Test of overload trip current in 18650 batteries

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HKJ
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Test of overload trip current in 18650 batteries

Somebody mentioned overload trip current when asking me something about batteries, this got me thinking, can I test it?
The answer is yes and it was fairly easy to rig the equipment for it. I used a computer controlled electronic load and a computer controlled power supply (the power supply is used to reset the protection with).

Here is my first test results:



I am using a current limit of 10 ampere and a lower voltage limit of 2 volt, i.e. if the current get above 10 ampere or voltage below 2 volt I stop the test and says the protection did not trip. With the unprotected IMR cell I increased the current limit to 20 ampere and did empty the battery during the 5 minutes testing time (This was mostly for fun).
Most of the cells are about a year old and comes from my 18650 roundup test, i.e. the specifications may have changed.
I did each cell 5 times, to see how stable the trip point is, some of the cells got rather hot during the test.
A few times the test shows 0 volt at the trip current, this is because I measure current and voltage at different time and the protection did trip between these measurements. This does also mean that the actual trip point is 0.1 ampere below the value in the table.
 For some of the batteries the trip point looks more like the under voltage trip point than a over current trip point.
The internal resistance is calculated from the voltage drop between 3A load and the trip point


Here is a look at the raw data for a few tests (My recording stops at the sample just before the protection trips):


The above curve has a regular slope, this means that the internal resistance calculation is valid for this cell.



With the IMR cell, only the first run is valid for internal resistance calculation.

I expect to include this test as part of my future LiIon tests, but will probably only include the lowest trip current measured and nothing else. 

My website with reviews of many chargers and batteries (More than 1000): https://lygte-info.dk/

08CivicSi
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wow, awesome post!

Budgeteer
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This deserves to be sticked somewhere. Perhaps it's time to make a section for BLF Knowledge database and treansfer all appropriate fancy work there.

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Budgeteer wrote:

This deserves to be sticked somewhere. Perhaps it's time to make a section for BLF Knowledge database and treansfer all appropriate fancy work there.

I think that's a great idea. Perhaps even a new sub-forum for such a knowledge base would be warranted. 

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HKJ
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There was two batteries that did not trip the protection in the test (The IMR does not count), I decided to retest them with a higher current limit:

The raw data for RediList 18650-29 looks this way:

 

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This is a great idea! The internal resistance measurements tells you how well the cell will handle high current operation, am I right?

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HKJ
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SPAMBOT wrote:

This is a great idea! The internal resistance measurements tells you how well the cell will handle high current operation, am I right?

 

Usual it does, but in this test the voltage might be a better indicator, because it is measured at the point where the protection trips (You also have to look at the actual trip current).

As you can see in the table the internal resistance does vary between measurements. The explanation can be found in the curve with the raw data: the cell does not always recover fully between runs and because I calculate the internal resistance over the full range, it get too low a value, except in the first run. If I am going to publish the internal resistance, it would probably be better to calculate it based on voltage drop for the last ampere, not for the full range.

My website with reviews of many chargers and batteries (More than 1000): https://lygte-info.dk/

old4570
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Is the voltage given the voltage the Protection circuit tripped ? around 3v or a little less ?

(From the DATA it looks like you were tripping the over discharge protection) .  

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HKJ
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old4570 wrote:
Is the voltage given the voltage the Protection circuit tripped ? around 3v or a little less ?

(From the DATA it looks like you were tripping the over discharge protection) . 

 

Yes, the voltage is from the last sample before the protection tripped. For some cells it looks like it is the over discharger protection, but not at 3 volt.

If you look at my 18650 roundup test, you will see that I discharge all cells down to 2.8 volt without tripping any protection, we also expect the protection on the 2900 cells to be below 2.5 volt.

The cells that might have tripped on discharger protection are: AW18650-22 and TrustFire18650-24 Flame.

 

One thing that is not included in my test is the PTC protection, I do the test to fast for the PTC to react. My guess is that any cell with a PCB protection around 10 ampere will trip the PTC if this current is drawn for a some minutes.

 

My website with reviews of many chargers and batteries (More than 1000): https://lygte-info.dk/

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benckie
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Good work HKJ

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XTAR+s 2200.2400,2600 tips at 2,8V so it did the WOW 2600, no other protected batteries i do have anymore. Well i don't even own any wow as those were grabbed instantly by friends when the were still cheap.

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Thanks for taking the time to share all of this information.

I am already visualizing the duct tape over your mouth.

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Great info HKJ!

Do you have the Solarforce 2400mAh (white&blue) to test the overload trip current.

HKJ
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Hikelite wrote:

Great info HKJ!

Do you have the Solarforce 2400mAh (white&blue) to test the overload trip current.

 

I do have some, but they are about a year old (They are from my 2011 test).

 

On the white/blue 2400mA SolarForce cell the protection is at about 10 ampere.

 

My website with reviews of many chargers and batteries (More than 1000): https://lygte-info.dk/