Author Topic: Adapting a 1xlithum battery tester to 2x batteries  (Read 710 times)

Offline Greekman

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Adapting a 1xlithum battery tester to 2x batteries
« on: August 09, 2017, 11:46:24 AM »
anyone good with electronics?
 i want to adapt this device to test/measure 7.2volt lithium batteries.
http://www.ebay.com/itm/18650-Li-ion-Lithium-Lead-acid-Battery-Capacity-Meter-Discharge-Tester-ZB2L3/172577675238?_trkparms=ao%3D1%26asc%3D20140212121249%26meid%3Dc82fa10580c04948a57ae9f3c3682466%26pid%3D100102%26&_trksid=p3693.c100102.m2452

it stands to reason that i should be connecting a power resistor -in series with he supplied one- to cut voltage in half, but i cannot predict how would the device act/measure.
any ideas?

Offline Carl

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Re: Adapting a 1xlithum battery tester to 2x batteries
« Reply #1 on: August 09, 2017, 01:34:07 PM »
  You should not test cells in series as one at a time would be most accurate.The tester you link to is made to test up to 12 volts (15 max) and so you  really need to do nothing to test 7.2 volt pack besides wire it up properly.

From description:

ZB2L3 battery capacity tester discharge type 1.2-12V external load capacity of the battery and other tests 18650
Tools, single-function, by controlling the load off and get real-time integrated discharge current capacity results
Maximum support 15V 3A discharged through the discharge voltage and current, itself does not discharge
Maximum capacity statistics support 9999Ah (9999000mAh)
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Offline Greekman

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Re: Adapting a 1xlithum battery tester to 2x batteries
« Reply #2 on: August 10, 2017, 01:38:10 AM »
you are correct....

but the Chinglish text is not easy to follow. I was fooled by the persistence in mentioning 8650 batteries

Offline badscooter

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Re: Adapting a 1xlithum battery tester to 2x batteries
« Reply #3 on: August 10, 2017, 09:03:17 AM »
Hi,

Carl is correct in that single cell testing is most accurate.  I often work with lithium ion cobalite and phosphate cells/packs, for what it is worth.

This is what I use in my shop, for pack-level testing...which can be useful for monitoring overall battery health although it won't tell you which cell is performing best/worst.  I can absolutely vouch for these things, we own three or four of them, along with the high power amp unit.

http://www.westmountainradio.com/product_info.php?products_id=cba4

Thanks
Mike

Offline Carl

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Re: Adapting a 1xlithum battery tester to 2x batteries
« Reply #4 on: August 10, 2017, 09:14:03 AM »
Hi,

Carl is correct in that single cell testing is most accurate.  I often work with lithium ion cobalite and phosphate cells/packs, for what it is worth.

This is what I use in my shop, for pack-level testing...which can be useful for monitoring overall battery health although it won't tell you which cell is performing best/worst.  I can absolutely vouch for these things, we own three or four of them, along with the high power amp unit.

http://www.westmountainradio.com/product_info.php?products_id=cba4

Thanks
Mike

I use one of the early CBA units and these have much more current capability and I think better software. I enjoy the graphing and comparison of graphs to judge cells under test.
Stop complaining about life and start Celebrating it .

I've reached the age where there is little left to learn the hard way.

If you had only one year,one month,or one day...Would you live your life differently?

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Offline Greekman

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Re: Adapting a 1xlithum battery tester to 2x batteries
« Reply #5 on: August 10, 2017, 11:40:55 AM »
I know but cost has always been an issue.
basically i want t know capacity. since i have some expensive 7.2V batteries that are getting old

Offline badscooter

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Re: Adapting a 1xlithum battery tester to 2x batteries
« Reply #6 on: August 11, 2017, 09:43:49 AM »
Hi Greek,

I took a quick look at that ebay page.  Looks like the device uses a set resistive load not a constant current, which will effect endpoint detection at the end of a discharge (Li-Co cells typically have some "droop" under voltage).

What current are your batteries normally operating at, wrt their capacity (i.e., "C" rate)?  For instance, if you have 2600mA-h cells, one (1) "C" equals 2.6A.  Dimension your power resistors to draw that (expected use) current when the battery is fully charged (at 8.4V), and terminate the test when battery voltage (under load) reaches down to 6V.  When you release the load, the voltage will spring up, this reflects the internal impedance (resistance) inside the cells.  This "spring" can also be measured under a set of test conditions over the age of a particular pack, and can serve as a rough-n-ready indicator of pack age/health.

In no case do I recommend bringing any individual cell below 2.8V.  As you go below that voltage, an internal change happens called lithiation (metallic lithium starts to form crystals) which can lead to very...unpleasant...failure modes.

Depending on what cells you are using, and the use case, generally speaking I'd suggest keeping under 1C average discharge rate.  The manufacturers' capacity ratings are generally based on lower than that, typically 1/2C discharge rate for premium cells.

How old is old?  The cells I deal with (premium) are typically operated in the 2C- range, with peaks up to 4-5C, and generally run well past 500+ effective full charge cycles, and have use spans of 3-5 years typical.

Final note...important!  State of charge has a dramatic effect on service life.  If you store cells at full charge (4.2V/cell) they deteriorate much much faster than if stored at partial charge.  This is why when you get cells from an OEM they always come at around 3.5-3.6V.  Has to be above the minimum, but they want to maximize storage life.  This is why any consumer electronics you buy with lithium in it is useable right away with a partial charge.

thanks
mike

Offline Greekman

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Re: Adapting a 1xlithum battery tester to 2x batteries
« Reply #7 on: August 13, 2017, 01:59:20 AM »
thanks for chiming in Mike.....

yes, i am familiar with lithium battery uses, I have been modding flashlights for about 10 years now.
Before I got my charger analyzer i was measuring single li-ion capacity on constant current drivers (having 1-8 350mA AMC7135 chips)  and timing the process. It is quite linear in low currents

But now my photo camera (3X) and Kenwood HT batteries are close to 10 years old and you cannot skip age. (The HT draws 2A, a bit more than 1C, and the camera I cannot know.)
Thus i will have to make some hard decisions. Replacement cost for genuine ones is..... woohaa!

I did not find the time to experiment with the said battery tester but, as you said, I will have to check he discharge voltage of it.