Well, the results even after just a couple of days are somewhat promising... maybe.
I'm really starting to believe that what has commonly been thought to be 'sulfation' is really more about dry cells. Not in every case, obviously, but I think there's a good possibility that this one sure is.
Collectively, the 6 cells took a total of about 10oz of water. Performance had a small but almost immediate effect (I'm sure this is from striation).
After 12 hours or so at 15.25V, the 'inactive' cell was still not bubbling, while the others were going at it fairly strongly. The 5 active cells had warmed up somewhat, not hot, just notably warmer than the 6th (which happened to be on the end, making it easy to feel the temp difference).
I took it off charge and let them settle for about 8 hours or so, and then checked the OTV. Not exactly promising; 11.6 or so. Indicative that the reason for the last cell not bubbling was likely because it was shorted. Hmm. Ok, so I set out to find out.
Loading at this point with the same stretch of nichrome showed most definite improvement in the response. It dipped down to 11.3 or so immediately, followed by a decline down to 9V or so. I did this in a bang-bang like way, allowing surface charge recovery each time.
As the voltage dropped, the short in the last cell began revealing itself. I took it down to about 7.5V, and then increased the frequency to somewhere in the 10 sec on, 10 sec off range. During rest periods, as the voltage would approach 9.2, it would suddenly jump to 10.2 and then continue to climb. Ahh, warped plate/debris induced short.
I pushed it a bit harder by increasing the current and carefully watching the meter. At the point that I let go and let it come to final rest to resume slow charging, I was pulling 8 or 9 amps. The current was never directly measured; this is calculated based on the wire being ~1 ohm/foot and I varied the length that the drop took place on from 8 to 10 inches. Taking into account the voltage drop of course, this comes out somewhere in that range. I had to be careful, I was dealing with red and orange hot nichrome and so had to vary the length as necessary.
One very odd phenomena that happened during this that I think is worth mentioning... During the heavy 'equalization' charging I gave it after adding the water, the 5 active cells provided heat. The inactive one remained cool. During the heavy discharges, the opposite took place, and the discharge current was more than double the charge current... The 5 active cells remained cool, the previously inactive one heated.
My only personal conclusion is that the short is resistive, and that maybe in the attempt to break it up, it generated heat, or, polarity reversal may have been taking place after breaking up whatever was causing the short, liberating heat... ? I don't have any idea if polarity reversal liberates any more heat than normal "charging", but its a thought. Reversal was definitely a very good possibility at the currents I was dealing with.
Ok, so once I was sure the short was at least at bay for the moment, I've learned in the past that if a shorted cell is suspect, heat will bring it out. And it did, during the discharge. So to avoid this, I've been letting it charge VERY slowly since, in the order of 0.05C or so; about 100mA.
It is responding well, and as the cells charge, it clamps the charger a little more and more, and the CTV actually drops very slowly (by 1/10 V) over the course of several hours, necessitating an adjustment in charge current.
I'm charging through a bank of resistors and switches that effectively become a binary potentiometer. I prefer this because I can keep track of how long a battery was on a given charge rate and if it had to be changed, etc etc.
More to come as this thing charges. It could be a while. Thats a very slow rate...
Steve
