I noticed the UMS2 cost nearly double the price of the UM2. So, what are the differences and is the UMS2 worth the extra cost and why?
I have several chargers (all from XTAR) but now I'm looking for a charger to connect to a foldable solar panel to charge my lithium and NiMh batteries. All thoughts and ideas of what to buy are very welcome.
That is more or less in line with HKJ's observation in his review. Mine leaves topped up batteries at resting voltages around 4.14 - 4.16V. Not great, not terrible.
If you are looking for a charger that clocks in at 4.20V check for Miboxer C4 or C4-12. All my Miboxer chargers settle very exactly at 4.20V (+/- 0.01V). It seems they have a much lower termination current (10mA or less) in the final CV phase. I have a Vapcell S4+ charger incoming. I hope this one will charge close to 4.20V, too.
It depends when you measure the OCV. Couple of minutes off-the-charger, the voltage typically should read 4.18-4.19 V, but it depends on the cell and the charging (end of charge current). Also, is your DMM calibrated?
It is best to measure the voltage during the CV-phase of the charge, it should read as close as possible to 4.200 V. Make sure that you use a trusty DMM, preferably with a 5000 count display (or more), so you can read voltage to 1 mV.
I may run some tests tonight on a calibrated (to within 2-3 mV) SkyRC MC3000 and report.
Here are the promised test results on a calibrated MC3000.
Cell: Samsung 50E
Charge current= 2.5 A (approx. c/2)
End of charge current= 250 mA (1/10 of charge current)
Voltage during CV phase of the charge =4.196 V
Voltage at 1 min. after end of charge =4.182 V
Voltage at 2 min. after end of charge = 4.180 V
Voltage at 5 min. after end of charge = 4.176 V
Voltage at 45 min. after end of charge = 4.165 V
All measurements done with a UNI-T UT139C. The DMM was checked against 5.0000 V reference source and found to be 2-3 counts out, i.e. the precision of the above measurements is 3 mV.
After testing the UM2 with NiMH I´m not so satisfied with it.
While the UMS4 was very reliable, except with some very problematic cells, the UM2 terminates to early. Not only because it stopps at 1,48V with NiMH, also because it terminates much to early, especially with AAA-cells. This happens not so often like with Xtar VC4SL, VC4 or ISDT C4 EVO, but it happens
My ums2 i have to plug it into the outlet a bunch of times trying different configurations before it will work and charge. If i just plug it in and try to charge a battery, it will turn the screen on show the Good charging indication display 66 resistance, but never actually charge. So i take the plug out of the wall flip it around or try different outlet until it shows a different resistance and that’s when it will start charging. Hella annoying. But it does charge quick when it finally works.