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Question regarding capacity testing of LTO cells

Claudi

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Apr 3, 2021
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Dear all,
thanks to Will Prose's great videos regarding LTO cells, I decided to run my photovoltaik plant on 40Ah LTO cells !

So far so good - I have ordered 10 Sets of 24 = 240 cells and now I want to test them before installing them, so that I do not get a buggy cell in my setup.
So I have ordered the cheap (40 US$) aliexpress capacity tester from Wills Video video to chek them one by one.

To be on the safe side I would like to operate them in production between 2.7 and 2.1 volt.
And here my trouble starts: I load one cell up to 2.7 Volt, connect it to the capacity tester and set the low voltage cut off limit to 2.1.

As soon as I turn the discharge amp on (not more than 5 A), the voltage drops down to 2.2 or lower and the test stops immediately. Thats a bit ... annoying

Could you perhaps give me a hint what values make sense for such a cell by cell validation and what limits I should use for test and operation ?

BR
Claudi
 
Check your connections, Those cells (if good) can give a 400a draw at that voltage drop. On a CCA test with copper buss bars (1/8 x 1-1/2 ) can test out at 1600 cca at 2.4v at start per cell .
I have taken my tests 0 v many time and not hurt them . Go use 1.8 v as a end voltage to test the capacity.
 
You were right .... after stabilizing the connection I was able to discharge with 15A ... in less than 2.5 hours per cell !

Is it dangerous (for the cell lifetime) to go down to 1.6 volt instead of 1.8 ?
If I disconnect the cell at 1.6 (15A) and measure the voltage afterwards (without load) it shows 2.0 .. thats ok, isn't it ?
 
I have used lto's for about 5-6 years , I have 18650 lto's that I have purposely shorted out to 0 volts for months at a time. they test to capacity.

I have had the 18650's for 2 years abusing them with over charge to 3v to zero and 0F to 140F and 25C discharge with a cool down period.
The only way I have hurt one lto is to go past 3v with a 65a pouch cell, I accidentally took it 5v . It looked like a balloon , let cool down, deflated it,and discharged tested it. Normally got 125-135 watts but got 450 watts out of it. I notice it had two power areas , one at 1.9v to 2.4 and one at 3.8v to 4.3v . If it wasn't for the electrolyte loss and expansion with the heat, it would have been going farther with it. Since I thought it was toast,
I recharged it to 3v and took it outside and took a 22 rifle and put a few holes in it. Definitely no fun, a got a half inch flame for about a second.
Nothing else but a little smoke-mist .

Going to 1.8v doubt that will hurt them at all
 
I have used lto's for about 5-6 years , I have 18650 lto's that I have purposely shorted out to 0 volts for months at a time. they test to capacity.

I have had the 18650's for 2 years abusing them with over charge to 3v to zero and 0F to 140F and 25C discharge with a cool down period.
The only way I have hurt one lto is to go past 3v with a 65a pouch cell, I accidentally took it 5v . It looked like a balloon , let cool down, deflated it,and discharged tested it. Normally got 125-135 watts but got 450 watts out of it. I notice it had two power areas , one at 1.9v to 2.4 and one at 3.8v to 4.3v . If it wasn't for the electrolyte loss and expansion with the heat, it would have been going farther with it. Since I thought it was toast,
I recharged it to 3v and took it outside and took a 22 rifle and put a few holes in it. Definitely no fun, a got a half inch flame for about a second.
Nothing else but a little smoke-mist .

Going to 1.8v doubt that will hurt them at all
Are the 18650's the only type LTO's you use? What is your application?
 
Most I have are 45 ah Yinlong Cells and other 6ah t0 30 ah cells are being made up for semi truck starting to motor cycle to riding tractor.
The 18650's are cheaper if your are purposely trying to torture them for info first hand . Pouch cells are mainly for stationary - lower C-rates apps , Round cells can handle stationary and vehicle uses at a higher C-rate 10c and higher
 
Most I have are 45 ah Yinlong Cells and other 6ah t0 30 ah cells are being made up for semi truck starting to motor cycle to riding tractor.
The 18650's are cheaper if your are purposely trying to torture them for info first hand . Pouch cells are mainly for stationary - lower C-rates apps , Round cells can handle stationary and vehicle uses at a higher C-rate 10c and higher
Do you have a reliable source to get good ones? ..... most seem to be selling cells that don't meet capacity tests.
 
Some one purchased for me from OSN 40 ah grade b LTO and i have 23.5 ah From 2.18 to 2,50 volt per cell, in this interval is 70 pecent of capacity,total capacity is 33Ah, is not indicated to keep them higher than 2,50v for hours, in 3 hours at 2.50 volt reaches 95 per cent SOC.
For a fast charge you may go at 2.7v and remove power source, for solar system is better to go at 2.5v and stay there.
 

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Dear all,
thanks to Will Prose's great videos regarding LTO cells, I decided to run my photovoltaik plant on 40Ah LTO cells !

So far so good - I have ordered 10 Sets of 24 = 240 cells and now I want to test them before installing them, so that I do not get a buggy cell in my setup.
So I have ordered the cheap (40 US$) aliexpress capacity tester from Wills Video video to chek them one by one.

To be on the safe side I would like to operate them in production between 2.7 and 2.1 volt.
And here my trouble starts: I load one cell up to 2.7 Volt, connect it to the capacity tester and set the low voltage cut off limit to 2.1.

As soon as I turn the discharge amp on (not more than 5 A), the voltage drops down to 2.2 or lower and the test stops immediately. Thats a bit ... annoying

Could you perhaps give me a hint what values make sense for such a cell by cell validation and what limits I should use for test and operation ?

BR
Claudi
You might want to think about a ZKE Tech tester...
You can automaticly run cycles and plot graphs. I made a post there, if you need more information on the Voltages and test parameters:
And there:
 
Ok, first thanks a lot for your answers ! :)
I set the max. voltage of my PV batteries to 60V now (=24 x 2.5V) and will not exceed it for long term usage.

Question 1:
what do you think is the low level counterpart (for long term usage).
I read 1.9V, I read 2.2V - based on several discharge graphs I would assume 2.1V

The max. load and unload power of the whole pack is 150A. As I have 8 cells in parallel (plan is to go up to 12) the charge power for one cell is 20 A (=0,5C).
What would you suggest as low level cuttoff voltage ?

Question 2:
The EBC-A40L tester looks nice and the price is ok ... but how can it plot graphs ? Is there a plotting enginge somewhere ?

BR
Claudi

 
Yes, for long term usage, 2.5V/cell is perfect.

1. After discharging to 1.9V/cell with 40A, the voltage rises again to 2.08V with the cell, that I tested. Depending on the internal resistance, the results may be different.
Half of the cells, I ordered, arrived with only 0.5V...and they have been sitting there for a long time. After charging, they fully recoverd. Deep discharge is not a big problem for those cells.
You can set 1.9V/cell at 20A or even lower discharge rates without any problem.

2. Yes, there is a software, you can download, when following the links on this website:

I also found a video from Andys Garage:
That might be helpful to get a impression on how it works.

That is how the graph looks like:
IMG_20211012_181222.jpg

BR, Raphael
 

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If you use a BMS lo cut off at 1.9v is ok, it takes in account the lowewst cell, if you do not use BMS 2.1v /cell is optimal, it represent the beginning of lower bend, from 2.1 to 2v is a reserve that can you use if you have no other option.
 
If you use a BMS lo cut off at 1.9v is ok, it takes in account the lowewst cell, if you do not use BMS 2.1v /cell is optimal, it represent the beginning of lower bend, from 2.1 to 2v is a reserve that can you use if you have no other option.
The main reason to set the BMS
low voltage disconnect to only 1.5V/cell and
the high voltage disconnect to 2.7V/cell
is to ensure, that your system does not fail easily.
Imagine your whole system fails, just because one cell / one parallel array drops below 1.9V/cell on a high C-Rate.
Of course it depends on your circumstances. But if you work not only for yourself, but for a customer,
you might want to consider to set the limits a bit higher.

I think we agree, that the inverter and also the charge controller should of course always stop before the BMS has to disconnect.
 
I use LTO cells from 4 years, in solar systems 10c rate is an exception, if you have 10kwh 10 c is 100kw, for such system at least 100kwh battery is used, 1c rate is common peak load for LTO 1c is nothing, even under 10c only is below 30 percent SOC may drop under 1.9v.
Such drop means defective cell, it must replaced anyway.
 
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