Hi folks, I’ve had a MiBoxer C4 v3 (2019 model) for a few months and it sees frequent use on an “every other day” basis where I’ll use it to charge between one and four cells at a time. I was using it this morning and came across what appears to be an intermittent fault.
I was charging a pair of cells - an ncr18650b and a vtc6 (both unprotected), whilst doing another task nearby. I was periodically monitoring their progress and knew that the vtc6 was due to finish. When I checked, I found the charger was showing 4.20V / 97%, but somewhat alarmingly, the charger was still pushing 1.5A (max current per slot on that charger). The charger was not set for HV li-ion/4.35V.
I pulled the cell as soon as I saw this as the charger seems to have failed to switch from CC to CV. I can only assume this would have resulted in an overcharged cell had I not been monitoring.
Unfortunately, I blew a fuse in my DMM just yesterday and had no accurate way to check the cell voltage, therefore I popped it back in briefly to see 4.20V displayed and a much more sensible charge current of 0.25A before pulling it again. I then put it in my old xtar vp1, which also said 4.20V. I didn’t charge the vtc6 any further, although I have marked it for future reference. The “B” was finished off in the xtar.
This is the first time that I’ve had a problem with the C4 charger, but I have since seen a few threads on here regarding issues with predominantly slot three of the C4-12. Interestingly, the vtc6 was in slot three. Unless this is just a coincidence, one can probably assume the issue lies with some piece of shared design and/or firmware.
The suggestion in the other threads (again, regarding the C4-12) is to just stop using slot three, however this begs the question: why can this happen only in slot three, or is it just a case of that slot “fails” first? I’m not really looking for answers to this as I’ve already decided that I’m going to retire and replace the charger as I believe that even occasional overcharges are wholly unacceptable. I did think this may be useful information for the community in general though.