Found a Quality Battery Resistance Tester

Zebretta · 2018-08-11T18:54:02.000Z

BlueSwordM:

It’s actually quite easy to calculate DC internal resistance.

The problem is that you need a battery holder that does not have piss poor resistance like you see with the cheap ones on eBay and Aliexpress.

If you just want, you just need some power resistor of a determined load, a multimeter, a soldering iron, and some 18AWG wire, and perhaps some brass buttons.

1. Solder one end of 30cm 18AWG wire to 2x brass buttons for nice contacts.

2. Solder the other end to the legs of a 5 Ohm resistor.

3. Wire a switch through the wires.

4. Clamp the brass buttons to the cell with the switch off.

5. Put your multimeter on voltage reading mode.

6. Measure the open circuit voltage of the cell. For example, it will be 4.2V.

7. Flip the switch, and measure the voltage of the cell instantly, then flip the switch again. The noted voltage will be 3,9V

8. Do math:

ΔV = voltage delta = 0,3V
R = 5r = resistance used
V = cell voltage = 4,2V
VL= Voltage under load = 3,9V
C= current flowing

V-VL = ΔV= 4,2V-3,9V = 0,3V

C= VL/R = 3,9V/5t = 0,78A

Internal resistance = ΔV/C = 0,3V/0,78A = 0,38R = 380 milliohm

Yeah, that is the real internal resistance of a cell, and how you calculate it.

Did you build a rig for this purpose?
Any pics?

BlueSwordM · 2018-08-11T19:04:57.000Z

I did build something like this before, but I used bypassed spring holders instead of brass buttons. That was very hard to do though, unlike the more refined method I presented to you guys.

However, now that I have made my Beryllium copper springs, I am going to do one that is much simpler to do for everybody, and is much easier to set up.

Zebretta · 2018-08-11T19:18:36.000Z

BlueSwordM:

I did build something like this before, but I used bypassed spring holders instead of brass buttons. That was very hard to do though, unlike the more refined method I presented to you guys.

However, now that I have made my Beryllium copper springs, I am going to do one that is much simpler to do for everybody, and is much easier to set up.

Awesome. I’d like to make one. But since you know what you’re doing I’ll wait to see how you did it.

klrman · 2018-08-11T21:27:26.000Z

BlueSwordM:

+1 I forgot to mention. The resistance measurements are at AC 1kHz sine wave. So while accurate, the resistance numbers are often measured to low. A 4-wire constant current tester is the only way to measure the real DC load resistance measurement.

When you decide to use your new springs to build your new tester, it won't test IR the same as the SM8124A will it, but instead the second method you mentioned above to give real IR readings?

Zebretta · 2018-08-13T10:13:49.000Z

I have doubts about this device.
I need to do some tests using the DC Calculation method to verify but I’m getting results that aren’t consistent.

That said, I removed the cable separator because the leads were too short to get to both sides of my batteries.
Does anyone know if there is some magic in that simple plastic separator that could affect the readings?

Lux-Perpetua · 2018-12-09T20:24:02.000Z

Today, I tested some new cells with my SM8124A. This is the impedance I measured:

Format	Name	Impedance (mΩ)
21700	Samsung 30T	6.0
21700	Samsung 40T	7.4
21700	Samsung 50E	22.0
21700	Sofirn 4.000mAh	13.6
20700	Acebeam 4.250mAh	21.6
18650	Sony VTC6	11.8
18650	Samsung 25R	12.2
18650	Samsung 30Q	12.5
18650	Imalent MRB186-P30	19.3
18650	Wuben 2.600mAh	23.4
18650	Sofirn 2.600mAh	41.9
18650	Sofirn 3.000mAh	45.2
18650	Xanes 2.600mAh	45.3

d_t_a · 2018-12-10T02:04:59.000Z

Lux-Perpetua:

Today, I tested some new cells with my SM8124A. This is the impedance I measured:

Format Name Impedance (mΩ)

21700 Samsung 30T 6.0

21700 Samsung 40T 7.4

21700 Samsung 50E 22.0

21700 Sofirn 4.000mAh 13.6

20700 Acebeam 4.250mAh 21.6

18650 Sony VTC6 11.8

18650 Samsung 25R 12.2

18650 Samsung 30Q 12.5

18650 Imalent MRB186-P30 19.3

18650 Wuben 2.600mAh 23.4

18650 Sofirn 2.600mAh 41.9

18650 Sofirn 3.000mAh 45.2

18650 Xanes 2.600mAh 45.3

Thanks for sharing! That would be a useful baseline reference.

I only have a few of those batteries from your list. I don't have the SM8124A, but instead got the YR1030. I wonder how different the measurements taken by the SM8124A compared to the YR1030...

klrman · 2018-12-10T02:51:34.000Z

Nice chart thanks. My Samsung 30Q from Illumn read 10 and 30Q from Banggood read 12 so close enough.

Lux-Perpetua · 2018-12-10T06:29:35.000Z

FWIW, it takes a lot of patience and two calm hands to get useful values with the SM8124A.
Especially, with button top batteries it’s quite a nightmare to align the probe correctly in order to get useful information.
I guess it’s the same with the YR1030 from Vapcell. They had it for a very decent price on Black Friday. Unfortunately, I forgot to buy one as I would have liked to verify my values with a second device.

klrman · 2018-12-10T07:09:47.000Z

Major PITA to align the probes on button tops. I use my desk lamp with the magnifying glass otherwise it takes too long.

Lux-Perpetua · 2018-12-10T07:16:22.000Z

LOL…“PITA”…that’s exactly what it feels like.
Later on, I try to amend my chart with values I took from my 26650s (Shockli 5.500mhAh, Keeppower 6.000mAh, Dolidada Fake PLB-55-As, Thrunite 5.000mAh, etc.).

Lux-Perpetua · 2018-12-10T13:04:43.000Z

I have now added some more batteries. All cells were measured in new, unused condition. However, the 26650 cells I bought had some differences between them.

Format	Name	Impedance (mΩ)
21700	Samsung 30T	6.0
21700	Samsung 40T	7.4
21700	Samsung 50E	22.0
21700	Sofirn 4.000mAh	13.6
20700	Acebeam 4.250mAh	21.6
18650	Sony VTC6	11.8
18650	Samsung 25R	12.2
18650	Samsung 30Q	12.5
18650	Imalent MRB186-P30	19.3
18650	Wuben 2.600mAh	23.4
18650	Sofirn 2.600mAh	41.9
18650	Sofirn 3.000mAh	45.2
18650	Xanes 2.600mAh	45.3

klrman · 2018-12-16T04:41:48.000Z

Here's my list so far. Need to find the data sheet but I think the 30Q's from ff are out of spec!

BlueSwordM · 2018-12-16T02:54:09.000Z

Yeah. That Illumn cell is either a beast, or something is wrong.

I don’t think the FF cell is bad though. The maximum internal resistance of a 30Q with AC testing is 26mOhms.

klrman · 2018-12-16T02:57:03.000Z

Thanks, saves me looking for the sheet! Tested all the illumn 30Q's too many times and always 9.

d_t_a · 2018-12-16T15:21:15.000Z

klrman:

Here’s my list so far. Need to find the data sheet but I think the 30Q’s from ff are out of spec!

Thanks for mentioning that 30Qs from Fireflies.

I also got 3pcs 30Qs bundled with the Fireflies ROT66 (I am unable to purchase 30Qs without flashlights [bare batteries from any foreign online store cannot ship to my country, except if inside a flashlight], so all my 30Qs are only purchased when I purchase a flashlight, either the “BLF A6+30Q” or the “S42+30Q” bundle from BG).

The 30Qs I got from BG have lower IR than the 30Q I got from Fireflies… Will do some measurements again. Forgot the figures but there are noticeably higher IR, measured either using the MC3000’s IR test or with the YR1030 battery resistance tester.

klrman · 2018-12-16T20:33:33.000Z

I think it was mentioned somewhere before that battery manufacturers use the AC method to grade the cells and then sort them depending on the results. It seems there may be A-B-C and possibly even D grade cells of the same make that are then sold off accordingly.

Lux-Perpetua · 2019-01-26T15:35:01.000Z

Update (see highlighted in red).

I am pretty much amazed about the extreme low impedance of the Tesla cell (Sanyo NCR21700A 5.000mAh 15A).

Format	Name	Impedance (mΩ)
21700	Samsung 30T	6.0
21700	Samsung 40T	7.4
21700	Samsung 50E	22.0
21700	Sofirn 4.000mAh	13.6
20700	Acebeam 4.250mAh	21.6
18650	Sony VTC6	11.8
18650	Samsung 25R	12.2
18650	Samsung 30Q	12.5
18650	Imalent MRB186-P30	19.3
18650	Wuben 2.600mAh	23.4
18650	Sofirn 2.600mAh	41.9
18650	Sofirn 3.000mAh	45.2
18650	Xanes 2.600mAh	45.3

Obviously, Sofirn rewraps cells of different manufacturers as can be seen on my comparison of two Sofirn 21700 4.000mAh batteries. Both batteries were part of two C8F 21700 flashlights. The one with the recessed ring in the bottom seems to be a Lishen 2170SA. Fortunately, both the one with ring and the one without seem to have similar specs in terms of capacity and performance.

klrman · 2019-02-28T06:16:24.000Z

Updated my list with legit Samsung 40T's that I got today. Inserted them in my two E07's and they shine seriously bright.

Maximus_Panin · 2022-12-12T19:45:13.000Z

I'm also looking for my first tester. I choose between YR1035+, SM8124A, Volcraft BT-501 - which is better ?