Perhaps let me start off by saying where we agree -
Temperature is a critical parameter
Voltage reversal is death for a cell
Regulating only the voltage across an entire pack can result in murdering individual cells within that pack
If I understand you correctly, you are suggesting that, after careful bottom-balancing, a string of cells can be assembled "... put them together in one column with no taps.
Without getting into the merits or mechanics of top- vs. bottom-balancing, that's where we disagree.
I personally would never dream of putting a lithium chemistry pack together without the ability to both monitor and control each individual cell's (or paralleled cells') voltage and temperature and hopefully rate-of-change of these parameters, regulating the amount of current going into not only the pack but having the ability to shunt current away from each cell as needed to control its voltage and temperature, as well as the ability to shut down the input should any parameter misbehave. Monitoring rate-of-change of voltage and temperture could provide some pre-emptive warning and corrective action.
As an example, for charging, my relatively simple Revolectrix PowerLab 8 (model airplane battery charger which I use on my electric scooter and electric outboard LiFePO4 packs) does a wonderful job of individually managing individual cells in an 8s string, never allowing any individual cell to not only not exceed its maximum voltage rating but also limiting its voltage (via current limiting) so all the cells in the string maintain the same voltage as the overall pack is being charged (they all increase in voltage together).
Where we also disagree - with all due respect, while I recognize that, despite the voltage vs. SOC curve being quite flat and varying for both charge and discharge currents as well as temperature, I believe the voltages ARE measurable and can be used as a simple first-order SOC indicator (which is all I'm trying to do here with the iMiEV). Are you suggesting that coulomb-counting is the only way of determining SOC? If so, what do you use as a reference point?
Finally, based upon the iMiEV's charger power draw, when fully charging the pack the last hour or so is a decaying curve which leads me to believe that they are indeed top-balancing the pack, the blue curve in this snapshot (the red voltage curve shown is only one leg of the actual 240vac input):
Mitsubishi's letter specifically asked us to discharge down to two bars and leave the charger alone to fully charge up the pack until it automatically shuts off - and do that periodically. I believe they WANT us to top-balance the pack periodically.
Thus, back to my original question: anyone have any specific voltage vs. SOC curve for the cells used in the North American iMiEV?
As a point of reference, if I read this correctly, 100%SOC is 3.96v/cell (348.48v pack):http://myimiev.com/forum/viewtopic.php?p=4817#p4817
I really don't want to get into a debate, but just wish to know what would be a reasonable and safe voltage to program a regulated dc-dc converter output to inject some current into our battery pack at approximately our iMiEV's 50%SOC point.