier than later.

 

[jkflow]

You are fine, bash on.
All you have done is take life out of your Lipo.
a) Never run to LVC, that setting is to protect the ESC from malfunctioning and not your Lipo from being damaged (even though it axcts like it).
b) If you drop below 3V on a cell, always use minimal current (~ 0.1C) to go back above 3.5'ish. Else you take out even more life as it heats up quickly.
c) When is this stupid saltwater myth ever going to die..I hate the facebook stupidity, besides making a mess it doesn't do much that you can't achieve a lot easier.
d) Your IR values are still good but you will notice that cell 3& 4 will now always be lower and might take a little longer to balance.

When is a Lipo dead enough?
When you get too frustrated with charging or run time. If you balancing for 2h and get 5 min runtime before a cell drops below 3.5V, that's when its time to simply discharge with a light-bulb (or similar) and let it go to zero. Once that is done you simply throw it in the trash, end of story.
Another good indicator is if it looks like a balloon animal, puffed is ok but if looks like it will burst I'd take it outside and use the lightbulb again. Let it sit for a day discharging and you know it's drained.

e) Always come back to this forum for good advice and stay far away from Facebook, they have some good advice but it's drowned out by saltwater type stupidity.