Re: (ET) Fully charged pack voltage

[Michael S Briggs <msbriggs alberti unh edu>]

Ohhh, I was forgetting about the affect the concentration of sulfate and 
hydrogen ions would have on the Gibbs free energy of the reaction (the 
voltage any battery produces is the change in gibbs free energy of the 
reactions that take place divided by the amount of charge that has to move 
for that much energy to be transferred). As you keep charging above the 
resting SOC voltage, you should be producing more H+ and SO42- ions, which 
will increase the Gibbs free energy of the reaction, thereby increasing 
the voltage of the pack. Those hydrogen and sulfate ions gradually 
recombine, bringing the gibbs free energy (and therefore voltage) back 
down to what it should be.
        Ok, I think I'm all set now....

Thanks,
Mike

--

--------------------------------------------------------------
Michael S. Briggs, PhD
UNH Physics Department
(603) 862-2828
---------------------------------------------------------------

On Thu, 23 Apr 2009, Tim Humphrey wrote:

> The act of charging causes a chemical reaction between the plates and
> the electrolyte. You already know how that works.
>
> The resultant change occurs where the plates and electrolyte are in
> contact with one another. The time delay for the surface charge to
> dissipate is a result of the time it takes the chemical change to
> absorb deeper into the plates.
>
>
> Stay Charged
> Hump
>
>
> > -----Original Message-----
> > From: elec-trak-bounces cosmos phy tufts edu
> > [mailto:elec-trak-bounces cosmos phy tufts edu] On Behalf Of Michael S
> > Briggs
> > Sent: Thursday, April 23, 2009 10:20 AM
> > To: SteveS
> > Cc: et
> > Subject: Re: (ET) Fully charged pack voltage
> >
> >
> > Oh - I'm still perplexed about *why* it takes so long for the pack
> > voltage
> > to drop back down to its resting voltage after charging. I'm a
> > physicist,
> > I feel compelled to understand why things are the way they are. :)
> >
> > Mike
> >
> > --
> >
> > --------------------------------------------------------------
> > Michael S. Briggs, PhD
> > UNH Physics Department
> > (603) 862-2828
> > ---------------------------------------------------------------
> >
> > On Thu, 23 Apr 2009, SteveS wrote:
> >
> > > It actually can take up to 24 hours to get to resting voltage. And I
> > don't
> > > think you can 'hurry' it up by momentarily applying a load.
> > >
> > > Here's a good reference:
> > http://www.trojanbattery.com/productLiterature/documents/UsersGuide_0109
> > _English_001.pdf
> > > - SteveS
> > >
> > > Michael S Briggs wrote:
> > > >  On Thu, 23 Apr 2009, John J Casey wrote:
> > > >
> > > > >  In my experience, the onboard ge charger takes my newish T-105's
> > up to
> > > > >  44-45v over an 18 hour cycle, the last 3-5 hrs between 44.4 and
> > 45v for
> > > > >  cell
> > > > >  equalization.  End the charge cycle and in a short time the
> > voltage
> > > > >  settles
> > > > >  back to 39v.Jack
> > > >
> > > >  So, the fully charged pack then has a voltage of 39 V (since that is
> > what
> > > >  it settles to after charging).
> > > >      One thing that is troubling me - what does it take a while for
> > the
> > > >  battery's voltage to gradually drop from the elevated charging
> > voltage
> > > >  down to its resting voltage. I know that while charging the voltage
> > > >  applied will be higher than the battery's voltage due to the voltage
> > drop
> > > >  across the internal resistance of the battery (batteries) - but once
> > the
> > > >  charger turns off, I would think that the battery pack voltage would
> > drop
> > > >  rather immediately down to its resting voltage (the potential
> > difference
> > > >  that the chemical reactions taking place at the electrodes produce).
> > > >      BTW, this has some interesting information about how the
> > internal
> > > >  resistance of the electrolyte changes with state of charge, which
> > gives
> > > >  lead acid batteries their unique voltage vs. state of charge curves:
> > http://www.arttec.net/Solar_Mower/4_Electrical/Battery%20Charging.pdf
> > > >      The main thing I'm trying to figure out right now is what to set
> > my
> > > >  Landis charge controller to to make sure that the pack gets fully
> > charged
> > > >  (and doesn't take 3 days to get there). It would seem that the
> > default 38V
> > > >  setting is too low, since the pack should be higher than that when
> > fully
> > > >  charged.
> > > >
> > > >  Thanks,
> > > >  Mike
> > > >
> > > > >  On Apr 23, 2009, at 8:13 AM, Michael S Briggs wrote:
> > > > >
> > > > >
> > > > >        I just got a nice new pack of Trojan T-605s (slightly lower
> > > > >        capacity than T-105s, with a proportionately lower price).
> > I'm
> > > > >        trying to figure out what the voltage of a fully charged new
> > > > >        pack *should* be, and I have seen very different things as
> > > > >        skimming through the archives.
> > > > >        My understanding is that the chemical reactions taking place
> > in
> > > > >        a lead-acid cell produce a potential difference of 2.13
> > Volts,
> > > > >        so a fully charged lead-acid battery measured with a very
> > high
> > > > >        impedance voltmeter should measure that 2.13 Volts per cell,
> > or
> > > > >        6.39V for a 6V battery, and 38.34 V for a 36V pack.
> > > > >        But, I have seen statements in the archives saying that a
> > fully
> > > > >        charged pack should have a voltage of 42V or so (various
> > posts
> > > > >        saying anywhere from about 40V up to 44V).
> > > > >
> > > > >        Thanks,
> > > > >        Mike
> > > > >
> > > > >        --
> > --------------------------------------------------------------
> > > > >        Michael S. Briggs, PhD
> > > > >        UNH Physics Department
> > > > >        (603) 862-2828
> > ---------------------------------------------------------------
> > > > >        _______________________________________________
> > > > >        Elec-trak mailing list
> > > > >        Elec-trak cosmos phy tufts edu
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