This is why top balancing needs to be closely monitored. Like equalizing flooded batteries you simply DO NOT leave them unattended. Once the cells hit 3.800 VPC you will need to adjust the power supply very carefully so it does not overshoot 3.800VPC. While these Mastech power supplies are reasonably priced they are rather sloppy to set voltage with because they lack a dedciated voltage sensing circuit. Power supplies such as those from BK Precision etc. use a dedicated voltage sensing circuit for accurate voltage settings.


Watch the DVM NOT the power supply display. Allow the voltage to rise to 3.8000V (for Winston cells only!) and hold the cells at 3.800VPC for about 15-20 minutes once you get there. Remember trust the DVM NOT the power supply.Some folks say you can stop once you hit 3.800 VPC but I like to let the current taper a bit and 15-20 minutes is plenty, once you hit the top balance voltage. Other manufacturers, of prismatic cells, have considerably lower maximum balancing voltages such as 3.65VPC. Once the current has tapered at 3.8V for 20 minutes or so I then dropped the voltage to 3.65V and let the current go to 0A.


If you wire in parallel, hold voltage steady then allow the current to taper to flickering between 0.0A and 0.1A the parallel pack is now balanced and can be disconnected. Despite doing this with my own bank, I would not advise top balancing at 3.800V but rather somewhere closer to 3.65V for a fractional C bank. I did not feel comfortable about holding the cells at 3.800V for very long so I dropped back to 3.65V.


After you do this disconnect the charge source you can continue to let them sit, in parallel, for as long as you want, after discharging them to a storage SOC of 50-60% SOC.


Once I have attained my peak top balance voltage I then let them drop to a lower peak voltage, such as 3.65V on Winston cells, or 3.55V on CALB and I then allow the power supply to take the batteries to 100% full with the power supply bouncing between 0.0A and 0.1A. This actually puts the cells in balance at that voltage. At this point you can un-wire the cells and they are balanced..


EDIT: I recently conducted an experiment on my test cells that pitted a "balancing BMS" against a 3.65V parallel top balance to 0.00A - 0.1A on the power supply. Holding the cells at 3.65V (CALB cells) the top balance in parallel actually balanced the cells in just under 3 hours. Using the "balancing BMS" after more than 7 hours at shunting / balancing voltages the cells were still not "balanced"..... Food for thought!


Please keep an infrared thermometer on hand and closely monitor cell temps. Hit all the cells at the same spot, when checking on the cells, to track any changes or anomaly's. They should ideally remain below 80-85F, these did.


Further Thoughts: After playing with multiple brands of prismatic cells for almost 4 years now it has become apparent that there is pretty much zero difference between these cells in terms of upper knee voltages. With that in mind I would strongly suggest there is NO NEED to top balance Winston cells, for fractional "C" use, beyond 3.65V per cell.