Found a Quality Battery Resistance Tester

[d_t_a]

@joechina

@pennzy

Isn’t the double probe set up just a redundancy to help assure minimum resistance ?

No, you need all four needles connected. It is called Kelvin measurement or 4 terminal sensing. It is good for measure low resistance.

https://www.allaboutcircuits.com/textbook/direct-current/chpt-8/kelvin-resistance-measurement/

Four-terminal sensing - Wikipedia

(a bit off-topic) but I notice in the ZY1276 USB meter, there are 2 types of resistance measurement available, one is the “regular” and the other is called “4-wire Kelvin”. Unfortunately, there’s not much info/documentation on what items are required to do the 4-wire Kelvin measurement on the ZY1276 USB meter… Maybe need to construct a 4-wire USB cable or something?

[Lux-Perpetua]

@ActiveAl

FlashTom, for measuring resistance, it may be easier to lay the battery horizontally on a surface where it will not roll around. That way both ends of the battery are easily accessible. Recommend for this procedure that you have good light, patients, and, indeed, where your glasses! It may not be easy to do, but, yes, it can be done. The picture was taken with the battery vertical to better show positive probe placement. The negative probe placement will be like with any other Li-ion battery. Cheers!

Thank you ActiveAl! So, now I’m well prepared.
Meanwhile my order has been released for shipping. It seems this big delay of 24 hours for payment verification is a usual procedure at AliExpress. It was something new to me as I never had such safety steps at Banggood or Gearbest. The seller also confirmed that he/she ships the new version of the SM8124A with the two-prong probes.

[klrman]

FlashTom, this is how it looks when I wear my reading glasses.

[Lux-Perpetua]

Wow…that’s supersharp! If I get as close as this to the object my visual field becomes hazy. Maybe I get back to you guys for some recommendations about reading glasses… :laughing:

[klrman]

@nottawhackjob

Idle uniformed question… Why not attach a wider magnet than the button top itself, compensating for the magnet’s resistance if any, then attach the dual probes?

Good idea for the eneloops. Have to try it on my liths and see how much it affects the numbers.

[Lux-Perpetua]

I recently recharged some of my eneloops from 1.24V to their cutoff voltage (1.55V) in my MiBoxer C4-12. According to the charger only 100-150mAh went into those cells. Recharging only took about 5-10min as voltage rose up instantaneously. Their iR was about 60mOhm. I assume these cells can be considered as worn out, right?

[joechina]

Sorry d_t_a,

I don’t know the device.
You should mail the manufacturer. He should know

Joe

[klrman]

I got some Protected NCR18650B's from Banggood today and they are all reading 60IR on my SM8124A tester. My other Protected NCR18650B's are all reading 48IR on my tester. Would the difference be because they are probably two different protection circuits and therefore showing different resistance numbers?

I'm assuming Banggood is using some cheapo no name circuit whereas my other NCR's are using genuine Seiko circuits.

[BlueSwordM]

Yep.

They are probably higher resistance FET on the Banggood cells.

[klrman]

Thanks! Any negatives you know of from the BG cells other than more resistance?

[BlueSwordM]

Hmmm no.

I actually have no protected cell, except for the one from my Imalent HR20.

[klrman]

I'm waiting nearly two months for my 30Q's from BG. They will be my first set of unprotected batteries.

[BlueSwordM]

Oh.

The customs must have seized your package.

They seize 4x18650s worth 25$CA, but not a phone with a pouch cell, much more dangerous, worth 250$CA.

[ImA4Wheelr]

@FlashTom

Can anyone please post a link to the SM8124A we can 100% trust? I mean there are how many sellers on AliExpress…six, seven?..who offer this nice device, sometimes with different brand names, sometimes without the “A”, sometimes with two cables on both probes, sometimes just one cable. I find it hard to decide whom to trust. I was unfortunately unlucky with some of these Dolidada batteries…claimed to be IMR-55A cells (like Shockli/Keeppower) but they turned out to be of rather poor quality with much less capacity and even less power drain capabilities.

Mine arrived yesterday. I didn't get a chance to use it, but it looks like the good model. It came in a plain white box with a decent pouch (maybe a holster, didn't look on back for belt loop). I got it from here.

[Lux-Perpetua]

That’s exactly where I ordered, too. So, I‘m confident to get the new version, too. Unfortunately, the shipping address in my Aliexpress order is missing the country even though it was correctly assigned in my account. Maybe just an displaying error.

[klrman]

@ActiveAl

@contactcr

I think it’s worth mentioning that the resistance values from this $50 AC tester should not be compared to other chargers and things that give resistance. AC resistance measurements are pretty far apart from DC load resistance measurements. Article: BU-902: How to Measure Internal Resistance - Battery University So while this device is still useful it is not giving you the same measurement you might find in other sources. Also, I don’t think it is as good of an indication of the max discharge a battery can sustain. (like what HKJ or Mooch are giving you)

I read through the article you linked and it was helpful. Thanks. Fortunately, there is a lot you can do with AC resistance measurements, such as:

1. Measure new cell when you first get them, and then take periodic reading afterward to monitor their health.
2. Compare measurements against the battery's datasheet to determine if it is in specification. For example, the Samsung 30Q datasheet identifies a typical 1 kHz AC resistance specification of 13.13 ± 2 mΩ. The SM8124A I recently purchased measured my six Orbtronics 30Qs with an average resistance of about 11.5 mΩ (See Table 2.), which is within the datasheet specification. I was shocked that my $50 AC tester was able to provide measurements with this seeming accuracy. Perhaps this is a one-off fluke.
3. Compare a known battery with one that is suspected of being a fake. For example, if a battery measures considerably more AC resistance than a real 30Q, then it is probably not a 30Q.

Update: I saved this post too quickly and had to make edits. Thanks!

I finally got 4 x 30Q button tops from Bangood today after waiting for over two months. They all test at 12.0 IR with the SM8124A tester so they are real samsungs!

[Zebretta]

Mine finally arrived today.

It’s the newer 4 prong model.

Someone said the measurements you get with this meter are not the same you get with your Battery Charger / Testers.

Yeah, I found that to be very true.

How would you convert between the two in order to determine if your charger/tester gives readings consistent with the SM8124A?

[klrman]

They measure differently so there probably is not a reliable conversion method. The SM8124A should give results close to the battery data sheets which use the same method as this meter to determine resistance which is a good start to see if you got originals or fakes. What I have found so far is that if I add 60% to SM8124A readings of protected cells, they match up with the battery charger IR readings. So far, different types of protected cells from different companies still seem to be 60% more or close enough across the board but for unprotected cells like the Samsung 30Qs, the difference was 200% higher with the battery charger than this tester.

[Zebretta]

@klrman

They measure differently so there probably is not a reliable conversion method. The SM8124A should give results close to the battery data sheets which use the same method as this meter to determine resistance which is a good start to see if you got originals or fakes. What I have found so far is that if I add 60% to SM8124A readings of protected cells, they match up with the battery charger IR readings. So far, different types of protected cells from different companies still seem to be 60% more or close enough across the board but for unprotected cells like the Samsung 30Qs, the difference was 200% higher  with the battery charger than this tester.

Good stuff there. Thanks!

[Zebretta]

@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?