How is max safe charge current determined in a li poly/li ion battery?

LowQCab

Joined Nov 6, 2012
2,645
Temperature-Rise is the correct way,
but to do that,
you have to know the ramifications of operating
the Cell / Battery at a particular Temperature.

The Cell / Battery may temporarily withstand extreme Temperatures,
but this will probably shorten the Cell / Battery Life-Expectancy,
( reducing the number of Charge-Cycles before performance-degradation ).

Batteries almost always have a Capacity-Rating provided
in "Amp-Hours" (Ah), or "Milliamp-Hours" (mAh).
If You Charge the Battery at this rating, it will take a little over an hour for a Full-Charge.
It's usually completely safe to Charge the Battery at this rate.
This would be referred to as a "1-C" Charge-Rate,
but many Batteries can be charged at substantially higher Rates than this with no problems.

A reliable, and conscientious, manufacturer will usually state
their maximum recommended Charge-Rate.
Sometimes even this conservative number may come at a reduction in Life-Expectancy,
( Battery manufacturers like to sell more Batteries )

Don't count on anything from Ebay, Amazon, Ali-Express, etc., to
provide accurate, reliable numbers.


"Sometimes" You get what You paid for, and sometimes You don't.

If You can't comfortably hold your hand on the Battery while Charging, it is definitely TOO HOT.

"Hobby" Batteries are quite often extremely stout,
and may be able to withstand a ~3-C to ~4-C Charge-Rate,
but slower is always better for Battery-Life.
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I think May be I am wrong but Li-Ion batteries commonly require a constant current, constant voltage (CCCV) type of charging algorithm. In other words, a Li-Ion battery should be charged at a set current level (typically from 1 to 1.5 amperes) until it reaches its final voltage.
 

LowQCab

Joined Nov 6, 2012
2,645
Not all Li-Ion-Batteries are crated alike.

What You may be referring to may be the manufacturers "recommendation"
for a particular Model of Battery that they sell, or
someone's personal "safe-recommendation" for a particular Battery.

Temperature-Rise is the only accurate way to determine the maximum-Charge-Current.
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Ya’akov

Joined Jan 27, 2019
6,856
Even though this thread is slightly stale, let me out a fine point on it.

In the absence of testing many specimens of the cell in question in a proper lab, the only source you have for this parameter is the manufacturer.

If you don’t know the manufacturer because the cell is being resold unlabeled, then you have to count on the data from the reseller. If this lies outside the typical range for similar cells, it is suspect on its face.

If you have to rely on it to charge at a higher rather than 1.5A, then it is very important to do some tests at the target current monitoring cell temperature and voltage. You need to do this more than once in case it is causing progressive damage.

If there is no catastrophic failure, you can use it with the caveat that LiPo cells are slow motion bombs when pushed to failure. Ensure that there is overcharge and overdischarge protection at the cell itself and a proper managed charger is doing the charging.

Most components fail by letting out the magic smoke, LiPos let out the hell fire.

C4BC012B-4B39-4398-8E02-99B394AEEFFA.gif
 

Audioguru again

Joined Oct 21, 2019
5,418
I think May be I am wrong but Li-Ion batteries commonly require a constant current, constant voltage (CCCV) type of charging algorithm. In other words, a Li-Ion battery should be charged at a set current level (typically from 1 to 1.5 amperes) until it reaches its final voltage.
When an older (not the new lower voltage Fe type) Li-Ion cell reaches its max 4.2V then it is not yet fully charged and is still charging until the charging current drops to a fairly low current, then the charger should detect the drop in current and shut off.
4.2V is reached when the cell is 70% to 80% fully charged. Some simple chargers wrongly stop charging when the cell reaches 4.2V.
 

Wendy

Joined Mar 24, 2008
23,078
Most AA or AAA lithium batteries have circuitry inside, I did not know this until @Audioguru again pointed it out to me. I couldn't find the YouTube video he linked to but these will show some of it. If you want to see more disc search for lithium battery teardowns on YouTube.
 
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