How to do lithium impedance test

[ekkekan]

I found this information on lithium. User has to do impedance testing.

How do you guys do your test?

[jcdup]

Does this come from a specific battery's documentation? If so, which brand/model?

[ekkekan]

Does this come from a specific battery's documentation? If so, which brand/model?

It comes from a long time seller and installer of PV and tubes solar geysers. It relates to the DIY lithium cells they are selling. I would have look up the brand.

[SAND]

Surely these cells wouldn't reach 70% of its capacity or 150% of initial internal resistance within a year? I'm clearly missing something

[stephenplumb]

.

[Fluffy]

Impedance is a term that has no meaning in a DC circuit. It is only used in an AC environment and the maths gets a bit messier.

Weeeelll, actually -- Impedance is the only thing that has meaning. In a DC circuit it just has zero reactive components, only has resistance.

ALL circuits have impedance.

Within the context of this thread, remember that although a battery is a DC device, it most definately IS NOT purely resistive and has very strong reactive components that cause all sorts of funny things for a varying DC Voltage and Current like you get on a battery.

A Lithium battery most definately has a Impedance and is as far away from a pure resistance DC device as you can get.

[ekkekan]

Impedance is a term that has no meaning in a DC circuit. It is only used in an AC environment and the maths gets a bit messier.

That I know and the more reason to have placed it.

Still hope someone will give some clues or how such a test is done. Let's then call it resistance testing. It would be easier I presume.

@Sand - Also my 1st thought when I read it and the effort for a 1 year warranty.

[faniedup]

In my simplistic way I would draw 1A from a new cell and measure voltage, then do the same at 20A (or whatever the cell is rated at), and use the data to calculate the internal resistance.

Repeat after one year to compare?

Then to measure impedance drop it from one meter height and measure the bounce... :-)

[Fluffy]

In my simplistic way I would draw 1A from a new cell and measure voltage, then do the same at 20A (or whatever the cell is rated at), and use the data to calculate the internal resistance.

Repeat after one year to compare?

Then to measure impedance drop it from one meter height and measure the bounce... :-)

What does it do as you change from 1A to 20A - that's impedance ......

[Fluffy]

I know - I know.

[jab2]

Weeeelll, actually -- Impedance is the only thing that has meaning. In a DC circuit it just has zero reactive components, only has resistance.

ALL circuits have impedance.

Within the context of this thread, remember that although a battery is a DC device, it most definately IS NOT purely resistive and has very strong reactive components that cause all sorts of funny things for a varying DC Voltage and Current like you get on a battery.

A Lithium battery most definately has a Impedance and is as far away from a pure resistance DC device as you can get.

Thanks for this explanation. I was also using the DC = resistance, AC = impedance logic. Just shows matric science is VERY basic and can leave you feeling like an arse.

[ekkekan]

Does this come from a specific battery's documentation? If so, which brand/model?

I found the link.

https://shop.thesunpays.co.za/produc...v-lifepo4-cell

[Tiaan Pot]

Use a battery impedance tester

https://www.fluke.com/en-us/learn/bl...c%20resistance.

[Tiaan Pot]

Thanks for this explanation. I was also using the DC = resistance, AC = impedance logic. Just shows matric science is VERY basic and can leave you feeling like an arse.

Don't feel like an arse because you are correct.

R = resistance. ( Resistor,)
Xl = impedance or resistance of in inducator
Where Xl = 2πfL. ( Inductive reactance)
Xc = impedance of and a capacitor
Where Xc = 1/2πfC ( capacitive reactance)

All of them summed gives you Z = impedance

I'm not even going to try and type that out on my phone but you can google it :-)

Now if you look at the formula for inductive and capacitive reactance you will not the f for frequency.

In DC circuits the f=0
Therefore Xl = 0. ( Short circuit no effect zero resistance)
Xc = 1/0 = infinite ( open circuit - infinite resistance)

Now as Fluffy said a battery does have reactive components but in order to measure them the Fluke uses an 1000Hz AC signal.

This type of battery test is really only usefull if you do the test periodically and trend the results but still gives you a good indication of the batteries state

If a battery didn't have internal resistance it would be able to give you infinite current if short circuit it