[time-nuts] OT Gel Cell question

[Alex Pummer]

it is not a high performance battery but extremely robust, see there 
http://www.nickel-iron-battery.com/
it is no polluting, it could be shorted out overcharged
if you are lucky and find one old forklift with Edison Battery -- which 
was built some fifty years ego....it will out last you too
you could charge in current mode, C/10, 2C nothing will happen just 
replace evaporated water in the elctrtrolyt which is KOH
73
Alex


On 7/27/2014 2:41 PM, Chuck Harris wrote:
> I too have spent a lot of time charging batteries using different 
> methods on
> various chemistries.  Once upon a time, I build a number of suitcase 
> battery
> chargers for the US Army that allowed them to charge every portable 
> secondary
> battery type that they had in inventory... SLA, AgO, NiCD, NIMH,
> LiIon...  I proved a concept, and someone else got to make all of the 
> money
> off of it when the ARMY shopped my prototypes around... but I digress.
>
> When you try to charge a sulfated lead acid cell, you can think of the 
> cell
> as being a bunch of little parallel lead acid microcells (uCell). Each 
> is in
> some state of charge/discharge.
>
> So imagine this:
>
> +--+--+--+--+--+--+.....+--+---Plus terminal
> S..S..S.[B].S..S..S.....S..S
> +--+--+--+--+--+--+.....+--+---Minus terminal
>
> In this case, all of the "S"s represent a microcell (uCell) that is 
> highly
> sulfated, and the "[B]" represents a microcell that is in perfect 
> condition,
> and is taking a charge normally.
>
> If you try to put current into this lead acid cell, the sulfated 
> uCells will
> appear as open circuits (due to the sulfate's insulating properties), 
> and the
> good uCell will take all of the current, and will keep the voltage 
> down to a
> low enough value that the sulfated uCells will not see any significant
> electrolysis action.
>
> So you say, "Pooh, I want the sulfated uCells to charge too!" and up the
> voltage across the lead acid cell, and poof!  The good uCell dies from 
> over
> heating, revealing a new uCell that wants to charge, and poof, it dies,
> revealing another uCell that wants to take a charge, and poof...
>
> You get into a situation where your success causes your failure.
>
> If, instead, you apply high voltage pulses to the lead acid cell, you can
> sometimes beat the system.  The good uCells will take a hit, but it is 
> short
> enough that they don't have time to burn up, and the sulfated uCells will
> get to draw enough current during the pulse that a little electrolysis 
> will
> happen, and convert some of their sulfate back into oxide and acid...
>
> Sometimes you can win by using a pulse charge system.
>
> However, there is a little physical problem that has to be 
> understood.  Part
> of the way the lead acid batteries get their high current handling 
> densities
> is because the lead plates are made to have high surface area. They 
> are kind
> of like sponges on the surface.  And, lead sulfate takes up 
> significantly more
> room than lead oxide.  Sorry, that is the way it just is.
>
> So, when a cell gets all sulfated up, the lead sulfate that forms in 
> the deep
> nooks in the mossy lead electrodes fills the nook up so full that it 
> breaks
> it apart, and damages the cell plate.  This happens, albeit slowly, 
> even when
> you treat the battery nicely.
>
> You can't win. Long term everything heads towards entropy.
>
> -Chuck Harris
>
>
> Brooke Clarke wrote:
>> Hi Robert:
>>
>> I've spent a lot of time charging batteries using different methods 
>> and on various
>> chemistries.
>>
>> When the charge is in the form of a pulse, ideally including a 
>> reverse polarity
>> pulse, the charge is more effective.
>> This is also a way to sometimes, but not always, will recover a 
>> battery that
>> otherwise will not take a charge from a DC source.
>>
>> I think this works because it takes some time for chemical reactions 
>> to work and by
>> using a pulse you can force the reaction to a higher level that you 
>> can't do using DC
>> without causing problems such as boiling the electrolyte.  For more 
>> info see Burp
>> Charging:
>> http://www.prc68.com/I/BatChg.shtml#Burp
>>
>> Have Fun,
>>
>> Brooke Clarke
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