The Biorad 200 supply I use to grid charge is unstable when directly attached to the battery, so it is now used through a 30 ohm drop resistor (bolted to a pretty large heat sink.) When used that way it is very stable. With the supply set to a current limit of 300mA and a target voltage of 185V, and starting from an SOC indicator which is all bars, it only took 4 hours to get up to 181V where it was stable for >2.5 hours, at which point it was turned off. This was in the evening but it was still fairly warm, probably 80F ambient. Voltages can only be read to a full volt, and currents to 10mA. At 181V it was only drawing 210-220mA. That gives a drop voltage 6.3V-6.6V, so the battery voltage was 181-drop = 174.4-174.7V. That grid charge did nothing to get rid of the recals. I can charge it longer than that but given the voltage observed (indirectly) it looks like all 120 cells are fully charged (it is 1.453-1.455 V/cell). Is there a good reason to keep charging beyond that? When my previous pack was on its way out grid charging would cause it to slowly increase in voltage for a long time, and that is not what was observed here.

 

On second thought, I'm going from memory since my notes aren't with me, I may have set the voltage limit to 181. Pretty sure it was 185 though. Either way, once it got to 181V the current stayed in the 210-220mA range, so the battery voltage would not have been changing.

 

Yeah, it was regulating voltage at that point. Why do you have it set so arbitrarily low? Why not set it to 200V? The battery will continue to increase until it's full. If anything, you'll see a drop once it heats up.

Why is it bolted to a heat sink? Aren't you only getting 9V * 0.3A = 2.7W of heat from it? Lots of 5W resistors that can handle that w/o heat sink.

 

Checked my notes and last time it was set to a voltage limit of 181V. This time it is set for 185V limit, so it should stay at 300mA.

The resistor (the kind in a metal case) can handle the wattage but it was darned hot at 300mA, hot enough to burn skin. Maybe hot enough to melt the insulation off a wire if it touched it. With the heat sink on it only gets warm.

Anyway, at 3 hours the power supply shows 183V and 300mA. The ambient temperature is much higher this time though, so not strictly comparable conditions. I'm going to let it run overnight at least.