Battery Internal Resistance Measurements

[bapgood]

Here is some battery internal resistance measurements I got using the Turnigy 7 in 1 from Hobby King.

Take notice that I get a significantly different reading when the battery is in a battery holder or even off soldered lead wires.

Sony 30a 2000mah 18650 (fairly new) in FT battery holder (modded to remove pcb) --- 95mΩ (*note - two of these batteries in the holder dropped to 60mΩ)
Sony 30a 2000mah 18650 (fairly new) direct leads held to ends of battery --- 18mΩ
AW 1600mah 18650 (fairly new) direct --- 18mΩ
AW 2000mah 18650 (well used) direct --- 39mΩ
Efest 2000mah 18650 (moderately used) direct --- 50mΩ
AW 1100mah 18490 (fairly new) direct --- 21mΩ
Efest 800 18350 (fairly new) direct --- 34mΩ
MNKE 26650 (moderately used) direct --- 139mΩ
MOLI 26700 (moderately used) direct --- 29mΩ
Turnigy A-Spec Nano 6000mah 65-130c (moderately used) measured off 20g soldered leads --- 6mΩ
Turnigy A-Spec Nano 6000mah 65-130c (moderately used) direct to tabs --- 0-1mΩ

 

[mikepetro]

Here is some battery internal resistance measurements I got using the Turnigy 7 in 1 from Hobby King.

Take notice that I get a significantly different reading when the battery is in a battery holder or even off soldered lead wires.

Sony 30a 2000mah 18650 (fairly new) in FT battery holder (modded to remove pcb) --- 95 mohm (*note - two of these batteries in the holder dropped to 60 mohm)
Sony 30a 2000mah 18650 (fairly new) direct leads held to ends of battery --- 18 mohm
..........
Turnigy A-Spec Nano 6000mah 65-130c (moderately used) measured off 20g soldered leads --- 6 mohm
Turnigy A-Spec Nano 6000mah 65-130c (moderately used) direct to tabs --- 0 mohm

Bap, is that device measuring µΩ or MΩ?

I dont know about the resistance of FT bat holder, but if 20g soldered leads added 6 MΩ on the Turnigy it would seem very odd. I would not expect to see 2 solder joints and a few inches of wire add much resistance at all. 20g wire is in the neighborhood of 1 Ω per 100 feet.
(knowing you and your skills, I am assuming they are not cold solder joints)
Of course, zero resistance on the leadless Turnigy seems equally odd to me.

I am confused.

 

[bapgood]

I don't know how to make the ohm symbol, but it is reading in milliohms.

I'm sure it's not the most accurate in absolute terms, but it should be accurate enough to compare readings from the same meter.

 

[bapgood]

Small m not big M

 

[supertrunker]

On a Windows machine: ALT+234

That's a great toy and just what i need to test my old batteries. I don't believe a value of 0 and i don't know enough about LiPo batteries to use them, but why do they all look ghetto like that? Like my sandwiches?

T

 

[bapgood]

On a Windows machine: ALT+234

That's a great toy and just what i need to test my old batteries. I don't believe a value of 0 and i don't know enough about LiPo batteries to use them, but why do they all look ghetto like that? Like my sandwiches?

T

How about on my phone

IIRC it would alternate between 0 and 1. Like I said this was a relatively cheap meter and I'm sure it's not 100% accurate, but it should be accurate enough to compare battery to battery.

 

[BJ43]

Baps is reading the resistance between his fingers???????

 

[supertrunker]

How about on my phone

IIRC it would alternate between 0 and 1. Like I said this was a relatively cheap meter and I'm sure it's not 100% accurate, but it should be accurate enough to compare battery to battery.

Thanks Bap - that's good enough for me - i just want to find out which of mine are no longer performing well compared to the others.

Can't help you with phones, i have a dumb phone!

T

 

[Visus]

Copy paste? Ω


Dang informative post about a lot bap,
the turnigy unit is close enough to choose a better contacts if needed for battery box
alt+234 is awesome as well I copy paste when not in laze mode..


whoa phones are awesome

 

[bapgood]

ΩΩΩΩΩΩΩΩΩ....Ha!!!!!

I just got the Greek keyboard for my phone and Bobs your uncle.


BTW the meter also works great great it wattage mode to give you voltage/amps/watts/etc and keeps the max values afterwords. Just have to have power to the balance port for 1S voltage.

 

[DrMA]

Thanks for the measurements, bap. Now you know why all this time I've been railing against round cells and proposing the exclusive use of flat LiPo packs.

One thing to note, though, is temperature and state of charge can have dramatic influence on IR measurements. I usually measure IR on my lipo's when they're fully charged. That's the only way I found to get consistent readings.

 

[mikepetro]

Thanks for the measurements, bap. Now you know why all this time I've been railing against round cells and proposing the exclusive use of flat LiPo packs.

One thing to note, though, is temperature and state of charge can have dramatic influence on IR measurements. I usually measure IR on my lipo's when they're fully charged. That's the only way I found to get consistent readings.

Does the IR go up or down as the charge declines?

 

[bapgood]

All of the batteries except the lipo were fully charged....some had been setting for a while.....the lipo was almost drained ~3.6v IIRC.

I have always been with you DrMA....I just like to have the means of testing and comparing.

Some of the 18650's are getting pretty good....I ordered some of the LG 2500mah 30a 18650's that mamu talked about.

The thing I like about single 18650 mods like my side by side is that I'm completely untethered. I usually carry a spare batt in my pocket and I'm good for awhile, especially since I usually have a second mod either on me or close by.

I will post some more lipo results, but the nano round cells were quite high. Which didn't really surprise me since they didn't really seem to be very robust when I have used them.

I think the A-Spec Nano's are pretty good quality. I have some other high end lipo's that I will be interested to test.

 

[Visus]

you know were lining up at your door for the test of the round nano lipo's
their price and size are so attractive

 

[mikepetro]

Will tracking the internal resistance give you an indication of when a LiPo cell is getting ready to give up the ghost?
And if so how much of a change are you looking for?

 

[bapgood]

you know were lining up at your door for the test of the round nano lipo's
their price and size are so attractive

Turnigy nano round cells 800/900/1200mAh all at around 3.95v.....all were right around 42mΩ....testing at the leads on the batteries....I tested three of the 1200's....I have two 1200's charging and will see if there is any difference at full charge.

I wouldn't say to necessarily stay away from them, they are great for small mods. If you have room for something different, then I might look at other options.

You have to keep in mind we are talking in milliohms..... 1mΩ=0.001Ω

 

[bapgood]

Will tracking the internal resistance give you an indication of when a LiPo cell is getting ready to give up the ghost?
And if so how much of a change are you looking for?

Yes to some degree....how much of a change....idk????

The real telling thing that I haven't even tried to look at is IR under load.

 

[Visus]

Yes to some degree....how much of a change....idk????

The real telling thing that I haven't even tried to look at is IR under load.

For comparison:

4-5amp load

Efest 2000
Test of Efest IMR18650 2000mAh (red)

Efest 18350 800 v1
Test of Efest IMR18350 V1 and V2 800mAh (Red)

Aw IMR 1600
Test of AW IMR 18650 1600mAh (Red)

AW IMR 2000
Test of AW IMR 18650 2000mAh (Red)

Battery test-review 18650 comparator


They do not list the other batteries unfortunately
AW batteries are just awesome

 

[Visus]

Smaller battery tester
Battery test-review 18650 comparator

 

[DrMA]

Does the IR go up or down as the charge declines?

IR generally goes up as the battery gets discharged. This is caused by ion depletion in the electrolyte of the packs (lithium ions in the electrolyte migrate to the positive electrode during discharge), leading to a decrease in the amount of charge carriers within the battery, thus an apparent increase in resistance.

However, an overdischarged Li battery may experience a sudden drop in IR due to precipitation of metallic lithium, potentially leading to an internal short - this makes charging an overdischarged Lithium battery extremely dangerous.

Will tracking the internal resistance give you an indication of when a LiPo cell is getting ready to give up the ghost?
And if so how much of a change are you looking for?

Yes. IR of a LiPo will increase with age and useage*. If you measure the IR of a broken-in new LiPo (see note below) we'll call this the initial IR. With recharge cycles and age, IR goes up. In my experience, a LiPo remains useful for its intended purpose until its IR gets to be ~4x its initial value (but this assumes the IR is low enough to begin with).

*Note: high-end LiPos are manufactured with a stabilizing compound to increase shelf life. IR is usually pretty high on a brand new LiPo and will decrease with the first 5-10 charge cycles, as the stabilizers gets broken down.