LiFePO Battery internal resistance test

[vaniusha92]

Hello everyone, recently i've bought from aliexpress some LiFePO batteries with the following specs: 3.2 V // 200Ah.
I would like to know if they are good, on the site in the spec section is written that the internal impedance shouldn't be more than 0.6 mili ohm.
The thing is that i don't know for real what internal impedance should have this type of battery with 3.2 V and 200Ah.
I received them, didn't charge them and tested them with impedance tester device, the numbers are 0.40 \\ 0.50 mili ohms
Could anyone tell me please if i have the good batteries or not? I'm new in this area.

 

[SeaGal]

Hello everyone, recently i've bought from aliexpress some LiFePO batteries with the following specs: 3.2 V // 200Ah.
I would like to know if they are good, on the site in the spec section is written that the internal impedance shouldn't be more than 0.6 ohm.
The thing is that i don't know for real what internal impedance should have this type of battery with 3.2 V and 200Ah.
I received them, didn't charge them and tested them with impedance tester device, the numbers are 0.40 \\ 0.50 ohms
Could anyone tell me please if i have the good batteries or not? I'm new in this area.

0.5 ohms doesn't sound right. That would mean they would drop 2.5V with just a 5A load.

but see https://diysolarforum.com/threads/t...ttery-and-inverter-to-mains.74684/post-947146
and the following posts, where it is explained in more depth.

Edited to add, just looked at your video - think you missed the 'm' = milli ohm!!

 

[McKravitts]

0.5 ohms doesn't sound right. That would mean they would drop 2.5V with just a 5A load.

but see https://diysolarforum.com/threads/t...ttery-and-inverter-to-mains.74684/post-947146
and the following posts, where it is explained in more depth.

The Impedance is the square root of (the sum of the square of the resistance plus square of the net reactance).
The net reactance is the inductive reactance minus the capacitive reactance. See formulas below.

As a rule, true power is a function of a circuit's dissipative elements, usually resistances (R). Reactive power is a function of a circuit's reactance (X). Apparent power is a function of a circuit's total impedance (Z).
Using just the resistive component of reactance give the real amount of power that will be disapated by the battery.
If a load connected to the battery has a reactive component that must be taken into consideration to determine actual current flow.
Most BMS's measure the total current and may shut down (high current) even if the load is not getting the power one would expect.



The reactive component depends on the frequency that the Impedance meter uses and the below diagram gives a sample curve of a lithium battery

As you clearly see, the actual internal power loss of the battery is highly dependant on any capacitive or Inductive component to the load Impedance. And the actual power disapated due to the measured Impedance could be much higher/lower than that predicted by Ohms power formula using published internal Impedance..

 

[vaniusha92]

0.5 ohms doesn't sound right. That would mean they would drop 2.5V with just a 5A load.

but see https://diysolarforum.com/threads/t...ttery-and-inverter-to-mains.74684/post-947146
and the following posts, where it is explained in more depth.

Edited to add, just looked at your video - think you missed the 'm' = milli ohm!!

Thanks a lot, that is like quantum physics for me. ) Yes, i'd like to correct myself- it's mili ohms. Could you say a more clear answer for me pleas as a "yes" the battery is good and the nominal impedance for this type of battery should be.... or if it is not. Thank you.

 

[squowse]

Thanks a lot, that is like quantum physics for me. ) Yes, i'd like to correct myself- it's mili ohms. Could you say a more clear answer for me pleas as a "yes" the battery is good and the nominal impedance for this type of battery should be.... or if it is not. Thank you.

You could look for a spec sheet for an Eve 200Ah cell for comparison.
Im not sure the resistance measuring devices are necessarily that accurate on these cells. I use dV/dI method

 

[Starex]

The picture attached to the opening post does not look like an impedance meter but a simple Ohm meter.
Ohm meters work by applying a small voltage across the test subject and measuring the current that flows through it.
If the device you are measuring is a battery, the voltage of the battery will mess up the reading.
An impedance meter uses a small ac voltage and measures only the ac component of the current, thereby eliminating any errors that the dc voltage could cause.

This is why battery manufacturers spec impedance which is measured with an impedance meter.
The problem is that any capacitive or inductive reactance will alter the measurement from the pure resistive component.

A good impedance meter will also show the phase angle between the applied ac voltage and the current. From this data the resistive component can be calculated.

A true impedance meter cost $600 minimum and good ones can cost in excess of $2000.00

 

[Skypower]

It is actually a very common, inexpensive and very good internal resistance meter. Probably not on the level of a $600 unit but a heck of a good bang for the buck. Several years later it’s still right on with no need to calibrate. Yes, I do use it for batteries but I use it a lot more for checking across connections and cable crimp quality or loss.

 

[Starex]

I know many manufacturers advertise their meters an “ Impedance” meters when they are really just resistance meters.
They can be very accurate at measuring resistance but not meant to measure impedance other than in circuits with zero reactance

 

[Skypower]

I know many manufacturers advertise their meters an “ Impedance” meters when they are really just resistance meters.
They can be very accurate at measuring resistance but not meant to measure impedance other than in circuits with zero reactance

I do know it’s been a time saver. I’ve compared it to passing current through and measuring voltage loss (multimeter) on different valued jumpers and found it correlates well. The advantage is it can be used as you assemble. The disadvantage is an assembly can not be in use (active circuit). For instance, an assembled battery circuit must be open and the bms off, whereas measuring voltage loss can be done active as long as the current is steady. The internal resistance meter is also excellent at matching groups, culling out dud or poor quality 18650 cells without having to run a full charge cycle to find out. In the near future I’m going to momentarily shutdown my battery banks and take new measurement. I’m curious how time has change them or if there is any difference to be measured on the cells that typically run high or low when reaching absorption voltage.

 

[SeaGal]

They can be very accurate at measuring resistance but not meant to measure impedance other than in circuits with zero reactance

The reactive component depends on the frequency that the Impedance meter uses and the below diagram gives a sample curve of a lithium battery

All true, but to be totally blunt, I cba with thinking about adding the complications of reactance for my batteries powering a dc load. The worst case is my inverter changing the current every second - in practice it ramps the draw up and down , so the highest frequency load my cells get is probably 0.05Hz to 0.1Hz.

Could you say a more clear answer for me pleas as a "yes" the battery is good and the nominal impedance for this type of battery should be.... or if it is not. Thank you.

It looks good

 

[McKravitts]

All true, but to be totally blunt, I cba with thinking about adding the complications of reactance for my batteries powering a dc load. The worst case is my inverter changing the current every second - in practice it ramps the draw up and down , so the highest frequency load my cells get is probably 0.05Hz to 0.1Hz.


It looks good

The only real effect at those low frequencies is the rapid voltage drop on startup, which indicates a large effective parallel capacitance. This is characteristic of all batteries.

The best way is to determine whether a battery is good is to charge it with a constant current for a fixed time from a starting soc using a power meter to integrate the power and display the actual power put into the battery. Then discharge with the same current for the same time and see how much power you get back.
I’ve seen Utube videos on line, some I believe were done by Will Prowse where he checks batteries using the charge/discharge method. I don’t recall the equipment he uses but I know he can make a pretty good guess as to the battery quality.

 

[Starex]

I trust we can all agree that using a standard multimeter no matter how expensive is not a good way to check a battery.

 

[SeaGal]

I trust we can all agree that using a standard multimeter no matter how expensive is not a good way to check a battery.

Bit of an open statement.. I'd say it depends on what you are attempting to check exactly.

 

[McKravitts]

Bit of an open statement.. I'd say it depends on what you are attempting to check exactly.

Can you live with; "not a great way"

 

[Starex]

I’ve had batteries that measured perfectly normal voltage wise and resistance wise but failed under a load.
Even the worlds cheapest battery testers sold at auto shops require that the battery be under a load for a few seconds before grading them.

 

[gotbeans]

The picture attached to the opening post does not look like an impedance meter but a simple Ohm meter.
Ohm meters work by applying a small voltage across the test subject and measuring the current that flows through it.
If the device you are measuring is a battery, the voltage of the battery will mess up the reading.
An impedance meter uses a small ac voltage and measures only the ac component of the current, thereby eliminating any errors that the dc voltage could cause.

This is why battery manufacturers spec impedance which is measured with an impedance meter.
The problem is that any capacitive or inductive reactance will alter the measurement from the pure resistive component.

A good impedance meter will also show the phase angle between the applied ac voltage and the current. From this data the resistive component can be calculated.

A true impedance meter cost $600 minimum and good ones can cost in excess of $2000.00

YR1030, YR1035, TR1035 etc are extremely reputable and known all over different forums for battery checking.
For example, plenty testing here: https://secondlifestorage.com/index.php?threads/ir-meter-recommendations.10361/

Bit of an open statement.. I'd say it depends on what you are attempting to check exactly.

Yep, they're perfectly good for checking voltage lmao. They're obviously talking about resistance but "check a battery" doesn't mean resistance only

It is actually a very common, inexpensive and very good internal resistance meter. Probably not on the level of a $600 unit but a heck of a good bang for the buck. Several years later it’s still right on with no need to calibrate. Yes, I do use it for batteries but I use it a lot more for checking across connections and cable crimp quality or loss.View attachment 183489View attachment 183490

from what I've seen they are on the level of $600 units
Fluke for example aren't the most accurate multimeters. They guarantee their readings are the same across every version and guarantee it for like 25 years or something, thus the price tag comes with.

 

[Starex]

I didn’t realize that the Chinese have started making inexpensive meters that can measure battery impedance. Sorry for the misinformation in my previous post.

 

[McKravitts]

I have access to a lab quality impedance meauring device at the lab at work.
I'm going to get one of those inexpensive ones and see how it compares.

 

[Skypower]

These internal resistance testers are not a common multimeter. They are referred to as a four wire type and the standard probe uses two spring loaded gold plated contact points in close proximity at each test point or polarity. From what I’ve gathered it injects a frequency and with an algorithm display a value. In most cases it simply confirms what the manufacturer states. It can identify a ringer, good or bad but and from what I’ve seen the cell are usually better than advertised or matches what’s printed on the label if one is attached.
It can’t determine capacity but it will tell you that the lot will likely have the same performance. Nothing beats a caloric/capacity test. It’s only by happenstance that this meter also gives great conductor resistance values(or reference).

As for a common volt meter, they are only accurate for measuring a battery at two conditions. At full and empty under no load. What’s in between is a very rough guess with that device.

 

[Skypower]

I have access to a lab quality impedance meauring device at the lab at work.
I'm going to get one of those inexpensive ones and see how it compares.

That would be interesting.