November 15, 2017

Notes on testing

Two things are worth testing. One is internal resistance (which can be easily and quickly measured by connecting a known load). The other is capacity, which requires fully discharging a fully charged cell. This takes a lot of time and requires patience.

Brand name cells are said to hold their capacity better than "no name" cells. One fellow reports:

Somebody did such a test a few years ago here on CPF. The results were noteworthy, because the difference between inexpensive cells and cells like Samsung's only became evident after a number of cycles. Initially they all performed pretty well, but after 50 cycles or so, the inexpensive cells suffered significant loss of capacity, and the "big brands" did not.
Also consider:
Unlike nickel based cells, whose performance actually improves during the first 50 cycles, Li-Ion cells are downhill from the start.

Battery testers

On 11-14-2017, I risked $15 of my hard earned money and ordered two of these from Banggood.com. Paypal makes this reasonably safe and this is not too much money to risk anyway. What I hope to be able to do is to characterize the capacity and internal resistance of 18650 cells I am harvesting from old laptop packs.

Go to the Banggood site and search for "18650 tester", no doubt you would also find these on AliExpress.

The first I ordered was an "original Zhiyu" for $10. I had to pick between 5 and 12 volt version. I chose 5 volt. This unit arrived 12-4-2017. It runs off of a micro-USB cable and it looks like there is a tiny daughter board that is a 5V to 12V converter.

The other unit was described as a "ZB2L3 Battery Capacity Tester External Load Discharge Type Module", and requires no external supply. For $5, it is worth trying out. It arrived on 12-8-2017, shipped from Bangkok. My cost $4.73

TEC-06 tester

Have any comments? Questions? Drop me a line!

Tom's electronics pages / tom@mmto.org