The ones from voltagestandard.com are rather nice for the money. You should consider getting one with a voltage that won’t shift the meter up a range (like a 3V one to test a meter with a 4V range). He does sell a ref that puts out 5 different voltages.
I have 2 Fluke meters exactly alike, same model and they don’t read exactly the same. I wouldn’t worry about it and .2 is nothing to worry about in the first place.
The plus can calibrate more ranges and the resistors for ohm calibration is slightly better.
The PentaRef is also very useful for DMM voltage calibration, because you can order one with a 4.2 volt value (Then you now your DMM is correct for LiIon), or for more general purpose, select as needed from: 1.9 (2000 count DMM), 2.9 (3000 count DMM), 3.9 (4000 count DMM), 4.9 (5000 count DMM), 5.9 (6000 count DMM).
Checking my batteries after they are on the i4, I'm also usually seeing 4.21-4.22 not 4.2 exactly. I don't think it's really a big enough of an issue, since it does stop charging at that point.
What batteries are you guys using to get these results? If they are newer higher cap batteries it could (Accurately) detect that it could push more voltage into them and do such. I had my i4 give out at 4.17 on my older sanyo 2200’s batteries and about 4.19 on my newer 2600’s.
Then again my meter is junk, but it still is reasonably consistent. I still trust my accucel 6 more than the i4, which on the same cells and meter stops at 4.15v and 4.17v respectively.
No. The differences in termination voltage are either
A) Random variation. The Analog Voltage measurement circuitry has precision error from one cycle to another, especially if the room temperature changes.
or
B) Caused by the time between actual charge termination and your measurement. Once the charge terminates, there will be a little fall-back in voltage. If you wait longer after termination, the fall back will be more.
or
C) Your meter has precision error from one measurement to another
or
D) The Charger follow correct CC/CV Charging protocol, and every battery will take current a little differently once near the end of the CV portion of the charge
or
E) a combination of the above.
They are not, however, due to the charger “Sensing” the higher voltage tolerance of the cell and charging it higher.
PPtk
edit: To add Option D - Brain malfunction and I forgot to type that one out…
my nitecore i2 charges the sanyo 2800 up tu 4,24v when measured right after charging and it drops to 4,23v an hour after…
the panasonic 2900 are terminated at 4,22v…
Despite of your suspicion, it is calibrated monthly every second month by a laboratory only dedicated to do such things. I can’t tell you the name,I don’t know it because the fluke is not exactly mine, it’s part of the tool set my company provides me to do my job. But I borrow it when I need to measure some important thing like this
Cat tell you much about the calibration process, but trust me, in my company they are really obsessed with precision-calibrations-torque settings-deviations, so I think the fluke is properly calibrated.
Edit: for future reference, all my other tools like caliper, feeling gauges or torque wrenches are also calibrated. The lab has ISO certification, is all I know
I posted over in gords i4 "poof" thread, but thought it more appropriate here since we're talking about the i4's termination voltage.
Charged up my two protected KeepPower 18650 3100's (charged in separate channels for the 750mA rate). Fresh off the charger I'm measuring 4.27v and 4.28v! I let them sit 20 minutes and still saw 4.27v & 4.28v. Here it is 4 hours and 25 minutes later and I'm still seeing 4.27v & 4.27v. I'm using the same meter I always use and no other charger I have charges this high. My i4 has a molded serial# which matches the box's label. This is my first use of this charger.
So how high is too high? And at what voltage should the over-charge protection kick in?