Multimeter & Resistor Capacity Testing

[Tarsun]

i did search a bit but could not find what i was looking for.

after joining the forum, ive learned that most of the people on here are on another level when it comes to harvesting and testing... Seriously i never would have imagined people buying/building/testing batteries in the thousands.
Because of this, most people on here have dedicated equipment for the job.

i am just starting out and do not harvest nearly as much. (not enough for dedicated equipment).

so my question is: how do i capacity test 18650's with a multi meter and a resistor?
I understand the basics of it but im having a hard time with it.

right now, i have a bunch of Sanyo UR18650Y.
1st, i check voltage. > 2.5v
2nd, i charge them.
3rd, leave them alone for a week or two (sometimes a month if work gets in the way lol) and then measure voltage again to see if it drops.
Now heres my question, i have a bunch of nice DALE RH-50w 3ohm resistors that i use.
i connect 1 resistor across the battery and measure the voltage drop. The problem is that the voltage never settles, it just continues to drop. I think i calculated the current at 900mA.
Is that too much current/resistance? Should voltage stabilize? is there a better way?

the batteries are going into 2s packs for RC boats and not a power wall.

 

[hbpowerwall]

Just grab your self a Liitokala Lii500 nice cheap way to get some cell testing done https://s.click.aliexpress.com/e/_9gz2n5

 

[Tarsun]

i dont have a spot welder so i leave a piece of the bridge tacked on. this allows me to solder a wire ontop without worrying too much.
i doubt it will fit in the charger with that on.

with a load applied to the battery, should the voltage eventually settle or will it continue to drop?

 

[floydR]

Using a tester such as hbpowerwall suggests the cell would stop discharging at a certain point .

Later floyd
P.S. an opus can handle cells with piece of tabbing left on the cell, not sure if the Liitokala can but it should as it has sliding contacts not fixed.

 

[nz_lifer]

Now heres my question, i have a bunch of nice DALE RH-50w 3ohm resistors that i use.
i connect 1 resistor across the battery and measure the voltage drop. The problem is that the voltage never settles, it just continues to drop. I think i calculated the current at 900mA.
Is that too much current/resistance? Should voltage stabilize? is there a better way?

the batteries are going into 2s packs for RC boats and not a power wall.

How many cell were you recovering?

You have to discharge them to 3v, to test capacity. Some are rated down to 2.8 but there is not much energy between 2.8-3v.
An instantaneous test like that only tests internal resistance.

If you don't want to get a fancy charger/discharger this will do the job for less than us$3.

0.8US $ 48% OFF|ZB2L3 Li ion Lithium Lead acid Battery Capacity Meter Discharge Tester Analyzer|Multimeters| - AliExpress

Smarter Shopping, Better Living! Aliexpress.com

www.aliexpress.com

Any of the slide type chargers should have enough room.

 

[Tarsun]

not many, compared to everyone here.
I think ill just get the opus.
thanks everyone

 

[Tarsun]

well, finally got around to getting a proper tester.

Liitokala Lii500

similar to an Opus.
i load it up when i get to work and bang out 4 at a time. (im in no rush and im not building a power wall)

well see how many i toss...

 

[Doc3G]

Thanks for the recommendations. I just bought one of each on amazon to see how they compare. I have an XTAR one now but it's sort of wonky so I think I'm sending it back.

 

[Tarsun]

the Liitokala seems fine for me.
im able to track my batteries more closely and build packs with matching parameters.

 

[Wolf]

well, finally got around to getting a proper tester.
Liitokala Lii500
similar to an Opus.

Unfortunately the LiitoKala is not similar to the OPUS. No offence intended just clarification.
The LiitoKala charges at 1000mA but will only discharge at a max of 500mA.
(Charge, fast discharger, normal discharge) and current (300, 500, 700, 1000mA). The current is charge current, discharge current will be either 250mA (300/500 selected) or 500mA (700/1000 selected).
It also uses a CC/CV style charging method which is just fine.
The OPUS uses a PWM charging/discharging method which makes it faster requiring it to have a fan to cool the components.
It will also charge and discharge at 1000mA
If you are going to use the OPUS at a full 1000mA C/D/C I recommend a fan enhancement to keep it cool. See here
Both the LiitoKala and the OPUS do have two things in common though.
1. The numbers they claim for internal resistance (IR) is based on a quick DC voltage drop test and is so far in left field that there is no way to trust it.
2. They constantly over rate the mAh's of the batteries by 5% to 9% (OPUS) and 6% to 11% (Liitokala)
Once you realise all of this they are not bad. You get what you pay for.

 

[italianuser]

...
2. They constantly over rate the mAh's of the batteries by 5% to 9% (OPUS) and 6% to 11% (Liitokala)
Once you realise all of this they are not bad. You get what you pay for.
View attachment 24731

Love your wolf-charts!
Wolf... but after charging 18650s with each different charger, have you tried connecting a load to the fully charged 18650 and timing how long it takes to get down to, lets say, 3.0V? I suppose you'd expect the same discharge timings in all cases, but they could be different. I'm supposing a charger charges more than another, could it be possible?

 

[Wolf]

I'm supposing a charger charges more than another, could it be possible?

Certainly and they do. Also the cutoff V and mA can be different. It also depends on the cells. The thing with the OPUS, LiitoKala, Zanflare, XTAR, etc. basically all sub US$ 50.00 charger/analyzers is that they are one size fits all for a variety of rechargeable batteries. The charging/discharging program is tailored to 80% of all the popular batteries. Usually a 4.2 max V with a 100mA cut off. The discharge is usually down to ≈2.8V with a similar 100mA cutoff.
Battery spec sheets do tell a different story though as the mA cutoff can vary but again is usually ≈50mA to 100mA. Also discharge max can vary from 2.5V to 3.0V.
The only real commercial tester that is adjustable and can be programed to the factory spec that the manufacturer claims is the SKYRC MC 3000.
and at $US 100.00 it should.
Also take a look at the charging charts that I posted of the Foxnovo compared to the OPUS

Opus BT-C3100 v2.2 Issues?

Interesting.... Very, very interesting....

secondlifestorage.com

You will see that the OPUS does indeed do a PWM cycle with discharge spikes as high as 2.5A and charge spikes as high as 1.5A.
The Foxnovo and others all use a CC/CV type of cycle as you can see a very even trace.
As far as timing a discharge I expect a 2500mAh battery to discharge to its factory spec min V with a 1A load on it in ≈2.5hrs.
To be honest 0.05 volts or 200mAh either way won't make much of a difference. The Li-ion cells we all work with will give up most of their charge between ≈3.9V to 3.4V above and below those voltages the gain in additional mAh is minimal at best.
Wolf

 

[italianuser]

Certainly and they do. Also the cutoff V and mA can be different.

Ah true, I did already see these parameters in a DIY Lithium charger, had a fixed cutoff at 50mA.

So, getting back to your very good comparison table, actually the offset you're reporting is what the device's screen reports. I was curious of what the real capacity of the 18650 was after a complete charge/discharge/charge cycle, considering:

- the % error of the mAh measurement shown on the screen, all devices have maybe (I suppose) a 1-2-3% error in their measurements;
- that each devices could really charge the 18650 a bit more (or less) than an another device (maybe with a 1-2-3% difference).

[ Maybe LiitoKala really charges 18650 3% more than another device and it's not totally overrating capacity ? ]

So, the only way to know is to use a common reference and measure the actual battery charge using a very precise device. And measuring charge current can be very tricky because it's based on a time-framed sampling... I'm doing this with AC current at home using a 5 second time frame.

P.S. I'm just thinking out loud!

 

[Wolf]

thinking out loud!

That is what we are here for isn't it? Civil discussions of what we think, our theories, the facts we can accumulate and sometimes our conclusions.

I can tell that you are a person of curiosity and precision and your mind works similar to mine as in yes/no, 0/1, black/white ( got to be careful with that analogy) in essence we think somewhat in binary true/false or maybe a bit more boolean.
We want complete accuracy and we demand it from our testers. Unfortunately that is not the case esp from out "cheep" test equipment. We have to put our prejudices aside and be satisfied with the results knowing that they are skewed to one side or the other.
The other thing is that you can measure the same cell multiple times and get somewhat different results. You may be one of the few who would appreciate this spreadsheet. It is an analysis of 2 MCM (Megacellchargers) with 32 brand new cells inserted then run 10 times and the variations and results graphed out . It also has a comparison of the same cells between OPUS, MCC, SKYRC, and "CCR" (a privately built 2 cell charger/discharger that was designed and constructed by an electrical engineer. The OPUS actually comes out pretty good in this study.
Well see for yourself and let me know what you think.
Wolf

 

[italianuser]

Yes, I think we do have something in common and that's cataloguing, collecting, things in a way that our families and friends really can't understand LOL. Our eyes shine of proud when we have all the data (or stamps or electronics components or else) aligned up and straight, and we can look at it and find hidden meanings. Absolutely!

Loved the spreadsheet, says so much about cells, chargers and all the main parameters. Ok, I think I also have at least one answer to my question/curiosity. The MegacellCharger gives me the same impression I had the first time I saw it here in the forum, it's a beast of a device for sure. Opus keeps up to it's name, it will be my next buy after my first love LiitoKala500. And maybe SKYRC has a slighly high threshold, that's why it charges less. The 1-2-3% of difference isn't so important as a matter of fact, having the big picture is more important.

Repeatability: repeatability of a test. I learnt this word 10 days ago when I bought the Fluke 8500 (here I posted the photos). The guy who sold me the device on Ebay, a professional electronic engineer, gave me that as a key factor for working with micro-electronics. I had to think about it quite a bit, and your spreadsheet confirms the importance of repeated tests to me. So, repeatability of a test gives us a higher degree of confidence about the results.

Oh no! I'm thinking out load again and now I must get back to coding, my customer will be here after tomorrow and will want to see results, too.

 

[Tarsun]

you gotta remember my point of reference here.
these 18650's are 2s1p battery packs for RC boats. no power wall here. the deviation in accuracy is not a huge concern of mine (even less of a concern if the deviation is consistent)
and it gives me a much better SOH than using a fluke DMM and a resistor.
i also have a few rando balance chargers that i use once the pack is made. (hobbyking dc4s and similar)
is the dc4s at least decent at charging?
it would be cheaper to buy packs on line for my application lol but my 18650 interests have peaked a little as we replace li-ion packs on a regular basis here in the hospital. (we literally have a 5gal bucket that we keep filling up)

most of the members on here are on a whole other level when it comes to pack design, building, and usage than i am. (most, if not all) lol

i must say, it is fun going through "dead" packs and finding that only one or 2 cells have failed and the rest are fine.

no offense was taken at all, so dont worry there either. im always up for learning but, my requirements and usage is minimal.

 

[Wolf]

you gotta remember my point of reference here.

Yes very true. We do get a bit out of hand sometimes responding.

 

[italianuser]

Now heres my question, i have a bunch of nice DALE RH-50w 3ohm resistors that i use.
i connect 1 resistor across the battery and measure the voltage drop. The problem is that the voltage never settles, it just continues to drop. I think i calculated the current at 900mA.
Is that too much current/resistance? Should voltage stabilize? is there a better way?

the batteries are going into 2s packs for RC boats and not a power wall.

Oh sorry Tarsun, I started speaking about all other stuff and lost your question. So, you connect a 50W resistor to the battery.

If it's fully charged, say at 4.2V that means that current going through the resistor is:

I = V/R = 4.2 / 3 = 1.4A... that's quite a lot, I suppose resistor heats up a bit! And I'd say it's normal that voltage goes down very quick. If the 18650 is a 2200mAh and you consume 1400mA per hour with the resistor, it should discharge in 1.57 hours.

For your questions... Is that too much current/resistance? To understand something more on charge/discharge rate here's a brief document: https://batteryuniversity.com/learn/article/discharge_characteristics_li

Should voltage stabilize? No, because the resistor is a load for your battery and will dissipate current in heat.

 

[Tarsun]

no worries.
ive since bought the liitokala (which works well for my application lol)

the dale resistors are pretty stout. the spec sheet says they are capable of 250degreeC for 2 hours.

Basically, i was looking for a quick way to test the SOH of these batteries. the liitokala fits the bill for now.

any info on the hobbyking DC4S charger; is that sufficient for small packs?

Funny enough, the other thing we toss a lot of are UPS's. if i get the RC battery packs sorted, ill look into better equipment and start messing with a lithium pack conversion for these....

last year we tossed 3 "Tripp Lite UPS Smart Online 1500VA 1350W Tower"s. i have an APC pro 1500 under my desk for the hell of it and few Powervar's on the rack behind me because i cant bring myself to toss them. lol
i also have a Powertronix isolation transformer that im looking to use for something... (i had 4)