LTO troubleshooting

[alex912005]

Hi guys. Trying to troubleshoot some LTO issues. These batteries are 5 and a half year old and have been in the spare tire well. This is an area where I couldn't check regularly cause the subs were right on top and to check it I had to disassemble everything. The car leaks water in the spare wheel well so not sure if that was the cause of the problem. There are 24 cells in total grouped in 2 banks. 

One day the batts just died. I was reading 1.2 volts from the whole bank instead of 14 ish. So 1.2 combined. Around 0.2 each some of them a bit better or worse. Didn't think they could recover from that. First time it happened I took them out and charged them (with an AGM charger cause I don't have a lithium one) and they seemed fine. Put them back and they worked fine for months. Also changed the balancers to brand new Heltec ones.

The 2nd time I also had a parasitic drain. The fuel pump relay was stuck On, so the pump didn't turn off when I removed the keys from the ignition. No idea how long that was happening but they died again and same symptoms. Don't know if they died by coincidence or if the fuel pump just discharged them. 1.2 volts from the whole bank. Removed them, charged them back. Seem to work fine but the water leak was worse this time and I can see some of the signs. Some of the posts are kinda missing a tiny chunk of the aluminum. I'm wondering if this is corrosion or I had a short. There is also this white dust everywhere on the posts. Either the corroded aluminum or lithium titanate powder from the inside?

Bought a resistance meter and most of them are around 0.30 milliohms. So far I found one that's at 42 milliohms so pretty sure that one is a goner. Resistance is supposed to be around 0.20 when they're new as far as I know.

Anyone had similar issues with LTO? Trying to understand exactly what happened. They've been around for some time now. And these are more than 5 years old.

I'm thinking I can check the resistance of all of them and choose the best 12 cells I got and put them back into a new location where there's no water leak and see if that works for a while.

Any input is appreciated. Thanks!

[SnowDrifter]

Water intrusion is far from ideal, but realistically - these cells are sealed. I doubt the guts got wet.

I'd be taking a wire brush to the threads and contact then running a tap and die set down the threads to clean everything up.

Then check the capacity of each cell individually. Charge them up to 2.8v then discharge down to 1.5v. You can get load testers off amazon. I don't have any suggestions on which one to get, I only know they exist. Note the capacity, check for any outliers, and go from there.

You might also try calling around some auto shops and see if they have a load tester (big wheel cart thing with a heat sink on it that'll put 2-300 amp draw on stuff) to check full pack voltage sag. You can go around with a multi meter and check the sag of each cell while under load and see if there are any weak cells there. Shoot, you could even back-math the internal resistance if you know the starting voltage of a cell, sag voltage, and how much current the load tester is putting on the pack.

I'm a little cagey about putting too much stock in handheld probe-based impedance testers, especially with the corrosion on the threads. When you're working with impedance that low, even things like surface humidity are going to cause some pretty wild swings in readings. For giggles... What do you get if you touch the probes together and tell the meter to read itself? 

[alex912005]

Will do the wire brush and tap and die. Some of the nuts were extremely difficult to remove, and I specifically used stainless steel ones after the first time the batteries died, and they still rusted.

My problem is that I'm in Europe so cannot really find any LTO chargers and getting a load tester just for this one task is a bit beyond my budget right now. I can only charge these when they're together as a bank, either with my AGM charger or on the car, and they never had more than 15 volts in them. At most 14.8-14.9 (so less than 2.5 per cell, unless some of them overcharge a bit, but then the balancer will slowly take care of that). Maybe in the future I will buy a load tester. I could just do a burp and check the voltage sag after I put back the 12 best ones with the lowest internal resistance. And most auto shops around here really don't know how to deal with this stuff so I'm kinda on my own. I saw a video of some Russian dudes load testing some of these with a resistance in a bucket of water but that's too sketchy for me to try 😅

This meter seems pretty accurate. Touching the probes together gives me a 0.03 milliohm value so almost 0. (touching them the other way around gave me an error so I think they have a polarity cause there are 2 tips on each probe). Did not check all the cells yet but the ones I did check, I did give them a clean with WD40 so I'll say I touched the probe to a clean part of the posts.

And it's the same meter used in screenshots on aliexpress where they sell some of these LTO cells. If that counts for anything.

 

[SnowDrifter]

Pretty good wire level calibration on that unit, honestly

I'll admit I'm out of my wheelhouse when it comes to being able to check and diagnose batteries with those tools. I might be a bit of a caveman on that front