Found a Quality Battery Resistance Tester

Off-topic Chatter
41

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.

42

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

43

Hahaha. Don’t you remember your electricity physics courses in college? Or was that too long ago?

It’s actually quite simple :wink:

44

The main advantages of using the SM8124A is the ease of use and quick reading, and quickly comparing internal resistance of cells.

So just use it for seeing if a seller is selling legit cells, or if they are playing with you.

An AC 1kHz internal resistance measurement is plenty easy for that.

45

I remember next to nothing unfortunately but will get up to speed with the help of all you guys and uncle google. I know I can do it!

46

This thing should do a four wire resistor measurement. The big thing is it zeros out the resistance in the probe leads. An important thing if you want to measure low resistance.

47

Gentlemen, could anyone of you please post a picture how to attach the probes correctly onto button top cells, so that I can measure their internal resistance? Sometimes a picture explains more than thousand words. :smiley: Thank you so much!

BTW: My purchase order at Aliexpress is still being “verified” in the iOS app after more than 12 hours. That’s somehow strange to me as Paypal and Aliexpress already confirmed my order.

48

Thanks, I’m glad I didn’t have to explain all of that myself :stuck_out_tongue:

You could just use some 8 or 10AWG wire like I do and it basically has a few microOhms of resistance, so you don’t really need to be concerned about leads as long as they are less than a foot long.

49

BlueSword, thanks for jogging my memory. Sadly, it made me think about it longer than I care to admit before it made sense. My question is why isn’t a similar device on the the market?

50

FlashTom, here is my best attempt:

You may want to verify with the seller what is going on with your order. Go to the SM1824A product page, click on the NewBeautifulLife link, and click on Contact Nu, and Take care!

51

Thanks a lot ActiveAl!
Well, this is close to how I see things when I do not have my glasses on….lol. :laughing:
So, I just need to go from a vertical direction and make sure both prongs have contact to it? Doesn’t look very difficult, though.

Concerning Aliexpress:
It’s really strange. If I look onto my order it still stays “your payment is still being verified” even though I got a confirmation both from Aliexpress and Paypal that everything’s set. I wait until tomorrow and after that contact seller or Aliexpress customer service to ask what’s going on.

52

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!

53

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?

54

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

55

Don't think so in this case as readings are way out of whack if both probes don't make contact on both ends.

56

I think the with the dual probes one goes through a resistor or makes the battery draw power while the other maybe measures the resistance?

57

Ok , that makes sense .

58

Oh this is even tested from HKJ
Vapcell Internal Resistance Tester YR1030

Page Not Found - Aliexpress.com ca. $60

Review Test/review of Vapcell Internal Resistance Tester YR1030

59

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

60

Thanks for the education joechina.