I’m cheap. Yes, I should have gotten a cottonpickers. I’m at a point where I have more time spent at my desk than disposable income.
I have one of these on the way from Fasttech to charge some Acer-Aspire-pulled Samsung –28A’s, and maybe later some of those pink LG’s RMM is selling. HKJ’s analysis concerns me due to the inconsistent channels and the absence of a termination at peak. But, it seems the indicator lights are consistent and there is a relatively consistent period of time between the indicator lights changing and the cells reaching 4.35v.
So I had the idea of using a DMM to test the voltages externally. While a cell is in my i4 with the third light blinking it reads 4.17, and when I remove it the cell is 4.15 (about a minute after doing this the third light went solid).
Would this be an accurate way to determine the charge state of a cell in the HXY charger? Subtract two hundredths from what I read off the charger to get to cell voltage?
Cell voltage is from two components, static cell voltage and charging current times internal resistance, so I would say no without know the charging current etc. you can’t make that assumption.
OTOH most DMM devices are very small loads, so voltage reading should be accurate, and isn’t that the issue with a cheap charger, overvoltage during charging like 4.4v?
I plan to put my $1.58 shipped charger from ebay to the test with my DMM soon. A bit more tricky to measure the current.
I do the 4.2v-up-to-4.3v part of the charge with an adjustable DC-DC converter board and monitor it with a DVOM. I adjust the voltage during the topping-up to stay around 4.32v, as they get closer to the end it has to be adjusted less often, around that time I switch off the charger and check the cell's voltage occasionally (I have a clicky switch on the side of my 4x18650 box), when it's at 4.31-4.32 after ~10 seconds, I find that the final voltage after they've been out of the charger for 20-30 minutes settles in at 4.29-4.30v. Note that the last part of the charge here from 4.20 to 4.30 is all in the CV phase, current is self-limited by the cells by that point and is very low. I have the board adjusted to a 1 amp limit but even 4 cells at a time in parallel doesn't hit that 1A limit.
That’s beyond my capability (and it sounds like budget too) at this point in time. It almost sounds like by the time I buy those parts and power supply I could afford a new/used entry-level hobby charger.
But it basically sounds like when the cells in the charger get to 4.32 (or 4.37 for the LG’s), take them out and periodically check voltage, is that about right?
Not really... Set the open circuit voltage of the DC-DC board down below 4.3v, put cells in the box, adjust voltage up to 4.32v. As the cells get full the voltage will rise, when it jumps up to 4.33v I turn it back down to 4.32v. Occasionally I hit the disconnect switch between the DC-DC board and the battery box to see what the cell voltage is without the charger. So for example after 10 minutes on the charger, disconnecting will show the cell at 4.23v. Another 10 minutes, 4.25. 30 minutes later it's at 4.28v. Eventually it'll be 4.31-4.32 with the charger disconnected. After they're allowed to rest they are at 4.29-4.30, and stay there for however many days/weeks it takes for them to stat naturally dropping from self discharge.
It's very cheap. A 10A CV/CC converter board, any 9-12v wall wart capable of at least 1A, and a battery box. The only hobby chargers that will do 4.3/4.35v cells are well over $100.
edit: And since the topping-up part is in the CV part of the charge, there's no reason why you need a 10A-capable board with separate voltage & current limiters. The dirt cheap LM2596 boards (adjustable voltage only) are around $1.50 each and will do the exact same charge.
