Last week I reported that I’d noticed an anomaly while running my new ZKE EBC-AO5 through repeated tests using the cycle-test feature of its accompanying PC software. I’ve since identified the likely cause, along with a workaround, and I’m expecting a firmware fix soon from the manufacturer.
The problem can be seen in this chart.
The charge phase is supposed to terminate when the current, shown in red, hits 0.12 A. Instead, it terminates at ~0.25A in the first cycle, and at ~0.5A in subsequent cycles.
I realized that the subsequent cycles were also terminating at about 90 minutes, which stood out, because I’d set a 90 minute timer for terminating the discharge phase if the voltage didn’t drop below a threshold first. A check of the raw data showed that the termination happened at ~88 minutes.
The device doesn’t allow a timer to be set during the charging phase, but I hypothesized that the timer from the previous discharge phase was somehow being utilized during the charging phase. I tried shortening and lengthening the discharge timer and found that, as I expected, it had a corresponding impact on the length of the charging cycle.
So, the workaround is to either omit the timer on the discharge phase, or set it to a duration larger than the time required to achieve a full charge for the cell under test. I’ve successfully run dozens of cycles now:
I also reported my findings to ZKE, using their published email address and received a reply thanking me for the report and letting me know that they would have an updated firmware by the end of the month.
I didn’t do much with my ZKE EBC-A05 battery tester last week while I waited for a cheap, small used PC to arrive to run the EB Test software for long-term tests.
The computer came earlier this week, and after getting Windows patched up, I set up a test to run overnight that would cycle between charging to 4.3v and 0.12A, pausing, discharging at 2.4A to 2.75v, waiting 10 minutes for the cell to cool down, and then repeating the cycle.
When I checked on the progress this morning, everything looked good at first glance.
Upon closer inspection though, I noticed that after the first charging cycle proceeded until 4.3v but terminated prematurely, at 0.25A current, and subsequent cycles cut of prematurely, at ~0.5A.
I tried stopping the test and restarting it again, and found that this time, the first charging cycle terminated at 0.5A.
I’ve powercycled the EBC-A05 and started a new testing cycle. So far, so good, the first charging cycle terminated at 0.12A, as desired. We’ll see if that holds for subsequent cycles.
I must say though, the fact that I’ve had this problem once makes me less enthusiastic about this device. I was thinking of buying another 3, so I could run duplicate control and experimental runs of multi-day experiments at a time, but that only makes sense if these things are generally reliable.
Finally received a new Apple USB Power Bank I ordered 3 weeks ago.
Did I say Apple? I mean, Millet, no, sorry, Xiaomi. Sorry for the confusion, but in my defense, Xiaomi is borrowing so much of Apple’s design language, from the satin white packaging, to the specific grey of the logo and the “swiss” typeface, not to mention the particular tone and finish on the aluminum case.
I got the 5,000 mAh hour version from Banggood for $15.99, shipped. It took a three weeks to get here, but arrived in good condition. The footprint is about the size of my iPhone 6’s, but the powerbank is almost twice as thick.
It doesn’t quite achieve the fit-and-finish of an Apple product, but it definitely feels well made. That general level of quality is more than skin deep too.
The plastic trim pieces at either end of the case are secured with a few locking tabs and double-sided tape. It takes some delicacy but prying off the plastic trim on the bottom end reveals two phillips head screws. Removing them allows another plastic plate to be removed, which allows the core, holding the battery and the circuit board to slide out easily.
The PCB is populated with surface mount components, including a very nice, highly integrated BQ24195 IC from Texas Instruments that is well suited for power bank use. This chip does double-duty, providing both a buck-converter based lithium ion charger and a highly efficient boost-converter to provide the 5V necessary for USB devices from the battery. Both functions share the same shielded inductor, and operate at 1.5MHz, providing >90% efficiency during both charging and discharging. This efficiency makes the most of the power in the battery, but in doing so, it also reduces heat generation, allowing the pack to be charged at up to 2A. Discharge current is up to 2.1A. My brief testing bears out these numbers.
The power bank also has a thermistor, allowing the power IC to monitor the temperature of the cell during charge and reduce the charging current to prevent overheating. I’d guess it also uses the ICs ability to limit charging current draw based on USB coding from the input source.
This chip can be microprocessor controlled, and the microprocessor can set the charging voltage and current. I’m sure this comes in handy for Xiaomi, allowing them to swap in cells with different charge termination voltages without having to change components. Xiaomi also uses similar chips in their larger power banks.
I’m thinking of looking into getting ICs made up into small modules that can be incorporated into DIY projects. They support input voltages up to 17v, charging currents up to 4.5A. The boost-converter output current is apparently limited to 2.1A, but that’s still pretty good, and the IC can provide discharge protection at battery voltage at up to 6A sustained.
The pouch cell in my example comes from Lishen, but other teardowns have cells from ATL, which reviewers have conspicuously noted, also supplies cells to Apple.
I haven’t put this through a full cycle of use or tests, but based on the reports of others, I expect this to be a capable USB power bank.
This is a electronic load and charger for battery testing.
It can charge at up to 3A using a variety of charging voltages and profiles. For discharge testing, it can draw up to 5A @12v. There is a TTL-serial interface with a USB adapter and accompanying software for logging and controlling battery tests.
Update: I ‘ve posted a preliminary review, and I’ll be updating it as I go in the coming weeks.
Update: According to this comment on Dangerous Prototypes, the charger chip’s support for lithium ion charging is quite primitive, and so this project depends on the Arduino to properly manage the charging. Too bad.