Delta V detection will not be reliable on many packs, especially if they are badly unbalanced. Once the pack has been through several cycles and gets better balanced, delta V should be more reliable. On an unbalanced pack, some cells will be dipping as they get into the delta V range others will still be on the rising side of the delta V curve, and cancel the dip. The 350ma with the fan running will top off all of the cells, then level off and stay at a steady voltage as seen on this charge graph.
http://www.99mpg.com/Projectcars/mim...ns_graph.jpg,0
On the new circuit I am suggesting, the detection circuits could first detect when to drop from 1A to 350ma, based on voltage. The second detection circuit could detect when the voltage reaches the full charge point based on the voltage reaching a steady state for say 10 minutes. A simple timer could also stop the charger a fixed time after the drop to 350ma, since this time should be repeatable.
Using this every night to top off the pack, is what I had in mind.
Using the temperature rise on the ptc strip without running the fan, is another way to determine end of charge, but it depends on there being enough current to generate a clear temperature rise, which 350ma just marginally can do.
This also depends on the pack being at ambient temperature when you start. As you can see from the graph, this pack started off warm from the 50 mile drive to my place, and actually cooled off as we charged it.
To do a full charge in a night, waiting for the pack to cool before charging would take too long.
A similar charger to set to a higher voltage to charge a Prius booster pack would be another use for this system.
