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Cell impedance question

Old 11-20-2012, 07:54 AM
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getterflash
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Default Cell impedance question

My new Turnigy 10XC charger measures individual cell impedance during the charge process. On all but one of my 5S 5000mAH packs this impedance number is in the range of 2.7 to 3.1 milliohms for each cell. I assume as cells are cycled and age this number will go up.

For those of you that have am method to measure cell impedance, what are the typical values for a reasonably fresh 5000mAH pack? Have you seen this number go up as the packs are used?

The reason I ask is I have one pack with cell#1 reporting 8.7milliohms, not a huge number but 3 times the value reported by the other cells in the same pack. This tells me either the cell is bad, or it is a wildly different "C" rating than the other cells. This same pack is the subject of another post about one pack out of 3 being "skinnier" by 1/8".
Old 11-20-2012, 09:24 AM
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wattsup
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Default RE: Cell impedance question

getterflash, I've typically seen impedance readings of 1.4 to 2.5 on "reasonably fresh 5000 mah" 5s packs from most of the retailers over the last 6 years. The numbers have been lower to start with on the newer brands that have become available for purchase during the last year or so. Yes, the individual cell numbers do go up as the packs age. As I stated in another thread here on RCU, I've been lucky to get 75 flights out of most of the packs I've purchased. Note, I ALWAYS charge at 1C. IMHO, the quality of most lipos is getting better! Someday, I hope to have packs that will indeed do 600 flights as advertised! Regards, Everette
Old 11-20-2012, 11:25 AM
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Default RE: Cell impedance question

The range of 2.7 to 3.1 sounds good. The absolute values will change with temperature but you want to see a narrow range of IRs at any temperature. They will drop during the first ten flights and remain low for about 50 flights. Then they will go up and eventually you won't get the required performance. The 8.7 cell is bad and will get worse before the others get to that value. Too bad we can't easily change out single cells.

Jim O
Old 11-20-2012, 11:25 AM
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mups53
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Default RE: Cell impedance question


ORIGINAL: getterflash

My new Turnigy 10XC charger measures individual cell impedance during the charge process. On all but one of my 5S 5000mAH packs this impedance number is in the range of 2.7 to 3.1 milliohms for each cell. I assume as cells are cycled and age this number will go up.

For those of you that have am method to measure cell impedance, what are the typical values for a reasonably fresh 5000mAH pack? Have you seen this number go up as the packs are used?

The reason I ask is I have one pack with cell#1 reporting 8.7milliohms, not a huge number but 3 times the value reported by the other cells in the same pack. This tells me either the cell is bad, or it is a wildly different "C" rating than the other cells. This same pack is the subject of another post about one pack out of 3 being "skinnier" by 1/8".
Flying electric is very scary Bob. Did you get your building bench back? Hope so, Mike

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