Testing battery capacity.

[Adrian_]

I have couple of batteries that I would like to test the capacity of as they have a lot of charging cycles on them. I have 1A load tester that I was thinking of plugging it into a fully charged battery and then start a stop watch and see how long it will take for the battery to discharge but I was wondering if cell ratings are measured from 0V to fully charged or minimum discharge voltage to fully charged? If it's from 0v to fully charged then the mearusment will be lower because the BMS will end up cutting out way before the battery reaches 0v.

 

[Hillhater]

Capacity is measured from “fully charged” to “minimum “ safe voltage…..at a specific constant discharge rate,..usually 0.2C, (amps)
Those voltages etc will vary depending on the type of cell being tested.
You must find out the makers specifications ..max, min voltage, capacity, etc etc, to test correctly.

 

[eMark]

I have couple of batteries that I would like to test the capacity of as they have a lot of charging cycles on them.

https://www.amazon.com/180W-Electronic-Adjustment-Constant-Discharge/dp/B09925SZF3/ref=asc_df_B09925SZF3/?tag=hyprod-20&linkCode=df0&hvadid=563646982761&hvpos=&hvnetw=g&hvrand=4316677965254226229&hvpone=&hvptwo=&hvqmt=&hvdev=c&hvdvcmdl=&hvlocint=&hvlocphy=9019693&hvtargid=pla-1600167892941&psc=1

Scroll down to read "Top Reviews" ... https://www.amazon.com/gp/product/B08MQ1G57D/ref=ppx_yo_dt_b_asin_image_o03_s00?ie=UTF8&psc=1

Used it to test capacity of p-group cells in my 10s3p 30Q pack (at 250 cycles), and individual 30Q cells with high self-discharge.
Although it's rated at 180 watts i don't use it over 150watts or over 8 amps (prolong its life ALAP)
(instructions are sparse, but you'll figure it out ... i couldn't get along without it ... well worth the price, IMO)

Also used it to check capacity of the Samsung 33G cells purchased from Battery Hookup ... https://batteryhookup.com/products/30-100-new-samsung-inr18650-33g-3150mah-18650-cells ... :thumb:

Also use my ATorch DL24P for bottom balancing p-groups in my 10s3p 30Q DIY Vruzend experimental pack before bulk charging.

 

[eMark]

Almost everything i've learned about DIY 18650 battery builds has been directly or indirectly THANKS to this ES Battery forum ... many hours googling on my Samsung Chromebook ... hours of hands-on experimenting along the way ... and i'm retired ... :thumb:

How did we ever survive before the WWW Internet Cloud? Spend a fair amount of time at McDs using their free internet.

The only reason i go to the Library anymore is to use their free internet with perk of up to $5 in free copies (B&W-10 cents or Color-50 cents) each and every week (so far) to all users with a [free] Library Card.

Can you explain how the circuit works to test battery capacity?

Don't have a clue ... excuse is i'm 78 and really don't care to know. What is EE ... :wink:

 

[amberwolf]

What is that flying saucer thing on the PCB? Looks like a heat shedder and presume that is the load source.

Do you mean the largest part on it, roughly cylindrical with the very colorful "spiralish" bit on top? If so, then that is a heatsink with fan in it. Presumably the load is under the heatsink.

 

[john61ct]

ONLY a CC dummy load is accurate, as V drops power is continuously increased to compensate.

Yes use a stopwatch rather than counting coulombs with a wattmeter.

A standard for the 100% Full needs to be set, only use the datasheet's maximum profile if you are trying to match / verify nameplate rating, in which case use 0.1C or lower discharge rate. Stop at the min V on the datasheet, maybe 3.0Vpc or even lower.

If you set a benchmark at first use (commissioning time, after breaking in) to compare SoH% later on

then CC-only HVC at 4.15Vpc is plenty, just do it at the same rate every time, say 0.4-5C

If your charger does CV based termination, then 0.02C is a good endAmps setpoint.

Again set your own LVC, say 3.2Vpc but you need again to ensure the same CC discharge rate every time, up to 1C if you're in a hurry.

 

[john61ct]

Specific voltages above are assuming li-ion chemistries at nominal 3.6-3.7Vpc

18650 type cylindricals, pouch cells, LiPo format doesn't matter. Ignore "HV 4.35" variants, mostly marketing BS.

LFP at 3.2V nominal

LTO at 2.3Vnom

would be very very different, ask if you need those HVC / LVC.

Also should mention such testing cycles are far more stressful than what you should normally be doing, so for "production cells" getting say 300 cycles, maybe 20 tests over their lifespan should be way more than you actually need.

That first "commissioning" benchmark is your 100% State of Health, and do not be upset if the mAh come out WAY below nameplate, that is normal.