LiFePO4 internal resistance question

Phil Orton

New Member
I have 4 cells: The IR readings using the 5 in 1 cell meter that Will used in one of his videos are: 010,002,002,007. My question is: Based on these readings are these 'normal' or are there any areas of concern that I need to watch? Did some research but could not find information or I just didn't understand it. LOL.
 

toothy

New Member
Good question, I signed up a few day ago to ask the same exact one, but with different numbers. I did find that taking repeated readings with an imax balance charger gave very different readings. I was going to do a reading with the Fluke and resister and some math but I think I need a way bigger resister to get usable results on a 400Ah cell. My 16 cells call for under or equal to 0.40mOhm and they are all 0.22 to 0.30 but like I say the measurements were jumping around. Take 4 readings one after another and some would be way different with no pattern.
 

Phil Orton

New Member
Good question, I signed up a few day ago to ask the same exact one, but with different numbers. I did find that taking repeated readings with an imax balance charger gave very different readings. I was going to do a reading with the Fluke and resister and some math but I think I need a way bigger resister to get usable results on a 400Ah cell. My 16 cells call for under or equal to 0.40mOhm and they are all 0.22 to 0.30 but like I say the measurements were jumping around. Take 4 readings one after another and some would be way different with no pattern.
My readings change some also. Interestingly the cells at 002 stay the same and the other 2 cells vary somewhat, however, not much.
 

MisterSandals

Participation Medalist
My readings change some also. Interestingly the cells at 002 stay the same and the other 2 cells vary somewhat, however, not much.
I just got my Tenergy 5 in 1 today so tested the IR on my 3 banks, 206AH LiFePO4. I got similar readings as Phil on all 3 of my new banks (4s). This is pretty suspicious that ALL 8 of the readings (Phils and mine) on the middle cells are 2!!?

Bank1: 10 - 2 - 2 -10 (first and last cells vary from 9-12 on different tests)
Bank2: 10 - 2 - 2 - 4 (last cell ended up as 5 on the last couple tests)
Bank3: 7 - 2 - 2 - 5 (consistent readings)

I am going to separate one of the banks and do tests on individual cells.

Anybody else with a Tenergy have some IR numbers?
 

MisterSandals

Participation Medalist
I ran quite a few more tests with cells in different 2s, 3s and 4s combinations.
Summary: 90% random, 10% dependent on location in series (first cell highest).

I used the 4 cells in Bank3 above in a few different 2s, 3s and 4s combinations. The Tenergy 5 in1unit does not handle 1s (i knew i should have sprung for the 6 in1 !!!)
Check out row 8 and 9 with cells 9+12 and cells 12+9 (different order). Random!
Anybody see a pattern other than first cell in series always highest?
Cell #'s4s (ohms)3s (ohms)2s (ohms)
1+2+3+410-2-2-10
5+6+7+810-2-2-4
9+10+11+127-2-2-5
10+11+1212-2-4
9+1010-4
10+118-5
11+128-5
9+1211-4
12+910-3
10+11+12+98-2-3-5
Summary
97,510,11,3
102,8124,8
112,225,8
125,345,4,10
 
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