3.9C cell with 28mΩ resistance?

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rg12
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3.9C cell with 28mΩ resistance?

Post by rg12 » Apr 16, 2018 4:58 am

Hey Guys,

I measured the awesome Samsung 25R (8C) and it has 8mΩ resistance.
Then tested the LG M26 (3.9C) and it has 28mΩ resistance.

Is that normal for a 3.9C cell to have such high resistance?
All cells are new and tested on a few different batches and they all show the exact same numbers.
Mongoose EC-D 2007 (19" motocross wheels), 21s 10Ah LiPo, Greentime 72V 80A Controller, 12kg Hub Motor

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MadRhino
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Re: 3.9C cell with 28mΩ resistance?

Post by MadRhino » Apr 16, 2018 6:09 am

The state of charge and temperature does affect impedance of a cell. Those parameters should be measured equal, to compare 2 cells.

Then, both impedance readings that you have measured are within the manufacturers spec
Your Samsung cell impedance should be 7 to 16 m/ohm, 28 m/ohm after trip
If my memory is good, I recall your LG cell should be 60 m/ohm after trip. So, probably twice the impedance of the Samsung cell when in exact same state of charge and temperature.
Make it fool-proof, and I will make a better fool.
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fechter
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Re: 3.9C cell with 28mΩ resistance?

Post by fechter » Apr 16, 2018 8:51 am

It might depend on how you are making the measurement too. AC measurements are pretty useless.
"One test is worth a thousand opinions"

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rg12
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Re: 3.9C cell with 28mΩ resistance?

Post by rg12 » Apr 17, 2018 3:55 am

It's a DC cell IR tester.
Both tested brand new, same temp, same state of charge.
Charged many from different batches (all new) and all have the same specs.
Can it be that a 4C cell has almost 4 times higher IR than 8C?
Mongoose EC-D 2007 (19" motocross wheels), 21s 10Ah LiPo, Greentime 72V 80A Controller, 12kg Hub Motor

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rg12
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Re: 3.9C cell with 28mΩ resistance?

Post by rg12 » Apr 21, 2018 8:39 am

rg12 wrote:
Apr 17, 2018 3:55 am
It's a DC cell IR tester.
Both tested brand new, same temp, same state of charge.
Charged many from different batches (all new) and all have the same specs.
Can it be that a 4C cell has almost 4 times higher IR than 8C?
Bump...
Mongoose EC-D 2007 (19" motocross wheels), 21s 10Ah LiPo, Greentime 72V 80A Controller, 12kg Hub Motor

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MadRhino
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Re: 3.9C cell with 28mΩ resistance?

Post by MadRhino » Apr 22, 2018 1:59 am

rg12 wrote:
Apr 21, 2018 8:39 am
rg12 wrote:
Apr 17, 2018 3:55 am
It's a DC cell IR tester.
Both tested brand new, same temp, same state of charge.
Charged many from different batches (all new) and all have the same specs.
Can it be that a 4C cell has almost 4 times higher IR than 8C?
Bump...
You will know when you pull 4C continuous off them. My guess is they will get hot.
Make it fool-proof, and I will make a better fool.
Current bikes
Street: https://s20.postimg.org/ewrvugywt/Session_04_2015.jpg
Dirt: https://s20.postimg.org/lbqwr55ml/IMG_0157.jpg

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parabellum
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Re: 3.9C cell with 28mΩ resistance?

Post by parabellum » Apr 22, 2018 10:22 pm

rg12 wrote:
Apr 21, 2018 8:39 am
rg12 wrote:
Apr 17, 2018 3:55 am
It's a DC cell IR tester.
Both tested brand new, same temp, same state of charge.
Charged many from different batches (all new) and all have the same specs.
Can it be that a 4C cell has almost 4 times higher IR than 8C?
Bump...
Looks fine 3.2W waste heat on 25R and 2.9W waste heat on M26. M26 will have to tolerate it for double time span but area of the the cell is enough to dissipate it.

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