Samsung 25R Internal Resistance

[rg12]

I remember a while back testing and getting a constant 7mO and these days it's between 11 to 13.
Do you guys have any measurements of your own? talking about brand new cell in room temp of about 27 celsius.

One weird thing, just opened a 24S 30Ah 25R pack I built a year ago for a customer that had a 100A controller on it.
One cell got physically hit, so disassembled one whole cell row (first one that connects to the main positive) and the cells are 11mO which is better than the new ones I have right now at 13mO (back then they were 7mO).
Does that make sense?
The pack was ridden hard for a long while...

 

[Punx0r]

If I remember correctly, it takes a few cycles for a brand new cell to achieve it's best IR (and capacity), so that might be why you could see a used cell with lower IR than a new cell.

 

[neptronix]

IMHO IR goes down with cycles and calendar life.
I have never heard of it getting better before.

There is also a J shaped curve for IR. IR is it's lowest around 50% SOC, higher at 100% soc, and super duper high at 0% SOC.
So your difference might be due to age or voltage that you measured it at.

Try measuring both cells around 3.6v for a more fair comparison.

 

[jonescg]

I often measure >100 mOhms on NCR18650GA cells. Talk about saggy.

 

[eee291]

I often measure >100 mOhms on NCR18650GA cells. Talk about saggy.

What?

I think you meant 10mOhm not 100

 

[jonescg]

Nope, 100. Even fairly new cells were giving about 80-90 mOhms. They are typical Alibaba cells though.

 

[neptronix]

Many 18650s overpromise and underdeliver.

Gosh, i was so spoiled with my 1mOhm 5ah 20C RC Lipo packs..
100mOhm..

 

[jonescg]

It's a common trap to order the most energy dense cells going, only to find their DCIR is so high that it sags like crazy.
At 0.2C, these Alibaba red cells are giving the promised 240 Wh/kg.
But at 1C they give 200 Wh/kg, and at 2C give <170 Wh/kg.

Meanwhile my LiPo cells are still at about 1-2 mOhm. Just a shame about the volumetric energy density being pretty bad.

 

[flippy]

Nope, 100. Even fairly new cells were giving about 80-90 mOhms. They are typical Alibaba cells though.

those are not real GA cells.

 

[neptronix]

lgyte-dk measured the GA at 38mOHM using the AC testing methodology.

https://lygte-info.dk/review/batteries2012/Sanyo NCR18650GA 3500mAh (Red) UK.html

Kinda saggy at 1C. That's about where i'd realistically use that cell.

Full claimed capacity at 0.2C on a possibly counterfeit cell sounds about right.
Sounds like an OK cell for a 500w bike that needs to do >100 miles.
Not cool if you're looking to do burnouts with a big DD or scale a wall with a 3000w mid drive.

There's a cell out there for every occasion.

 

[999zip999]

Back to the 25r"s. As I want a 20s9p of 25r or 30q. Still a toss up. For a muxus 3,000 4t and 18fet at 90amps. ???

 

[Hillhater]

lgyte-dk measured the GA at 38mOHM using the AC testing methodology.

https://lygte-info.dk/review/batteries2012/Sanyo NCR18650GA 3500mAh (Red) UK.html

Its simple to calculate the DC IR of any cell on the lygte site from his discharge test data.
The 25r measures at 0.039 ohm
And the GA shows 0.042 ohm
Both results from mid range DOD (3.6v)
Lygte also have a very useful comparator for any cell tested..
https://lygte-info.dk/review/batteries2012/Common18650comparator.php

 

[Punx0r]

Back to the 25r"s. As I want a 20s9p of 25r or 30q. Still a toss up. For a muxus 3,000 4t and 18fet at 90amps. ???

If you have the choice I would definitely pick the 30Q. Performance is very similar but the 30Q has greater capacity and, I believe, better cycle life. Google the datasheet for each to see

 

[jonescg]

Nope, 100. Even fairly new cells were giving about 80-90 mOhms. They are typical Alibaba cells though.

those are not real GA cells.

Almost certainly rip-offs. Or at least the second-cut cells form the same factory. New out of the box they manage about 60 mOhms.

 

[brumbrum]

If I remember correctly, it takes a few cycles for a brand new cell to achieve it's best IR (and capacity), so that might be why you could see a used cell with lower IR than a new cell.

Have to agree. I was first dissapointed when building a 20s 27ah samsung 30Q pack. First 3 cycles gave higher sag and lower range compared to how the pack is now. I was surprised by this as i thought that cycling new cells a few times for max performance was a myth. But thinking about it, IR was probably greater as i had to reach a deeper/lower soc for same range than i do now. But capacity was definitly worse.

 

[999zip999]

Dogman 8 years ago praised cycling and breaking in your pack.

 

[flippy]

Nope, 100. Even fairly new cells were giving about 80-90 mOhms. They are typical Alibaba cells though.

those are not real GA cells.

Almost certainly rip-offs. Or at least the second-cut cells form the same factory. New out of the box they manage about 60 mOhms.

i have about 400 on the shelf, known originals. i get 38~41mohms on average with a (way too expensive) tester.

 

[docware]

I have few new cells from nkon here. Some after few cycles.
Samsug 25R shows 11,5 miliohms AC and 18 miliohms DC at 4,08 V.
Sanyo GA shows 20,4 (24 new) miliohms AC and 35 miliohms DC at 4,08 V.
Temperature during measurement cca 25 C

Sanyo GA cells in my one year old battery 10s5p are about 38 miliohms DC average.

I little bit miss clearly stated information about method of measurement, AC or DC internal resistance. Some are speaking about AC, others about DC IR.

To Hillhater :
You definitely are not able properly calculate 25R resistance from lygte site. 39 miliohm is obviously far away from the reality. 25R was done at the old clamp, but there is probably another issue in this measurement.

 

[brumbrum]

I have few new cells from nkon here. Some after few cycles.
Samsug 25R shows 11,5 miliohms AC and 18 miliohms DC at 4,08 V.
Sanyo GA shows 20,4 (24 new) miliohms AC and 35 miliohms DC at 4,08 V.
Temperature during measurement cca 25 C

Sanyo GA cells in my one year old battery 10s5p are about 38 miliohms DC average.

I little bit miss clearly stated information about method of measurement, AC or DC internal resistance. Some are speaking about AC, others about DC IR.

To Hillhater :
You definitely are not able properly calculate 25R resistance from lygte site. 39 miliohm is obviously far away from the reality. 25R was done at the old clamp, but there is probably another issue in this measurement.

But you can bet that your nearly new 25r cells will soon double in IR.

 

[jonescg]

i have about 400 on the shelf, known originals. i get 38~41mohms on average with a (way too expensive) tester.

Haha, I just pulled one out of its packet and tested it - its sitting at 3.48 volts. I passed a 3.35 A load through it and watched it sag...

164 mOhm :lol:

Now granted this is at the J-curve end of the DCIR, but I doubt it would be much better than half this value at the best of starting voltages.