Found a Quality Battery Resistance Tester

+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.

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 Ā± 2 mā„¦. The SM8124A I recently purchased measured my six Orbtronics 30Qs with an average resistance of about 11.5 mā„¦ (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!

ActiveAl, those numbers are really close to the spec sheet. I would say more than good enough for a $50 tester, especially considering the consistency of the readings which is what I really like about it. My numbers are higher on my cells as they are all protected, but soon my 30Q's will arrive and I can see what numbers they read.

I have the latest model with the two prong cables that BlueSwordM linked in post #3 https://www.ebay.ca/itm/Battery-Resistance-Voltmeter-Internal-Impedance-Meter-LCD-Rechargeable-SM8124A/273104104104?hash=item3f9645eaa8:g:BEIAAOSwWmNapAyf

I also purchased mine from the same ebay seller (i.e., tangzhimin1008) as Kirman (link above). We got the new model with the double-pronged probes and, so far, it is exceeding my expectations in performance. I used it to determine that six 30Qs from the LiitoKala Factory Store were probably fakes. In this endeavor, my SM8124A readings were very consistent and reasonable. See Table 1 and Table 2 in this post for my data. Note that the average reading for the six real 30Qs (Table 2) was within the typical 1 Hz AC specification of 13.13 Ā± 2 mā„¦ given in the 30Q data sheet. This blows me away.

The cheapest purchase alternative for a SM6124A appears to be from this Ali Express Store. But there is no confirmation that they are selling the new model. Suspiciously, this store is displaying pictures of both the old and new models.

Did you get the SM8124A with the two prong-probes or the predecessor without the ā€žAā€œ and single-prong probes?

Has HKJ already put an eye on this fine device?

I sent the following message to the AliExpress store in question (NewBeautifulLife Store, #1183073) last night:

Reference: Battery Resistance Voltmeter Internal Impedance Meter LCD Rechargeable Battery Impedance Internal resistance Tester SM8124A

Are you selling the newer version of this meter that has the two-pronged probes, or the older version that has the thicker single probes? The reason I ask is because you have both versions pictured on the product page. Thanks!

And got the following response this morning from Summer Sun:

Just the new version SM 8124A with two pronged probe.

After receiving this documentation, I would be willing to take a chance on ordering from them to get the best known deal on a SM8123A. Thanks!

Thanks for asking. I just bought one via your link.

One thing I noticed with the newer version is that you can't test eneloops as the prongs are too far apart. Older version with the single prong could do that, but I purchased this for lithium batteries so it's fine.

Good point. I noticed that you can't test button top Li-ion cells either - the probes are too far apart. But never-the-less, I believe the new version may be more accurate.

You can test button tops, but in my case I needed to use eyeglasses to make sure the probes make contact. A little tricky but I could successfully test all of my button tops Li-ions in no time. Trick is to avoid the vents on the button tops and the two pins will have enough room to make contact.

Talked to the seller and they may contact the manufacturer of the sm1824a and ask if they can make a slip on adapter for smaller batteries for us to use. I think it would be very useful.

You're right about the Li-ion button top batteries, Klrman! Thanks!

An adapter is a good idea. One could probably measure any additional resistance that would result and then allow for it. I would buy one if it was just a couple of bucks. Take care my friend!

Why exactly is everyone buying resistance meters if you can just calculate the internal resistanceā€¦?

Because we are not as knowledgeable as you.

Because you never told us how.

...... and finally, please let us know how so that we can test this against our meters readings. Would be a great way to move

forward in learning to compare the two. I'm all ears

They say if thereā€™s smoke, thereā€™s fire. This guy wants fire, even thereā€™s no smoke!

haha. I don't mind being the guinea pig if others can save money to avoid buying the tester if there is a reliable calculation to get the same results. After starting another thread on cpf, also learned that the sm8124a is using the same testing method as battery manufacturers use, but that there are much better ways to determine internal degradation as our little tester just tests one part of the internals from what I understand. It's been fun getting up to speed on all this in the last few days.

No problem, it stumped me too a little, that is why I had to put on my reading glasses so that I can actually place the prongs on the button tops good enough to make contact.

Itā€™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:

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

V-VL = Ī”V= 4,2V-3,9V = 0,3V

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

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

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

Excellent BlueSwordM. Now give me a few months to digest all of that and I'll know what you are talking about lol. OK, I see the equation there. I'm going to give it a try in a week or two and see what I get. Another fun project, thanks