What is the application? If we are talking less than 0.5C max, and average under 0.2C, I wouldn't even bother. Instead, once you get the pack built and balanced, put a good load on it, and measure each cells voltage. If you see a big difference, you would then start investigating.
Cell internal resistance (what does it mean)
- Thread starter legacyturbo
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What is the application? If we are talking less than 0.5C max, and average under 0.2C, I wouldn't even bother. Instead, once you get the pack built and balanced, put a good load on it, and measure each cells voltage. If you see a big difference, you would then start investigating.
Capt Bill
Sailing Options
Interesting. I do not yet know if the resistance value showing up on that fan capacity test is same as internal resistance? ... and wonder if it is relative to amp draws or charges. I think it can change with the amps ??? That Alibaba meter look interesting to me. I found this one on a different thread in this forum: https://www.amazon.com/gp/product/B01L6IC8A4/ref=ask_ql_qh_dp_hza ... I asked there on Amazon: Will this work to measure the internal resistance of a 3.2v 280 ah lifepo4 cell? I just got two; "It should" ... ; and one: "Yes, I've tested it on Li-Fe,Li-po,Li-ion,Lto and NiMH cells." I'm still on my learning curve about Internal Resistance measurements; How to; ... plus still wondering if it worth tooling up w a good meter to further evaluate a LiFePO4 purchase.
ArthurEld
Solar Wizard
I bought that same internal resistance tester. It gave me numbers that I didn't understand. My average internal resistance was 2.6 with that meter.
I returned it. The meter from Aliexpress is the same as what the cell resellers use. At least that is what I was told.
Importance of knowing the internal resistance of any battery
Been using a HP4328A for several decades quite reliably measuring the resistance of any chemistry battery .
When receiving any battery regardless of chemistry, always reach for the HH4328A , it will give a clear indication what condition the battery is in.
Knowing the impedance of the battery allow one to determine 1) maximum charging and/or discharging current simple math ( in Amps ) I = V/2R
As an example: using a 12 battery , if the measured resistance is 0.10 ohms then Max current capable of being drawn out of this battery = 12 /0.2 = 60 A
for how long is depended on A/H of the battery .
In my humble opinion a resistance measurement is far not valuable than V or A/H , you can have a 120V 100 A/H Battery which technically has 12,000W/H , but if
it internal resistance is 10 ohm you can only take out a measly 720 peak watt ( about a 1 HP) , now take the same battery with 0.05 ohm resistance will allow you 144,000 peak watts or close to 200 HP.
In summary, resistance is the MOST IMPORTANT PARAMETER in a battery to know , will dictate how fast you can discharge and/or charge it .....
ArthurEld
Solar Wizard
Thanks for the reply. I got my tester and the cells I have tested so far are .16 - .18
Most of them are .17
I was checking at the cell level. I am not sure if your example is for a battery pack.
Cell - 3.2/.36=8.89A
Battery pack - 48/.36=133A
I have used more than 8.89A charging and discharging cells and didn't have any issues.
I have not used more than 133A on my battery. My limits will be below that.
Just for giggles, I looked up the HP4328A. Good luck finding one of those. They're hard to come by.
Capt Bill
Sailing Options
I notice internal resistance reading for each 3.2v LiFePO4 cells show up in my Chargery BMS8T, and those figures vary with amount of Amps IN & Out ... ... kind of thing a bad or below par cell would have more internal resistance that other up to par cell, that might especially show up at higher amp charge rates ... Still learning, and kind of letting go of desire to tool up for measuring internal resistance, for now. Got my BMS info pages to look at, and seeing graphic of even cell voltages is reassuring.
100kwh-hunter
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The more a cell is (ab)used the higher the ir is going to be, always check ir charts before buying, if your cells arrive with a higher ir than fabric advised ir---> then the cells are used or very old(age degeneration) return them immediately, ask no questions.
With every cycle a cells has done, the ir will climb up...
You pay for A grade or new or a certain amount of cycles left in the cell....ir will reveal what is left, a capacity check only reveal what they can do now, so no future and no past, ir can predict future amount of cycles if you know the new fabric ir!
The yr**** ir meter are the best for 50$ you can buy them in English or in Mandarin language....
Ir is more important than a capacity check, aldo both correlate and are interconnect, ir is your friend when testing new arrived or bought cells....
Best Igor
With every cycle a cells has done, the ir will climb up...
You pay for A grade or new or a certain amount of cycles left in the cell....ir will reveal what is left, a capacity check only reveal what they can do now, so no future and no past, ir can predict future amount of cycles if you know the new fabric ir!
The yr**** ir meter are the best for 50$ you can buy them in English or in Mandarin language....
Ir is more important than a capacity check, aldo both correlate and are interconnect, ir is your friend when testing new arrived or bought cells....
Best Igor
scott harris
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The video from Amy showed my cells 280AH cells range between 0.13 to 0.18 mOhms. That did not look so good so I bought a YR1035+ to measure them when they arrived.
All have arrived now and I measured them with the YR1035+ (the same type of meter as in the video) and get measurements ranging between 2.12 to 2.48 mOhms. 15x higher and still quite a bit of variance.
I am very confused. I have 2 questions that I would greatly appreciate help with.
1) Assuming the measurements in the video are correct, is a difference between 0.13 and 0.18 going to be a problem?
2) Can IR change during shipping, or do I have a bad meter?
Thanks
All have arrived now and I measured them with the YR1035+ (the same type of meter as in the video) and get measurements ranging between 2.12 to 2.48 mOhms. 15x higher and still quite a bit of variance.
I am very confused. I have 2 questions that I would greatly appreciate help with.
1) Assuming the measurements in the video are correct, is a difference between 0.13 and 0.18 going to be a problem?
2) Can IR change during shipping, or do I have a bad meter?
Thanks
100kwh-hunter
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.1 In % on that capacity NO
. 2 No, it can not.
When does the ir change?
Simple: over time with age degradation.
Side note what applies for all li chem cells, the have there own life span, used or unused!
Ir will rise quicker when you use the cell.
Ir will rise faster when abuse.
If you have a cell that is rated for 1c 4000 cycles at 80% dod it will reach also a 80% soh witch is meaning the ir is climbing up to 10% of factory standart
But if you use it for just 0.25c at 4000 cycles at 80% dod it can reach just 90% soh with is meaning the ir is climbing up to just 5% of factory standard....But age degradation will play a role now.
If lets say it will take you in both cases 15 years the age degradation, dendrite forming will cous a 10 to even 25% increase in resistance.
Having fun havent we?
To make it worse:
If your cell will only see a discharge and charge from 40% to 70% they can get lazy and will never will do a full cycle, it is proven that in this case it would be best to disconnect them once in a while and fully discharge(from solar) them and full charge them(disconnect from inverter)
This was a very short version of a book that contains 1000 pages, to keep it simple, there are a lot of things to take in consideration and account.
The cells they sended you are probably from a batch that was manufactured begin of this year or from a batch of chemicals that was "left over" and mixed with a batch that was designed for a higher discharge rate(3c for example)
Try to get a data sheet from the cells they sended you.
Google the format plus the rated A and the c rating.
A other hint:
Every year at the same date measure the ir and write that ON the cell, plus the number of cycles and if you can disconnect one string and manually test the capacity per cell: charge all the way up, discharge all the way down.
Hope this was a little helpfull, Best Igor
. 2 No, it can not.
When does the ir change?
Simple: over time with age degradation.
Side note what applies for all li chem cells, the have there own life span, used or unused!
Ir will rise quicker when you use the cell.
Ir will rise faster when abuse.
If you have a cell that is rated for 1c 4000 cycles at 80% dod it will reach also a 80% soh witch is meaning the ir is climbing up to 10% of factory standart
But if you use it for just 0.25c at 4000 cycles at 80% dod it can reach just 90% soh with is meaning the ir is climbing up to just 5% of factory standard....But age degradation will play a role now.
If lets say it will take you in both cases 15 years the age degradation, dendrite forming will cous a 10 to even 25% increase in resistance.
Having fun havent we?
To make it worse:
If your cell will only see a discharge and charge from 40% to 70% they can get lazy and will never will do a full cycle, it is proven that in this case it would be best to disconnect them once in a while and fully discharge(from solar) them and full charge them(disconnect from inverter)
This was a very short version of a book that contains 1000 pages, to keep it simple, there are a lot of things to take in consideration and account.
The cells they sended you are probably from a batch that was manufactured begin of this year or from a batch of chemicals that was "left over" and mixed with a batch that was designed for a higher discharge rate(3c for example)
Try to get a data sheet from the cells they sended you.
Google the format plus the rated A and the c rating.
A other hint:
Every year at the same date measure the ir and write that ON the cell, plus the number of cycles and if you can disconnect one string and manually test the capacity per cell: charge all the way up, discharge all the way down.
Hope this was a little helpfull, Best Igor
ArthurEld
Solar Wizard
Something isn't right. I have that same meter and my EVE cells are .16 - .18
Are your terminals are clean?
It is very easy to get bad readings with these meters.
You have to clean the tape off of the terminals and scuff them up with scotch bright or emery cloth.
But to be honest, I think you will find your cells are in spec. I spent a lot of time using that meter but haven't found the information to be helpful.
scott harris
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Thanks for your advice. I scuffed the terminals with scotch bright. It lowered the IR but not to the factory readings. I now get readings centered around 1.55 m Ohms. I am thinking that there is a problem with the meter.
Do you get repeatable measurements with your meter? My measurements jump around a bit.
How is the info not helpful? Do you find no correlation between measured IR and cell performance? Am I wasting my time trying to get accurate IR readings?
ArthurEld
Solar Wizard
Mine do jump around but if the terminals are clean I can get reliable numbers.
I have my range set to auto auto. I think your values should be somewhere between .12 and .18
And hopefully they are all similar.
90% of mine are .17. There are a few that are .16 and a few that are .18.
When I find a cell that is weaker or stronger I look at the IR numbers I have recorded for that cell. But I can't find any consistent relation showing weak cells having higher resistance.
I assume .01 difference is insignificant.
100kwh-hunter
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Your meter is oke.....your cells are a bit older than advertised....read my comments in this thread again.
Yr are perfect meters, enough said......
No problem, it is how much deviation in %.....think about that, and do you calculation and show me if the deviation is above 5%
With best regards Igor K
Yr are perfect meters, enough said......
No problem, it is how much deviation in %.....think about that, and do you calculation and show me if the deviation is above 5%
With best regards Igor K
If I recall correctly were you getting high readings when you initially used the YR1035+ ? Or was that only happening with the other tester you tried. The meter has a Hold Zeror button. Does that zero out the meter before using it? I think scott harris should be seeing around the same readings as you are and the video Amy showed him.
100kwh-hunter
New Member
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The yr is one of the best.....clean your terminals on your cells before measuring.
if want a better one than the yr use the ones mit have...2500+
if want a better one than the yr use the ones mit have...2500+
ArthurEld
Solar Wizard
That was a different meter. I see the numbers moving around but when they stop I see .17 with the YR1035+
Igor,
I think the thing that made him initially think the meter might be the problem, is that the seller used the same yr1035+ meter, but got very different readings even though they were using the same meter on the same cells.
Also what is the math for determining the deviation?
scott harris
New Member
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Yes, the video from Amy and my measurements do not match even though we use the same model of YR meter. My readings are about 10x higher. even after cleaning with scotch brite. I have not used acetone yet. I think that I will go get some and see if that makes a difference.
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