Author Topic: Battery chemistry questions  (Read 2156 times)

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Offline Ford Prefect

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Battery chemistry questions
« on: December 16, 2013, 12:21:23 pm »
I would love to learn about battery chemistry, especially as it relates to desulfation.

I have recently learned from Robbie that it's possible to at least partially rejuvenate lead-acid batteries, by desulfating them. Apparently a "range of frequencies" are applied in order to break up lead sulfate crystals?

I'd like to understand this better.  What happens to the lead ions freed from the broken-up crystals? Do they go back into the plates or form new compounds in solution?  The latter seems like the most entropic result...

Robbie has a BatteryMINDer(tm) device that can desulfate a battery, but I've read that it can take 3 weeks for this process to run to completion.

I've found plans for a circuit to desulfate a battery.  The parts are not expensive.
« Last Edit: December 16, 2013, 12:56:05 pm by LimaGolf »

Offline daletersey

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Re: Battery chemistry questions
« Reply #1 on: December 16, 2013, 12:48:45 pm »
When two lead plates are immersed in pure sulfuric acid and a DC charge is applies to the two plates, One becomes the "anode" and the other becomes the "cathode" .  The anode forms a surface plating of Lead sulfide that will be reduced to pure lead upon complete charging.  The cathode is driven into a lead oxide that will then be driven into lead sulfate when fully charged.  Although the lead sulfate will reduce to lead oxide on battery discharge, the sulfide is less soluble and often sheds off of the plates to accumulate on the bottom of the cell in the space below the plates.  Once the free lead sulfate accumulates to a sufficient depth it can short out the two plates that are normally separated by a dielectric (rubber) sheet. 

Successfully restoring the lead sulfate to the surface of the cathode is not really practical.  Wet battery renovation can be done by draining and flushing the battery cells, using the saved acid and restoring the sulfuric acid to full (charged) working strength.  This will prolong the life of the battery but you do not have any idea of the amount of life remaining.  The sulfate removed during rinsing is actually lead from the plates that has left a weaker and "eaten up" lead plate.

Marine batteries contain much thicker plates and a much larger space below the plates to accumulate lead sulfate cruft.  There is also a vactor of alloyed metals in the lead for stiffening and other performance properties that have a bearing on the ability to regenerate.

Offline Ford Prefect

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Re: Battery chemistry questions
« Reply #2 on: December 16, 2013, 01:22:49 pm »
Thanks, Dale, for that explanation!

Photos from BatteryMINDer show the plates new, sulfated, and de-sulfated. Looks like the latter are pitted, as you mentioned.  Pitted plates would have more effective surface area.  I am not suggesting these would hold more charge, but is there reason to believe they'd hold less?

Offline Robbie L

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Re: Battery chemistry questions
« Reply #3 on: December 16, 2013, 03:26:09 pm »
I also have a "super strength" kit based desulphator I built that really attacks the batteries. It's basically a overpowered beast that just attacks the batteries vs most "desulphation" chargers that use much weaker signals.
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Offline Jeremy Briddle

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Re: Battery chemistry questions
« Reply #4 on: December 19, 2013, 10:19:37 pm »
A project I've been thinking about building is an alkaline battery recharger for AA, AAA, etc that runs off an Arduino. I would really like to implement some of the capabilities of Robbie's charger in it if I could.

Jeremy