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How healthy are your batteries? (How to measure internal resistance)

IsaacT

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This may be a necro post, but this is kind of a sticky so meh :/ I'll go for it and ask forgiveness later.

1. Is there a certain point at which I should throw my batteries away very swiftly and with no regret? And by throw away I mean take to have disposed of in a manner befitting of the nature of LiIon Batteries.
2. Will a 10Ohm resistor work? Thats all I have, and radioshack keeps wanting all my money for resistors. Like "That'll be 3 bucks for ONE resistor".
3. Is it dangerous to keep cells that have a certain level of IR?

Thanks,
Isaac
 



LarryDFW

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1. Yes . When the Internal Resistance reaches over 300milliohms :
. . . IR Cell Ranges
50-100 mOhm - Excellent (50mOhm new Panasonic)
100-250 mOhm - OK
250-Up mOhm - Marginal (may overheat, leading to thermal runaway)

Cells charging at 1 amp or so, will be too hot to grasp in your hand

2. A 10 ohm resistor is a little high.
Two in Parallel would be 5 ohms which is good.

3. High IR is only dangerous when charging or discharging,
so that is when you have to check for heat rise.

LarryDFW
 
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IsaacT

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Time to go rummage about in my garage to search for another 10ohm resistor...maybe i missed one haha. Does thermal runaway created a lot of heat? Could that be why my laser heats up within 10 seconds or so?

I thought it was just my host.
 
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IsaacT

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Okay so: my 2 year old CR123 is:
V1=4.11
V2=3.86
R=5
IR=324mOhms

And my AW CR123 is:
V1=4.15
V2=3.98
R=5
IR=213mOhms

Does that look about right?

Thanks,
Isaac
 

LarryDFW

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Your 2 yr old CR123 is getting tired (@ 324mohms).

Good job !

LarryDFW
 

grainde

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I measured my AW's and Panasonic's (NCRA and NCRB) with an old 2.2 Ohm resistor (actually measured 2.5 Ohm on DMM so used that).

AW 16340 (1) V1 = 3.85, V2 = 3.71 Rbat = 94 mOhm ( 9 - 10 months old)
AW 16340 (2) V1 = 3.88, V2 = 3.74 Rbat = 94 mOhm ( 9 - 10 months old)
AW 16340 (3) V1 = 4.15, V2 = 3.98 Rbat = 107 mOhm (9 - 10 months old)

AW 14500 (1) V1 = 4.05, V2 = 3.94 Rbat = 70 mOhm (9 - 10 months old)
AW 14500 (2) V1 = 4.05, V2 = 3.94 Rbat = 70 mOhm (9 - 10 months old)

Both have always been used together running my 2.6 W 455 and hence the same start potential.

AW 18650 (2000) V1 = 4.12, V2 = 4.02 Rbat = 62 mOhm :) (9 - 10 months old)


Panasonic NCRB V1 = 4.17, V2 = 4.03 Rbat = 87 mOhm (NEW bat :) )


Panasonic NCRA V1 = 4.17, V2 = 3.97 Rbat = 126 mOhm (6 months old)

re-measured after some use: NCRA V1 = 3.92, V2 = 3.83 Rbat = 59 mOhm??
recharged and left 1 day: NCRA V1 = 4.19, V2 = 3.93 Rbat = 165 mOhm???


So it seems to vary and is dependent on the state of charge of the battery. I guess this is due to the rapid drop from 4.2 V down to (4 ish) V of Li bats under load (approx. 4.1 V for IMR and 3.9 V for LiCo). The drop in potential is less rapid below this, until around 3 V. I plotted a curve of this battery linked to a test load @ 710 mA for a few hours. The capacities are close enough as it was only a rough test! I realize it is not very accurate as I was measuring current at the test load and not the tail cap. However, the driver was a linear AMC based driver, which draws very little current and the test load was set for around 3 V. The driver cut out around 2.8 - 2.9 V.

Interested to hear your opinions on whether there is a valid testing range for batteries?:beer:

Edit: Ran down NCRA again: V1 = 4.08, V2 = 3.96 Rbat = 76 mOhm?
also ran down the NCRB: V1 = 3.87, V2 = 3.74 Rbat = 87 mOhm
 

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LarryDFW

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So it seems to vary and is dependent on the state of charge of the battery. I guess this is due to the rapid drop from 4.2 V down to (4 ish) V of Li bats under load (approx. 4.1 V for IMR and 3.9 V for LiCo). The drop in potential is less rapid below this, until around 3 V. I plotted a curve of this battery linked to a test load @ 710 mA for a few hours. The capacities are close enough as it was only a rough test!
Interested to hear your opinions on whether there is a valid testing range for batteries?

In testing hundreds of cells, I have seen the same phenomenon.

Look at the curves you posted.

Initially, the downward slope (internal resistance) is quite sharp.

Then the curve levels off in the middle of the discharge (lower I.R.).

This is the best region to test the I.R. of the cells.

It has the same slope for a good portion of the discharge.

The cells also are supposed to rest for an hour or so before testing.

I notice the AW 14500 cells performing better than the 16340 cells.

I think that is because the 14500 cells are Sanyo,

while the 16340 cells are not made by a major manufacturer.

LarryDFW

P.S. Manufacturers test for Internal Impedance with more elaborate AC testing equipment.
 
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grainde

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Ah ok great thanks for the info. :)

So basically we shouldnt test fully charged, and even rested cells, but rather cells which have been slightly run down to around 4 ish V? Would that also suggest that measurements taken in this steep section of the V vs time curve would not be an accurate estimation of the IR? :thinking::beer:
 
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BShanahan14rulz

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Grainde: That's what I take away from it, and it makes sense that we're trying to measure the slope, so pick the slope that is most prevalent.
 

TeufelWolf

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Great thread. I clobbered together one using a toggle switch on the resistor.
I'm using a 5W 4.7 Ohm resistor - but when I test it with my DMM it shows a resistance of 6.4 Ohms. This is new from Fry's. Is that normal or a bad resistor?
 

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qumefox

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remember when reading low ohms, the wires of your leads have resistance too.. touch them together and see what it reads, then subtract that from what it reads the resistor as.
 

TeufelWolf

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remember when reading low ohms, the wires of your leads have resistance too.. touch them together and see what it reads, then subtract that from what it reads the resistor as.

:thanks:

That makes so much more sense. I am thinking of replacing the DMM with a digital voltmeter component to see if I can make it self contained.
 

Cube777

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Hey guys,

I got my new 18650 batteries today (not from china, a trusted supplier) and this is the reading that I got:

Batt 1:

V1: 4.21
V2: 3.04
R: 2
Ir: (4.21-3.04)*2/3.04= 0.77 Ohms

Batt 2:

V1: 4.19
V2: 3.04
R:2
Ir: (4.19-3.04)*2/3.04= 0.756 Ohms

On his site they say it has a very low internal resistance, is there maybe something wrong with my batteries? Thanks guys!
 
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Cube777

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3.04/2=1.52A and when the I'm going to use the batteries in my laser it's going to draw >2A because I'm going to use a boost driver. It is suppose to be able to easily handle that current.

EDIT: Ok, since the first reading was directly after I charged the batteries, I put it in the refrigerator for about ten hours and then took the reading again, it is much better now with a readings just under 0.2 Ohms. I put it back in the fridge to see if the readings would improve 24 hours after the initial charge. Will update with the final readings.
 
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