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Sulphated Cell or What?

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Posted by ~~NoMad~~ on October 5, 2007, 3:35 pm

Of my four Trojan T-105 batteries one seems to be going bad. The battery
won't equalize with the others.

At a 10 amp charge rate the bad battery reads 7.6 volts and its series
partner reads 8.3. On the other string both batteries will read 8.3 volts at
a 2 amp charge rate. I seems that no amount of overcharging will bring this
weak battery voltage up. The SG reads full in all cells of the weak battery
and under load it seems to have near full capacity. After three days rest
after charging the weak battery reads 6.32 volts and the strong one reads

Do I have a sulfated cell or what? The batteries are less than 4 years old
but get cycled 25% or more every day.


Posted by Solar Flare on October 5, 2007, 6:32 pm
Sounds quite minor to me. Did you expect your cells to last longer
than 4 years and be perfect?

Our battery bank testing is done by equalizing for 24 hour, resting
for 24 and then the SG readings are done. It sounds like yours came
our fairly close with the rest method.

Posted by daestrom on October 5, 2007, 11:41 pm

One thing about this that surprises me is that they both read 8.3 volts when
charged at the low rate in series?  If that's the case and you get a
*different* voltage when the charge rate is higher, then I suspect something
in your inter-battery connections versus your voltage measurements.  While
discharging at the high rate, carefully go around and feel each connection
and cable, looking for one that is a lot warmer than the others.  A hotter
than normal connection or lug crimp indicates a problem spot.  Be careful to
remove any metal from your hands/wrists before doing this and if you have
some nice insulated mat to stand on, use that and only use one hand to avoid

Depending on exactly where you take the voltage measurements, the voltage
drop thru a bad connection may add to the voltage seen on one battery and
subtract from that seen on another in series.

If SG is equal across all the cells and open-circuit voltage is that close,
it sounds like all cells are pretty close to the same level of charge.
*UNLESS* you've been naughty and tried to 'spike' some cells with battery
acid or something.  Then SG will be high even though a lot of sulphate is on
the plates.  Normally you can't get a good SG without driving sulphates off
the plates and back into the electrolyte.  But various 'spiking' additives
or just adding acid instead of water when level is low screws that all up
and makes the SG reading pretty much useless.


Posted by bealiba on October 6, 2007, 8:10 am
3 Problems:

1) Testing battery condition while charging.
2) You seem to have a series/ parallel battery bank.
3) T105 batteries.

A 12Volt battery will read ~12.7 volts after charging and several
hours rest. 12.7 V is fully charged.

A 6Volt battery will therefore read ~6.35V after charging and resting
for several hours.

A single cell in a 12Volt battery will read ~2.12V after charging and
resting for several hours.

Operator error. Do not pass go, do not collect $00.

Posted by wmbjkREMOVE on October 6, 2007, 2:11 pm
 On Sat, 06 Oct 2007 08:10:30 -0000, bealiba@gmail.com wrote:

He stated the voltage readings of the rested batteries.


So what? They've been discharged at least 25% every day for 4 years.
Probably not a bad life span for low-cost batteries.

Or 6.35V for his T105s.

Your post is typical "power consultant" error, pretty much like all
the other examples here http://www.citlink.net/~wmbjk/tbfduwisdumb.htm


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