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Lead acid batt analyser

Discussion in 'General Electronics Chat' started by Mosaic, May 3, 2012.

  1. Mosaic

    Mosaic Well-Known Member

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    First off, let's not have another dispute over whether batteries are recoverable by desulfation or not. I intend to do some science regarding the matter and that's what this thread is about.

    I have devised an approach which I'd like to discuss. Here it is:

    Assumptions
    1) The equalizing charge (@15V+) serves the purpose to minimize creeping sulfation due to under charging which can happen to individual cells as they age and chemistry alters cell to cell. Thus occasional higher voltage charging has benefits.

    2) Analyzing each cell (6 in a auto batt) voltage under constant current charge will reveal differences in cell internal resistance. A higher relative cell Pd => sulfation or grid corrosion etc. An unusually low cell Pd => a developing short etc.

    3) After a charge, discharge, equalize cycle, data from step 2 can reveal weak or faulty cells and serve to justify attempts at service or designate for recycling.

    4) Swept frequency pulse charging modulation on top of the regular charging current won't harm the battery and 'may' enable enhanced ionic activity in a sulfated cell.

    5) The enhanced ionic activity is derived from sharp rise time pulses treating a sulfated cell as a capacitor. Such a cell would otherwise have reduced ionic activity due to IR and Pd increase. Such a cell would induce other series cells to be undercharged due to a faulty end of charge battery voltage being detected. This in turn induces 'creeping' sulfation in other cells.

    6) Perhaps 40 to 50% of battery 'failure' is due to sulfation from poor charging regimens.


    The science I intend to perform involves dismantling an old battery with bad cells as determined by spec. gravity after proper charging. Reassemble said battery in a transparent polycarbonate case with access to all cells. Examine samples of battery plates under a microscope and take imagery of the samples. Log all this data and assess which plates are sulfated.

    Assuming that several cells have sulfated plates (quite likely from a battery put down for a year or 2) the following is carried out:

    a) Internal resistance of each cell is measured by both ac and dc methods.
    b) Sulfated cells are discharged and then pulse charged with varying frequencies for a fixed time with the same pulse charger.
    c) New measurements of internal resistance are taken. Plate samples are taken for inspection under microscope.
    d) Results are compared and an assessment is made which may justify further pulse charging cycles.

    Am I missing anything useful?
     
  2. duffy

    duffy New Member

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    Doesn't look like it. One of the important things is to build an easy-to-disassemble test battery, and you mentioned that. The easier you make it to take apart and reassemble, the more the plates will get weighed, spectrum-analyzed for sulfur content, etc.
     
  3. ronv

    ronv Well-Known Member Most Helpful Member

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    Why not measure the capacity to see if there is any improvement.
     
  4. dave

    Dave New Member

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  5. Mosaic

    Mosaic Well-Known Member

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    Going thru the discharge cycle after the pulse charging will reveal more capacity.
    Also Ron, a lower int resistance means that the lead sulphate has gone back in H2SO4 electrolyte once it hasn't fallen off to the bottom of the cell.

    That equates to more active plate material and capacity.
     
  6. ronv

    ronv Well-Known Member Most Helpful Member

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    Yep, It's just that the bottom line is more capacity. I'm curious to see how you come out. I live in a retirement community and everyone has an electric cart. One guy bought a desulfator so they all wanted one. I built 25 of them and put them on. That was about 4 years ago. Interestingly they seemed to get about 300 charge discharge cycles with or without them, but one guy is still on his original set. He showed poor cells (Specific gravity) when I put his on. Think he still does.
     
    Last edited: May 3, 2012
  7. duffy

    duffy New Member

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    LOL! YES. Missed the most obvious one.
     
  8. Mosaic

    Mosaic Well-Known Member

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    Well, it's been two years and I have done the science.
    I have processed scores of batteries and developed a desulfation engine.
    Approx. 30% of batteries left for dead can be recovered and placed back into original service. Not necessarily at full capacity...but with reasonable capacity.
    I attach a 'scope trace of the process in action.
    This battery a 55B24L japanese unit was flat at 3.75V and >2000 milli ohms resistance. Its cathode busbars were visibly coated with white crystalline sulfate deposits as well as chocolate crystalline on the anodes.
    The process involves a relatively low pulse charge followed by ramping the current as the battery resistance decreased and temperature remained within tolerance across the cells.

    This scope pic shows 8.4Amps average translated into a 500Hz pulse charge event of 640A measured by an ion physics current transformer custom built to spec. I have high hopes for this battery recovery as it will be ongoing for another day or so.
    55b24L-10_8Amps.png
     
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  9. tvtech

    tvtech Well-Known Member Most Helpful Member

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    WOW :cool:

    Interesting stuff Mosaic.
     
  10. MrAl

    MrAl Well-Known Member Most Helpful Member

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    Hello there,

    Yes this is interesting. It would be nice to know the charging technique that is best.

    As to charging at a higher than normal voltage once in a while, what would you say about a way to use the alternator itself to do this. Any way you know to fool the alternator into putting out more voltage than it is made for? For example, another 0.5v or so.
    Unfortunately the schematic for my alternator is very poor and too low in detail to figure out where they sample the battery voltage to determine the current battery voltage.
    Any ideas would be nice.
     
  11. NorthGuy

    NorthGuy Well-Known Member

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    Looking forward to the results.

    People often try to restore batteries by relatively long overcharge (e.g. 5-6 hours at 15.5-16V for 12V battery). In theory, if you do this 2-3 times to a sulphated battery, it may restore some of the capacity. Have you included such treatment as a comparison to the high-frequency methods?
     
  12. audioguru

    audioguru Well-Known Member Most Helpful Member

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    I used lead-acid batteries only in cars. A good battery lasts 5 years and a bad battery also lasts 5 years.
    A replacement battery is inexpensive so why bother trying to salvage a worn out one that will fail soon after you "restore" it?

    Do you also "zap" a shorted old Ni-Cad battery? Then you zap it again and again every time you try to use it?
     
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  13. tvtech

    tvtech Well-Known Member Most Helpful Member

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    I love it when people go on a Mission.

    Mosaic said he would "do the science" two years ago. And indeed he has :)
    Thread resurrected out of nowhere...and wham, bam, thank you Mam...results for all to see.

    I wish you the best Mosaic. This is really good stuff :)

    Regards,
    tvtech
     
  14. tvtech

    tvtech Well-Known Member Most Helpful Member

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    Common AG. We all love you but now and again stuff happens that pushes boundaries.

    I think this is pretty cool :).

    Regards,
    tvtech
     
  15. NorthGuy

    NorthGuy Well-Known Member

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    Golf cart batteries are more expensive. Fork lift batteries are several thousands.
     
  16. Mosaic

    Mosaic Well-Known Member

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    The batteries I process come from a used car dealer who uses an industrial charger (on wheels) to rapid charge used/dead batteries. The batteries I get are the ones that 'failed to hold a charge' from that system.
    So I don't re-attempt 'regular' charging on them, they go straight onto the pulse charging process.
    The 'recovered' batteries I return to the dealer as per my rating system (CCA & AH) go into customer vehicles and on the road.

    Why restore them?
    In my country there is massive backyard battery lead smelting to make terminals, fishing weights and Tyre balancing weights with children becoming brain and kidney damaged permanently. I felt if I could create better value from these old batteries at least a % of the damage is mitigated.

    I have been asked to process Forklift batteries and Manlift (golf cart type )batteries. I will design for that once I have a reliable automotive system done as auto/truck batteries represent 95% of lead battery use here.

    Due to exceedingly high pulse currents involved (capable of welding) I have been refining system safeguards and simplifying operations via a microcontroller. The current system (not yet finished) can hotswap batteries and auto sequence their processing to run 24/7 to optimize commercial value. I want the system to auto maintain about a dozen 'recovered' batteries at a float voltage as well to keep their performance optimized for over the counter sales.

    AG, the used car market here only requires a 90 day warranty to be upheld. Thus a recovered battery must meet that spec. I have not purchased a battery in a long time. I use the recovered ones in my vehicles 100% of the time. In the Caribbean we don't have temperature extremes and spent lead acid batteries designed for all weather use can be recovered and perform adequately in the tropics.

    One man's trash is another man's treasure.
     
    Last edited: Nov 8, 2014
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  17. tvtech

    tvtech Well-Known Member Most Helpful Member

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    ^^^And that is worth another rep Mosaic.

    So proud of you putting your money where your mouth is and actually walking the talk..

    Few do that.

    You have my support 100% with your Mission. Money I cannot help you with but moral support is what really counts. And that you have in abundance.

    Regards,
    tvtech
     
    Last edited: Nov 8, 2014
  18. Mosaic

    Mosaic Well-Known Member

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    The support is invaluable. :)
    There have been many hurdles along the way. The current transformer alone cost $600USD, then many hours in simulations, coding, testing, detonating TVS diodes :eek:, destroyed MOSFETS & Mosfet drivers, melted current sense resistors, acid damaged clothes, back strain from toting batteries. :(

    Here is another scope pic., the AH delivered is now 150% of rated and the battery is equalizing happily. Temperatures across all cells are 36/37C which is a good sign, also all cells gassing. Battery V is now 15v with the 2A avg (C/20) current charge.
    Over the last 2 hours the avg Spec. grav. has moved up to 1200 ( about 17 points). Note that originally (yesterday) some cells were just water, no acid at all => 100% sulfation in those cells.
    55b24-10b.png
     
  19. MrAl

    MrAl Well-Known Member Most Helpful Member

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    Hello,

    So are you recommending a higher than usual charge voltage of 15 volts? How often?
     
  20. Mosaic

    Mosaic Well-Known Member

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    For the purposes of degrading hard sulfation, high voltages are required to overcome the insulating properties of the sulfate.

    High voltages (up to 100V I have seen used) can cause severe overheating, thus the duty cycle of the hi voltage must be small. Enter pulse charging and thermal monitoring.

    The constraints on the minimum pulsewidth have to do with battery and wiring inductances. You need enough width to overcome the time needed for the current ramp as seen in the scope traces. Then the frequency is decided by the average currents you want to achieve. A higher freq= higher avg currents and probably lower peak currents as the DC% gets smaller in absolute time as frequency increases.

    Some commercial desulfators claim to operate directly on batteries attached to a vehicle. I have purchased and tested several common units. Invariably they use very small amplitude pulses and take weeks to months to make a difference in optimum conditions. I have found their claims to be of the flavoured snake oil variety with merely a hint of reality.

    Automotive circuitry cannot permit too many transient pulses to live for long, in fact auto circuity includes transient protection to ISO standards. You can only pulse a battery effectively & safely out of circuit.
     
    Last edited: Nov 8, 2014
  21. MikeMl

    MikeMl Well-Known Member Most Helpful Member

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    I use the boat's alternator to equalize my boat batteries. I store my boat at a location where there is no AC power line, so cannot use an AC powered constant-current supply to equalize them like I can do to my automotive and aircraft batteries at home.

    I trick the boat's alternator Voltage Regulator into jumping the output voltage from a nominal 14.2V to about 16V. I installed a toggle switch that controls the VR.

    At 16V, the battery initially absorbs an (over) charge of ~ 30A, but as the battery voltage approaches 15.5V and higher, the charging current naturally drops to 5 to 10A. Doing this for about 20 to 30 min once every three to six months gets me several years more out of a starting or house battery than I previously got without equalizing.

    I routinely equalize my flooded aircraft batteries and batteries in little-used vehicles like my Jeep and Motorhome. I have found that periodic equalizing does more for infrequently driven or used flooded lead acid batteries than pulse chargers.

    As to Mosaic's experiments, I see no real science there; just more claims and anecdotes...
     

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