As per the subject. During my investigation of the CyanSky BL1834U battery, I found the NCR18650GA to be the OEM battery closest to it, and therefore started investigating it more fully. In summary, I’m interested in finding the following parameters:
- Recommended discharge current, in order to reach its nominal capacity;
- Recommended discharge cut-off voltage (ie, at what voltage the battery discharge should be stopped, again in order to reach the nominal capacity;
- Recommended charge termination current (so the battery is maximally charged and will, during discharge, reach the nominal capacity).
I did the obligatory search here in BLF and found this review of the NCR18650GA by the legendary @HKJ, but it did not answer all my questions, so I started digging deeper, and by the grace of Google I was able to find a 2-page short spec sheet (archive), as well as a longer (17-pages!) “draft specification”(archive). Additionally, the longer document is dated explicitly as 2015-01-15, and while the short document shows no explicit date, it can be seen from in the PDF metadata a creation date of 2017-02-14 (so the shorter document is about 2 years more recent).
Here’s what I’ve been able to gleam after reading both:
-
Recommended discharge current: the short document doesn’t mention it explicitly, but on the first graph (p.2) it can be seen the discharge current that gives the rated 3400mAh capacity is 2A; the longer document does mention it explicity as 1.675A. I would use 1.675A.
-
Recommended discharge cut-off voltage: again the short document doesn’t mention it explicitly, but again at the same graph that all discharge tests terminate at 2.5V; the longer document does mention it explicitly also at 2.5V, so they’re in agreement here and 2.5V it is.
-
Recommended charge termination current: this is where things get weird:
- the longer document doesn’t mention that at all, but describes a “Full charge” (p.7) as: “The battery is charged at 1.675A constant current until the voltage reaches 4.20V. The current is then reduced to keep a constant voltage of 4.20V. The total charge time is 4.0 hours at 25°C”.
I interpret this (in terms of MC3000 charging parameters) as using the smallest possible charge termination current (0.01A = 10mA in the app) and setting a timer cut-off of 4 hours. - The shorter document states, at the top of the same above-mentioned graph, “Charge :CC-CV:1.675A-4.2V(67mA cut) at 25℃” which agrees with the longer document in terms of charge current and target voltage, but explicitly indicates a “cut” current of 67mA, which I interpret as being the same as a “charge termination current”.
- Additionaly, the shorter document does state on p.1 “Charging time Std. 270 min”, which is 4.5 hours and not 4.0 as in the longer document.
- the longer document doesn’t mention that at all, but describes a “Full charge” (p.7) as: “The battery is charged at 1.675A constant current until the voltage reaches 4.20V. The current is then reduced to keep a constant voltage of 4.20V. The total charge time is 4.0 hours at 25°C”.
As y’all can see, The first 2 parameters I’m looking for are pretty clear, but the third is anything but, as it seems these 2 documents recommend three(!) different charge-termination approaches:
a) charge the battery with constant current 1.675A (1.68A in the MC3000) up to 4.2V, and then reduce current to keep that voltage until 4.0 hours total charging time;
b) ditto, until 4.5 hours total charging time;
c) Use 67mA (0.07A in the MC3000) termination current and limit total charging time to 4.5h;
Given that (c) is what can be inferred from the newest document (see above), I’m tempted to use it. What would you folks do?
TIA!