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Thought I'd drop in an update for posterity. I did a couple dozen tests over the holidays with the nickel irons I have. I'll post raw data if anyone cares to see it, but here's a quick summary of what it says to me...
My test bank is made up of Edison C6 sells. My cells are between 50 and 60 years old and had not been reconditioned at the point when I got them. Using my reconditioning process without opening the cells, I got them up to about 300 amp-hr when overstuffed with "juice". The only reference I can find on these cells are that they are said to have an original capacity of 337.5 amp-hr (but that a single source with no Edison reference). So I'm about as good as I can expect for what I've done to revive them.
The coulombic efficiency of the cells on charge / discharge was very surprizing high when only using the bottom half of the batteries' amp-hr of storage - 90%+ efficient (perhaps 95% or even more at low amp draws). Since this was from scores of tests, I deem it to be real. This efficiency is much higher than anything I have seen reported before and suggests the batteries indeed might be quite useful for solar applications if you operate in these ranges, but it means you need even more cells (and $$ to invest). NOTE: As one should also suspect, the water consumption by the cells is also dramatically reduced when operating within this improved coulombic efficiency range.
There are two major "watch outs" that these experiments point out....
(1) The discharge-charge efficiency takes a major nose dive as you continue to pack the cells. The more you try to store, the worse the incremental efficiency gets. This makes it very wasteful to attempt to utilize all of the stated capacity. While this might be fine for on-line backup power devices, efficiencies of 30% and less are most assuredly way too low for most of us attempting to store electricity being generated from from solar panels. NOTE: I should emphasize, I only know the coulombic efficiency break point for the cells in my possesion. That same point of diminishing returns for other cells would have to be independantly determine, and it would be unfair to generalize that other cells should also only be used to 50% of stated capacity.
(2) Coulombic efficiency is NOT total efficiency - ie even if amp-hr out is equal to amp-hr in (100% efficient), you still have to take into account the volts necessary to charge the cell versus the natural volts the cell runs at during discharge. WHile there is no one specific set of values I can give you because charge rate comes into play, typically my charge source was at about 1.6v when the cells were at their 50% capacity level (150 amp-hr). Using 1.2v as the average discharge volts, that gives us a "real" wattage efficiency of about 75% as the best we can expect to achieve (compare that to 90% for LA cells using the same type of analysis).
Finally, after reviewing all these experiments I'll expand my initial generalization to Mike and sugest there is about 15-20% power remaining at the 1.1v level as you continue the discharge to 1.0v.
My test bank is made up of Edison C6 sells. My cells are between 50 and 60 years old and had not been reconditioned at the point when I got them. Using my reconditioning process without opening the cells, I got them up to about 300 amp-hr when overstuffed with "juice". The only reference I can find on these cells are that they are said to have an original capacity of 337.5 amp-hr (but that a single source with no Edison reference). So I'm about as good as I can expect for what I've done to revive them.
The coulombic efficiency of the cells on charge / discharge was very surprizing high when only using the bottom half of the batteries' amp-hr of storage - 90%+ efficient (perhaps 95% or even more at low amp draws). Since this was from scores of tests, I deem it to be real. This efficiency is much higher than anything I have seen reported before and suggests the batteries indeed might be quite useful for solar applications if you operate in these ranges, but it means you need even more cells (and $$ to invest). NOTE: As one should also suspect, the water consumption by the cells is also dramatically reduced when operating within this improved coulombic efficiency range.
There are two major "watch outs" that these experiments point out....
(1) The discharge-charge efficiency takes a major nose dive as you continue to pack the cells. The more you try to store, the worse the incremental efficiency gets. This makes it very wasteful to attempt to utilize all of the stated capacity. While this might be fine for on-line backup power devices, efficiencies of 30% and less are most assuredly way too low for most of us attempting to store electricity being generated from from solar panels. NOTE: I should emphasize, I only know the coulombic efficiency break point for the cells in my possesion. That same point of diminishing returns for other cells would have to be independantly determine, and it would be unfair to generalize that other cells should also only be used to 50% of stated capacity.
(2) Coulombic efficiency is NOT total efficiency - ie even if amp-hr out is equal to amp-hr in (100% efficient), you still have to take into account the volts necessary to charge the cell versus the natural volts the cell runs at during discharge. WHile there is no one specific set of values I can give you because charge rate comes into play, typically my charge source was at about 1.6v when the cells were at their 50% capacity level (150 amp-hr). Using 1.2v as the average discharge volts, that gives us a "real" wattage efficiency of about 75% as the best we can expect to achieve (compare that to 90% for LA cells using the same type of analysis).
Finally, after reviewing all these experiments I'll expand my initial generalization to Mike and sugest there is about 15-20% power remaining at the 1.1v level as you continue the discharge to 1.0v.
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