Last Fall I finished my off-grid solar power system. This computer is running on it.
About 800W of PV panels, and 28 100A_Hr 6v flooded Lexan case Exide batteries all from scrapyard. Outback charge controller and inverter. System voltage 24, have "high 12V" and "low 12 v" legs (think 120/240) at the house, to run all possible loads without waking up the inverter.
My batteries are about 12 yr old. Look very clean, no sediment in bottoms of jars, no swelling, but plates are whitish, which I read is sulfate. Based on how fast voltage goes down with use, I suppose that I have available only a tiny fraction of the bank's rated capacity. Fully charged resting voltage 25.4. I have not checked SG.
(I also have eight dry-charged 1680 A-Hr 2V cells, never filled or charged, also 12 years old, that I can't figure out how to use. Someone somewhere has four more that they can't use, or needs mine.)
So, I want to desulfate.
The 6V batteries are in 7 series strings of four each, parallelled with 1/2" diam copper rod busbars (also from scrapyard, of course!), with a "center tap" bus, allowing the bank to be split into two 12V banks.
To desulfate the whole bank at once seems, to my ignorance, to present two problems.
First, the sheer size would seem to mean that a BIG pulse of energy would be needed to achieve adequate voltage saturation at plate surfaces. My heavy busses have low DC impedance, not so good for fast pulse, I guess.
Second, it SEEMS to me that only the "outside" cells of a battery (series string of cells) would actually see any reasonable approximation of the pulse waveform, because conductance to the "inside" cells is solely ionic, not metallic.
Here is my idea: My batteries have terminals for each cell How about desulfating each cell individually? Obviously, since I have 84 cells, that would take a while, but if I had a powerful pulser optimized for a 100A-Hr 2V cell, perhaps I could move it from one cell to another every day, or twice a day, and thus "clean" the whole composite battery bank in...84 days or less. Further reading of this board suggests that such short times are not possible, so it might be better to build 7 pulsers, and do it in (12 cells x however many days it takes per cell) days.
Another question. Some say that the frequency of the pulses has to be matched to some property of the sulfate crystal, somewhere in the low Megahertz range. True?
I'm an old-tech kind of guy. My favorite tractor is 78 years old. I was going to grumble about computer-chips in a desulfator and ask Why not use an oscillator (tank circuit), but reading of the Board has convinced me that the benefits of being able to control and respond to many parameters are worth the complexity.
I have looked at the "high-power" design from 2002, have not seen more recent references to its use; also it appears to be 120VAC line-powered, which would entail running my inverter continuously for long periods, with substantial energy loss. I am very curious about a capacitive-discharge design referred to by Don, and I think it would be best to build a unit or units powered by DC (any voltage up to 24 is available)
I asked Outback if they thought there was any chance of damaging the inverter with desulfating pulses, and they said, "No". Does anyone on this Board agree or disagree?
I'll be glad to report on results from any system I build with the assistance of this Board.
Thanks!
John
About 800W of PV panels, and 28 100A_Hr 6v flooded Lexan case Exide batteries all from scrapyard. Outback charge controller and inverter. System voltage 24, have "high 12V" and "low 12 v" legs (think 120/240) at the house, to run all possible loads without waking up the inverter.
My batteries are about 12 yr old. Look very clean, no sediment in bottoms of jars, no swelling, but plates are whitish, which I read is sulfate. Based on how fast voltage goes down with use, I suppose that I have available only a tiny fraction of the bank's rated capacity. Fully charged resting voltage 25.4. I have not checked SG.
(I also have eight dry-charged 1680 A-Hr 2V cells, never filled or charged, also 12 years old, that I can't figure out how to use. Someone somewhere has four more that they can't use, or needs mine.)
So, I want to desulfate.
The 6V batteries are in 7 series strings of four each, parallelled with 1/2" diam copper rod busbars (also from scrapyard, of course!), with a "center tap" bus, allowing the bank to be split into two 12V banks.
To desulfate the whole bank at once seems, to my ignorance, to present two problems.
First, the sheer size would seem to mean that a BIG pulse of energy would be needed to achieve adequate voltage saturation at plate surfaces. My heavy busses have low DC impedance, not so good for fast pulse, I guess.
Second, it SEEMS to me that only the "outside" cells of a battery (series string of cells) would actually see any reasonable approximation of the pulse waveform, because conductance to the "inside" cells is solely ionic, not metallic.
Here is my idea: My batteries have terminals for each cell How about desulfating each cell individually? Obviously, since I have 84 cells, that would take a while, but if I had a powerful pulser optimized for a 100A-Hr 2V cell, perhaps I could move it from one cell to another every day, or twice a day, and thus "clean" the whole composite battery bank in...84 days or less. Further reading of this board suggests that such short times are not possible, so it might be better to build 7 pulsers, and do it in (12 cells x however many days it takes per cell) days.
Another question. Some say that the frequency of the pulses has to be matched to some property of the sulfate crystal, somewhere in the low Megahertz range. True?
I'm an old-tech kind of guy. My favorite tractor is 78 years old. I was going to grumble about computer-chips in a desulfator and ask Why not use an oscillator (tank circuit), but reading of the Board has convinced me that the benefits of being able to control and respond to many parameters are worth the complexity.
I have looked at the "high-power" design from 2002, have not seen more recent references to its use; also it appears to be 120VAC line-powered, which would entail running my inverter continuously for long periods, with substantial energy loss. I am very curious about a capacitive-discharge design referred to by Don, and I think it would be best to build a unit or units powered by DC (any voltage up to 24 is available)
I asked Outback if they thought there was any chance of damaging the inverter with desulfating pulses, and they said, "No". Does anyone on this Board agree or disagree?
I'll be glad to report on results from any system I build with the assistance of this Board.
Thanks!
John
